U.S. patent application number 15/763556 was filed with the patent office on 2018-10-04 for abrasive blast modification of surfaces.
The applicant listed for this patent is ENBIO LIMITED. Invention is credited to Paolo Vincenzo Ercole FIORINI, John O'DONOGHUE, Liam O'NEILL, Kevin ROCHE, Barry TWOMEY.
Application Number | 20180282874 15/763556 |
Document ID | / |
Family ID | 54544224 |
Filed Date | 2018-10-04 |
United States Patent
Application |
20180282874 |
Kind Code |
A1 |
TWOMEY; Barry ; et
al. |
October 4, 2018 |
ABRASIVE BLAST MODIFICATION OF SURFACES
Abstract
A metal surface treatment method wherein the surface (10) is
simultaneously bombarded with a mixture of abrasive particles (4)
and dopant particles (6) which are delivered at a velocity in the
range of 50-250 m/sec, and thereby depositing the dopant material
on the surface. Also provided is an article (8) having a surface
treated by such a method.
Inventors: |
TWOMEY; Barry; (Dublin 18,
IE) ; O'DONOGHUE; John; (Co. Waterford, IE) ;
ROCHE; Kevin; (Dublin 6, IE) ; O'NEILL; Liam;
(Co. Cork, IE) ; FIORINI; Paolo Vincenzo Ercole;
(Dublin 16, IE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ENBIO LIMITED |
Dublin 11 |
|
IE |
|
|
Family ID: |
54544224 |
Appl. No.: |
15/763556 |
Filed: |
September 28, 2016 |
PCT Filed: |
September 28, 2016 |
PCT NO: |
PCT/EP2016/073155 |
371 Date: |
March 27, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B24C 1/00 20130101; C23C
24/04 20130101; B24C 11/005 20130101 |
International
Class: |
C23C 24/04 20060101
C23C024/04; B24C 11/00 20060101 B24C011/00; B24C 1/00 20060101
B24C001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 28, 2015 |
GB |
1517128.3 |
Claims
1. A metal surface treatment method wherein the surface is
simultaneously bombarded with a mixture of abrasive particles and
dopant particles which are delivered at a velocity in the range of
50-250 m/sec, and thereby depositing the dopant material on the
surface.
2. A method as claimed in claim 1, wherein the particles are
delivered at a velocity in the range of 100-200 m/sec.
3. A method as claimed in claim 2, wherein the particles are
delivered at a velocity in the range of 120-180 m/sec.
4. A method as claimed in claim 1, carried out at ambient
temperature.
5. A method as claimed in claim 1, wherein the abrasive particles
have an irregular or angular morphology.
6. A method as claimed in claim 1, where the dopant is directly
chemically bonded to the metal surface without any intermediate
oxide layer.
7. A method as claimed in claim 1, wherein the dopant particles are
agglomerated together on the metal surface.
8. A method as claimed in claim 1, wherein the abrasive has a
hardness greater than 6.0 on the Mohs scale.
9. A method as claimed in claim 1, wherein the abrasive has a
hardness of 8.0 or above on the Mohs scale.
10. A method as claimed in claim 1, wherein the abrasive has a
hardness at least 2 levels higher than that of the dopant on the
Mohs scale.
11. A method as claimed in claim 1, wherein the abrasive has a
hardness at least 3 levels higher than that of the dopant on the
Mohs scale.
12. A method as claimed in claim 1, wherein the dopant is a polymer
and the abrasive has an average particle size in the range of
5-5000 microns.
13. A method as claimed in claim 12, wherein the abrasive has an
average particle size in the range of 5-1500 microns.
14. A method as claimed in claim 13, wherein the abrasive has an
average particle size in the range of 10-150 microns.
15. A method as claimed in claim 13, wherein the dopant is a
polymer and the abrasive has an average particle size in the range
of 150-1500 microns.
16. A method as claims in claim 15, wherein the abrasive has an
average particle size in the range of 250-1000 microns.
17. A method as claimed in claim 16, wherein the abrasive has an
average particle size in the range of 350-750 microns.
18. A method as claimed in claim 1, wherein the dopant is a polymer
and the abrasive has an average particle size of greater than 300
microns.
19. A method as claimed in claim 12, wherein the abrasive
constitutes at least 60 wt % of the mixture of abrasive and dopant
particles.
20. A method as claimed in claim 19, wherein the abrasive
constitutes at least 70 wt % of the mixture of abrasive and dopant
particles.
21. A method as claimed in claim 20, wherein the abrasive
constitutes at least 80 wt % of the mixture of abrasive and dopant
particles.
22. A method as claimed in claim 1, wherein the dopant is a
non-polymeric material and the abrasive has an average particle
size of less than 500 microns.
23. A method as claimed in claim 22, wherein the abrasive has an
average particle size of less than 200 microns.
24. A method as claimed in claim 23, wherein the abrasive has an
average particle size of less than 150 microns.
25. A method as claimed in claim 22, wherein the dopant constitutes
at least 20 wt % of the mixture of abrasive and dopant
particles.
26. A method as claimed in claim 25, wherein the dopant constitutes
at least 25 wt % of the mixture of abrasive and dopant
particles.
27. A method as claimed in claim 26, wherein the dopant constitutes
at least 40 wt % of the mixture of abrasive and dopant
particles.
28. A method as claimed in claim 1, wherein the dopant particles
have an average particle size in the range of 1-100 microns.
29. A method as claimed in claim 1, wherein less than 10 microns of
dopant material are deposited on the surface.
30. A method as claimed in claim 1, wherein at least some of the
dopant particles penetrate the metal surface and remain physically
impregnated in the metal.
31. A method as claimed in claim 1, further comprising applying an
additional coating on top of the deposited dopant material.
32. A method as claimed in claim 31, wherein the additional coating
is applied through a bombardment technique selected from cold
spray, peen plating or microblasting.
33. An article having a surface treated by a method as claimed in
claim 1.
34. An article as claimed in claim 33, wherein the surface is at
least a part of: an implantable medical device; a marine or
land-based vehicle; an aerospace vehicle, satellite, rocket, or
spacecraft; an electronic device or component; a mould; or a pipe,
tube or storage vessel.
35-36. (canceled)
Description
FIELD OF THE INVENTION
[0001] The present invention relates to surface treatment
techniques in the field of materials science.
BACKGROUND TO THE INVENTION
[0002] Metal surface finish is often provided using particle
bombardment. This can vary from material removal using abrasive
blasting through to material deposition using cold spraying. The
difference in these approaches rests in the energy of the
processes. Despite its name, the cold spray process actually uses
elevated temperatures. The gas used to carry the particles is
heated to a temperature of several hundred degrees, typically
between 200.degree. C. and 1000.degree. C., before it is mixed with
the bombardment particles. This increases the gas velocity without
increasing the line pressure feeding the gas. Typically cold spray
processes operate at elevated temperatures but below the melting
point of the metallic bombardment particles that are employed. In
addition to the thermal energy provided by the heated gas, the
kinetic energy of the bombarding particles is also higher in cold
spray systems as the particles travel at significantly higher
velocities than in abrasive blasting. The particles are typically
accelerated to supersonic speeds (greater than 342 m/sec). At high
velocities, greater than 300 m/sec, the energy imparted by the
impact of the particle against the surface can be sufficient to
cause both the metal surface and the bombarding metal particle to
deform and the resultant interaction causes the particle to spread
out and coat the surface. The minimum velocity required to achieve
this coating deposition is referred to as the `critical velocity`
in cold spray technology. Due to the requirement for the bombarding
particle to deform upon impact, there has been limited
applicability of this technology to the deposition of non-metallic
materials. At values below the critical velocity, very little
impregnation of the surface occurs and the bombarding particles
typically bounce off the surface. The widely quoted minimum
critical velocity for a wide range of materials is 400 m/sec, as
outlined in Grigoriev et al. (Surf. Coat. Technol., 268 (2015), pg
77-84) and as shown in the present FIG. 1, which is taken from that
publication. This value can vary depending upon the bombarding
particles and the properties of the substrate surface.
[0003] In most metallic materials an oxide layer forms at the
surface, which will be harder than the bulk metal or alloy. Metal
surfaces (especially those of titanium and titanium derived alloy)
are naturally contaminated in air by a variety of contaminants. The
detailed physical and chemical properties of any metal surface
depend on the conditions under which they are formed. The inherent
reactivity of the metal can also attract various environmental
chemicals/contaminants that oxidize on the surface. For example,
titanium is a highly reactive metal, which is readily oxidized by
several different media. This results in titanium, and most other
metals, always being covered in an oxide layer. This oxide layer is
chemically stable and much harder than the bulk metal underneath.
As the metal oxide is typically much harder and less reactive than
the metal, the ability of the bombarding particles to bond to the
substrate is often limited by the properties of the oxide and not
by the properties of the underlying metal.
[0004] This is also true of cold spray technologies, which are also
limited by the properties of the surface that can be treated. In
order for the cold spray coating to adhere, the substrate surface
must be cleaned and roughened. This is often accomplished by
abrasively blasting the surface before cold spraying. In some
instances, cold spray coatings have been undertaken which also
incorporate some abrasive particles alongside the metal dopant, but
these have all been deposited at high velocities and at elevated
temperatures beyond the range of abrasive blasting. Experimentally,
it has been found that the presence of the ceramic particles acts
to increase the deposition rate of the metal. In addition, the
presence of the ceramic may enhance the wear resistance of the
deposit.
[0005] Most surface bombardment processes are not focussed on
material deposition, but rather on surface roughness and stress. If
round particles are used to bombard the surface and the velocity is
low enough, at subsonic speeds that are below the critical
velocity, then the surface is merely deformed and dimpled by the
bombardment. This is referred to as shot peening and it is
routinely used to control surface stress by applying compressive
stress to the surface, and this process leaves a characteristic
dimpled surface appearance.
[0006] If particles with an angular or irregular morphology are
used to bombard the surface at values below the critical velocity,
then the edges and corners of the bombarding particles can cut up
and erode material from the substrate metal. This results in
abrasion of the surface, and abrasive blasting is widely used to
clean and roughen metal surfaces. For optimum abrasive effects, the
abrasive particles are chosen to have a Mohs hardness of at least
5, though harder particles are preferred as the abrasion increases
with hardness.
[0007] During the abrasive blasting process, it has been observed
that some particles of abrasive are left impregnated in the
substrate. For many applications, this is considered a detrimental
effect and further etching or cleaning steps are required to remove
the contamination. However, there are applications where the
contamination arising from abrasive blasting has been postulated to
be beneficial. U.S. Pat. No. 4,194,929 describes a process wherein
a stainless steel surface is blasted with iron or steel abrasive.
As ferrous particles are embedded in the corrosion resistant steel
surface, this causes a passivating coating to form in a
conventional phosphating solution. In U.S. Pat. No. 7,377,943,
Muller et al. describe a process for improving the bioactivity of a
metal surface by blasting the surface with a powder wherein each
particle comprises a vitreous crystalline material made from a
combination of CaO, P.sub.2O.sub.5, ZrO.sub.2 and fluoride. The
resultant particles are embedded in the surface to improve the
biocompatibility of the metal surface. These methods all involve
bombarding the surface with a single type of particle and feature a
combination of abrasion and impregnation.
[0008] In a further development of this, Ishikawa et al. (J.
Biomed. Mat. Res. (Appl. Biomat.), vol. 38, pg. 129-134, 1997)
reported on the blasting of titanium with a hydroxyapatite powder
using conventional abrasive blasting equipment. They observed that
the powder built up on the metal surface without any evidence of
substrate abrasion when examined using electron microscopy. They
attributed this coating formation to the reactivity of the
hydroxyapatite material which resulted in a form of particle
sintering and to some adhesion to the surface. Although stable to
ultrasonic washing, the coating was removed by scratching with a
steel blade, indicating only moderate coating adhesion was
achieved. This suggests minimal bonding of the bombarding particles
to the metal and microscopy seems to confirm this, with no evidence
of metal abrasion evident. This may be due to the hard passive
oxide layer that is present on titanium. The soft hydroxyapatite
particles would therefore not be expected to rupture and abrade the
metal oxide.
[0009] Others have sought to deposit materials on the surface of a
metal using a combination of two sets of particles which are
dissimilar. U.S. Pat. No. 3,754,976 describes a process for metal
plating. While cold spray uses high velocity bombardment to adhere
a metal to a surface, this patent disclosed a process for metal
plating in which a mixture of metallic powder and small shot
peening particles are sprayed against a surface at a velocity
sufficient to impact and bond the metallic powder onto the surface.
The peening particles effectively deform and plate the metal
particles onto the surface without any significant uptake of
peening particles in the coating. This technique was later expanded
to include additional materials that could be deposited. U.S. Pat.
No. 4,552,784 describes a process for depositing rapidly solidified
metal powder using this technique. U.S. Pat. No. 4,753,094 claims a
process wherein a combination of molybdenum disulphide and round
metal shot was blasted at a surface to deposit a layer of
molybdenum disulphide. US 2006/0089270 claims a process wherein
shot peening particles are mixed with a primary lubricant such as
molybdenum disulphide and a polymeric lubricant such as
polytetrafluoroethylene (PTFE) and blasted at a surface to deposit
a mixture of the two lubricants on the surface. In all of these
dual blasting methods, the inventors chose to use shot peening
particles to bombard the surface alongside the coating material as
the spherical shot peen particles would not abrade the coating as
it deposited. Convention dictated that blasting with a combination
of abrasive particles and a coating precursor would not produce a
deposited coating as the abrasive would have been expected to
remove any coating that formed.
[0010] In order to combine roughening of an abrasive blast process
and a deposition process in a single step, others have looked at
complex stratified particles in which an abrasive is covered with
the coating forming material. The Rocatec.TM. system for the
silicization of metallic and other surfaces uses individual
particles having multiple components. This technology is used
extensively in the dental arena. In this instance an alumina
particle having an outer adherent layer of silica is propelled at a
pre-roughened surface and upon impact the local heat generated in
the vicinity of the impact causes the shattered silica outer layer
to become fused to the surface through a process referred to as
ceramicization. Similar strategies are outlined U.S. Pat. No.
6,468,658 and U.S. Pat. No. 6,431,958 in which abrasive particles
are coated with a material and then blasted at a surface in order
to embed the outer layer in the surface. In all of these cases, the
abrasive is contained within an outer shell and therefore abrasion
is limited and the surface is chemically modified. However these
techniques all require the use of complex coated media which is
expensive to produce, and this was deemed necessary as simply
blasting with a simple mix of abrasive particles and coating
material was not considered due to the expected removal of the
coating by the abrasive action.
[0011] Despite this widespread belief, it was discovered by
O'Donoghue et al. (EP 2061629 and U.S. Pat. No. 8,119,183) that a
combination of abrasives and coating materials could prove
beneficial. Previous mixed media coatings had focussed on the use
of round shot peen media that merely deposited the precursor powder
as a laminate layer on top of the passive oxide that covered the
metal. These laminate layers were prone to poor adhesion and could
delaminate. By grit blasting the surface with a combination of
abrasive and dopant, it was found that the abrasive removed the
passive oxide layer and roughened the surface. With the hard
passive oxide layer removed and a reactive layer of metal exposed,
this facilitated impregnation of the dopant into the metal. This
did not produce a laminate layer and ensured excellent adhesion of
the dopant to the substrate, and this technique has been
commercialised under the trade name CoBlast. Due to the tendency of
metal dopants to deform and spread rather than shattering and
embedding into the surface, the method is better suited to the
deposition of non-metallic dopants.
[0012] While blasting a mixture of abrasive and dopants at a
surface using the established CoBlast technique was effective at
depositing materials into the substrate (and indeed there is no
question that EP 2061629 (and related patents) discloses its
invention in a manner sufficiently clear and complete for it to be
carried out by a person skilled in the art) the optimum process
parameters for CoBlast were not well understood. In particular, the
critical particle delivery velocity required to impregnate the
surface with a dopant was not well established, and sub-optimal
coatings could therefore result.
[0013] There has therefore been a desire to improve the CoBlast
technique through improved identification of process parameters, in
particular in respect of the particle delivery velocity.
SUMMARY OF THE INVENTION
[0014] According to a first aspect of the present invention there
is provided a metal surface treatment method wherein the surface is
simultaneously bombarded with a mixture of abrasive particles and
dopant particles which are delivered at a velocity in the range of
50-250 m/sec (metres per second), and thereby depositing the dopant
material on the surface.
[0015] For instance, the particles may be delivered at a velocity
in the range of 100-200 m/sec, for example at a velocity in the
range of 120-180 m/sec.
[0016] The method may be carried out at ambient temperature.
[0017] Preferably the abrasive particles have an irregular or
angular morphology.
[0018] The dopant may be directly chemically bonded to the metal
surface without any intermediate oxide layer. Alternatively, or in
addition, the dopant particles may be agglomerated together on the
metal surface.
[0019] Preferably the abrasive has a hardness greater than 6.0 on
the Mohs scale. For example the abrasive may have a hardness of 8.0
or above on the Mohs scale.
[0020] Preferably the abrasive has a hardness at least 2 levels
higher than that of the dopant on the Mohs scale. Particularly
preferably the abrasive has a hardness at least 3 levels higher
than that of the dopant on the Mohs scale.
[0021] In certain embodiments the dopant may be a polymer or other
low density material (having a density of less than 2.5 g/cm.sup.3)
and the abrasive may have an average particle size in the range of
150-1500 microns (.mu.m). For example, the abrasive may have an
average particle size in the range of 250-1000 microns, such as in
the range of 350-750 microns. As a further example, the abrasive
may have an average particle size of greater than 300 microns.
[0022] In other embodiments the dopant may be a polymer (or
alternatively may be a non-polymer), and the abrasive may have an
average particle size in the range of 5-5000 microns, such as in
the range of 5-1500 microns. For example, the dopant may be a
polymer and the abrasive may have an average particle size in the
range of 10-150 microns. Merely as two illustrative examples, we
have achieved good deposition of polymer dopants using abrasive
particles having an average particle size of 13 microns and,
separately, using abrasive particles having an average particle
size of 50 microns. The variation in abrasive size is typically
associated with the desired texture required on the finished
surface.
[0023] With the dopant being a polymer, the abrasive may constitute
at least 60 wt % of the mixture of abrasive and dopant particles.
Preferably the abrasive constitutes at least 70 wt % of the mixture
of abrasive and dopant particles. More preferably the abrasive
constitutes at least 80 wt % of the mixture of abrasive and dopant
particles.
[0024] In other embodiments the dopant may be a non-polymeric
material and the abrasive may have an average particle size of less
than 500 microns. For example, the abrasive may have an average
particle size of less than 200 microns, or less than 150 microns.
With the dopant being a non-polymeric material, the dopant may
constitute at least 20 wt % of the mixture of abrasive and dopant
particles. Preferably the dopant constitutes at least 25 wt % of
the mixture of abrasive and dopant particles. More preferably the
dopant constitutes at least 40 wt % of the mixture of abrasive and
dopant particles.
[0025] More generally, the dopant particles may have an average
particle size in the range of 1-100 microns.
[0026] Typically less than 10 microns of dopant material are
deposited on the surface.
[0027] At least some of the dopant particles may penetrate the
metal surface and remain physically impregnated in the metal.
[0028] Depending on the application, one or more additional
coatings may subsequently be applied on top of the deposited dopant
material. For example, an additional coating may be applied through
a bombardment technique selected from cold spray, peen plating or
microblasting. Other ways of applying an additional coating are
also possible, such as powder coating or painting.
[0029] According to a second aspect of the present invention there
is provided an article having a surface treated by a method in
accordance with the first aspect of the invention.
[0030] According to various embodiments of the first and second
aspects of the invention, the surface that is treated may be at
least a part of: [0031] an implantable medical device; [0032] a
marine or land-based vehicle; [0033] an aerospace vehicle,
satellite, rocket or spacecraft; [0034] an electronic device or
component; [0035] a mould; or [0036] a pipe, tube or storage
vessel.
[0037] Other applications are also possible, as those skilled in
the art will appreciate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] Embodiments of the invention will now be described, by way
of example only, and with reference to the drawings in which:
[0039] FIG. 1 illustrates the classification of thermal spray
processes in accordance with particle velocity and flame
temperature (from Grigoriev et al.);
[0040] FIGS. 2a, 2b and 2c schematically illustrate a process for
treating a metal substrate;
[0041] FIGS. 3a, 3b and 3c are schematic diagrams of three
different nozzle configurations to deliver abrasive particles and
dopant particles to a surface;
[0042] FIG. 4 shows optical micrographs of a 12 micron thick nickel
layer electrolytically plated onto aluminium, (A) untreated and (B)
following a CoBlast treatment to deposit calcium phosphate;
[0043] FIG. 5 shows EDX analysis of the untreated nickel plate of
FIG. 4(A) and of the calcium phosphate surface of FIG. 4(B)
deposited onto the nickel plate (the calcium phosphate example
being referred to as "Solar Black" in FIG. 5); and
[0044] FIG. 6 shows optical micrographs of a superelastic NiTi wire
onto which polytetrafluoroethylene (PTFE) had been deposited (a)
without the use of abrasive particles, (b) by a CoBlast treatment
using <50 .mu.m alumina abrasive particles, and (c) by a CoBlast
treatment using <90 .mu.m alumina abrasive particles, in each
case before and after flexural testing of the wire.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0045] The present embodiments represent the best ways known to the
applicants of putting the invention into practice. However, they
are not the only ways in which this can be achieved.
Overview of CoBlast Method
[0046] For the general details of the CoBlast method, the reader is
initially referred to WO 2008/033867, which describes techniques
for the substantially simultaneous deposition of first and second
sets of particles. Naturally, as those skilled in the art will
appreciate, the first and second sets of particles are different
from one another. That is to say, the dopant species is different
from the abrasive.
[0047] Embodiments of the CoBlast method are encompassed in but not
limited to the schematic representation shown in FIGS. 2a, 2b and
2c.
[0048] FIG. 2a schematically shows a fluid jet (nozzle) 2 that
delivers a stream 3 comprising a set of abrasive particles 4
substantially simultaneously with a set of dopant particles 6.
Particle sets 4 and 6 bombard a surface 10 of a metal substrate 8,
to impregnate the surface of the metal substrate with the
dopant.
[0049] In the schematic representation of FIGS. 2a, 2b and 2c, the
surface 10 is a metal oxide layer. As a result of bombardment by
the abrasive particles 4, the surface oxide layer is disrupted, and
breaches in the oxide layer 10 result to expose a new surface 10a
of substrate 8 (FIG. 2b). In the case of a metal substrate, the
newly exposed surface is a metal surface. As the particle stream 3
continues to impinge the substrate 8, the dopant particles 6 are
integrated into the surface 10 of the substrate 8 (FIG. 2c).
[0050] In some embodiments, the blasting equipment can be used in
conjunction with controlled motion such as CNC (computer numerical
control) or robotic control. Either the blast nozzle, the substrate
or both may be manipulated so as to achieve the desired surface
treatment. The blasting can be performed in an inert environment.
The use of an inert atmosphere is typically required to manage
explosion or flammability risks associated with dopant or substrate
materials and is not a specific requirement in forming a
coating.
[0051] In one embodiment, the dopant and abrasive particles are
contained in the same reservoir and are delivered to a surface from
the same jet (nozzle). In another embodiment, the dopant particles
are contained in one reservoir and the abrasive particles are
contained in a separate reservoir, and multiple nozzles deliver the
dopant and abrasive particles. The multiple nozzles can take the
form of a jet within a jet, i.e., the particles from each jet
bombard the surface at the same incident angle. In another
embodiment, the multiple nozzles are spatially separated so as to
bombard the surface at different incident angles yet hit the same
spot on the surface simultaneously.
[0052] FIGS. 3a, 3b and 3c are schematic diagrams of three
different nozzle configurations to deliver the dopant and abrasive
particles to a surface: single nozzle (FIG. 3a); multiple nozzles
with dopant and abrasive particles delivered from separate
reservoirs where one nozzle is situated within another nozzle (FIG.
3b); and multiple, separate nozzles with dopant and abrasive
particles delivered from separate reservoirs (FIG. 3c). More
specifically, FIG. 3a shows a single nozzle 20 for delivering a
single stream 23 of abrasive particles 24 and dopant particles 26
to a substrate 28. FIG. 3b shows that multiple nozzles with dopant
and abrasive particles delivered from separate reservoirs can be
used, with FIG. 3b illustrating one nozzle 30 for delivering a
stream 33 of abrasive particles 24 situated within another nozzle
40 for delivering a stream 43 of dopant particles 26, where streams
33 and 43 are coaxial. Multiple, separate nozzles with dopant and
abrasive particles delivered from separate reservoirs can also be
used, as indicated in FIG. 3c, which shows nozzles 30 and 40, for
delivering streams 33 and 43 of abrasive particles 24 and dopant
particles 26, respectively.
[0053] The distance D between the nozzle(s) and the substrate
surface can be in the range of 0.1 mm to 250 mm, such as a range of
0.1 mm to 130 mm, or a range of 5 mm to 50 mm. The angle of the
nozzle to the surface can range from 10 degrees to 90 degrees, such
as a range of 30 degrees to 90 degrees, or a range of 70 to 90
degrees.
[0054] More than one type of dopant species can be used. It will
readily be appreciated that where more than one type of dopant is
used, the dopants may be delivered from a single nozzle, or each
type may respectively be delivered from a separate nozzle.
[0055] More than one type or size of abrasive can be used. This may
be undertaken to both assist in the deposition of dopant material
and also to customise the surface topography and level of texturing
during processing. It will readily be appreciated that where more
than one type of abrasive is used, the abrasives may be delivered
from a single nozzle, or each type may respectively be delivered
from a separate nozzle.
Optimised CoBlast Method
[0056] Although higher particle velocities are known to assist with
deposition, these require increased gas pressures or temperature
and this increases the cost of the process. Therefore, an optimised
coating can result from premixing an angular abrasive with a
particulate dopant, and delivering the powder mix to a metal
substrate surface at a velocity of 50-250 m/sec, so as to remove
the oxide layer from the surface, and simultaneously depositing
less than 10 microns of dopant on the surface. At least a portion
of the deposited materials penetrate the metal surface and remain
impregnated within the metal. This process also results in direct
chemical bonding of the dopant to the surface, without the presence
of any intermediate oxide layer. In a preferred embodiment, the
mixture of abrasive and dopant particles is delivered at a velocity
of 100-200 m/sec to the surface. Optimally, the particles are
delivered at a velocity of 120-180 m/sec. If the dopant particles
are delivered at a different velocity than the abrasive particles,
then it has been found that the velocity of the abrasive particles
dominates the effect at the surface, and therefore it is the
abrasive that has to be delivered at the correct velocity.
[0057] To achieve optimal impregnation of the dopant into the
surface, an angular abrasive particle with a hardness greater than
6.0 on the Mohs scale is required. Using a harder abrasive can
increase the deposition rate and an abrasive with a hardness of 8.0
or above is preferred. Using an abrasive such as this is sufficient
to remove the oxide layer from a metal even at low velocity. In
addition, the abrasive cleans the surface and ensures that no
complex cleaning or roughening of the surface is needed prior to
deposition. However, when mixed with a dopant delivered at a
velocity of 100-200 m/sec, it has been found that the abrasive
removes the oxide and also erodes some of the metal underneath. Due
to the simultaneous abrasion and dopant delivery, several microns
of dopant are deposited and this replaces the lost metal and metal
oxide, and the cumulative effect is that the overall thickness of
the substrate remains similar to that of the starting material.
When using an angular or irregularly shaped abrasive with a Mohs
hardness greater than 6.0 and a velocity of 100-150 m/sec, it has
been found that less than 5-10 microns is removed by abrasion and
this can be largely replaced by the dopant deposition.
[0058] The impact of the abrasive also acts to roughen and twist
the metal surface, thereby embedding and interlocking the dopant
into the surface. In order to maximise deposition of the dopant,
the Mohs hardness of the abrasive is preferably chosen to be at
least 2 levels higher than that of the dopant. This ensures
preferential uptake of the dopant and minimal impregnation of the
abrasive into the surface. Particularly preferably, the abrasive is
at least 3 levels harder than the dopant on the Mohs scale.
[0059] The dopant is found to be chemically bonded to the surface.
Given that the reaction happens in ambient atmosphere, it is
surprising that there is no evidence of oxide layers between the
dopant and the metal. Instead, the dopant is bonded directly to the
reactive metal. This ensures excellent adhesion of the dopant to
the metal. In addition, the dopant particles are shattered and torn
by the impact on the surface and the ongoing abrasive action of the
abrasive particle bombardment. For crystalline or semi-crystalline
dopant powders, this can produce nano-crystalline dopant particles
on the surface, and the resultant high surface energy and
reactivity of these sub-micron particles results in materials that
bond readily with the metal and which also agglomerate and fuse
together on the surface.
[0060] Due to the reactivity induced by the abrasion, high
velocities, similar to those found in cold spray, are not required.
In addition, the process can occur at ambient temperature and
neither the substrate nor the gas stream need be heated as in cold
spray. All of the reactions occur at less than 100.degree. C.
Although there is no direct heating and it is a room temperature
process, the localised heating induced by the kinetic energy of the
impact of the particles may be important in localised reactions.
For example, during the deposition of polymeric dopants, the
localised reactions may give rise to T.sub.G modification of the
polymer material.
[0061] Although carried out at low temperatures, the bombardment of
the surface does alter the structure of the substrate. Without
being bound by theory, aside from the erosion of surface material
by the process, microscopic analysis has shown that the abrasive
alters the structure of the metal substrate, switching it from
coarse grains to fine grains, thereby making it more reactive. The
formation of nano-crystallinity also occurs on the substrate side
of the interface. Blasting induces a level of Severe Plastic
Deformation (SPD) on the substrate and the bombardment thereby
increases the dislocation density at the newly exposed surface,
which increases the numbers of ultra-fine grains and therefore the
overall density of grain boundaries. Grain boundaries provide
reaction sites and thus increase the reactivity of a surface. This
increase in grain boundary availability increases the reactivity of
the metal interface to a depth of 20 .mu.m. When combined with the
energy transferred from the impacting abrasives and the removal of
the passivating oxide layer, this work hardening of the metal could
also be expected to enhance the bonding of the dopant to the
substrate. In addition, there is no heat affected zone as would be
expected from a high energy plasma spray or hot deposition process.
This combination of effects gives rise to direct chemical bonding
of the dopant to the substrate. In the case of ceramic dopants,
this can give rise to a diffusion bonded material. The work
hardening also improves the fatigue life of the metal substrate
when compared to untreated components.
[0062] The localised reactions also allow for materials to be
deposited in an adherent manner which do not normally stick. For
example, materials such as PTFE are routinely used as non-stick
surfaces as it is notoriously difficult to make PTFE adhere to
anything. Despite this, it is possible to deposit an adherent PTFE
deposit by mixing PTFE with an angular abrasive and blasting it at
a surface. Without being bound by theory, it is possible that the
abrasive actually shreds the polymer chain and leaves dangling,
unreacted chemical bonds where the chain was cut. Those would
provide very reactive sites that could bind to reactive sites on
the metal surface and thereby facilitate chemical bonding of the
PTFE to the substrate. Because polymeric materials such as PTFE are
stable and quite non-reactive, additional energy may be required to
induce the reactions that bond the material to the surface.
Therefore, when depositing polymeric materials, it may be
beneficial to use higher velocity deposition parameters. However,
higher velocities require higher gas flows and therefore it is
instead preferred to use a larger size abrasive grit to provide
additional kinetic energy. If abrasive particles greater than 1500
microns in size are used, then there are insufficient impacts per
unit area to bond the polymer to the surface. If small grit
particles less than 150 microns in size are used, then the
impinging abrasive may lack the kinetic energy to induce reactions
with the non-reactive polymer material. When depositing polymeric
materials it is therefore preferred to use abrasive particles of
150 to 1500 microns in size, preferably 250 to 1000 microns in
size, and most preferably 350 to 750 microns in size as these
possess higher kinetic energy and produce enhanced surface abrasion
and roughening. However, nowithstanding the above, we have also
achieved good deposition of polymer dopants using abrasive
particles having an average particle size of the order of 50
microns or smaller, and, separately, using abrasive particles
having an average particle size of the order of 13 microns or
smaller.
[0063] In addition, when depositing polymeric dopants, the blend of
dopant and abrasive should be altered to be rich in abrasive. While
standard blasting is carried out with equal mixtures by weight of
dopant and abrasive, for polymer dopants it has been found that a
ratio of at least 60 wt % abrasive and a maximum of 40 wt % dopant
is preferred. A more preferred ratio comprises at least 70 wt %
abrasive and no more than 30 wt % dopant. In the most preferred
ratio, the mixture comprises 80-90 wt % abrasive and 10-20 wt %
dopant. At mixtures above around 90 wt % or 95 wt % abrasive, there
is limited polymer deposition due to excess abrasion, although
mixtures having between 90 wt % and 95 wt % abrasive can
advantageously be used to produce (deliberately) a very thin dopant
layer.
[0064] Although using a high loading of abrasive in the mixed media
and a high average particle size has been beneficial for polymeric
dopants, this does not hold true for other dopants. When attempting
to deposit ceramics, salts, metals or other materials, it has been
found that the particle size of the abrasive is key to producing an
optimal coating. While larger abrasive particles give rise to
enhanced surface roughness, it has been found that the use of
smaller abrasives can give rise to higher surface loadings of
dopant. As the loading of the surface is driven by the impaction of
the abrasive on the surface, it is preferred to bombard the surface
with a large number of smaller particles rather than fewer large
particles. This produces more impacts and more surface reactions
per unit surface area and thereby facilitates enhanced surface
loading of dopant. While deposition of dopant materials can be
achieved using abrasives with an average particle size of 500-1000
microns, it has been observed that better results occur with
abrasive particles that are less than 500 microns, preferably less
than 200 microns, and ideally in the range of 10-150 microns
average particle size. In addition, for non-polymeric dopants, the
maximum ratio of abrasive to dopant has been found to be 80 wt %
abrasive to 20 wt % dopant, with better loading of the dopant
formed when the mixture contains no more than 75 wt % abrasive and
at least 25 wt % dopant. The optimum surface loading of
non-polymeric dopants is achieved when the mixture contains no more
than 60 wt % abrasive and greater than 40 wt % dopant. Although a
range of abrasive particles have been successfully employed in
CoBlast, the average dopant particle is typically in the range of
1-100 microns in size.
[0065] A blend of abrasive sizes may also be used when depositing
dopant particles using the CoBlast process. For example, large
abrasive particles may be used for surface profile and cleaning
effects, simultaneously with small abrasive particles in order to
achieve good surface coverage and improved reactivity. For these
reasons, and by way of example, we have successfully used a blend
of approximately 600 micron and approximately 50 micron alumina
abrasive particles when depositing epoxies, zinc phosphate and
others as the dopant species.
[0066] In some cases where high surface profile is required it may
be most efficient to grit-blast first with large abrasive particles
(e.g. having an average particle size of the order of 1500 microns
or greater), and then subsequently employ a CoBlast process using
small abrasive particles simultaneously with the dopant
particles.
[0067] Smaller dopants are more reactive, but larger dopant
particles are easier to flow in a powder feeder and are therefore
often preferred. In order to commercialise a coating process, the
optimal coating may be produced using smaller particles, but the
requirement to flow the particles in a smooth and continuous manner
from one or more hoppers to the/each delivery nozzle may require
the addition of flow agents or the use of larger abrasive or dopant
particles. In order to ensure a continuous flow of media from
the/each hopper to the/each nozzle it has been found that the
mixture of abrasive and dopant should have a Hausner ratio of less
than 1.2 (and particularly preferably less than 1.15). For mixtures
with a Hausner ratio greater than this value but less than around
1.3-1.5, it is possible to flow the material from a pressure pot as
long as the powders are dry, sealed and the total load of powder
does not exceed 1.5 kg. If the mixture has a Hausner ratio greater
than around 1.3-1.5, then it is necessary to physically agitate the
mixture using stirring rods, bars, blades or other devices to
prevent the powder from compacting and to maintain a constant flow.
If the Hausner ratio exceeds around 1.5-1.6, then the maximum load
that can be fed from the hopper is 500 g in order to ensure that
the powder does not compact and block the system. For optimum
performance, the hopper should be loaded with no more than 400 g of
mixed media. In order to ensure a constant supply to the nozzle, it
may be beneficial to employ multiple powder feeders each loaded
with small quantities of mixed media, preferably less than 500
g.
[0068] The Hausner ratio values in the above paragraph are by way
of example only, in respect of a specific deposition system we use.
For other configurations of the apparatus the Hausner ratio values
may differ.
[0069] The deposited CoBlast layer is typically limited to a thin
deposit of 2-5 microns, although thicker deposits of up to 10
microns are possible. When attempting to produce thicker deposits,
the presence of the abrasive eventually begins to produce excess
abrasion and thicker coatings are rapidly removed, meaning that the
process is self-limiting with a maximum thickness of 10 microns
achievable. In order to deposit thicker coatings, it is beneficial
to first deposit a CoBlast layer using a combination of dopant and
abrasive. This produces a thin and chemically bonded primer layer
onto which additional materials can then be deposited. In a
preferred embodiment, the CoBlast process is used to deposit a thin
layer of dopant on the surface. The flow of abrasive and dopant is
then switched off or redirected and a second bombardment of the
surface takes place. This second bombardment can be based on a cold
spray process in which additional materials are blasted at the
surface with the required critical velocity to adhere the particles
to the surface. The benefit of first employing the CoBlast process
is that this facilitates the direct chemical bonding of the coating
to the metal without an intervening oxide layer and thereby
minimises the risk of coating delamination. Alternatively, the
second bombardment may be carried out using a mixture of dopant
particles and round shot peen particles. The switch from angular
abrasive grit to spherical shot peen particles ensures that the
secondary process is not dominated by abrasive erosion, and thick
coatings can be grown which are anchored to the metal surface by
the CoBlast primer layer. This secondary bombardment can be carried
out using the same equipment as used in the CoBlast treatment or
can comprise a second set of equipment. In a third alternative, the
secondary bombardment may involve simply blasting a dopant, without
any additional material, at the CoBlast treated surface so as to
build up a thicker coating, but without using the high temperatures
or high velocity of the cold spray process. This represents a
microblast process similar to that described by Ishikawa. The
dopant used in any of the secondary bombardment steps may be
identical to the dopant used in the CoBlast treatment or it may be
different from the CoBlast dopant materials. In each case, the
CoBlast layer will act to improve adhesion of the secondary coating
by directly bonding the top coat to the metal without any oxide
interface. In a preferred method, the top coating is then further
processed using thermal, laser, e-beam or some other high energy
method in order to cross-link, melt, densify or cure the coating.
This also causes the top layer to fuse with the CoBlast primer
layer, thereby chemically bonding the top coat directly to the
metal substrate.
[0070] Instead of using a bombardment process, the secondary
surface treatment may be added using traditional methods such as
painting, sputtering, CVD, plasma deposition, ion plating, PVD, ion
beam assisted deposition, electron beam PVD, cathodic arc
deposition, magnetron sputtering, vacuum evaporation, laser
assisted deposition, PECVD, electroplating, spraying, HVOF, powder
coating, dip coating, inkjet printing, roller coating, lithography,
spin coating or other such technologies. In each case, the initial
layer of dopant acts as a primer that allows the top coating to be
bound directly to the metal substrate without any intermediate
oxide layer. Further curing or heating of the top coat can enhance
the bonding to the substrate further.
[0071] There are a wide variety of dopants that can be used in this
process. The dopant can comprise materials such as polymers,
metals, ceramics (e.g., metal oxides, metal nitrides), and
combinations thereof, e.g., blends of two or more thereof.
[0072] Exemplary dopants include modified calcium phosphates,
including Ca.sub.5(PO.sub.4).sub.3OH, CaHPO.sub.4.2H.sub.2O,
CaHPO.sub.4, Ca.sub.8H.sub.2(PO.sub.4).sub.6.5H.sub.2O,
.alpha.-Ca.sub.3(PO.sub.4).sub.2, .beta.-Ca.sub.3(PO.sub.4).sub.2,
tetracalcium phosphate, beta calcium phosphate or any modified
calcium phosphate containing carbonate, chloride, fluoride,
silicate or aluminate anions, protons, potassium, sodium,
magnesium, barium or strontium cations.
[0073] Other dopants include titania (TiO.sub.2), hydroxyapatite,
silica, calcium carbonate, biocompatible glass, calcium phosphate
glass, carbon, graphite, graphene, chitosan, chitin, barium
titanate, zeolites (aluminosilicates), including siliceacous
zeolite and zeolites containing at least one component selected
from phosphorous, silica, alumina, zirconia.
[0074] In one embodiment, the dopant is a therapeutic agent. The
therapeutic agent can be delivered as a particle itself, or
immobilized on a carrier material. Exemplary carrier materials
include any of the other dopants listed herein (those dopants that
are not a therapeutic agent) such as polymers, calcium phosphate,
titanium dioxide, silica, biopolymers, biocompatible glasses,
zeolite, demineralized bone, de-proteinated bone, allograft bone,
and composite combinations thereof.
[0075] Exemplary classes of therapeutic agents include anti-cancer
drugs, anti-inflammatory drugs, immunosuppressants, an antibiotic,
heparin, a functional protein, a regulatory protein, structural
proteins, oligo-peptides, antigenic peptides, nucleic acids,
immunogens, and combinations thereof.
[0076] In one embodiment, the therapeutic agent is chosen from
antithrombotics, anticoagulants, antiplatelet agents,
thrombolytics, antiproliferatives, anti-inflammatories,
antimitotic, antimicrobial, agents that inhibit restenosis, smooth
muscle cell inhibitors, antibiotics, fibrinolytic,
immunosuppressive, and anti-antigenic agents.
[0077] Exemplary anticancer drugs include acivicin, aclarubicin,
acodazole, acronycine, adozelesin, alanosine, aldesleukin,
allopurinol sodium, altretamine, aminoglutethimide, amonafide,
ampligen, amsacrine, androgens, anguidine, aphidicolin glycinate,
asaley, asparaginase, 5-azacitidine, azathioprine, Bacillus
calmette-guerin (BCG), Baker's Antifol (soluble),
beta-2'-deoxythioguanosine, bisantrene HCl, bleomycin sulfate,
busulfan, buthionine sulfoximine, BWA 773U82, BW 502U83.HCl, BW
7U85 mesylate, ceracemide, carbetimer, carboplatin, carmustine,
chlorambucil, chloroquinoxaline-sulfonamide, chlorozotocin,
chromomycin A3, cisplatin, cladribine, corticosteroids,
Corynebacterium parvum, CPT-11, crisnatol, cyclocytidine,
cyclophosphamide, cytarabine, cytembena, dabis maleate,
dacarbazine, dactinomycin, daunorubicin HCl, deazauridine,
dexrazoxane, dianhydrogalactitol, diaziquone, dibromodulcitol,
didemnin B, diethyldithiocarbamate, diglycoaldehyde,
dihydro-5-azacytidine, doxorubicin, echinomycin, edatrexate,
edelfosine, eflornithine, Elliott's solution, elsamitrucin,
epirubicin, esorubicin, estramustine phosphate, estrogens,
etanidazole, ethiofos, etoposide, fadrazole, fazarabine,
fenretinide, filgrastim, finasteride, flavone acetic acid,
floxuridine, fludarabine phosphate, 5-fluorouracil, Fluosol.RTM.,
flutamide, gallium nitrate, gemcitabine, goserelin acetate,
hepsulfam, hexamethylene bisacetamide, homoharringtonine, hydrazine
sulfate, 4-hydroxyandrostenedione, hydrozyurea, idarubicin HCl,
ifosfamide, interferon alfa, interferon beta, interferon gamma,
interleukin-1 alpha and beta, interleukin-3, interleukin-4,
interleukin-6, 4-ipomeanol, iproplatin, isotretinoin, leucovorin
calcium, leuprolide acetate, levamisole, liposomal daunorubicin,
liposome encapsulated doxorubicin, lomustine, lonidamine,
maytansine, mechlorethamine hydrochloride, melphalan, menogaril,
merbarone, 6-mercaptopurine, mesna, methanol extraction residue of
Bacillus calmette-guerin, methotrexate, N-methylformamide,
mifepristone, mitoguazone, mitomycin-C, mitotane, mitoxantrone
hydrochloride, monocyte/macrophage colony-stimulating factor,
nabilone, nafoxidine, neocarzinostatin, octreotide acetate,
ormaplatin, oxaliplatin, paclitaxel, pala, pentostatin,
piperazinedione, pipobroman, pirarubicin, piritrexim, piroxantrone
hydrochloride, PIXY-321, plicamycin, porfimer sodium,
prednimustine, procarbazine, progestins, pyrazofurin, razoxane,
sargramostim, semustine, spirogermanium, spiromustine,
streptonigrin, streptozocin, sulofenur, suramin sodium, tamoxifen,
taxotere, tegafur, teniposide, terephthalamidine, teroxirone,
thioguanine, thiotepa, thymidine injection, tiazofurin, topotecan,
toremifene, tretinoin, trifluoperazine hydrochloride, trifluridine,
trimetrexate, tumor necrosis factor, uracil mustard, vinblastine
sulfate, vincristine sulfate, vindesine, vinorelbine, vinzolidine,
Yoshi 864, zorubicin, and mixtures thereof.
[0078] Exemplary therapeutic agents include immunogens such as a
viral antigen, a bacterial antigen, a fungal antigen, a parasitic
antigen, tumor antigens, a peptide fragment of a tumor antigen,
meta static specific antigens, a passive or active vaccine, a
synthetic vaccine or a subunit vaccine. The dopant may be a protein
such as an enzyme, antigen, growth factor, hormone, cytokine or
cell surface protein.
[0079] The dopant may be a pharmaceutical compound such as an
anti-neoplastic agent, an anti-bacterial agent, an anti-parasitic
agent, an anti-fungal agent, an analgesic agent, an
anti-inflammatory agent, a chemotherapeutic agent, an antibiotic or
combinations thereof.
[0080] The dopant could also be growth factors, hormones,
immunogens, proteins or pharmaceutical compounds that are part of a
drug delivery system such as those immobilized on zeolite or
polymeric matrices, biocompatible glass or natural porous apitic
templates such as coralline HA, demineralised bone, deproteinated
bone, allograft bone, collagen or chitin.
[0081] In one embodiment, the dopant is an anti-inflammatory drug
selected from non-steroidal anti-inflammatory drugs, COX-2
inhibitors, glucocorticoids, and mixtures thereof. Exemplary
non-steroidal anti-inflammatory drugs include aspirin, diclofenac,
indomethacin, sulindac, ketoprofen, flurbiprofen, ibuprofen,
naproxen, piroxicam, tenoxicam, tolmetin, ketorolac, oxaprosin,
mefenamic acid, fenoprofen, nambumetone, acetaminophen, and
mixtures thereof. Exemplary COX-2 inhibitors include nimesulide,
NS-398, flosulid, L-745337, celecoxib, rofecoxib, SC-57666,
DuP-697, parecoxib sodium, JTE-522, valdecoxib, SC-58125,
etoricoxib, RS-57067, L-748780, L-761066, APHS, etodolac,
meloxicam, S-2474, and mixtures thereof. Exemplary glucocorticoids
include hydrocortisone, cortisone, prednisone, prednisolone,
methylprednisolone, meprednisone, triamcinolone, paramethasone,
fluprednisolone, betamethasone, dexamethasone, fludrocortisone,
desoxycorticosterone, and mixtures thereof.
[0082] Other exemplary therapeutic agents include cell cycle
inhibitors in general, apoptosis-inducing agents,
antiproliferative/antimitotic agents including natural products
such as vinca alkaloids (e.g., vinblastine, vincristine, and
vinorelbine), paclitaxel, colchicine, epidipodophyllotoxins (e.g.,
etoposide, teniposide), enzymes (e.g., L-asparaginase, which
systemically metabolizes L-asparagine and deprives cells that do
not have the capacity to synthesize their own asparagine);
antiplatelet agents such as G(GP) IIb/IIIa inhibitors, GP-IIa
inhibitors and vitronectin receptor antagonists;
antiproliferative/antimitotic alkylating agents such as nitrogen
mustards (mechlorethamine, cyclophosphamide and analogs, melphalan,
chlorambucil), ethylenimines and methylmelamines
(hexamethylmelamine and thiotepa), alkyl sulfonates-busulfan,
nitrosoureas (carmustine (BCNU) and analogs, streptozocin),
triazenes-dacarbazine (DTIC); antiproliferative/antimitotic
antimetabolites such as folic acid analogs (methotrexate),
pyrimidine analogs (fluorouracil, floxuridine, and cytarabine),
purine analogs and related inhibitors (mercaptopurine, thioguanine,
pentostatin and 2-chlorodeoxyadenosine (cladribine)); platinum
coordination complexes (cisplatin, carboplatin), procarbazine,
hydroxyurea, mitotane, aminoglutethimide; hormones (e.g.,
estrogen); anticoagulants (heparin, synthetic heparin salts and
other inhibitors of thrombin); fibrinolytic agents (such as tissue
plasminogen activator, streptokinase and urokinase), aspirin,
dipyridamole, ticlopidine, clopidogrel, abciximab; antimigratory;
antisecretory (breveldin); anti-inflammatory: such as
adrenocortical steroids (cortisol, cortisone, fluorocortisone,
prednisone, prednisolone, 6.alpha.-methylprednisolone,
triamcinolone, betamethasone, and dexamethasone), non-steroidal
agents (salicylic acid derivatives e.g., aspirin; para-aminophenol
derivatives e.g., acetominophen; indole and indene acetic acids
(indomethacin, sulindac, and etodalac), heteroaryl acetic acids
(tolmetin, diclofenac, and ketorolac), arylpropionic acids
(ibuprofen and derivatives), anthranilic acids (mefenamic acid, and
meclofenamic acid), enolic acids (piroxicam, tenoxicam,
phenylbutazone, and oxyphenthatrazone), nabumetone, gold compounds
(auranofin, aurothioglucose, gold sodium thiomalate);
immunosuppressives: (cyclosporine, tacrolimus (FK-506), sirolimus
(rapamycin), azathioprine, mycophenolate mofetil); antigenic
agents: vascular endothelial growth factor (VEGF), fibroblast
growth factor (FGF); angiotensin receptor blockers; nitric oxide
donors; anti-sense oligionucleotides and combinations thereof; cell
cycle inhibitors, mTOR inhibitors, and growth factor receptor
signal transduction kinase inhibitors; retinoid; cyclin/CDK
inhibitors; HMG co-enzyme reductase inhibitors (statins); and
protease inhibitors (matrix protease inhibitors).
[0083] In one embodiment, the dopant is an antibiotic chosen from
tobramycin, vancomycin, gentamicin, ampicillin, penicillin,
cephalosporin C, cephalexin, cefaclor, cefamandole and
ciprofloxacin, dactinomycin, actinomycin D, daunorubicin,
doxorubicin, idarubicin, penicillins, cephalosporins, and
quinolones, anthracyclines, mitoxantrone, bleomycins, plicamycin
(mithramycin), mitomycin, polyketide antibiotics such as
tetracycline, and mixtures thereof.
[0084] In one embodiment, the dopant is a protein chosen from
albumin, casein, gelatin, lysosime, fibronectin, fibrin, chitosan,
polylysine, polyalanine, polycysteine, Bone Morphogenetic Protein
(BMP), Epidermal Growth Factor (EGF), Fibroblast Growth Factor
(bFGF), Nerve Growth Factor (NGF), Bone Derived Growth Factor
(BDGF), Transforming Growth Factor-.beta.1 (TGF-.beta.1),
Transforming Growth Factor-.beta. (TGF-.beta.), the tri-peptide
arginine-glycine-aspartic acid (RGD), vitamin D3, dexamethasone,
and human Growth Hormone (hGH), epidermal growth factors,
transforming growth factor .alpha., transforming growth factor
.beta., vaccinia growth factors, fibroblast growth factors,
insulin-like growth factors, platelet derived growth factors,
cartilage derived growth factors, interlukin-2, nerve cell growth
factors, hemopoietic cell growth factors, lymphocyte growth
factors, bone morphogenic proteins, osteogenic factors,
chondrogenic factors, and mixtures thereof.
[0085] In one embodiment, the dopant is a heparin selected from
recombinant heparin, heparin derivatives, and heparin analogues or
combinations thereof. In one embodiment, the dopant is an
oligo-peptide, such as a bactericidal oligo-peptide. In one
embodiment, the dopant is an osteoconductive or osteointegrative
agent.
[0086] In one embodiment, the dopant is an immunosuppressant, such
as cyclosporine, rapamycin and tacrolimus (FK-506), ZoMaxx,
everolimus, etoposide, mitoxantrone, azathioprine, basiliximab,
daclizumab, leflunomide, lymphocyte immune globulin, methotrexate,
muromonab-CD3, mycophenolate, and thalidomide.
[0087] In one embodiment, the carrier material is a polymer such as
polyurethanes, polyethylene terephthalate, PLLA-poly-glycolic acid
(PGA) copolymer (PLGA), polycaprolactone,
poly-(hydroxybutyrate/hydroxyvalerate) copolymer,
poly(vinylpyrrolidone), polytetrafluoroethylene,
poly(2-hydroxyethylmethacrylate), poly(etherurethane urea),
silicones, acrylics, epoxides, polyesters, urethanes, parlenes,
polyphosphazene polymers, fluoropolymers, polyamides, polyolefins,
and blends and copolymers thereof.
[0088] In one embodiment, the carrier material is a biopolymer
selected from polysaccharides, gelatin, collagen, alginate,
hyaluronic acid, alginic acid, carrageenan, chondroitin, pectin,
chitosan, and derivatives, blends and copolymers thereof.
[0089] In one embodiment, the dopant is a radio opaque material,
such as those chosen from alkalis earth metals, transition metals,
rare earth metals, and oxides, sulphates, phosphates, polymers and
combinations thereof.
[0090] In one embodiment, the dopant is a pigment designed to alter
the emission, absorbance or reflectance of a surface. The deposited
pigment may comprise part of a thermal control surface.
[0091] In one embodiment, the surface containing the deposited
dopant may be electrically conductive. This conductivity may be
sufficient to prevent the build-up of electrical static charge on
the surface.
[0092] In one embodiment, the dopant is a component present within
an adhesive or paint. This component may bind to the adhesive or
paint as it cures thereby chemically bonding the top layer to the
substrate. Examples of such components include monomers,
pre-polymers, pigments, silanes, fillers such as silica or clay.
The dopant may be fusion bonded epoxy, including of derivatives of
bisphenol A and epichlorohydrin. The dopant may be an epoxy
prepolymer or may be derived from bisphenol A, bisphenol F,
Novolac, Glycidylamine epoxy resins or aliphatic epoxy resin. The
component may be an additive such as accelerators, corrosion
inhibitors, adhesion promoters, fire retardants or fungicides.
Typical corrosion-inhibiting dopant species that may be used in the
present method include but are not limited to a chromate,
phosphate, polymer, oxide or a nitride. For example, the dopant may
be ceria. In a preferred method, the coating is derived from a
phosphate compound. The phosphate may comprise iron phosphate,
manganese phosphate, zinc phosphate or combinations thereof.
Alternatively, or in addition, a primer-forming dopant species may
comprise a silane, siloxane, acrylate, epoxy, hydrogen bonded
silicon compound or material which contains one or more vinyl,
peroxyester, peroxide, acetate or carboxylate functional group.
[0093] Abrasive species that may be used in the present method (as
a second set of particles, delivered substantially simultaneously
with the first) include but are not limited to shot or grit made
from silica, sand, alumina, zirconia, barium titanate, calcium
titanate, sodium titanate, titanium oxide, glass, biocompatible
glass, diamond, silicon carbide, boron carbide, dry ice, boron
nitride, sintered calcium phosphate, calcium carbonate, metallic
powders, carbon fibre composites, polymeric composites, titanium,
stainless steel, hardened steel, carbon steel chromium alloys or
any combination thereof. The abrasive is chosen to be a different
material than the dopant.
[0094] Examples of substrates that may be treated using this
technology include metals and intermetallic compounds, such as
those metals chosen from pure metals, metal alloys, intermetallics
comprising single or multiple phases, intermetallics comprising
amorphous phases, intermetallics comprising single crystal phases,
and intermetallics comprising polycrystalline phases. Exemplary
metals include titanium, titanium alloys (e.g., NiTi or nitinol),
ferrous alloys, stainless steel and stainless steel alloys, carbon
steel, carbon steel alloys, aluminum, aluminum alloys, nickel,
nickel alloys, nickel titanium alloys, tantalum, tantalum alloys,
niobium, niobium alloys, chromium, chromium alloys, cobalt, cobalt
alloys, magnesium and magnesium alloys, copper and copper alloys,
precious metals, and precious metal alloys.
[0095] In one embodiment, the substrate is an implantable medical
device. Exemplary medical devices include catheters, guide wires,
stents, dental implants, pulse generators, implantable orthopedic,
spinal and maxillofacial devices, cochlear implant, needles,
mechanical heart valves and baskets used in the removal of
pathological calcifications. In the case of biomedical devices it
is desirable that the level of impregnation of the abrasive itself
in the surface is minimal. The abrasive should further be
biocompatible as it is likely that some impregnation will
occur.
[0096] In one embodiment, the substrate is a vehicle component,
including an automotive chassis, body or panel component, or an
aerospace vehicle, satellite, rocket or spacecraft component, or a
marine ship or boat component, specifically the outer hull. In one
embodiment, the substrate is an engine or an engine component
including exhaust outlets.
[0097] The substrate may be an electronic component, including
components for use in applications in the Communication
Infrastructure, Aerospace and Defence, Automotive, Mobile and
Consumer Electronics, and High Speed Digital markets. The
electronic components may include circuit boards, cases, housing,
switches, terminals, protection devices, transducers, capacitors,
resistors, heat exchangers, antennas, human interfaces,
dielectrics, thermal control surfaces, power sources or display
components.
[0098] In one embodiment, the substrate is a mould such as that
used in the manufacture of plastic, silicone, rubber, composite,
polymer, clay, glass, metal or ceramic materials. The dopant may be
chosen to enhance release of the cast part from the mould and the
dopant may comprise a fluoropolymer or silicone material.
[0099] In one embodiment the substrate may be a pipe, tube or
storage vessel, specifically one used in the petrochemical, marine,
pharmaceutical, chemical, biotech or food and beverage industry.
The deposited dopant may be chosen to minimise fouling or build-up
of materials on the inside of the container.
[0100] The dopant and abrasive are preferentially mixed together
and blasted at a surface. The blasting may be carried out using
wheel abrading equipment or fluid based blast equipment. Where
fluid blasting is carried out, the fluid may be a gas or a liquid,
such as water. Appropriate gases include air, nitrogen, argon,
helium, carbon dioxide or mixtures thereof. If using combustible or
explosive media, the fluid may comprise water or may be largely
composed of an inert gas.
Example 1
[0101] An aluminium sample was electrolytically plated to produce a
uniform 12 micron thick metallic Ni layer. This surface was then
subjected to a CoBlast surface treatment using alumina as the
abrasive and calcium phosphate as the dopant. The powders were
pre-mixed and blasted at the surface. As can be seen from the
optical micrographs in FIG. 4 and the EDX analysis in FIG. 5,
following the CoBlast treatment the nickel was still evident on the
surface of the substrate, indicating that there was less than 12
microns eroded from the substrate surface. In addition, the EDX
shows the presence of additional elements attributed to the
presence of the calcium phosphate dopant impregnated into the
surface. Close examination of the optical micrographs in FIG. 4
shows that all of the nickel plating is not removed during the
CoBlast treatment. However, it can be seen that there is some level
of nickel removal from the surface during CoBlast, based on the
cross-sectional analysis. Although the removal rate is not uniform,
there is typically 2-10 microns of metal removed. The overall
thickness of the substrate does not alter significantly as any
metal removal is offset by deposition of the dopant material. It is
also clear that the CoBlast treated surface is rougher than the
untreated nickel surface.
Example 2
[0102] 150 micron alumina abrasive was mixed with calcium phosphate
(Hydroxyapatite or HA, 20-65 micron average particle size) and
blasted at a series of grade 2 titanium coupons. The velocity of
the bombarding particle was varied from 170-195 m/sec. Samples were
then washed and examined using SEM. In each case, the surface was
found to be loaded with high levels of calcium and phosphorous,
confirming that calcium phosphate had been deposited in each case.
Samples were also subjected to XRD analysis. In each case, the
analysis detected only peaks associated with titanium and the
calcium phosphate deposit. Analysis of the ratio of the intensity
of the HA (211) peak to the intensity of the Ti (101) peak showed
approximately equivalent signals for all samples.
[0103] The adhesion of the deposited material was measured using a
test method based on ASTM F1147. This determined that the adhesion
of the deposit was in excess of 58 MPa, which was the failure point
of the adhesive.
[0104] This experiment was then repeated, but instead of using
angular alumina abrasive, the calcium phosphate was mixed with
round shot peening particles made from grade 5 titanium. Initial
SEM analysis detected calcium phosphate on the surface, though
there appeared to be significantly less material present. This was
confirmed by XRD analysis. A comparison of the ratio of the
intensity of the HA (211) peak to the intensity of the Ti (101)
peak showed significant differences from the result achieved using
the alumina abrasive. The Ti peak was significantly more pronounced
in the spectra derived from the shot peen samples and was found to
be 3-4 times more intense than the HA peak, confirming that
significantly less calcium phosphate material was deposited using
the spherical shot peen media.
[0105] The maximum adhesion measured for the shot peen samples was
also measured and an average value of 25 MPa was recorded. This is
significantly below the level measured for the samples deposited
using an abrasive, thereby confirming that the samples produced by
abrasive blasting had a much stronger adhesive bond to the
substrate, as would be expected from a chemically bonded
material.
[0106] This data confirms that deposition of a ceramic dopant using
abrasive media can be accomplished at lower velocities than are
used in cold spray processes and that the shape of the bombarding
particle is key. Rough, irregular shaped abrasive particles can
assist with the deposition of a dopant in far higher loadings than
can be achieved with a spherical shot peen bombardment particle.
Furthermore, the abrasive particles enhance the adhesion of the
dopant to the substrate.
Example 3
[0107] A series of 1 mm thick Grade 5 titanium samples were
subjected to abrasive bombardment using a 50:50 mixture of 100
micron alumina abrasive and hydroxyapatite (25-60 microns particle
distribution) and a bombardment height of 41 mm. Particle image
velocimetry (PIV) was used to quantify the velocity of the
bombarding particles. The samples were subject to bombardment at
various particle velocities and the surface of the blasted
substrates was then subjected to 5 minutes cleaning in an
ultrasonic bath filled with deionised water. The samples were air
dried and then analysed using SEM-EDX. Signals arising from lighter
element such as carbon and oxygen were not measured and instead the
analysis focussed on the heavier elements of Ca, P and Ti.
[0108] At velocities less than 100 m/sec, there was minimal
hydroxyapatite detected on the surface of the titanium coupons. At
velocities in excess of 100 m/sec, there was significant
hydroxyapatite loading of the metal. Samples blasted at a velocity
of 115 m/sec had an average loading of calcium+phosphorous of 29%,
with the remained of the material comprising titanium. SEM imaging
detected significant loading of material on the surface. Increasing
the velocity further to 194 m/sec resulted in significantly higher
loading of 46% calcium+phosphorous, with the remainder comprising
titanium.
Example 4
[0109] Polytetrafluoroethylene (PTFE) was deposited onto a
superelastic NiTi wire at ambient temperature using <50 .mu.m
and <90 .mu.m alumina with a blend ratio of 50:50 by mass. The
CoBlast coated wires were compared to wire treated with PTFE only.
The coated samples were examined using a variety of techniques:
microscopy, surface roughness, wear testing and flexural tests, for
which the results are shown in FIG. 6. It can be seen that the
CoBlast coated samples (samples (b) and (c) in FIG. 6) had an
adherent coating with a significant resistance to wear compared to
the samples coated with PTFE only (sample (a) in FIG. 6). This
study indicates that the CoBlast process can successfully be used
to deposit thin adherent coatings of PTFE onto the surface of
superelastic NiTi.
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