U.S. patent application number 15/259804 was filed with the patent office on 2017-03-30 for methods for color and texture control of metallic glasses by the combination of blasting and oxidization.
The applicant listed for this patent is Apple Inc.. Invention is credited to Naoto Matsuyuki, Kazuya Takagi, Theodore A. Waniuk, Yoshihiko Yokoyama.
Application Number | 20170087691 15/259804 |
Document ID | / |
Family ID | 57124092 |
Filed Date | 2017-03-30 |
United States Patent
Application |
20170087691 |
Kind Code |
A1 |
Yokoyama; Yoshihiko ; et
al. |
March 30, 2017 |
METHODS FOR COLOR AND TEXTURE CONTROL OF METALLIC GLASSES BY THE
COMBINATION OF BLASTING AND OXIDIZATION
Abstract
Methods of altering the surface of a metallic glass are
provided. The methods include blasting and oxidation of a metallic
glass surface, blasting a metallic glass surface using multiple
shot media sizes, and thermal spray blasting a metallic glass
surface with controlled cooling.
Inventors: |
Yokoyama; Yoshihiko; (Tokyo,
JP) ; Takagi; Kazuya; (Tokyo, JP) ; Matsuyuki;
Naoto; (Kasugai-shi, JP) ; Waniuk; Theodore A.;
(Lake Forest, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Apple Inc. |
Cupertino |
CA |
US |
|
|
Family ID: |
57124092 |
Appl. No.: |
15/259804 |
Filed: |
September 8, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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62235072 |
Sep 30, 2015 |
|
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|
62265866 |
Dec 10, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B24C 1/06 20130101; C23C
4/129 20160101; C23C 8/10 20130101; C23C 8/02 20130101 |
International
Class: |
B24C 1/06 20060101
B24C001/06 |
Claims
1. A method of altering a surface of a metallic glass, the method
comprising: blasting the surface of the metallic glass with a shot
media to form a porous blasted metallic glass surface having an
oxidized layer having a first thickness; oxidizing the porous
blasted metallic glass surface at an elevated temperature to form
an oxidized metallic glass surface having an oxidized layer with a
second thickness larger than the first thickness.
2. The method of claim 1, further comprising blasting the oxidized
metallic glass surface to form a modified metallic glass surface;
and oxidizing the modified metallic glass surface to change color
and texture of the modified metallic glass surface.
3. The method of claim 1, wherein the shot media comprises
ZrO.sub.2.
4. The method of claim 1, wherein the shot media has sizes from 10
.mu.m to 100 .mu.m.
5. The method of claim 1, wherein the porous blasted metallic glass
surface contains fewer surface features than the surface of the
metallic glass before blasting.
6. The method of claim 1, wherein the oxidized metallic glass
surface has a roughness from 5 .mu.m to 10 .mu.m.
7. A method of altering a surface of a metallic glass, the method
comprising: blasting the surface of the metallic glass with a large
shot media having an average diameter from 100 .mu.m to 2000 .mu.m;
blasting the surface of the metallic glass with a fine shot media
having an average diameter from 10 .mu.m to 100 .mu.m; and
oxidizing the blasted surface of the metallic glass to form an
oxidized metallic glass surface.
8. The method of claim 7, wherein the large shot media comprises a
polymer base and a protruded sharp ceramic vertex, and the fine
shot media comprises fine round ceramic particles.
9. The method of claim 7, wherein blasting with the large shot
media and blasting with the fine shot media is simultaneous.
10. The method of claim 7, wherein the oxidized metallic glass
surface has a roughness from 2 .mu.m to 10 .mu.m.
11. The method of claim 7, wherein a processing time of blasting
with large shot media and fine shot media, and oxidizing, is
greater than 3000 seconds.
12. A method of treating a surface of a metallic glass, the method
comprising: thermal spray blasting the surface of the metallic
glass; and simultaneously with the thermal spray blasting, spray
cooling the surface of the metallic glass, to form an oxide layer
on the surface of the metallic glass.
13. The method of claim 12, wherein a temperature of the surface of
the metallic glass is further controlled using a temperature
controlled sample holder.
14. (canceled)
15. The method of claim 12, wherein the thermal spray blasting
proceeds for less than 2 minutes.
16. The method of claim 12, wherein the thermal spray is produced
using a high velocity oxygen fuel (HVOF) thermal spray system.
17. The method of claim 12, wherein the thermal spray comprises a
blasting media for blasting of the surface of the metallic
glass.
18. The method of claim 17, wherein the blasting media comprises
ZrO.sub.2 media.
19. The method of 17, wherein the blasting media has sizes varying
from 10-100 .mu.m.
20. The method of claim 12, further comprising blasting the surface
of the metallic glass with a blasting media to control surface
smoothness, porosity, or a combination thereof.
21. The metallic glass of claim 12, wherein the oxidized surface
includes a non-uniform oxidized surface that exhibits surface
variations to a depth of about 5-20 .mu.m.
22.-29. (canceled)
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This patent application claims the benefit of U.S. Patent
Application No. 62/235,072, entitled "Color and Texture Control of
Metallic Glass Surfaces by the Combination of Blasting and
Oxidization," filed on Sep. 30, 2015 under 35 U.S.C. .sctn.119(e),
which is incorporated herein by reference in its entirety.
[0002] This patent application also claims the benefit of U.S.
Patent Application No. 62/265,866 under 35 U.S.C. .sctn.119(e),
entitled "Surface Treatment with Thermal Spray Blasting to Control
Appearance of Metallic glass Surfaces," filed on Dec. 10, 2015,
which is incorporated herein by reference in its entirety.
FIELD
[0003] The disclosure is directed to methods for providing surface
treatment to control color and texture of metallic glass surfaces,
and the resulting materials. More particularly, the embodiments
relate to the surface treatment of metallic glass surfaces with the
combination of blasting and oxidization, thermal spray blasting,
and dissimilar shot media or blasting media.
BACKGROUND
[0004] Metallic glasses are metallic alloys that do not have a
crystalline structure. Instead, like glass, their structure is
amorphous. Metallic glasses have a number of material properties
that make them viable for use in a number of engineering
applications. Some of the properties of metallic glasses can
include high strength, stiffness, toughness, corrosion resistance
and processability from the molten state.
[0005] Casting metallic glasses can promote gas porosity and
formation of surface features such as voids, crystals, and shedding
parts on the metallic glass. Often such surface features are only
visible after raw materials have been consumed and hours of
manufacturing processes have been performed. Efforts have been made
to manufacture metallic glasses having oxidized surfaces and
textures and/or without certain surface features. However, there
are limitations with current methods.
[0006] Metallic glasses typically do not have black surfaces.
Further, as-cast metallic glass surfaces can include non-uniform
surface features such as crystals, voids, shredding parts,
flowlines, coldshuts, and misruns.
SUMMARY
[0007] The present disclosure provides methods of altering the
surface of a metallic glass.
[0008] In certain aspects of the disclosure, methods include
blasting and oxidation of a metallic glass surface. The metallic
glass surface is blasted with shot media to form a porous blasted
metallic glass surface. The porous blasted metallic glass surface
has an oxidized layer. The porous blasted metallic glass surface is
then oxidized, for example by annealing, to form a second oxidized
layer thicker than the first oxidized layer. The blasting and
oxidation steps can be repeated.
[0009] In another aspect, the methods include blasting a metallic
glass surface using two different shot media sizes. A large shot
media size can have an average diameter from 100 .mu.m to 2000
.mu.m. The fine shot media has an average diameter from 10 .mu.m to
100 .mu.m. In some variations, the large and fine shot media are
used to blast the metallic glass surface simultaneously. In some
aspects, the large shot media has particles that include a polymer
base and a protruded sharp ceramic vertex.
[0010] In certain aspects of the disclosure, systems and methods
for thermal spray blasting a metallic glass surface with controlled
cooling. The metallic glass surface is blasted using a thermal
spray gun with an integrated spray cooling in a flame nozzle. In
various aspects, the thermal spray gun can be a high velocity
oxygen fuel (HVOF) or high velocity air fuel (HVAF) thermal spray
gun.
[0011] Additional embodiments and features are set forth in part in
the description that follows, and will become apparent to those
skilled in the art upon examination of the specification or can be
learned by the practice of the disclosed subject matter. A further
understanding of the nature and advantages of the present
disclosure can be realized by reference to the remaining portions
of the specification and the drawings, which forms a part of this
disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The description will be more fully understood with reference
to the following figures and data graphs, which are presented as
various embodiments of the disclosure and should not be construed
as a complete recitation of the scope of the disclosure,
wherein:
[0013] FIG. 1A illustrates blasting for controlling surface
structure of a metallic glass before oxidization.
[0014] FIG. 1B shows a Ti-base metallic glass and a Zr-based
metallic glass revealing flashing like a small firework.
[0015] FIG. 2A is a graph showing weight loss versus blasting time
in a metallic glass resulting from blasting.
[0016] FIG. 2B is an optical photo of a metallic glass surface in
an as-cast condition.
[0017] FIG. 2C is an optical photo of the metallic glass surface of
FIG. 2B after blasting for 10 minutes.
[0018] FIG. 3 illustrates an exemplary process flow, including a
first blasting followed by oxidization and a second blasting, and
the respective surface features of metallic glasses.
[0019] FIGS. 4A-4D show optical images of a metallic glass (A)
as-cast; (B) after a first blasting; (C) after oxidizing the first
blasted surface; and (D) after a second blasting of the oxidized
surface.
[0020] FIG. 5A shows an optical image of an oxidized Zr-based
metallic glass surface without any blasting.
[0021] FIG. 5B shows a magnified optical image of FIG. 5A.
[0022] FIGS. 6A-6D show optical images of an outer appearance of
the Zr-based metallic glass after (A) blast ZrO.sub.2; (B)
oxidization; (C) blasted after oxidization; and (D) oxidization
again.
[0023] FIGS. 7A-D show optical photos illustrating that blasting
and oxidization can eliminate crystals for the Zr-based metallic
glass including (A) as-polished; (B) one minute ZrO.sub.2 blast;
(C) after oxidization; and (D) three minute ZrO.sub.2 blast.
[0024] FIGS. 8A-D show optical photos illustrating the removal of
micro-voids by blasting and oxidization of the Zr-based metallic
glass including (A) as-polished; (B) one minute ZrO.sub.2 blast;
(C) after oxidization; and (D) three minute ZrO.sub.2 blast.
[0025] FIGS. 9A-D show optical photos illustrating the healing of
the contrast of shredding portions by blasting and oxidization of
the Zr-based metallic glass including (A) as-polished; (B) one
minute ZrO.sub.2 blast; (C) after oxidization; and (D) three minute
ZrO.sub.2 blast.
[0026] FIG. 10A shows scanning electron microcopy (SEM) images of
the microstructure of the oxide layer of the metallic glass formed
after oxidization.
[0027] FIG. 10B shows microstructural analysis of the metallic
glass of FIG. 10A by X-ray diffractometry.
[0028] FIG. 11A illustrates an example system for thermal spray
blasting of a metallic glass surface with controlled cooling,
according to an embodiment of the disclosure.
[0029] FIG. 11B illustrates example scan patterns of thermal spray
blasting, with and without sample overrun, according to embodiments
of the disclosure.
[0030] FIGS. 12A-12B illustrate example thermal spray blasting
effects on metallic glasses, below and above Tg, according to
embodiments of the disclosure.
[0031] FIGS. 13A-13D illustrate oxidized surface morphology of
metallic glasses treated in accordance with an embodiment of the
disclosure, and a comparative example of an oxidized surface
morphology of a metallic glass treated with blasting and
annealing.
[0032] FIG. 14 shows the surface structure of black Ni-based bulk
metallic glass obtained by using a chemical etching treatment.
[0033] FIG. 15 illustrates desired blast shots for deep and sharp
indentation on a sphere rubber base using a ceramic material (e.g.
silicon carbide (SiC)) as a shot material.
[0034] FIG. 16A shows a SEM image of an outer appearance of a
Zr-based metallic glass blasted by large shot media (e.g. Sirius
#320).
[0035] FIG. 16B shows a back scattered electron (BSE) image of an
outer appearance of a Zr-based metallic glass blasted by a first
large shot media (e.g. Sirius #320).
[0036] FIG. 16C shows the surface structure and texture change
versus gas pressures of the large shot media (e.g. Sirius #320) on
a Zr-based metallic glass.
[0037] FIG. 17A shows an optical image of a metallic glass surface
blasted by using large shot media (e.g. Sirius #320) and a depth
profile of the metallic glass surface.
[0038] FIG. 17B shows a predicted cross-sectional image of the
metallic glass blasted by using the large shot media (Sirius
#320).
[0039] FIG. 18A shows an optical image of a blasted metallic glass
surface blasted by using fine blast shot media (B505), and a
corresponding depth profile on the metallic glass surface shown in
the optical image of FIG. 18A.
[0040] FIG. 18B shows a predicted cross-sectional image of the
metallic glass surface blasted by using the fine blast shot media
(e.g. B505).
[0041] FIG. 19 shows a predicted metallic glass surface blasted by
using a combination of the large shot (e.g. Sirius #320) and the
fine blast shot (e.g. B505).
DETAILED DESCRIPTION
[0042] The disclosure can be understood by reference to the
following detailed description, taken in conjunction with the
drawings as described below. It is noted that, for purposes of
illustrative clarity, certain elements in various drawings may not
be drawn to scale.
[0043] The disclosure provides methods of a blasting metallic glass
surfaces that can be used to control the surface color and texture.
Blasted surfaces of metallic glasses are porous such that, in
various embodiments, the blasted surfaces can provide uniform oxide
growth to reduce spectacular light reflection and increases
diffused reflection. Blasting also can remove surface features,
such as crystals, voids, shredding parts, flowlines, and coldshuts,
among others. In various aspects, oxidized surfaces can have a dark
color and/or consistent texture.
[0044] In some embodiments, the metallic glass can have a
consistent oxidized surface that exhibits surface roughness Rz
equal to or less than 10 .mu.m. In some embodiments, the metallic
glass can have a consistent oxidized surface that exhibits surface
roughness Rz equal to or less than 8 .mu.m. In some embodiments,
the metallic glass can have a consistent oxidized surface that
exhibits surface roughness Rz equal to or less than 6 .mu.m. In
some embodiments, the metallic glass can have a consistent oxidized
surface that exhibits surface roughness Rz equal to or less than 4
.mu.m. In some embodiments, the metallic glass can have a
consistent oxidized surface that exhibits surface roughness Rz
equal to or less than 2 .mu.m. In some embodiments, the metallic
glass can have a consistent oxidized surface that exhibits surface
roughness Rz equal to or greater than 1 .mu.m. In some embodiments,
the metallic glass can have a consistent oxidized surface that
exhibits surface roughness Rz equal to or greater than 1.5 .mu.m.
In some embodiments, the metallic glass can have a consistent
oxidized surface that exhibits surface roughness Rz equal to or
greater than 2 .mu.m. In some embodiments, the metallic glass can
have a consistent oxidized surface that exhibits surface roughness
Rz equal to or greater than 4 .mu.m. In some embodiments, the
metallic glass can have a consistent oxidized surface that exhibits
surface roughness Rz equal to or greater than 6 .mu.m. In some
embodiments, the metallic glass can have a consistent oxidized
surface that exhibits surface roughness Rz equal to or greater than
8 .mu.m. In various aspects, a laser microscope can be used to
measure the roughness of surface.
[0045] In various aspects, the methods described herein can produce
metallic glass surfaces with various colors. An L*a*b* color space
is a color space with dimension L* for lightness and dimensions a*
and b* for color-opponent dimensions. Values of the L*a*b* color
space are used for quantitative measurement of color change. The
lightness, an L* value, represents the darkest black at L*=0, and
the brightest white at L*=100. The color values a* and b* represent
true neutral gray values at a*=0 and b*=0.
[0046] In various aspects, the color of the metallic glasses is
darkened. In the L*a*b* color space, darker colors is characterized
by lower L* values, and a* value and b* approaching zero. In other
embodiment, the color can be grey or other colors. When diffusion
reflection is reduced from a metallic glass surface, the L* value
becomes lower.
[0047] Blasting and Oxidation for Color and Texture Control
[0048] In one aspect, the disclosure provides methods of blasting a
surface of a metallic glass and subsequently oxidizing the metallic
glass surface. In a first step, the metallic glass surface is
blasted using blasting media. In a second step, the blasted
metallic glass surface is oxidized.
[0049] FIG. 1A illustrates blasting for controlling surface
structure of a metallic glass before oxidization. The initial
texture of the metallic glass surface is machined or as-cast. As
shown in FIG. 1A, shot media particles 102 are blasted over a top
surface of a metallic glass, creating shear bands 106. Oxidization
occurs after the first blasting step to form an oxidized metallic
glass surface. On the right side of FIG. 1A, a treated surface 112
includes a consistent texture after a second blasting step that
modifies the oxidized metallic glass surface.
[0050] In various aspects, blasting refers to forcibly propelling a
stream of abrasive material against the metallic glass surface
under high pressure. A pressurized fluid, such as compressed air,
or a centrifugal wheel is used to propel the blasting material,
which is often called the shot media. In various aspects,
conventional blasting systems and methods can be used. For example,
a Sirius processing and ultra-precision processing system by Fuji
can be used.
[0051] The metallic glass can be blasted using any blasting media
known in the art. The shot media generally includes ceramic, metal,
glass, or polymer. It will be understood that any such blasting
media known in the art can be used. In some embodiments, ceramic
shot media such as zirconia beads (ZrO.sub.2) (Saint Gobain B170)
are used. In a particular embodiment, blasting can be performed
using spheres of ZrO.sub.2 (containing .about.30% SiO.sub.2 and
<10% Al.sub.2O.sub.3) incident on the metallic glass. With
reference to FIG. 1B, blasting the surface of a metallic glass can
cause the surface to flash like a small firework, indicated by
arrow 116. The shot media 118 includes particles in a sphere shape.
For example, when Zr-shot media is used on a Zr-based metallic
glass, flashing can cause burning of the Zr metal on the Zr-based
metallic glass surface and thus generate a high temperature at
local area 110.
[0052] In various aspects, blasting the surface can remove a small
amount of surface material from the surface of the metallic glass.
In some aspects, at least 5 microns of metallic glass is blasted
from the metallic glass surface during the blasting step. In some
aspects, at least 10 microns of metallic glass is blasted from the
metallic glass surface during the blasting step. In some aspects,
at least 15 microns of metallic glass is blasted from the metallic
glass surface during the blasting step. In some aspects, up to 20
microns is blasted from the surface.
[0053] The blasting step can reduce the weight of the metallic
glass. An example of this weight loss during blasting is depicted
in FIG. 2A. As shown, the weight loss increases with blasting time.
The weight loss can be 0.12 g at a blasting time of 1200 seconds.
For instance, a blasting period of ten minutes results in the
weight loss of about 0.07 g, equivalent to removing 8 .mu.m depth
of the surface. In this example, the sizes of the blast shot media
are between 45 to 100 .mu.m and the blast has a low gas pressure of
about 0.2 MPa.
[0054] FIG. 2B is an optical photo of an as-cast metallic glass
surface. FIG. 2C is an optical photo of the metallic glass surface
of FIG. 2B after 10 minutes of blasting, corresponding to a weight
loss of 0.07 g. The resulting blasted surface, as shown in FIG. 2C,
appears dark compared with the as-cast surface, as shown in FIG.
2B.
[0055] The amount of metallic glass surface material that can be
removed during blasting can be increased based on the time of
blasting, the intensity of the blast, the type of blasting media
used, and other variables. The type of shot media impacting the
surface, gas pressure of the blasting beam, size of a blasting shot
media and blasting time, and other conditions known in the art can
be altered. As the blasting time increases, more material will be
removed from the metallic glass surface. In some aspects, the
blasting time can be at least 300 seconds. In some aspects, the
blasting time can be at least 600 seconds. In some aspects, the
blasting time can be at least 900 seconds. In some aspects, the
blasting time can be at least 1200 seconds. In some aspects, the
blasting time can be at least 1500 seconds. In various aspects, and
without limitation, the blasting time can be up to 1800 seconds or
30 minutes. Shorter blasting times result in more rapid
processing.
[0056] The blasted surface can be plastically deformed to create
shear bands. Without wishing to be held to a particular mechanism
or mode of action, shear bands are stress induced shear deformed
areas with lower density. The diffusibility in shear bands is high,
and therefore oxidization of the metallic glass surface area can be
accelerated. The blasting step provides a thin oxide layer on the
metallic glass surface.
[0057] Blasting the metallic glass surface can modify the metallic
glass surface before the subsequent oxidization step. The blasting
step can create a porous structure on the metallic glass surface.
The blasting step can promote formation of a thin oxide layer due
to the high-energy produced at the metallic glass surface. Metallic
glass surfaces are often coated with a hydroxide layer. Hydroxide
can be formed on surface of a metallic glass in air atmosphere. For
example, spray of cooling mist can lead to the formation of
hydroxides, which generate a porous oxide layer on the surface of
the metallic glass. The thickness of the oxide layer can be up to 1
micron, up to 2 microns, up to 3 microns, or up to 4 microns in
thickness. The thin oxide layer can serve as a seeding layer for
annealing to grow the oxidization layer into a thick oxidization
layer in a second step. In various aspects, blasting can also
remove surface features such as crystals, voids, shredding parts,
flowlines, coldshuts, and misruns.
[0058] In a second step, the blasted surface is oxidized. Oxidation
can be performed in any manner known in the art. In some aspects,
metallic glass surfaces can be oxidized by heating the metallic
glass to an elevated temperature for a period of time. In various
aspects, the oxidation temperature can be at least 300.degree. C.
In various aspects, the oxidation temperature can be at least
350.degree. C. In various aspects, the oxidation temperature can be
at least 400.degree. C. In various aspects, the oxidation
temperature can be at least 450.degree. C. In various aspects, the
oxidation temperature can be at least 500.degree. C. In various
aspects, the oxidation temperature can be at least 550.degree. C.
In various aspects, the oxidation temperature can be at least
600.degree. C. In various aspects, the oxidation time can be at
least 10 minutes, at least 20 minutes, or at least 30 minutes. In
some aspects, the oxidation time can range from 10 minutes to 30
minutes. Further, the temperature and oxidation time can vary. For
example, the oxidation time can be shortened when the temperature
increases and vice versa.
[0059] The oxidation step forms a thick oxidization layer on the
metallic glass surface. In various aspects, the oxidation layer is
at least 10 microns in thickness. In various aspects, the oxidation
layer is at least 15 microns in thickness. In various aspects, the
oxidation layer is at least 20 microns in thickness. In various
aspects, the oxidation layer is at least 25 microns in thickness.
In various aspects, the oxidation layer is at least 30 microns in
thickness.
[0060] Without wishing to be limited to any mechanism or mode of
action, the area of impact on the metallic glass surface can be a
blast-impacted plastic deformed area. The blast-impacted plastic
deformed area can contain a large number of shear bands on the
metallic glass surface. The shear bands can act as a diffuse path
of oxygen, and form micro-cracks in an oxide layer. Blasting can
also cause oxidization of the metallic glass due to high-energy
release at the surface area, and forms a thin oxide layer. After a
separate oxidation step following the blasting step, the oxide
layer can have an increased thickness, as well as a porous texture.
The shear bands and micro-cracks can allow for increased absorbance
of oxygen into the metallic glass. The blasting step can create a
diffusion path and seed an oxide layer, while the oxidation step
can grow the oxide layer to produce a thick oxidized surface over a
large number of shear bands in the blast-impacted surface
region.
[0061] The metallic glass can be any metallic glass known in the
art. In various aspects, the metallic glass is a metallic glass
that can oxidize. In some non-limiting aspects, the metallic glass
can be Zr-based, Ti-based, Hf-based, and Nb-based, among others.
The metallic glass can include one or more elements that oxidize.
In one embodiment, the metallic glass is Zr-based. When the
Zr-based metallic glass (e.g. the LM105 metallic glass) is used, a
normal oxidized color is blue on the surface.
[0062] In various aspects, the combined blasting and oxidization on
a metallic glass surface can form a darker color (e.g., grey or
black) and a consistent texture surface (i.e. lack of variation in
texture across the surface) on the metallic glass. FIG. 3 shows an
example process that combines blasting and oxidization on a
metallic glass surface resulting in a darker color and a consistent
texture surface. As shown, after a first blasting step, shear bands
304 are created on a top surface of the metallic glass 302, and a
thin oxide layer 310 is formed over shear bands 304. A second
oxidizing step on the blasted surface produces a thick oxide layer
306 is formed over the shear bands 304 to form an oxidized surface.
By using a second blasting step over the oxidized surface, the
thick oxide layer 306 is removed and a microstructure/texture layer
308 is created on the top surface of the metallic glass 302. The
microstructure/texture layer 308 is modified from the shear bands
304 by the second blasting step. The microstructure/texture layer
308 results in a darkened and/or consistent surface formed on the
metallic glass. The metallic glass can thereby have an L* value
under 50 in the L*a*b* color spectrum.
[0063] The steps of blasting and oxidizing can be repeated on the
same surface. The second blasting step can provide for altered
color and/or texture. FIGS. 4A-D show optical images of a Zr-based
metallic glass after four stages: 1) as-cast; 2) after a first
blasting step; 3) after an oxidation step; and 4) after a second
blasting step. As shown in FIG. 4A, the as-cast texture of a
metallic glass is that of a machined or cast surface. Generally,
blasting can increase the surface roughness of the metallic glass.
Further, porosity increases from the as-cast surface, as shown in
FIG. 4A when compared to the first blasted surface (by shot media
ZrO.sub.2) shown in FIG. 4B, or the blasted surface after
oxidization shown in FIG. 4D. The porosity microstructure can be
used to darken the structural color of the metallic glass surface.
The surface after blasting, as shown in FIG. 4B, is darker than the
as-cast surface shown in FIG. 4A. The porosity remains after
oxidization, as shown in FIG. 4C, when compared to the first
blasted surface shown in FIG. 4B. As can be observed in FIG. 4D,
the second blasting after oxidization can result in a more smooth
and porous surface than the surface after oxidization shown in FIG.
4C.
[0064] The porous structure after oxidization shown in FIG. 4C is
not observed on an oxidized Zr-based metallic glass surface without
the first blasting step, as shown in FIGS. 5A-B. FIG. 5A shows an
optical image of an oxidized Zr-based metallic glass surface
without any blasting. FIG. 5B shows a magnified optical image of
FIG. 5A. The resulting value of L* in the L*a*b* color spectrum
with a blasting step is lower than without a blasting step.
Likewise, a* and/or b* can be reduced. The oxidized surface appears
darker than the blasted surface. The reason for this is that light
scattering may be efficiently caused by the microstructure of the
oxide layer including granular growth, which may be good for low
reflection of light. With blasting, the granular growth of crystals
can spread from a nucleation point. Without blasting, the growth
direction can be parallel to the depth direction.
[0065] To further modify color and texture, the second blasting
after the oxidation step can provide additional darkening. FIGS.
6A-C show optical photos of outer appearance of three stages shown
in in FIG. 3 including (1) a first blasting, (2) oxidization, and
(3) a second blasting after oxidization.
[0066] In various aspects, one or both of a* and b* values can be
closer to zero by controlling the second blasting step. By
oxidizing a blasted surface, as shown in FIG. 6B, the surface
becomes darker than the blasted surface without further oxidization
as shown in FIG. 6A. By blasting after oxidization, the surface in
FIG. 6C becomes even darker than the surface after oxidization
without further blasting as shown in FIG. 6B. For example, the
color after oxidization, as shown in FIG. 6B, has an L* value of
less than 45, an a* value of between -2 and zero, and a b* value of
between -4 and zero. The color after the second blasting step, as
shown in FIG. 6C, has a slightly lower L* value than that shown in
FIG. 6B, and an a* value of greater than zero and less than 2, and
a b* value of greater than zero and less than 2.
[0067] Without wishing to be limited to any mechanism or mode of
action, when accumulating the oxidized layer by oxidization, the b*
value can be closer to zero. The surface in FIG. 6D becomes lighter
after a second oxidization (e.g. the b* value is increased) when
compared to the surface shown in FIG. 6C for a second blasting
step. For example, the color of the surface shown in FIG. 6D has an
L* value slightly higher than that shown in FIG. 6C, an a* value
that remains unchanged, and an increased the b* value than that
shown in FIG. 6C.
[0068] By repeating the blasting and oxidizing steps, the color of
the surface can be darkened or lightened and the texture can also
be modified, for example, such that the surface becomes porous.
[0069] The as-cast metallic glass surface can contain features such
as voids, coldshuts, flowlines, and misruns. Blasting can reduce
these features. In further variations, the methods described herein
can be used to improve or smooth surface features resulting from
the combination of the blasting and oxidizing method described
herein. In various aspects, the presence of surface features such
as voids and crystalline particles can be reduced and/or
concealed.
[0070] FIGS. 7A-D depict blasting and oxidation for reducing or
removing crystals from a Zr-based metallic glass surface by using
ZrO.sub.2 sphere shot media. A first panel, as shown in FIG. 7A,
depicts a crystal 704 on a metallic glass surface 702. A second
panel, as shown in FIG. 7B, depicts the metallic glass surface
after a one minute ZrO.sub.2 blasting step, where the crystal 704
was removed on the surface 702. A third panel, as shown in FIG. 7C,
depicts the surface after oxidation, where the crystal 704 was also
removed on the surface 702. A fourth panel, as shown in FIG. 7A,
depicts the surface after a second ZrO.sub.2 blasting step, where
the crystal 702 was removed on the surface.
[0071] FIGS. 8A-D depict blasting and oxidation for reducing or
removing micro-voids from a Zr-based metallic glass surface. The
blasting shot media was ZrO.sub.2. A first panel, as shown in FIG.
8A, depicts micro-voids 804 on a metallic glass surface 802. A
second panel, as shown in FIG. 8B, depicts the metallic glass
surface after a one minute ZrO.sub.2 blasting step, where the
micro-voids 804 were removed. A third panel, as shown in FIG. 8A,
depicts the surface after oxidation, where the micro-voids 804 were
also removed. A fourth panel, as shown in FIG. 8D, depicts the
surface after a second ZrO.sub.2 blasting step, where the
micro-voids 804 were also removed.
[0072] FIGS. 9A-D depict the blasting and oxidation steps for
reducing shedding parts from a Zr-based metallic glass surface.
Again, the blasting shot media was ZrO.sub.2. A first panel, as
shown in FIG. 9A, depicts a shedding part 902 on a polished
metallic glass surface. A second panel, as shown in FIG. 9B,
depicts the metallic glass surface after a one minute ZrO.sub.2
blasting step, in which the shedding part 902 on the metallic glass
surface was reduced. A third panel, as shown in FIG. 9C, depicts
the surface after oxidation and a further reduction of the shedding
part 902. A fourth panel, as shown in FIG. 9D, depicts the metallic
glass surface after a second ZrO.sub.2 blasting step, where the
shedding part 902 was reduced still further. Shedding can be
further reduced with additional blasting and oxidation steps.
[0073] FIG. 10A depicts an SEM image of the microstructure of the
oxide layer formed after oxidization. As shown, fine equiaxed oxide
crystals can be formed at the surface and grow down through the
metallic glass matrix as columnar structures with a preferential
growth direction. The microstructure in the thin surface region can
be changed to a porous structure (e.g. dendrite crystal) by a first
blasting or a preliminary blasting, which ensures the stability and
strength of the oxide layer on the metallic glass surface.
[0074] FIG. 10B depicts microstructural analysis of the metallic
glass surface of FIG. 10A by X-ray diffractometry. As shown in FIG.
10B, significant broadening of the tetra ZrO.sub.2 (111) peak was
observed after the secondary blasting step compared to the peak
just after oxidization. The peak broadening suggests inhomogeneous
strain introduction and implies formation of small amount of
monoclinic-ZrO.sub.2. Monoclinic-ZrO.sub.2 can be formed by stress
induced phase transformation of tetra-ZrO.sub.2. This mechanism can
be used for strengthening of ZrO.sub.2 ceramics by stopping
cracks.
[0075] In addition, a small peak shift to a lower angle of
tetra-ZrO.sub.2 (111) for the second blasted sample suggests an
increased lattice parameter (i.e. expanding volume of the metallic
glass). Without wishing to be held to mechanism or mode of action,
the compressive residual stress can also strengthen the oxidized
layer.
[0076] In some embodiments, a total processing time including
blasting and annealing is greater than 2000 seconds, alternatively
greater than 2500 seconds, alternatively greater than 3000 seconds,
alternatively greater than 3500 seconds, or alternatively greater
than 4000 seconds.
[0077] In various embodiments, the L*, a*, and/or b* color values
can be controlled in accordance with the embodiments of the
disclosure. For instance, the a* and b* values can be greater than
or equal to -20, alternatively greater than or equal to -15,
alternatively greater than or equal to -10, alternatively greater
than or equal to -5, alternatively greater than or equal to -4,
alternatively greater than or equal to -3, alternatively greater
than or equal to -2, or alternatively greater than or equal to -1.
Further, the a* and b* values can be less than or equal to 20, less
than or equal to 15, less than or equal to 10, less than or equal
to 5, alternatively less than or equal to 4, less than or equal to
3, less than or equal to 2, or less than or equal to 1. In various
aspects, the L* value can be less than or equal to 75. In various
aspects, the L* value can be less than or equal to 50.
Alternatively, the L* value can be less than or equal to 45.
Alternatively, the L* value can be less than or equal to 40.
Alternatively, the L* value can be less than or equal to 35.
Alternatively, the L* value can be less than or equal to 30. In
various aspects, the L* value can be greater than or equal to 20.
Alternatively, the L* value can be greater than or equal to 25.
Alternatively, the L* value can be greater than or equal to 30.
Alternatively, the L* value can be greater than or equal to 35.
[0078] Thermal Spray Blasting and Controlled Cooling
[0079] In a further aspect, the disclosure provides systems and
methods for thermal spray blasting a metallic glass surface
combined with controlled cooling. The systems and methods can be
used to control surface appearance, including color hue and
texture. The resulting metallic glass material is also
provided.
[0080] Thermal spray blasting is able to create a thick oxide layer
and a random surface texture on metallic glass material. In various
aspects, the surface is modified within a very short time, e.g.,
approximately 30-60 seconds. When the surface texture becomes
random, light reflection is reduced and thus the L* value of the
metallic glass surface can be reduced.
[0081] Further, an additional oxidation step need not be taking in
order to generate an oxide layer at the surface of the metallic
glass. Instead, thermal spray blasting combines blasting and
oxidization in a single step. In other words, the blasting and
oxidization occur simultaneously in thermal spray blasting.
[0082] In certain embodiments, the thermal spray blasting can be
generated by high velocity oxygen fuel (HVOF) or high velocity air
fuel (HVAF) thermal spray systems. Thermal spray blasting
parameters can be varied to obtain a desired surface modification
and appearance. For example, combustion parameters, scan pattern
and speed, type of shot media impacting the surface, intensity of
blasting beam, and other conditions known in the art can be
modified to control temperature and surface modification.
Temperature can be controlled using, e.g., spray cooling of the
thermal spray and the surface of the metallic glass. In certain
embodiments, the temperature of the thermal spray and the blasted
surface is additionally controlled, at least in part, by
controlling the combustion parameters and the scan pattern and
speed of the thermal spray. In some embodiments, temperature is
further controlled by a temperature-controlled sample holder.
[0083] In certain aspects, thermal spray blasting a metallic glass
surface with controlled cooling can provide an oxidized surface
modification in the surface treated metallic glass material. The
oxidized surface modification can control the appearance of the
metallic glass material, including, e.g., color and texture of the
metallic glass surface. By way of example and without limitation,
dark (e.g., black) colored surfaces can be achieved by the thermal
spray blasting methods with controlled cooling as described
herein.
[0084] Without wishing to be held to a particular mechanism or mode
of action, thermal spray blasting of the surface of a metallic
glass with controlled cooling can form a surface oxide layer. In
certain embodiments, the surface of the metallic glass is at least
partially melted during the thermal spray blasting, resulting in
impregnation of the blasted surface with blasting media. Further,
thermal spray blasting can create a minimally impacted surface
region containing shear bands or a supercooled liquid region due to
a high temperature gradient. In certain aspects, the controlled
cooling serves to quench the blasted surface below oxidation for
sufficient vitrification. The diffusibility in shear bands is high,
and therefore oxidization into the metallic glass surface area can
be accelerated, thus reducing processing time.
[0085] Again, without wishing to be held to a particular mechanism
or mode of action, the thermal spray blasting can create a distinct
temperature gradient on the blasted surface region due to the high
temperature of the flame. As such, sufficient cooling and
temperature control is used for vitrification of the melted region
on the surface of the metallic glass. The systems and methods of
the disclosure, including thermal spray blasting and controlled
cooling, therefore, can realize a combination of superheating,
blasting and super cooling to provide modified metallic glass
surface.
[0086] In various aspects, thermal blasting is performed using a
shot media. The size, morphology, and material of the shot media
can be selected and controlled to provide the desired surface
modification. For instance, the shot media can be a high melting
temperature material that does not partially or completely melt
during thermal spray blasting. In certain embodiments, the shot
media is a fine, e.g., having a median size between 10-100 .mu.m,
alternatively 10-45 .mu.m. In certain embodiments, the shot media
is a Zr-based, such as ZrO.sub.2 shots or beads.
[0087] In certain embodiments, the thermal spray flame can be
generated to provide any suitable temperature at the metallic glass
surface. For instance, depending on the specific materials of use,
the thermal spray flame can provide a temperature at the metallic
glass surface of between 200.degree. C. to 400.degree. C., or
alternatively between 250.degree. C. and 350.degree. C.
[0088] The methods described herein can be performed using any
suitable system. By way of example, in certain embodiments, a
system for thermal spray blasting of a surface with controlled
cooling can include a thermal spray gun with integrated spray
cooling in the flame nozzle, and a sample holder in operational
alignment with the thermal spray gun. The system can further
include at least one, two, three, or four spray cooling components
exterior to the thermal spray gun. In certain embodiments, the
thermal spray gun positioning and movement can be controlled by a
programmable robotic arm. In other embodiments, the sample holder
can be a temperature-controlled sample holder. The system can
further include thermocouples to monitor temperature at various
locations within the system.
[0089] Metallic glasses treated in accordance with the methods
described herein are also provided. In certain embodiments, the
metallic glass has an inconsistent oxidized surface morphology. By
way of example, the inconsistent oxidized surface morphology
exhibits rough surface variations having a depth of about 5-20
.mu.m. The surface roughness can be measured by laser
microscopy.
[0090] Various embodiments are discussed below with reference to
FIGS. 11-14. However, those skilled in the art will readily
appreciate that the detailed description given herein with respect
to these Figures is for explanatory purposes only and should not be
construed as limiting.
[0091] With reference to FIG. 11A, in accordance with certain
aspects of the disclosure, a system 1100 is illustrated, including
a thermal spray system 1102, e.g., an HVOF thermal spray system,
and spray cooling system 1104, e.g., a water mist spray cooling
system. In accordance with certain embodiments, the spray cooling
directly reduces the temperature of the thermal spray flame by
using, e.g., a mist water nozzle 1104a set inside the combustion
nozzle 1102a in thermal spray gun. Additional mist sprays 1104b,
which cool the blasting substrate, can also be included for
quenching after the thermal spray blasting. Further, a temperature
controlled sample holder 1106 can be included to provide additional
temperature control. In various aspects, the blasting angle can be
perpendicular to the sample. Alternatively, the blasting angle can
vary at an angle from perpendicular with the sample.
[0092] Thermal spray blasting parameters can be varied to obtain a
desired surface modification and appearance. In certain
embodiments, the thermal spray can be generated with various
blasting parameters so as to control temperature of the thermal
spray flame. By way of example, the combustion parameters, scan
pattern and scan speed, type of shot media impacting the surface,
intensity of blasting beam, and other conditions known in the art
can be varied to achieve desired temperature control. In certain
embodiments, the scan pattern can be generated with and without
sample overrun to increase or decrease temperature at the surface
of the metallic glass (discussed further below).
[0093] In other embodiments, the scan speed and frequency can be
varied to increase or decrease temperature at the surface of the
metallic glass. For instance, scan speeds can range from 25 mm/s to
200 mm/s, for example 50 mm/s to 100 mm/s. The temperature on the
metallic glass surface increases with the scan speed increases.
Further, scan frequency can range from 5 cycles to 25 cycles, for
example 10 cycles to 20 cycles. The blasting cycle does not affect
the surface temperature, but affects the surface smoothness. When
the number of blasting cycles increases, the blasted surface
becomes smoother. FIG. 11B illustrates example scanning patterns
for thermal spray blasting. Two sample scanning paths are
illustrated, one scanning path with sample overrun 1112 and one
scanning path without sample overrun 1114 to change the heating
effect of the thermal spray. Separately, the distance between the
thermal spray gun and sample can be varied to change the heating
effect of the thermal spray. For instance, the distance can be set
between 200-500 mm, for example 300 mm.
[0094] The L*, a*, and/or b* color values can be controlled in
accordance with the methods of the disclosure. For instance, the a*
and b* values can greater than or equal to -20, alternatively
greater than or equal to -15, alternatively greater than or equal
to -10, alternatively greater than or equal to -5, alternatively
greater than or equal to -4, alternatively greater than or equal to
-3, alternatively greater than or equal to -2, or alternatively
greater than or equal to -1. Further, the a* and b* values can be
less than or equal to 20, less than or equal to 15, less than or
equal to 10, less than or equal to 5, alternatively less than or
equal to 4, less than or equal to 3, less than or equal to 2, or
less than or equal to 1.
[0095] In various aspects, the L* value can be less than or equal
to 75. In various aspects, the L* value can be less than or equal
to 50. Alternatively, the L* value can be less than or equal to 45.
Alternatively, the L* value can be less than or equal to 40.
Alternatively, the L* value can be less than or equal to 35.
Alternatively, the L* value can be less than or equal to 30. In
various aspects, the L* value can be greater than or equal to 20.
Alternatively, the L* value can be greater than or equal to 25.
Alternatively, the L* value can be greater than or equal to 30.
Alternatively, the L* value can be greater than or equal to 35.
[0096] In accordance with certain embodiments, the thermal spray
blasting conditions can be varied so as to achieve desired color
hue, e.g., a* values and/or b* values of less than 5 and or greater
than -5, and L* values below 50. In various aspects, the a*and b*
values can separately be greater than -5, greater than -4, greater
than -3, greater than -2, or greater than -1. Alternatively, the a*
and b* values can separately be less than 5, less than 4, less than
3, less than 2, and less than 1. In various aspects, the L* value
can be less than 50. Alternatively, the L* value can be less than
45. Alternatively, the L* value can be less than 40. Alternatively,
the L* value can be less than 35. Alternatively, the L* value can
be less than 30.
[0097] For comparison, a non-blasted oxide surface shows an L*
value of less than 40, an a* value below zero (e.g., -1 to -5), and
b* value below zero (e.g., -5 to -15).
[0098] As an example, Sample 1 zirconium based metallic glass was
prepared according to embodiments of the disclosure, and shows a
dark color with the L*a*b* parameters having an L* value below 35,
an a* value near zero, and a b* value near zero. Thermal spray
operating parameters utilized to generate Sample 1 included a
ZrO.sub.2 blast media included a ZrO.sub.2 blast media (e.g.
Z10-45/10 by Fuji), and a scan speed of 50 mm/s for 10 cycles with
pattern overrun. The resulting thermal spray achieved a temperature
of about 270.degree. C. on the surface of the metallic glass. The
temperature can be measured by using a thermal sensor, such as a
radiation thermometer.
[0099] As another example, Sample 2 zirconium based metallic glass
was prepared according to embodiments of the disclosure. Sample 2
was prepared with a modified scan speed and pattern to eliminate
scan overrun and to increase the heating effect. Thermal spray
operating parameters utilized to generate Sample 2 included a
ZrO.sub.2 blast media (e.g. 210-45/10) and a scan speed of 100 mm/s
for 10 cycles without pattern overrun. The resulting thermal spray
achieved a temperature of about 370.degree. C. Under these
operating parameters, Sample 2 was bent by both softening above the
glass transition and strong HVOF blasting forces. Sample 2 showed a
dark color with L*a*b* parameters having an L* value below 35, an
a* value of less than 5 and greater than -5, and a b* value of less
than 5 and greater than -5. Compared to Sample 1, Sample 2
exhibited a slightly higher L* value and a* and b* values near
zero.
[0100] Following the observed bending of Sample 2, a support plate
was added to the system behind the sample to suppress bending. For
example, an example Sample 3 was prepared according to embodiments
of the disclosure with a reduced temperature of the HVOF flame to
avoid excessive heating. Thermal spray operating parameters
utilized to generate Sample 3 included a ZrO.sub.2 blast media
(e.g. Z10-45/10) and a scan speed of 100 mm/s for 10 cycles without
pattern overrun. The resulting thermal spray achieved a temperature
of about 310.degree. C. Sample 3 showed a good black color with the
L*a*b* parameters having an L* value below 35, an a* value of less
than 5 and greater than -5, and a b* value of less than 5 and
greater than -5. Compared to Sample 1 and Sample 2, Sample 3
exhibited a mid-range L* value, an a* value nearer Sample 1, and a
slightly positive b* value of less than 5 and greater than -5.
[0101] Sample 4 depicts a zirconium based metal glass prepared with
an increased number of thermal spray blasting cycles. The blasted
surface of Sample 4 became smoothed, revealing a slightly
blue-black color variation. Thermal spray operating parameters
utilized to generate Sample 4 included a ZrO.sub.2 blast media
(e.g. Z10-45/10) and a scan speed of 100 mm/s for 20 cycles without
pattern overrun. The resulting thermal spray achieved a temperature
of about 370.degree. C. A back support plate supported the metallic
glass.
[0102] Sample 4 showed a dark color with the L*a*b* parameters
having an L* value below 35, an a* value of less than 5 and greater
than -5, and a b* value of less than 5 and greater than -5.
Compared to other samples, Sample 4 exhibited a slightly higher L*
value, an a* value of less than 5 and greater than -5, and a
slightly more negative b* value of less than 5 and greater than
-5.
[0103] In all cases, HVOF blasting dramatically reduced the time
for oxidization-related black coloring treatment of Zr-based
metallic glasses (e.g. about 30 seconds) compared with processes of
blasting and oxidization by annealing (e.g. a total processing time
greater than 3000 seconds or 50 minutes). Dark color L*a*b*
parameters were obtained for all samples. In some embodiments, the
blasting time is less than 2 minutes, alternatively less than 1
minute, alternatively, less than 50 seconds, alternatively less
than 40 seconds, alternatively less than 30 seconds, alternatively
less than 20 seconds, or alternatively less than 10 seconds.
[0104] In accordance with certain aspects of the disclosure, FIGS.
12A-12B show schematic illustrations which depict the effect of
thermal spray blasting. As illustrated, the process is
characterized by a combination of simultaneous blasting and
oxidizing. FIG. 12A depicts thermal spray blasting 1202 generating
a temperature at the metallic glass surface 1204 below Tg. As
shown, below Tg, blast-introduced shear bands 1206 are formed that
act to increase the diffusibility of gas 1208 into the blasted
metallic glass matrix 1210. The depth and degree of improved
diffusibility can be controlled, e.g., by the size and type of shot
media. In addition, spray cooling mist can lead to the formation of
hydroxides, which generate a porous oxide layer 1212 on the
metallic glass surface 1204. Furthermore, as illustrated in FIG.
12B, when thermal spray blasting 1202 is continued and generates a
temperature at the metallic glass surface 1204 above Tg, the
surface region can be a supercooled liquid state 1214.
[0105] The thermal spray blasting described herein can cause
high-speed heating of the surface of the metallic glass. When
performed with the high scan speeds described herein in combination
with cooling control, the temperature gradient of the blasted
region in the depth direction becomes steeper. This steep
temperature gradient is quite important for creating a surface
melted region in the supercooled liquid state (above Tg, but not
yet crystallized). In accordance with certain aspects of the
disclosure, it has been found that thermal spray blasting above Tg
leads to significant splashing and generates a random surface
morphology. Specifically, the surface becomes random, reducing
light reflection and decreasing the L* value of the metallic
glass.
[0106] In accordance with certain aspects of the disclosure, during
thermal spray blasting, a distinct flashing at or near the surface
of the metallic glass can be observed, which indicates that the
surface region is heated above Tg, causing splashing and burning
(rapid oxidation) of the resulting metallic glass droplets. This
phenomenon can result in the roughened surface observed on the
blasted surface of the metallic glass samples.
[0107] In accordance with certain aspects of the disclosure, the
systems and methods can alter the metallic glass at temperatures
below Tg and above Tg. However, given the speed and intensity of
the process, the resulting high-speed heating and cooling can
effectively suppress crystallization and structural relaxation of
the metallic glass. By using thermal spray blasting and cooling
conditions, oxidized black-colored metallic glass, such as Zr-based
metallic glasses, can be generated without substantial
embrittlement due to structural and microstructural changes.
[0108] By way of example, with reference to FIGS. 13C-13D, cross
sectional images of Sample 3 described above reveal a random
surface morphology. As illustrated in FIGS. 13C-13D, a rough
surface with surface variations having a depth of about 5-20 .mu.m,
e.g., 10 .mu.m, is observed, though the oxide layer thickness is
not consistent. The random morphology of this surface is indicative
of the high temperature state (supercooled liquid above Tg) of the
surface during thermal spray blasting. For comparison, FIGS.
13A-13B illustrate an oxidized surface created through a
combination of blasting and annealing. As can be seen in FIGS.
13C-13D, the rough surface morphology and uneven oxide layer
thickness of the metallic glass material subjected to thermal spray
blasting with controlled cooling is not observed in the oxidized
surface of the metallic glass material subjected to a combination
of blasting and annealing.
[0109] In some embodiments, after a combination of blasting and
oxidization, the metallic glass can have an inconsistent oxidized
surface that exhibits rough surface variations having a depth of
equal to or less than 20 .mu.m, alternatively equal to or less than
15 .mu.m, or alternatively equal to or less than 10 .mu.m. In some
embodiments, the metallic glass can have an inconsistent oxidized
surface that exhibits rough surface variations having a depth of
equal to or greater than 5 .mu.m, alternatively equal to or greater
than 10 .mu.m, or alternatively equal to or greater than 15
.mu.m.
[0110] Dissimilar Shot Blasting
[0111] The disclosure also provides a method of using a combination
of different shot types during blasting, referred to herein as
dissimilar shot blasting. The dissimilar shots can result in
control of hue color, and can provide different impacts on
complementary and structural color. In various aspects, dissimilar
shot blasting media includes both large shot media and fine shot
media. The combination of media provides for different material
properties on the same metallic glass.
[0112] Without wishing to be limited to a particular effect or mode
of action, large shot media (e.g. shot media average size between
100 .mu.m and 2000 .mu.m) has a larger impact and makes a deeper
residual compressive stress in the metallic glass than fine shot
media. In contrast, fine shot media (e.g. shot media average size
between 10 .mu.m and 100 .mu.m) can create thin blast-impacted
region on the surface. In addition, the density, shape, and
stiffness of the shot material are important factors that allow
control of the texture and structure of blasted surface. Blasting
using dissimilar blast shot media can provide additional control of
dark color of the metallic glass, such as in Zr-based metallic
glasses, by oxidizing the blasted metallic glass surface. The
blasting system and method are similar to that disclosed earlier by
a combination of blasting and oxidization described herein.
[0113] In some aspects, large shot media can include sphere shaped
base particles with sharp vertex. In some aspects, the sphere
shaped particles can include a softer base material such as rubber,
into which sharp harder components such as ceramics are embedded.
The large shot media with sharp harder component can produce the
microstructure observed in a supper black Ni-based metallic
glass.
[0114] FIG. 14 shows the surface structure of a dark Ni-based
metallic glass obtained with a chemical etching treatment. The
black Ni-based metallic glass has certain L*, a*, and b* values of
color space, i.e. an L* value of less than 10, an a* value of less
than 1 and greater than -1, and a b* value of greater than -1 and
less than 0. When the L*, a*, and b* values are nearly zero, the
color is substantially black. The microstructure surface of the
black Ni-based metallic glass is characterized by existence of
deep-sharp indentation marks. This surface structure provides a
structural color of the black Ni-based metallic glass.
[0115] In order to fabricate the black color and the surface
texture as shown in FIG. 14, the shape of an example of a sphere
shaped rubber based shot medium is shown in FIG. 15. The rubber
based shot media 1502 creates mass for blast energy and stiffness
for the lifetime of the shot. A ceramic material 1504 partially
embedded in and protruding from the sphere shaped rubber base 1502
has a sharp vertex, such as vertex SiC media. In some embodiments,
the shot media may have no vertex but can have a diamond coating.
In some aspects, the diamond coating may be suitable for polishing
surface. The vertex is configured to make deep/sharp indentation
marks on a blasted surface. It will be recognized that the ceramic
material can be selected from any ceramic known in the art. In some
aspects, the ceramic is made of SiC, which is low cost and has
sharp vertex. Any ceramic known in the art can be used. In some
aspects, the large shot media can be Sirius #320 (Fuji
Manufacturing). Because the large shot media has sufficient mass or
weight to achieve high energy for blasting, the weight of SiC
blasting media can be increased by combining SiC with a resin.
Furthermore, the resin can have a damping effect for suppression of
breakage of SiC particles.
[0116] Without wishing to be held to a particular mechanism or mode
of action, the greater the mass, size, and shape of the base and
protruded protrusion of large shot media such as that depicted in
FIG. 15, the greater the indentation of the shot on the metallic
glass. It will be appreciated by those skilled in the art that the
shape and size and the materials including base 1502 and protruded
portion 1504 of the shot media can vary depending upon the depth of
the indentation desired for a blasted surface.
[0117] In various aspects, blasting using large shot media on a
Zr-based metallic glass can have any incident angle. In many
aspects, the incident angle of shot media can be at a right angle
or nearly a right angle with a slight deviation of about 2 degrees
from the surface. Blasting can be performed at room temperature, or
a variation of temperatures.
[0118] In some aspects, the gas pressure of the blasting beam can
be at least 0.3 MPa. In some aspects, the gas pressure is at least
0.4 MPa. In some aspects, the gas pressure is at least 0.5 MPa.
Such pressures can create a deeper or sharper indentation on the
metallic glass surface.
[0119] In various aspects, the blasting time for the large shot
media or the fine shot media can be at least 5 minutes. In various
aspects, the blasting time can be at least 7 minutes. In various
aspects, the blasting time can be at least 9 minutes. In various
aspects, the blasting time can be at least 11 minutes. In various
aspects, the blasting time can be at least 13 minutes. In various
aspects, the blasting time can be at least 15 minutes.
[0120] FIG. 16A shows a SEM image of the outer appearance of the
surface of a Zr-based metallic glass blasted using large shot media
(Sirius #320). FIG. 16B shows an example of the surface structure
and texture of the metallic gas when treated with blast media at
various gas pressures. As shown, the highest gas pressure of 0.5
MPa created deeper and shaper indentation marks than when blasting
proceeded at lower gas pressures (e.g. 0.15 MPa and 0.3 MPa). As
shown in FIG. 16C, the depth of indentation is as deep as 3.658
.mu.m when a gas pressure of 0.5 MPa and two blasting passes were
applied to the metallic glass. The depth of indentation is as deep
as 1.981 .mu.m with a gas pressure of 0.16 MPa and two passes
applied to the metallic glass, while the depth is as deep as 1.562
.mu.m with a gap pressure of 0.3 MPa and two passes applied to the
metallic glass.
[0121] FIG. 17A shows that more metallic glass can be removed at an
increased depth by using large shot media. FIG. 17A shows an
optical image of the metallic glass surface blasted by using large
shot media (Sirius #320). FIG. 17A also shows a cross sectional
depth profile along the respective lines on the image. For example,
point [1] has a depth of 0 .mu.m, point [2] has a depth of 3.934
.mu.m, point [3] has a depth of about -5 .mu.m, and point [4] has a
depth of about zero .mu.m. The distance between point [2] and point
[4] is 15.422 .mu.m. The surface roughness can be measured by laser
micro scope.
[0122] FIG. 17A also shows a predicted cross-sectional image of a
metallic glass by using the large shot media. A deep indentation
layer 1702 is formed on the surface of a metallic glass 1704. As
shown, a surface roughness Rz of the metallic glass 1704 is about 7
.mu.m, which indicates that the combination of large shot media and
a high gas pressure can make a deep profile of residual stress. The
presence of shear bands is depicted in FIG. 17B. The deep
indentation marks can provide for structural color and reduce light
reflection.
[0123] Without wishing to be limited to a specific mechanism or
mode of action, deep and coarse shear bands can be characterized by
loose random packing of atoms. Loose random packing can increase
the mobility of atoms and is an important structural factor for
increasing chemical reactions, for example, oxidization. Both the
density and distribution of shear bands can be adjusted for making
a desired chemical reacted region on a blasted surface.
[0124] Dense shear bands formed in a blasted region can be obtained
by blasting a small sized or fine shot media. To avoid the effect
of contaminated/penetrated media on a metallic glass surface, a
fine zirconia (ZrO.sub.2) shot media that are sphere like particles
without sharp vertex (e.g. B505 by Fuji) can be used. B505 may
include ZrO.sub.2, SiO.sub.2, Al.sub.2O.sub.3, or CuO among
others.
[0125] FIG. 18A shows an optical image of the fine Zr-based
blasting media metallic glass surface and a corresponding cross
sectional depth profile along the lines on the optical image. As
shown, the maximum value of surface roughness Rz is about 2 .mu.m,
which is about the same value as the as-cast state before the
blasting, which indicates that the combination of small sized shot
media and low gas pressure would make the very thin impacted
region. As such, the shear bands would be condensed in a surface
region with a depth of a few microns.
[0126] FIG. 18B shows the predicted cross-sectional image of a
metallic glass blasted by using a second fine blasting shot media
(e.g. B505). A layer of dense shear bands 1802 can be formed on the
surface of the metallic glass 1704 by blasting with the fine
blasting shot media (B505). The dense shear bands can have a
thickness of about 2 microns. The dense shear bands can increase
diffusibility and accelerate the growth rate of an oxide layer
under oxidization. Therefore, this treatment using fine shot media
is good for black color after oxidization as a result of forming a
thick oxide layer. This surface treatment can promote surface
oxidization, and accelerate oxide segregation at a grain boundary
of an oxide layer. For instance, a complementary color by CuO (e.g.
black color) might be assisted by using this surface treatment.
[0127] In accordance with certain embodiments, blasting with a
combination of dissimilar shot media and oxidization can be varied
so as to achieve desired color hue, e.g., an a* value and/or a b*
value of less than 3 and or greater than -3, and an L* value below
35. In various aspects, the a* and b* values can separately be
greater than -3, greater than -2, or greater than -1.
Alternatively, the a* and b* values can separately be less than 3,
less than 2, less than 1. In various aspects, the L* value can be
less than 35. Alternatively, the L* value can be less than 30.
Alternatively, the L* value can be less than 25.
[0128] For comparison, a non-blasted oxide surface has an L* value
of less than 40, and an a* value close to zero (e.g., -1 to -5),
and a negative b* value below zero (e.g., -5 to -15).
[0129] The combination of the two dissimilar blasting media can
make a deep black color. FIG. 19 shows a predicted blasted profile
by using a combination of fine blasting shot media (e.g. B505) and
large shot media (e.g. Sirius #320). The profile includes the dense
shear band layer 1802 over the deep indentation layer 1702. The
blasted metallic glass surface is then oxidized. The large shot
media can reduce only the L* value, but does not affect the b*
value, when compared to an oxidized Zr-based metallic glass without
blasting. In contrast, the fine blasting shot media can reduce both
the a* and b* values to be nearly zero, while the L* value remains
unchanged when compared to an oxidized Zr-based metallic glass
without blasting. With the combination of the blasting media B505
and blasting media Sirius #320 before oxidization, a deep black
color is created.
[0130] By way of example and not limitation, the black color has an
L* value below 30, an a* value of greater than -2 and less than 2,
and a b* value of greater than -15 and less than 15 for a blasted
Zr-based metallic glass surface by using the large shot media
Sirius #320.
[0131] A dark color has an L* value below 45, an a* value of
greater than -2 and less than 2, and a b* value of greater than -2
and less than 2 for a blasted Zr-based metallic glass surface by
using B505. By way of example and not limitation, the color is
lighter than the blasted Zr-based metallic glass surface using the
large shot media Sirius #320.
[0132] A dark color with an L* value below 35, an a* value of
greater than -1 and less than 1, and a b* value of greater than -1
and less than 1 for a blasted Zr-based metallic glass surface by
using a combination of large shot media Sirius #320 and fine shot
media B505. The color is lighter than the blasted Zr-based metallic
glass surface by using Sirius #320, but is darker than the blasted
Zr-based metallic glass surface by using B505.
[0133] Compared to the single blasting by large shot media or the
single blasting by fine media, the combined blasting of both large
shot media and fine shot media provides a reduced L* value and a b*
value closer to zero than the blasted metallic glass surface by
using the fine shot media with a first blasting step and a second
blasting step as illustrated in FIG. 3, an L* value of less than 40
and a b* value of less than 2 or greater than -2 can be obtained.
The L* value of less than 40 of the fine shot media with a first
blasting step and a second blasting step is higher than an L* value
of 35 for the blasted surface by using the combination of
dissimilar shot media. The b* value of less than 2 or greater than
-2 of the fine shot media with a first blasting step and a second
blasting step is larger than a b* value of 1 or greater than -1 for
the blasted surface by using the combination of dissimilar shot
media.
[0134] The combination of dissimilar shot blasting provided a
darker surface color. For example, a deep black color of Zr-based
metallic glass (e.g. LM105) can be created by blasting a
combination of fine blasting shot media (e.g. B505) and another
large blasting shot media (e.g. Sirius #320). The fine blasting
shot media can reduce the b* value to be nearly zero (e.g. a b*
value between -1 and 1), while the large shot media Sirius #320 can
reduce the L* value toward nearly zero (e.g. an L value below
35).
[0135] In some embodiments, a total processing time including
blasting and annealing is greater than 2000 seconds, alternatively
greater than 2500 seconds, alternatively greater than 3000 seconds,
alternatively greater than 3500 seconds, or alternatively greater
than 4000 seconds.
[0136] In alternative embodiments, the large shot media and the
fine shot media can be premixed. The mixture of the dissimilar shot
media can then be blasted on a metallic glass. In some embodiments,
the method can include an additional oxidation step. The metallic
glass can be first blasted by large shot media (e.g. Sirius #320),
followed by fine size shot media (e.g. B505), then followed by
oxidization of the blasted metallic glass surface.
[0137] In some embodiments, the sequence of the blasting the
dissimilar shot media can be reversed. For example, the metallic
glass can be first blasted by a fine shot media (e.g. B505),
followed by large shot media (e.g. Sirius #320), then followed by
oxidization of the blasted metallic glass surface.
[0138] In some embodiments, the fine media shot has a median size
equal to or less than 100 .mu.m, alternatively equal to or less
than 90 .mu.m, alternatively equal to or less than 80 .mu.m,
alternatively equal to or less than 70 .mu.m, alternatively equal
to or less than 60 .mu.m, alternatively equal to or less than 50
.mu.m, alternatively equal to or less than 40 .mu.m, alternatively
equal to or less than 30 .mu.m, alternatively equal to or less than
20 .mu.m. In some embodiments, the fine media shot has a median
size equal to or greater than 10 .mu.m, alternatively equal to or
greater than 20 .mu.m, alternatively equal to or greater than 30
.mu.m, alternatively equal to or greater than 40 .mu.m,
alternatively equal to or greater than 50 .mu.m, alternatively
equal to or greater than 60 .mu.m, alternatively equal to or
greater than 70 .mu.m, alternatively equal to or greater than 80
.mu.m, alternatively equal to or greater than 90 .mu.m.
[0139] The depth of the oxide layer can be strongly affected by
alloy composition. In various aspects, the blasted oxide layer may
have a depth varying from 2 to 4 .mu.m. However, an increased depth
of the oxide layer can help increase the darkness of the resulting
surface color.
[0140] In some embodiments, after blasting by a combination of
dissimilar shot media and oxidization, the metallic glass can have
a consistent oxidized surface that exhibits rough surface
variations having a depth of equal to or less than 10 .mu.m,
alternatively equal to or less than 8 .mu.m, alternatively equal to
or less than 6 .mu.m, alternatively equal to or less than 4 .mu.m,
or alternatively equal to or less than 2 .mu.m. In some
embodiments, the metallic glass can have a consistent oxidized
surface that exhibits rough surface variations having a depth of
equal to or greater than 2 .mu.m, alternatively equal to or greater
than 4 .mu.m, alternatively equal to or greater than 6 .mu.m, or
alternatively equal to or greater than 8 .mu.m.
[0141] Metallic Glasses
[0142] The systems and methods described herein can be applicable
to any suitable metallic glass known in the art. In some
non-limiting aspects, the metallic glass can be based on, or
alternatively include, one or more elements that oxidize, such as
Zr, Ti, Ta, Hf, Mo, W and Nb. In some variations, the metallic
glass includes at least about 30% one or more of Zr, Ti, Ta, Hf,
Mo, W and Nb. In some variations, the metallic glass includes at
least about 40% one or more of Zr, Ti, Ta, Hf, Mo, W and Nb. In
some variations, the metallic glass includes at least about 50% one
or more of Zr, Ti, Ta, Hf, Mo, W and Nb. In certain embodiments,
the metallic glass can be based on, or alternatively include, Zr.
In some variations, the metallic glass includes at least about 30%
Zr. In some variations, the metallic glass includes at least about
40% Zr. In some variations, the metallic glass includes at least
about 50% Zr. Similarly, the surface treated metallic glass
material described herein as a constituent of a composition or
article can be of any type.
[0143] The metallic glass can include multiple transition metal
elements, such as at least two, at least three, at least four, or
more, transitional metal elements. The metallic glass can also
optionally include one or more nonmetal elements, such as one, at
least two, at least three, at least four, or more, nonmetal
elements. A transition metal element can be any of scandium,
titanium, vanadium, chromium, manganese, iron, cobalt, nickel,
copper, zinc, yttrium, zirconium, niobium, molybdenum, technetium,
ruthenium, rhodium, palladium, silver, cadmium, hafnium, tantalum,
tungsten, rhenium, osmium, iridium, platinum, gold, mercury,
rutherfordium, dubnium, seaborgium, bohrium, hassium, meitnerium,
ununnilium, unununium, and ununbium. In one embodiment, a metallic
glass containing a transition metal element can have at least one
of Sc, Y, La, Al, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe,
Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, and Hg.
Depending on the application, any suitable transitional metal
elements, or their combinations, can be used.
[0144] Depending on the application, any suitable nonmetal
elements, or their combinations, can be used. A nonmetal element
can be any element that is found in Groups 13-17 in the Periodic
Table. For example, a nonmetal element can be any one of F, Cl, Br,
I, At, O, S, Se, Te, Po, N, P, As, Sb, Bi, C, Si, Ge, Sn, Pb, and
B. Occasionally, a nonmetal element can also refer to certain
metalloids (e.g., B, Si, Ge, As, Sb, Te, and Po) in Groups 13-17.
In one embodiment, the nonmetal elements can include B, Si, C, P,
or combinations thereof. Accordingly, for example, the alloy can
include a boride, a carbide, or both.
[0145] In some embodiments, the metallic glass described herein can
be fully alloyed. The term fully alloyed used herein can account
for minor variations within the error tolerance. For example, it
can refer to at least 90% alloyed, such as at least 95% alloyed,
such as at least 99% alloyed, such as at least 99.5% alloyed, or
such as at least 99.9% alloyed. The percentage herein can refer to
either volume percent or weight percentage, depending on the
context. These percentages can be balanced by impurities, which can
be in terms of composition or phases that are not a part of the
alloy. The alloys can be homogeneous or heterogeneous, e.g., in
composition, distribution of elements, amorphicity/crystallinity,
etc.
[0146] The metallic glass can include any combination of the above
elements in its chemical formula or chemical composition. The
elements can be present at different weight or volume percentages.
Alternatively, in one embodiment, the above-described percentages
can be volume percentages, instead of weight percentages.
[0147] In certain embodiments, the metallic glass can be
zirconium-based. The metallic glass can also be substantially free
of various elements to suit a particular purpose. For example, in
some embodiments, the metallic glass can be substantially free of
nickel, aluminum, titanium, beryllium, or combinations thereof. In
one embodiment, the alloy or the composite is completely free of
nickel, aluminum, titanium, beryllium, or combinations thereof.
[0148] The afore described metallic glasses can further include
additional elements, such as additional transition metal elements,
including Nb, Cr, V, and Co. The additional elements can be present
at less than or equal to about 30 wt %, less than or equal to about
20 wt %, less than or equal to about 10 wt %, or less than or equal
to about 5 wt %. In one embodiment, the additional, optional
element is at least one of cobalt, manganese, zirconium, tantalum,
niobium, tungsten, yttrium, titanium, vanadium and hafnium to form
carbides and further improve wear and corrosion resistance. Further
optional elements can include phosphorous, germanium and arsenic,
totaling up to about 2%, or less than 1%, to reduce the melting
point. Otherwise incidental impurities should be less than about 2%
or less than 0.5%.
[0149] In some embodiments, the metallic glass can include a small
amount of impurities. The impurity elements can be intentionally
added to modify the properties of the composition, such as
improving the mechanical properties (e.g., hardness, strength,
fracture mechanism, etc.) and/or improving the corrosion
resistance. Alternatively, the impurities can be present as
inevitable, incidental impurities, such as those obtained as a
byproduct of processing and manufacturing. The impurities can be
less than or equal to about 10 wt %, about 5 wt %, about 2 wt %,
about 1 wt %, about 0.5 wt %, or about 0.1 wt %. In some
embodiments, these percentages can be volume percentages instead of
weight percentages.
[0150] The disclosed methods herein can be valuable in the
fabrication of electronic devices using a metallic glass-containing
part. An electronic device herein can refer to any electronic
device known in the art. For example, it can be a telephone, such
as a mobile phone, and a land-line phone, or any communication
device, such as a smart phone, including, for example an
iPhone.RTM., AppleWatch, and an electronic email sending/receiving
device. It can be a part of a display, such as a digital display, a
TV monitor, an electronic-book reader, a portable web-browser
(e.g., iPad.RTM.), and a computer monitor. It can also be an
entertainment device, including a portable DVD player, conventional
DVD player, Blue-Ray disk player, video game console, music player,
such as a portable music player (e.g., iPod.RTM.), etc. It can also
be a part of a device that provides control, such as controlling
the streaming of images, videos, sounds (e.g., Apple TV.RTM.), or
it can be a remote control for an electronic device. It can be a
part of a computer or its accessories, such as the hard drive tower
housing or casing, laptop housing, laptop keyboard, laptop track
pad, desktop keyboard, mouse, and speaker. The article can also be
applied to a device such as a watch or a clock.
[0151] The methods can also be valuable in forming wearable
metallic glass products that have a good cosmetic profile and do
not readily degrade or show evidence of wear.
[0152] Any ranges cited herein are inclusive. The terms
"substantially" and "about" used throughout this Specification are
used to describe and account for small fluctuations. For example,
they can refer to less than or equal to..+-.5%, such as less than
or equal to .+-.2%, such as less than or equal to .+-.1%, such as
less than or equal to .+-.0.5%, such as less than or equal to
.+-.0.2%, such as less than or equal to .+-.0.1%, such as less than
or equal to .+-.0.05%.
[0153] Having described several embodiments, it will be recognized
by those skilled in the art that various modifications, alternative
constructions, and equivalents can be used without departing from
the spirit of the disclosure. Additionally, a number of well-known
processes and elements have not been described in order to avoid
unnecessarily obscuring the present disclosure. Accordingly, the
above description should not be taken as limiting the scope of the
disclosure.
[0154] Those skilled in the art will appreciate that the presently
disclosed embodiments teach by way of example and not by
limitation. Therefore, the matter contained in the above
description or shown in the accompanying drawings should be
interpreted as illustrative and not in a limiting sense. The
following claims are intended to cover all generic and specific
features described herein, as well as all statements of the scope
of the present method and system, which, as a matter of language,
might be said to fall therebetween.
* * * * *