U.S. patent application number 15/006885 was filed with the patent office on 2016-07-28 for biodegradable magnesium alloy.
The applicant listed for this patent is Medtronic Vascular, Inc.. Invention is credited to Jeffrey Allen, Ya Guo, Syamala Rani Pulugurtha.
Application Number | 20160215372 15/006885 |
Document ID | / |
Family ID | 55697440 |
Filed Date | 2016-07-28 |
United States Patent
Application |
20160215372 |
Kind Code |
A1 |
Pulugurtha; Syamala Rani ;
et al. |
July 28, 2016 |
BIODEGRADABLE MAGNESIUM ALLOY
Abstract
A magnesium alloy includes a rare earth element alloy component
comprising yttrium, a rare earth element (REE) other than yttrium,
and a balance of magnesium. The rare earth element other than
yttrium may comprise two or more rare earth elements other than
yttrium. The rare earth element other than yttrium may include a
heavy rare earth element and a light rare earth element. The alloy
may include about 4-10 wt-% yttrium, 0-9 wt-% heavy REE, 0-7 wt-%
light REE, 0-7 wt-% zinc, 0-0.7 wt-% zirconium, and a balance of
magnesium. The balance of magnesium may be in an amount up to 90
wt-%.
Inventors: |
Pulugurtha; Syamala Rani;
(Santa Rosa, CA) ; Allen; Jeffrey; (Santa Rosa,
CA) ; Guo; Ya; (Santa Rosa, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Medtronic Vascular, Inc. |
Santa Rosa |
CA |
US |
|
|
Family ID: |
55697440 |
Appl. No.: |
15/006885 |
Filed: |
January 26, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62108923 |
Jan 28, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 23/06 20130101 |
International
Class: |
C22C 23/06 20060101
C22C023/06 |
Claims
1. An alloy comprising: a rare earth element alloy component in an
amount greater than 6 wt-% comprising: yttrium in an amount greater
than 2 wt-%; and a rare earth element other than yttrium in an
amount greater than 1% selected from gadolinium, dysprosium,
erbium, neodymium, lanthanum, cerium, and combinations thereof; and
magnesium in an amount up to 90 wt-%.
2. The alloy according to claim 1, wherein the amount of yttrium is
no less than 4.5 wt-%.
3. The alloy according to claim 2, wherein the amount of the rare
earth element other than yttrium is no less than 4 wt-%.
4. The alloy according to claim 3, wherein the amount of the rare
earth element alloy component is no less than 9.5 wt-%.
5. The alloy according to claim 3, wherein the rare earth element
other than yttrium is a heavy rare earth element selected from
gadolinium, dysprosium, and erbium.
6. The alloy according to claim 2, wherein the amount of the rare
earth element other than yttrium is no less than 5 wt-%.
7. The alloy according to claim 6, wherein the rare earth element
other than yttrium comprises a combination of two rare earth
elements other than yttrium.
8. The alloy according to claim 7, wherein the rare earth element
other than yttrium comprises a heavy rare earth element and a light
rare earth element, wherein the heavy rare earth element is
selected from gadolinium, dysprosium, erbium, and combinations
thereof, wherein the light rare earth element is selected from
neodymium, lanthanum, and cerium, and combinations thereof.
9. The alloy according to claim 8, wherein the amount of the heavy
rare earth element is greater than the amount of the light rare
earth element.
10. The alloy according to claim 1, wherein the amount of yttrium
is greater than or equal to the amount of the rare earth element
other than yttrium.
11. The alloy according to claim 1, further comprising at least one
of zinc in an amount greater than 0.1 wt-% and zirconium in an
amount greater than 0.3 wt-%.
12. The alloy according to claim 1, comprising a substantial
absence of an element selected from: scandium in an amount less
than 1 wt-%, calcium in an amount less than 0.05 wt-%, indium in an
amount less than 0.1 wt-%, and combinations thereof.
13. An alloy comprising: a rare earth element alloy component
comprising: yttrium in an amount greater than 3 wt-%; and a rare
earth element other than yttrium in an amount greater than 1%
selected from gadolinium, dysprosium, erbium, neodymium, lanthanum,
cerium, and combinations thereof; and magnesium in an amount up to
90 wt-%.
14. The alloy according to claim 13, wherein an amount of the rare
earth element alloy component is no less than 9.5 wt-%.
15. The alloy according to claim 14, wherein the rare earth element
other than yttrium comprises a combination of two rare earth
elements other than yttrium.
16. An alloy comprising: a rare earth element alloy component
comprising: yttrium in an amount greater than 3 wt-%; and a heavy
rare earth element other than yttrium in an amount no less than 0.1
wt-% selected from gadolinium, dysprosium, erbium, and combinations
thereof; and magnesium in an amount up to 90 wt-%.
17. The alloy according to claim 16, wherein an amount of the rare
earth element alloy component is no less than 9.5 wt-%.
18. An alloy comprising: a rare earth element alloy component in an
amount no less than 10 wt-% comprising: yttrium in an amount
greater than 2 wt-%; and a rare earth element other than yttrium in
an amount greater than 1 wt-% selected from gadolinium, dysprosium,
erbium, neodymium, lanthanum, cerium, and combinations thereof; and
magnesium in an amount up to a balance of the alloy.
19. The alloy according to claim 18, wherein an amount of the rare
earth element alloy component is no less than 9.5 wt-%.
20. The alloy according to claim 18, comprising a substantial
absence of an element selected from: scandium in an amount less
than 1 wt-%, calcium in an amount less than 0.05 wt-%, indium in an
amount less than 0.1 wt-%, and combinations thereof.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of U.S.
Provisional Patent Application Ser. No. 62/108,923, filed Jan. 28,
2015, which is incorporated herein by reference for all
purposes.
BACKGROUND
[0002] Magnesium demonstrates specific properties that may be
suitable in several mobile and medical applications. For example,
in various medical applications, such as cardiovascular or
orthopedic, magnesium may be biodegradable, or bioabsorbable, and
less toxic than other conventional materials.
[0003] The use of magnesium in many applications is inhibited by
potentially high degradation rates and related losses in mechanical
integrity. Furthermore, the impurities typically found in
magnesium, such as nickel, copper, and iron, may compound the
problem by enhancing the corrosion rate.
[0004] The discussion of prior publications and other prior
knowledge does not constitute an admission that such material was
published, known, or part of the common general knowledge.
SUMMARY
[0005] It is desirable to develop a suitable magnesium alloy that
is lightweight compared to conventional materials used in a broad
range of applications (e.g., mobile or medical) that exhibits
significantly improved properties (e.g., per unit mass or volume).
Non-limiting examples of improved properties include
bioabsorbability/biodegradability, biocompatibility (e.g., low
toxicity), creep resistance, corrosion resistance, strength,
toughness, durability, flexibility, deliverability, minimal recoil,
ductility, elongation to failure, castability, and grain
refinement, which may be defined at various application-specific
temperatures (e.g., room temperature, body temperature, etc). In
particular, improved mechanical and corrosion performance over
existing magnesium and magnesium alloys may be provided.
[0006] In one illustrative embodiment, an alloy comprises a rare
earth element alloy component in an amount greater than 6 wt-% and
magnesium in an amount up to about 90 wt-%. The rare earth element
alloy component comprises yttrium in an amount greater than 2 wt-%
and a rare earth element other than yttrium in an amount greater
than 1 wt-%. The rare earth element other than yttrium may be
selected from gadolinium, dysprosium, erbium, neodymium, lanthanum,
cerium, and combinations thereof.
[0007] In another illustrative embodiment, an alloy comprises a
rare earth element alloy component and magnesium in an amount up to
about 90 wt-%. The rare earth element alloy component comprises
yttrium in an amount greater than 3 wt-% and a rare earth element
other than yttrium in an amount greater than 1%. The rare earth
element other than yttrium may be selected from gadolinium,
dysprosium, erbium, neodymium, lanthanum, cerium, and combinations
thereof.
[0008] In a further illustrative embodiment, an alloy comprises a
rare earth element alloy component and magnesium in an amount up to
about 90 wt-%. The rare earth element alloy component comprises
yttrium in an amount greater than 3 wt-% and a heavy rare earth
element other than yttrium in an amount no less than 0.1 wt-%. The
heavy rare earth element may be selected from gadolinium,
dysprosium, erbium, and combinations thereof.
[0009] In yet another illustrative embodiment, an alloy comprises a
rare earth element alloy component in an amount no less than 10
wt-% and magnesium. The rare earth element alloy component
comprises yttrium in an amount greater than 2 wt-% and a rare earth
element other than yttrium in an amount greater than 1 wt-%. The
rare earth element other than yttrium may be selected from
gadolinium, dysprosium, erbium, neodymium, lanthanum, cerium, and
combinations thereof.
[0010] In some embodiments, the amount of yttrium may be no less
than 4.5 wt-%. In at least one embodiment, the amount of rare earth
element other than yttrium may be no less than 4 wt-%. The amount
of the rare earth element alloy component may be no less than 9.5
wt-%. The rare earth element other than yttrium may be a heavy rare
earth element selected from gadolinium, dysprosium, and erbium.
[0011] In further embodiments, the amount of the rare earth element
other than yttrium is no less than 5 wt-%. The rare earth element
other than yttrium may comprise a combination of two rare earth
elements other than yttrium. The rare earth element other than
yttrium may comprise a heavy rare earth element and a light rare
earth element. The heavy rare earth element may be selected from
gadolinium, dysprosium, erbium and combinations thereof. The light
rare earth element may be selected from selected from neodymium,
lanthanum, cerium, and combinations thereof.
[0012] In at least one embodiment, the amount of the heavy rare
earth element is greater than the amount of the light rare earth
element. In at least one other embodiment, the amount of yttrium is
greater than or equal to the amount of the rare earth element other
than yttrium.
[0013] In various further embodiments, the alloy comprises at least
one of zinc in an amount greater than 0.1 wt-% and zirconium in an
amount greater than 0.3 wt-%.
[0014] In various additional embodiments, the alloy comprises a
substantial absence of an element selected from scandium in an
amount less than 1 wt-%, calcium in an amount less than 0.05 wt-%,
indium in an amount less than 0.1 wt-%, and combinations
thereof.
[0015] The above summary of the present disclosure is not intended
to describe each disclosed embodiment or every implementation of
the present disclosure. The detailed description that follows more
particularly exemplifies illustrative embodiments. In several
places throughout the application, guidance is provided through
lists of examples and illustrative embodiments, which may be used
in various combinations. In each instance, the recited list serves
only as a representative group and should not be interpreted as an
exclusive list. Various other features and advantages will become
apparent upon reading the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The disclosure may be more completely understood in
consideration of the following detailed description of various
embodiments of the disclosure in connection with the accompanying
drawings.
[0017] FIGS. 1A, 1B, and 1C are each visualizations of imaging data
at various scales for a magnesium alloy of the present disclosure.
FIG. 1A shows a visualization of scanning electron microscope (SEM)
data at a 100 micron scale (e.g., micrometers). FIG. 1B shows a
visualization of the SEM data of FIG. 1A at a 10 micron scale. FIG.
1C shows a visualization of the SEM data of FIG. 1A at a 2 micron
scale.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0018] In the following detailed description, reference is made to
several specific embodiments. It is to be understood that other
embodiments are contemplated and may be made without departing from
the scope or spirit of the present disclosure. The following
detailed description, therefore, is not to be taken in a limiting
sense.
[0019] All scientific and technical terms used herein have meanings
commonly used in the art unless otherwise specified. The
definitions provided herein are to facilitate understanding of
certain terms used frequently herein and are not meant to limit the
scope of the present disclosure.
[0020] Unless otherwise indicated, all numbers expressing feature
sizes, amounts, and physical properties used in the specification
and claims are to be understood as being modified in all instances
by the term "about." Accordingly, unless indicated to the contrary,
the numerical parameters set forth in the foregoing specification
and attached claims are approximations that can vary depending upon
the properties sought to be obtained by those skilled in the art
utilizing the teachings disclosed herein.
[0021] The recitation of numerical ranges by endpoints includes all
numbers subsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2,
2.75, 3, 3.80, 4, and 5) and any range within that range. Herein,
the terms "up to" or "no greater than" a number (e.g., up to 50)
includes the number (e.g., 50), and the term "no less than" a
number (e.g., no less than 5) includes the number (e.g., 5).
[0022] Unless otherwise noted, all parts, percentages, ratios, etc.
are by weight. Weight percent is defined by the percentage of a
component in the composition of components (e.g., 10 wt-% of an
alloy component means that 10 percent of the weight of the alloy is
the alloy component). The weight may be measured by any suitable
technique, such as energy dispersive x-ray spectroscopy (EDS) or
inductively coupled mass spectrometry (ICP-MS), for example.
References to "about" X wt-% may refer to the precision of the
instrument for measuring weight or the precision of available
components for manufacturing, for example. These abbreviations are
used herein: wt=weight, atm=atomic, .degree. C.=degrees Celsius,
and ppm=parts per million.
[0023] As used herein, "have", "having", "include", "including",
"comprise", "comprising" or the like are used in their open ended
sense, and generally mean "including, but not limited to". It will
be understood that "consisting essentially of", "consisting of",
and the like are subsumed in "comprising," and the like.
[0024] As used in this specification and the appended claims, the
singular forms "a", "an", and "the" encompass embodiments having
plural referents, unless the content clearly dictates otherwise. As
used in this specification and the appended claims, the term "or"
is generally employed in its sense including "and/or" unless the
content clearly dictates otherwise.
[0025] Also used herein, a "balance" is used to indicate at least
part of the remaining portion of a composition or the entire
remaining portion. For example, a composition comprising 10 wt-%
alloy component and a balance of magnesium means that at least part
or the entire remaining portion of the composition (e.g., up to 90
wt-%) is magnesium. The balance of material may include impurities
in the balance material utilized in the composition (e.g., 99.99
wt-% pure magnesium comprises 0.01 wt-% impurity in the magnesium).
Further, the balance of material may include other material in an
amount generally less than the amount (e.g., wt-%) of the balance
material utilized in the composition (e.g., a balance of magnesium
up to 90 wt-% does not exclude 1 wt-% zirconium, 6 wt-% zinc,
etc.).
[0026] The term "and/or" means one or all of the listed elements or
a combination of any two or more of the listed elements (e.g.,
casting and/or treating an alloy means casting, treating, or both
casting and treating the alloy).
[0027] The phrases "at least one of," "comprises at least one of,"
and "one or more of" followed by a list refers to any one of the
items in the list and any combination of two or more items in the
list.
[0028] Reference to "one embodiment," "an embodiment," "certain
embodiments," or "some embodiments," etc., means that a particular
feature, configuration, composition, or characteristic described in
connection with the embodiment is included in at least one
embodiment of the disclosure. Thus, the appearances of such phrases
in various places throughout are not necessarily referring to the
same embodiment of the disclosure. Furthermore, the particular
features, configurations, compositions, or characteristics may be
combined in any suitable manner in one or more embodiments.
[0029] The words "preferred," "preferably," and "optionally" refer
to embodiments of the disclosure that may afford certain benefits,
under certain circumstances. However, other embodiments may also be
preferred, under the same or other circumstances. Furthermore, the
recitation of one or more preferred embodiments does not imply that
other embodiments are not useful, and is not intended to exclude
other embodiments from the scope of the disclosure.
[0030] The present disclosure provides a magnesium and rare earth
element alloy. In particular, the magnesium alloy includes yttrium
and at least one other rare earth element. The alloy may be
lightweight and may exhibit significantly improved properties
(e.g., per unit mass or volume). Non-limiting examples of improved
properties include bioabsorbability/biodegradability,
biocompatibility (e.g., low toxicity), creep resistance, corrosion
resistance, strength, toughness, durability, flexibility,
deliverability, minimal recoil, ductility, elongation to failure,
castability, and grain refinement, which may be defined at various
application-specific temperatures (e.g., room temperature, body
temperature, etc).
[0031] The alloy may be used in a broad range of applications,
which may be mobile or medical, for example. Non-limiting examples
of medical applications include bioabsorbable/biodegradable heart
stents, valve scaffolds, staples, bone screws, and fasteners.
Non-limiting examples of mobile applications include bicycle
components (e.g., frame), aircraft components, automobile
components, and electronics enclosures or components (e.g.,
laptop).
[0032] Desirable properties may have different priorities for
different applications. In a medical stent application (e.g.,
cardiovascular stent), for example, corrosion performance of the
alloy may be more important than ductility or strength, and
ductility may be more important than strength. In a medical
fixation application (e.g., staples, orthopedic screws, fasteners,
etc), for example, ductility of the alloy may be more important
than strength or corrosion performance, and strength may be more
important than corrosion performance. The balance of elements in
the alloy may be selected to achieve the desired priority of
properties as described herein in more detail.
[0033] In general, the alloy includes magnesium and one or more
alloying components. The alloy may include one alloying component.
The alloy may include two alloying components. The alloy may also
include three, four, five, six, or seven alloy components, among
others. In many embodiments, each alloy component may be introduced
to modify or improve the properties of magnesium, for example, by
way of solid solution strengthening, precipitation hardening,
grain-boundary strengthening, or combinations thereof.
[0034] In illustrative embodiments, the alloy includes a solid
solution alloy component. The atoms of the solid solution alloy
component (e.g., rare earth element or metal) can diffuse into the
crystalline lattice (e.g., matrix) of a base metal (e.g.,
magnesium) to substitute for base metal atoms or to fill the
interstices in the base metal matrix. Magnesium has a hexagonal
close-packed (hcp) crystal structure with an ideal axial ratio
(c/a) of 1.624 and an atomic diameter of 0.320 nanometers (nm) and
may form solid solutions with a diverse range of elements, such as
rare earth elements and metals, which may be selected to strengthen
the magnesium matrix, for example.
[0035] In various embodiments, the alloy includes a grain refiner.
The grain refiner (e.g., zirconium) can be introduced to a
magnesium alloy melt to limit the growth of grains as the melt is
cooled below a melting temperature (e.g., casting temperature). The
limited size of the grain increases the presence of grain
boundaries, which may limit the propagation of dislocations (e.g.,
defects in the crystalline lattice) in the matrix and may improve
strength of the alloy.
[0036] In many embodiments, the alloy includes one or more
precipitates (e.g., impurity phase). In at least some embodiments,
the alloy component has a high temperature-dependent solubility in
magnesium. Precipitate particles may be formed due to changes in
solid solubility (e.g., rare earth element or metal solubility in
magnesium) with temperature, which may produce particles of an
impurity phase that may limit the propagation of dislocations in
the matrix. A heat treatment may be used to form or grow the
precipitate particles at an annealing temperature below a melting
temperature (e.g., casting temperature) and in a heat treatment
window.
[0037] In one case, a cast alloy is formed using a conventional
casting technique. The magnesium and alloying components are heated
together in a crucible to a suitable casting temperature to form a
liquid alloy, or melt, and the liquid alloy is poured into a static
mold and allowed to cool to the room temperature (e.g., 25.degree.
C.). The formed alloy may be utilized as a whole or be separated
into multiple pieces of alloy (e.g., ingots).
[0038] In another case, a cast alloy is formed using a continuous
casting technique. The melted, liquid alloy is continuously poured
into a mold that forms a strand of alloy instead of a static mold.
The strand moves through the mold and is continuously cooled by
quenching with water along the whole of the strand, which may form
a thin solidified shell on the cast. The strand may be cut, for
example, by a torch, to form separate pieces of alloy (e.g.,
ingots).
[0039] The microstructure of a continuously cast alloy may be
slightly different than that of an alloy formed in conventional
casting. For example, the grain structure may be more refined, and
the chemical composition and microstructure may be more uniform
across the thickness of the cast.
[0040] In yet another case, a cast alloy is formed using a rapid
solidification process. For example, the melted, liquid alloy may
be poured onto a fast-rotating copper wheel. The wheel may freeze
the alloy instantaneously, in some cases, via cooling at a rate of
1,000,000.degree. C. per second. A homogenous crystalline structure
of the alloy may be retained in the material. The rotation of the
wheel may further direct the alloy toward a chopper to form
separate pieces of alloy (e.g., ingots).
[0041] Magnesium (Mg) utilized in the alloy may be have various
levels of purity. In various embodiments, magnesium is provided in
ultra-pure form (e.g., 99.999 wt-% magnesium or less than 10 ppm
non-Mg components). Ultra-pure magnesium may have a creep
resistance that does not exceed about 0.02 mg/cm.sup.2/day in many
cases. However, ultra-pure magnesium is typically manufactured by
the expensive process of vacuum sublimation to achieve the high
purity level and creep resistance, which impedes its use in many
applications, at least due to cost-effective availability.
[0042] In many embodiments, magnesium utilized in the alloy may be
in non-ultra-pure form. In other words, the magnesium in the alloy
may have a purity level no greater than about 99.999 wt-% magnesium
(e.g., no less than 10 ppm non-Mg components) and/or a creep
resistance greater than about 0.02 mg/cm.sup.2/day. The use of
non-ultra-pure magnesium may be preferable in applications wherein
availability and cost-effective manufacturing are more important,
such as certain medical applications, as well as many mobile
applications.
[0043] In illustrative embodiments of the alloy, one or more alloy
components and magnesium are included. Generally, the magnesium is
present in a greater amount than another element or all other
elements, including alloying components. Thus, the alloy may
conveniently be described as a magnesium alloy (e.g., primarily
comprising magnesium). In some particular embodiments, the alloy
includes magnesium in an amount up to 90 wt-% (e.g., alloy
components are present in an amount of at least 10 wt-%). In at
least one embodiment, the alloy includes magnesium in an amount up
to 89.5 wt-%. In some illustrative embodiments, the alloy includes
various alloy components and a balance of magnesium (e.g., the
balance of material in the alloy).
[0044] The alloy may include various alloying components. In
particular, the alloy may include a rare earth element (REE) alloy
component, which may comprise one or more specific rare earth
elements. Specific rare earth elements include scandium (Sc),
yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr),
neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu),
gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho),
erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).
[0045] In general, the rare earth element alloy component includes
yttrium. In many embodiments, the rare earth element alloy
component includes yttrium and a rare earth element other than
yttrium. In some embodiments, the rare earth element alloy
component includes yttrium and two rare earth elements other than
yttrium. As used in the description herein, "rare earth element"
may mean "rare earth element other than yttrium," as will be made
clear by the context of usage.
[0046] In addition, the term "rare earth element" may refer to a
subset of known rare earth elements. The REEs referred to may be
only those commercially available. In particular, the REEs may
refer to those commercially available in a pure form. A pure form
may include 99 wt-% REE, 99.9 wt-% REE, or 99.99 wt-% REE, among
others. For example, a rare earth element added to the alloy may
optionally be provided in 99.99 wt-% REE form. In other
embodiments, the rare earth element can be provided as misch-metal
(e.g., an alloy of various rare earth elements, which may include
cerium, lanthanum, neodymium, and praseodymium). Although the rare
earth element can be provided in any form, in illustrative
embodiments, only pure rare earth elements are used to form the
alloy.
[0047] In certain illustrative embodiments, the term "rare earth
element" in the alloy may refer to the subset of rare earth
elements (e.g., other than yttrium) selected from gadolinium,
dysprosium, erbium, neodymium, lanthanum, cerium, and combinations
thereof. In various embodiments, a rare earth element other than
yttrium is selected from gadolinium, dysprosium, erbium, neodymium,
and combinations thereof. In at least some embodiments, a rare
earth element other than yttrium is selected from gadolinium,
neodymium, or both.
[0048] Furthermore, rare earth elements may be classified herein,
for example, into light rare earth elements (light REEs) and heavy
rare earth elements (heavy REEs), which corresponds to relative
atomic number or weight. In various embodiments, a rare earth alloy
element other than yttrium is selected from a light REE, a heavy
REE, or both.
[0049] For example, in some embodiments, a light REE is selected
from lanthanum, cerium, praseodymium, neodymium, promethium, and
combinations thereof. In further embodiments, a light REE is
selected from neodymium, lanthanum, cerium, and combinations
thereof. In yet further embodiments, a light REE is neodymium.
[0050] Also, for example, in various embodiments, a heavy REE is
selected from samarium, europium, gadolinium, terbium, dysprosium,
holmium, erbium, thulium, ytterbium, lutetium, and combinations
thereof. In further embodiments, a heavy REE is selected from
gadolinium, dysprosium, erbium, and combinations thereof. In yet
further embodiments, a heavy REE is gadolinium.
[0051] One or more alloying components may be provided in an amount
that is at least partially soluble in magnesium, at least partially
insoluble in magnesium, or both depending on temperature. The
solubility may refer to liquid solubility, solid solubility, or
both, for example. In general, solubility in magnesium versus
temperature mainly depends on the atomic size of the alloy
component with regard to magnesium and its valence band
configuration. In some specific examples, at about room temperature
(e.g., 25.degree. C.), neodymium has a solid solubility limit of
less than about 1 wt-% in magnesium, gadolinium has a solubility
limit of about 4 wt-% in magnesium, zinc has a solubility limit of
about 2 wt-%, zirconium is not soluble, and yttrium is not
soluble.
[0052] In many embodiments, one or more alloying components are
included in the alloy below the solubility limit of magnesium at a
desired temperature (e.g., the application requires use at room
temperature or body temperature). In some embodiments, one or more
alloying components are included in the alloy above one-fourth,
one-third, one-half, etc. the respective solid solubility in
magnesium. In various embodiments, one or more alloying components
are included in the alloy above the respective solubility in
magnesium, which may result in precipitates at room temperature,
for example. In particular illustrative embodiments, an alloy
component (e.g., yttrium, another rare earth element, or both) are
included above their respective solubility limits in magnesium. The
present disclosure recognizes that the inclusion of more than one
alloying component in the alloy may alter the solubility of each
respective alloying component (e.g., element) in magnesium.
[0053] Although the soluble amount of an alloy component may
strengthen the matrix or have other desirable effects on the
properties of magnesium alloy, the insoluble amount of an alloy
component may form precipitate particles at various temperatures
and provide further desirable effects on the magnesium alloy.
Precipitate particles at a desired temperature may be useful in
certain applications (e.g., for grain refinement and/or precipitate
hardening).
[0054] A precipitate particle may be of a particular type, or
phase, and the amount of each alloy component, relative amounts of
each alloy component, or total of the alloy components may
determine the precipitate phases formed in the alloy at the desired
temperature. For example, the amount of yttrium, rare earth
element, and/or any other alloy component may be selected to form
precipitates with magnesium or another alloying component, which
may improve the mechanical properties of the magnesium alloy. In
some illustrative embodiments, the alloy includes magnesium-rich
precipitates. In various illustrative embodiments the amount of
yttrium is selected to form yttrium-rich precipitates, the amount
of rare earth element is selected to form REE-rich precipitates,
the amount of another particular alloy element is selected to form
a particular alloy element-rich precipitate, or combinations
thereof. The precipitates may be visible by imaging, such as
computed tomography (CT), scanning electron microscopy (SEM), etc.,
which may facilitate identification and analysis of the precipitate
phases and particles.
[0055] The one or more alloying components may be selected for
their desirable effects on the properties of the magnesium alloy.
In one example, the amount of yttrium may be selected to improve
mechanical properties, such as elongation to failure and/or
strength of the alloy. Yttrium may improve creep resistance in a
range of temperatures. In various medical applications, for
example, creep resistance at body temperature is important to
maintaining the shape of a component comprising the alloy, such as
in a cardiovascular stent application.
[0056] To illustrate potential amounts of yttrium, in many
embodiments, the alloy can include yttrium in an amount greater
than about 1 wt-%, greater than about 2 wt-%, greater than about 3
wt-%, no less than about 4 wt-%, no less than about 4.5 wt-%, no
less than about 5 wt-%, greater than about 5.5 wt-%, no less than
about 5.7 wt-%, no less than about 6 wt-%, no less than about 6.7
wt-%.
[0057] Furthermore, in various embodiments, the alloy includes
yttrium in an amount up to about 10 wt-%, up to about 9 wt-%, up to
about 7.7 wt-%, up to about 7 wt-%, up to about 6.7 wt-%, up to
about 6 wt-%, or up to about 5 wt-%.
[0058] Yet further, in some embodiments, the alloy includes yttrium
in an amount ranging from about 4.5 to about 7.7 wt-%, from about 5
to about 7 wt-%, from about 5.5 to about 6.7 wt-%, from about 5.7
to about 10 wt-%, from about 6 to about 10 wt-%, from about 6.7 to
about 9 wt-%, or from about 4 to about 6 wt-%.
[0059] In at least one embodiment, the alloy includes yttrium in an
amount equal to about 5 wt-%. The ranges or specific amount of
yttrium may be selected depending on the particular application,
some of which are described herein.
[0060] Other than yttrium, a rare earth element may also be
included in the alloy to augment the same or additional properties
of the magnesium alloy. For example, the rare earth element may be
selected to improve corrosion resistance and/or mechanical
properties of the alloy. The rare earth element other than yttrium
may improve the strength of the alloy at elevated temperatures
and/or may reduce porosity in casting (e.g., by reducing the
freezing range).
[0061] To illustrate potential amounts of yttrium, in many
embodiments, the alloy includes a rare earth element other than
yttrium in an amount greater than 0 wt-%, no less than about 0.1
wt-%, greater than about 1 wt-%, greater than about 3 wt-%, no less
than about 4 wt-%, no less than about 4.5 wt-%, no less than about
5 wt-%, greater than about 5.5 wt-%, or no less than about 6
wt-%.
[0062] Further, in various embodiments, the alloy includes a rare
earth element other than yttrium in an amount no greater than about
9 wt-%, no greater than about 8 wt-%, no greater than about 7 wt-%,
no greater than about 6 wt-%, no greater than about 5.5 wt-%, no
greater than about 5 wt-%, no greater than about 4 wt-%, no greater
than about 3.5 wt-%, no greater than about 3 wt-%, less than about
2.5 wt-%, no greater than about 2 wt-%, or no greater than about 1
wt-%.
[0063] Yet further, in some embodiments, the alloy includes a rare
earth element other than yttrium in an amount ranging from about 0
to about 4 wt-%, from about 0 to about 3 wt-%, from about 0 to
about 2 wt-%, from about 4 to about 6 wt-%, from about 5 to about 7
wt-%, from about 4.5 to about 9 wt %, or from about 5.5 to about 9
wt-%.
[0064] In further embodiments, the alloy includes a rare earth
element other than yttrium in an amount equal to about 1 wt-%,
about 5 wt-%, or about 6 wt-%. The ranges or specific amount of
rare earth element may be selected depending on the particular
application, some of which are described herein.
[0065] In illustrative embodiments, the rare earth element may
include at least one heavy REE, at least one light REE, or both.
For example, in some illustrative embodiments, the rare earth
element other than yttrium is a heavy REE. In at least one
embodiment, the rare earth element other than yttrium is
gadolinium. Gadolinium may useful as it has the highest solubility
in magnesium as compared to other rare earth element or heavy REE
candidates. Yet in various illustrative embodiments, the rare earth
element other than yttrium is a light REE. In at least one
embodiment, the rare earth element other than yttrium is neodymium.
Neodymium may be useful, in part, due to its cost-effective
availability as a rare earth element.
[0066] The amount of rare earth element in the alloy may be set
relative to the amount of yttrium. For example, the relative amount
of each element may influence the properties of the alloy. The rare
earth element may be included in an amount greater than, no greater
than, less than, no less than, or about equal to the amount of
yttrium.
[0067] In various illustrative embodiments, the rare earth element
comprises only one specific rare earth element. However, in other
illustrative embodiments, the rare earth element comprises a
combination of specific rare earth elements. For example the rare
earth element other than yttrium may comprise two or more rare
earth elements, such as a first REE, a second REE, etc. In at least
one embodiment, the rare earth element other than yttrium comprises
two rare earth elements other than yttrium.
[0068] There may be advantages in including at least two rare earth
elements in the alloy. For example, a second REE may be selected as
a substitute for a first REE and may impart similar improvements in
alloy properties. In some cases, the second REE may be selected as
a more cost-effective substitute for the first REE. Each specific
rare earth element (e.g., first REE, second REE, etc) may be
included in any amount as described herein for the rare earth
element, for example.
[0069] In addition to the various ranges and specific amounts
described herein for each alloy component, the alloy may include
two or more alloy components in a particular range or specific
amount as a total amount, which may be selected to achieve certain
desirable properties (e.g., more than one type/phase of
precipitate). For example, in many embodiments, the rare earth
element alloy component includes yttrium and the rare earth element
other than yttrium (including potential combinations) in a total
amount greater than about 6 wt-%, no less than about 6.5 wt-%, no
less than about 9.5 wt-%, no less than about 10 wt-%, or no less
than about 10.5 wt-%. In various embodiments, the REE alloy
component includes yttrium and one or more rare earth elements in a
total amount no greater than about 15.7 wt-%. The REE alloy
component may include yttrium and a first REE. The REE alloy
component may also include yttrium, a first REE, and a second
REE.
[0070] In various embodiments, the rare earth element comprises a
combination of two or more rare earth elements other than yttrium
in a total amount greater than about 4 wt-%, greater than about 5
wt-%, no less than about 5.5 wt-%, or no less than about 6
wt-%.
[0071] In some embodiments, a first REE may be a heavy REE and a
second REE may be a light REE. For example, the heavy REE may be
gadolinium. The light REE may be neodymium. In at least one
embodiment, the rare earth element includes gadolinium and
neodymium.
[0072] In additional embodiments, the alloy may also optionally
include an alloy component other than a rare earth element. For
example, the alloy may include a metal as an alloy component. In
some cases, the alloy may include zinc, zirconium, or both. In some
conventional alloys, aluminum is used for castability. Instead, in
many embodiments, zinc may be included in an amount to improve
castability. Zirconium may be included in an amount for grain
refinement and/or improvement of mechanical properties.
[0073] In many embodiments, the alloy includes zinc in an amount
greater than 0 wt-%, no less than about 0.1 wt-%, no less than
about 0.2 wt-%, or no less than about 0.22 wt-%. In various
embodiments, the alloy includes zinc in an amount no greater than
about 7 wt-%, no greater than about 6 wt-%, no greater than about
0.3 wt-%, or no greater than about 0.2 wt-%. In at least one
embodiment, the alloy includes zinc in an amount of about 0.2
wt-%.
[0074] In many embodiments, the alloy includes zirconium in an
amount greater than 0 wt-%, no less than about 0.3 wt-%, no less
than about 0.4 wt-%, no less than about 0.5 wt-%, or no less than
about 0.6 wt-%. In various embodiments, the alloy includes
zirconium in an amount no greater than about 0.7 wt-%, no greater
than about 0.6 wt-%, no greater than about 0.5 wt-%, or no greater
than about 0.4 wt-%. In at least one embodiment, the alloy includes
zirconium in an amount of about 0.4 wt-%. In at least one other
embodiment, the alloy includes zirconium in an amount of about 0.6
wt-%.
[0075] In addition to including certain elements in the alloy,
other elements may be substantially absent in the alloy, which may
affect the properties of the alloy and/or the cost of manufacturing
the alloy. In many embodiments, a substantial absence of an element
comprises an amount of the element less than about 1 wt-%, less
than about 0.1 wt-%, less than about 0.05 wt-%, less than about
0.01 wt %, less than about 0.001 wt-% (e.g., 10 parts per million),
or about 0 wt-%. In some embodiments, elements substantially absent
in the alloy are selected from aluminum, calcium, indium,
manganese, scandium, silicon, zinc, or zirconium, as well as any
selected rare earth element (e.g., a rare earth element other than
yttrium, such as lutetium, a heavy REE, a light REE, etc), and
combinations thereof.
[0076] Illustrative embodiments of particular alloys disclosed
herein may be described as Mg--Y--Gd alloys, Mg--Y--Nd alloys, and
Mg--Y--Gd--Nd alloys. In each alloy, an element may be present in a
higher percentage than another element. For example, in an
Mg--Y--Gd alloy, magnesium may be present in a higher amount than
yttrium and/or gadolinium. However, any relative amount of
magnesium, yttrium, and gadolinium may be present. Exemplary
embodiments may further include zirconium, zinc, or both. Various
embodiments may be more suitable for certain applications, wherein
desirable properties have different level of importance.
[0077] Non-limiting examples of precipitate phases include Mg24Y5,
Mg5Gd, and Mg41Nd5, which are identified according to a standard
commercial designation (e.g., ASTM standards developed by ASTM
International). For example, the designation Mg24Y5 indicates a
ratio of 24 magnesium atoms to 5 yttrium atoms. The precipitate
phases may be identified, for example, by ICP-MS measurements down
to a precision of about 1-10 ppm depending on the element measured.
In general, a particle of precipitate comprises two or more major
elements forming the phase, which may identify the phase of the
precipitate. However, a precipitate particle may also comprise an
additional minor element (e.g., a third element), which may not
define the dominant structure of the precipitate particle due to
its relatively smaller amount in the phase. In at least some
embodiments, the Mg24Y5 precipitate includes some rare earth
element other than yttrium, such as gadolinium and/or neodymium. In
at least some embodiments, the Mg5Gd precipitate includes some rare
earth element other than gadolinium, such as yttrium. In at least
some embodiments, the Mg41Nd5 precipitate includes some rare earth
element other than neodymium, such as yttrium. In at least one
embodiment, the Mg41Nd5 precipitate is formed if there is no
gadolinium in the alloy.
[0078] In many embodiments, the alloy is formed by a casting and
optional heat treatment process. The components of the alloy may be
provided to the melt as pure elements, master alloys, or both. The
components are melted at a casting temperature to form a liquid,
alloy melt. The alloy melt is cooled from the casting temperature.
As the alloy is cooled toward room temperature, for example,
precipitates may form a portion of the microstructure of the cast
alloy. The microstructure may also include one or more phases of
precipitates. Desirable properties may be imparted upon the cast
alloy because of the identity of the precipitates, the amount of
the precipitates, the phase of the precipitates, the location of
the precipitates, or any combinations thereof.
[0079] The cast alloy may then be heat treated. In some
embodiments, the cast alloy is subjected to a range of temperatures
in a heat treatment window (e.g., annealing temperatures below the
casting temperature). Heat treating may increase the size of
precipitate particles and/or refine grain boundaries to impart
further desirable properties into the alloy. The precipitate
particle sizes may be distributed, for example, as small or large
particles. Some precipitate particles may be uniformly or
non-uniformly distributed.
[0080] In at least some embodiments, one or more master alloys are
provided for casting. Non-limiting examples of master alloys
include magnesium-gadolinium (Mg--Gd), magnesium-neodymium
(Mg--Nd), magnesium-yttrium (Mg--Y), and
magnesium-gadolinium-zirconium (Mg--Gd--Zr). Any relative amount of
identified element may be may be present in the master alloy (e.g.,
more, less, or equal relative amounts of magnesium and gadolinium
in Mg--Gd). In further embodiments, one or more elements in pure
form are provided for casting. In other embodiments, only elements
in pure form are provided for casting.
[0081] With various aspects of the composition and formation of the
alloy being described, various illustrative combinations are also
described to further illustrate various combinations of alloy
components that may be useful in certain applications, some of
which are described herein.
[0082] In various illustrative embodiments, an alloy may include,
but not be limited to, about:
4-10 wt-% yttrium, 0-9 wt-% heavy REE, 0-7 wt-% light REE, 0-7 wt-%
zinc, 0-0.7 wt-% zirconium, and magnesium (optionally comprising
the balance of the alloy).
[0083] In these particular embodiments, the alloys may exhibit
superior strength, ductility, corrosion resistance, or combinations
thereof. The alloy may be suitable for a broad range of
applications, including mobile and medical applications.
[0084] In some illustrative embodiments, alloys may include, but
not be limited to, about:
4.5-7.7 wt-% yttrium, 0-9 wt-% heavy REE, 0-6 wt-% light REE, 0-0.3
wt-% zinc, 0-0.5 wt-% zirconium, and magnesium (optionally
comprising the balance of the alloy).
[0085] In these particular embodiments, the alloys may exhibit
superior strength (e.g., due to yttrium-rich precipitates),
ductility, corrosion resistance, or combinations thereof. The alloy
may be suitable for various medical applications, such as
implantable devices.
[0086] In further illustrative embodiments, alloys may include, but
not be limited to, about:
4.5-7.7 wt-% yttrium (preferably about 5.5-6.7 wt-%), 4-9 wt-%
heavy REE (preferably about 5 wt-% or about 5.5-8 wt-%), 0-0.3 wt-%
zinc (preferably about 0.2 wt-%), 0-0.5 wt-% zirconium (preferably
about 0.4 wt-%), and magnesium (optionally comprising the balance
of the alloy).
[0087] In these particular embodiments, the alloys may exhibit
superior corrosion resistance, ductility, and strength in
descending order of importance, which may be a desirable set of
properties in medical applications, such as biodegradable stents.
Mg24Y5 and/or Mg5Gd may form as precipitate phases in the alloy and
may strength the alloy. The precipitates may be very finely
distributed having sizes between 5 to 10 microns. Large
precipitates may be non-uniformly distributed. Also, corrosion
resistance may be comparable to AE42 double melt when compared, for
example, by using an ASTM B 117 Salt Fog test.
[0088] In additional illustrative embodiments, alloys may include,
but not be limited to, about:
4.5-7.7 wt-% yttrium (optionally about 5.5-6.7 wt-%), 0-2 wt-%
heavy REE (optionally about 1 wt-%), 4-6 wt-% light REE (optionally
about 5 wt-% neodymium), 0-0.3 wt-% zinc (optionally about 0.2
wt-%), 0-0.5 wt-% zirconium (optionally about 0.4 wt-%), and
magnesium (optionally comprising the balance of the alloy).
[0089] In these particular embodiments, the alloys may exhibit
superior ductility, strength, and corrosion resistance in
descending order of importance, which may be a desirable set of
properties in medical applications, such as bone screws (e.g.,
spinal), staples, or other fixation devices. Because the corrosion
resistance is not as important as in other embodiments, less of the
heavy REE may be used when compared to other illustrative
embodiments. Also, more light REE than heavy REE may be used.
Certain light REEs (e.g., neodymium) may be more readily available
than heavy REEs (e.g., gadolinium) and may allow for more
cost-effective manufacturing.
[0090] In yet further illustrative embodiments, alloys may include,
but not be limited to, about:
5.7-10 wt-% yttrium (optionally about 6.7-9 wt-%), 0-3.5 wt-% heavy
REE (optionally less than about 2.5 wt-%), 0-0.3 wt-% zinc
(optionally about 0.2 wt-%), 0-0.5 wt-% zirconium (optionally about
0.4 wt-%), and magnesium (optionally comprising the balance of the
alloy).
[0091] In these particular embodiments, the alloys may exhibit
superior strength (e.g., due to yttrium-rich precipitates),
ductility, and corrosion resistance in descending order of
importance. The alloy may be suitable for mobile applications, such
as in automobile, bicycle, or aircraft. The higher amount of
yttrium than rare earth element may allow for more cost-effective
manufacturing and thus may be more suitable in such applications
than other embodiments.
[0092] In still further illustrative embodiments, alloys may
include, but not be limited to, about:
4.5-7.7 wt-% yttrium (optionally about 5.5-6.7 wt-%), 5-7 wt-%
light REE (optionally about 6 wt-% neodymium), 0-0.3 wt-% zinc
(optionally about 0.2 wt-%), 0-0.5 wt-% zirconium (optionally about
0.4 wt-%), and magnesium (optionally comprising the balance of the
alloy).
[0093] In these particular embodiments, the alloys may exhibit
superior strength (e.g., due to yttrium-rich precipitates),
ductility, and corrosion resistance in descending order of
importance. The alloy may be suitable for mobile applications, such
as in automobile, bicycle, or aicraft. The use of a light REE and
yttrium rather than a heavy REE may allow for more cost-effective
manufacturing and thus may be more suitable in such applications
than other illustrative embodiments.
[0094] In some additional illustrative embodiments, alloys may
include, but not be limited to, about:
5.7-10 wt-% yttrium (optionally about 6.7-9 wt-%), 0-5.5 wt-% light
REE (optionally less than about 4.5 wt-% neodymium), 0-0.3 wt-%
zinc (optionally about 0.2 wt-%), 0-0.5 wt-% zirconium (optionally
about 0.4 wt-%), and magnesium (optionally comprising the balance
of the alloy).
[0095] In these particular embodiments, the alloys may exhibit
superior strength (e.g., due to yttrium-rich precipitates),
ductility, and corrosion resistance in descending order of
importance. The alloy may be suitable for mobile applications, such
as in automobile, bicycle, or aircraft. The use of a higher amount
of yttrium than rare earth element, as well as the use of a light
REE rather than a heavy REE, may allow for more cost-effective
manufacturing and thus may be more suitable in such applications
than other illustrative embodiments.
[0096] In various additional illustrative embodiments, alloys may
include, but not be limited to, about:
4-6 wt-% yttrium (optionally about 5 wt-%), 4-6 wt-% heavy REE
(optionally about 5 wt-%), 0-4 wt-% light REE (optionally no
greater than about 3 wt-%), 0-0.3 wt-% zinc (optionally about 0.22
wt-%), 0-0.7 wt-% zirconium (optionally about 0.6 wt-%), and
magnesium (optionally comprising the balance of the alloy).
[0097] In yet further illustrative embodiments, alloys may include,
but not be limited to, about:
4-6 wt-% yttrium (optionally about 5 wt-%), 4-6 wt-% heavy REE
(optionally less about 5 wt-%), 0.1-7 wt-% zinc (optionally about
0.22-6 wt-%), 0-0.7 wt-% zirconium (optionally about 0.6 wt-%), and
magnesium (optionally comprising the balance of the alloy).
[0098] In at least some illustrative embodiments, alloys may
include, but not be limited to, about:
4-6 wt-% yttrium (optionally about 5 wt-%), 4-6 wt-% heavy REE
(optionally about 5 wt-%), 0-4 wt-% light REE (optionally no
greater than about 3 wt-%), 0-0.7 wt-% zirconium (optionally about
0.6 wt-%), and magnesium (optionally comprising the balance of the
alloy).
[0099] While the present disclosure is not so limited, an
appreciation of various aspects of the disclosure will be gained
through a discussion of the specific example(s) and illustrative
embodiments provided below, which provide alloys with superior
mechanical and corrosion properties. Various modifications of the
example(s) and illustrative embodiments, as well as additional
embodiments of the disclosure, will become apparent herein.
Example 1
[0100] Alloys with various illustrative compositions as disclosed
herein may have superior mechanical and corrosion performance at
least based upon calculations of thermodynamic modeling and/or
analysis of casted alloys.
[0101] In one example, an example alloy was calculated to cool from
a casting temperature in a heat treatment window from about 500 to
about 550.degree. C. The example alloy included 5 wt-% yttrium, 5
wt-% gadolinium, 0.4 wt-% zirconium, 0.2 wt-% zinc, and a balance
of magnesium (e.g., which can be described as Mg5Gd5Y0.4Zr0.2Zn). A
thermodynamic model was calculated to describe the zinc
concentration versus temperature for 5Gd5Y without zirconium (e.g.,
Zr was excluded from the calculations). The model indicated that
the above described alloy would have a four phase microstructure
including a magnesium phase, an Mg24Y5 phase, an Mg5Gd phase, and
an MgGdZn phase.
[0102] The example alloy was formed, cast, and analyzed for
microstructure properties by CT and SEM. Visualizations of CT data
showed an ingot of the example alloy having pores with a volume of
about 2 cubic millimeters. Visualizations of SEM data showed
precipitates having sizes between 5 to 10 micrometers finely
distributed throughout the alloy (see FIG. 1A). The large
precipitates were non-uniformly distributed (see FIG. 1B). At least
three types of phases were identified (as seen in FIG. 1C),
including an MgGd matrix phase 9, a GdMgY phase 10, 11 (e.g.,
Gd-rich precipitate), MgYGd phase 12, 13, and an MgGd divorced
eutectic phase 8. The composition of each phase measured via SEM
data is listed in Table I below:
TABLE-US-00001 TABLE I Phase % Mg Y Gd MgGd divorced eutectic phase
8 wt-% 86.9 5 8 atm-% 97.09 1.53 1.38 MgGd matrix phase 9 wt-% 96.2
1.6 2.2 atm-% 99.2 0.45 0.35 GdMgY phase 10, 11 wt-% 41.9 5.5 52.5
atm-% 81.31 2.92 15.77 GdMgY phase 12, 13 wt-% 68.5 16.9 14.6 atm-%
90.88 6.13 2.99
[0103] The alloy was also analyzed for corrosion performance by
ASTM B 117 Salt Fog testing. Samples of the example alloy were
provided for testing as small plates having about a 22 millimeter
diameter and a 3 millimeter height. The samples were grinded and
polished to prepare for salt fog testing at 35.degree. C. for 48
hours. Average corrosion performance was then compared to a control
sample of AE42 double melt (AE42 DM), which is one standard
commercial designation for Mg-4Al-2RE (indicating about 4 wt-%
aluminum, 2 wt-% rare earth element, and a balance of magnesium).
The average corrosion depth of the example alloy (about 150
microns) and was found to be comparable to the average corrosion
depth of the AE42 DM control sample (about 50 microns).
Example 2
[0104] In another example, a heart stent was fabricated with the
example alloy described in Example 1. The example heart stent was
fabricated by laser cutting. Example heart stent samples were
analyzed for corrosion performance soaked in fetal bovine serum.
Radial strength testing and quantitative cross-sectional
measurements at each end-point of the heart stent were measured at
one week, two weeks, and four weeks for samples of the example
heart stent and compared against sample stents formed of AE42
magnesium alloy and sample stents formed of WE43 magnesium alloy.
The AE42 alloy utilized was described in Example 1. WE43 is one
standard commercial designation for another magnesium alloy, which
may comprise about 4 wt-% yttrium, about 2.4 to about 4.4 wt-% or
rare earth elements, about 0.4 wt-% zirconium, and a balance of
magnesium.
[0105] According to the radial strength testing, at one week,
radial stiffness in the example heart stent samples, as measured in
Newtons per millimeter, was observed to be greater than the AE42
samples but less than the WE43 samples. At two weeks, the radial
stiffness was observed to be less than both the AE42 and the WE43
samples. At four weeks, the radial stiffness of one example heart
stent sample was observed to be greater than both the AE42 and WE43
samples, even though breaks were observed at the crowns at
deployment of the example stent samples. Other observations at four
weeks included the example heart stent samples having more uniform
corrosion than the AE42 samples. The WE43 samples developed
corrosion issues at the ends of the stent.
[0106] According to the quantitative cross-sectional analysis, the
example heart stent showed more fraction metal remaining in the
example stent than the WE43 and AE42 samples after one week. After
two weeks, the fractional metal remaining was about the same as the
AE42 samples and more than the WE43 samples. The arms of the
example stent samples and the WE43 samples fell apart after four
weeks. Only the AE42 samples were measured at four weeks and showed
a significant drop in fraction metal remaining compared to the two
week measurement.
Illustrative Embodiments
[0107] Embodiment 1 is an alloy comprising a rare earth element
alloy component in an amount greater than about 6 wt-%, comprising
yttrium in an amount greater than about 2 wt-% and a rare earth
element other than yttrium in an amount greater than about 1 wt-%,
and magnesium in an amount up to about 90 wt-%. The rare earth
element other than yttrium may be selected from gadolinium,
dysprosium, erbium, neodymium, lanthanum, cerium, and combinations
thereof (e.g., heavy or light rare earth elements).
[0108] Embodiment 2 is an alloy comprising a rare earth element
alloy component, comprising yttrium in an amount greater than about
3 wt-% and a rare earth element other than yttrium in an amount
greater than about 1%, and magnesium in an amount up to about 90
wt-%. The rare earth element other than yttrium may be selected
from gadolinium, dysprosium, erbium, neodymium, lanthanum, cerium,
and combinations thereof (e.g., heavy or light rare earth
elements).
[0109] Embodiment 3 is an alloy comprising a rare earth element
alloy component, comprising yttrium in an amount greater than about
3 wt-% and a heavy rare earth element other than yttrium in an
amount no less than about 0.1 wt-%, and magnesium in an amount up
to about 90 wt-%. The heavy rare earth element may be selected from
gadolinium, dysprosium, erbium, and combinations thereof (e.g.,
heavy rare earth elements).
[0110] Embodiment 4 is an alloy comprising a rare earth element
alloy component in an amount no less than about 10 wt-%, comprising
yttrium in an amount greater than about 2 wt-% and a rare earth
element other than yttrium in an amount greater than about 1 wt-%,
and magnesium in an amount up to a balance of the alloy. The rare
earth element other than yttrium may be selected from gadolinium,
dysprosium, erbium, neodymium, lanthanum, cerium, and combinations
thereof (e.g., heavy or light rare earth elements).
[0111] Embodiment 5 is the alloy of any one of embodiments 1
through 4 comprising a precipitate impurity phase of Mg24Y5 and
optionally a rare earth element.
[0112] Embodiment 6 is the alloy of any one of embodiments 1
through 5 comprising a precipitate impurity phase of Mg5Gd and
optionally yttrium, as applicable.
[0113] Embodiment 7 is the alloy of any one of embodiments 1
through 5 comprising a precipitate impurity phase of Mg41Nd5 and
optionally yttrium, as applicable.
[0114] Embodiment 8 is the alloy of any one of embodiments 1
through 7 comprising zinc in an amount no less than about 0.1 wt-%
and/or no greater than about 7 wt-%.
[0115] Embodiment 9 is the alloy of embodiment 8, wherein the
amount of zinc is no greater than about 0.3 wt-%.
[0116] Embodiment 10 is the alloy of embodiment 9, wherein the
amount of zinc is about 0.2 wt-%.
[0117] Embodiment 11 is the alloy of embodiment 8, wherein the
amount of zinc is no less than about 0.2 wt-%.
[0118] Embodiment 12 is the alloy of embodiment 8, wherein the
amount of zinc is no greater than about 7 wt-%.
[0119] Embodiment 13 is the alloy of any one of embodiments 11, and
12, wherein the amount of zinc is no less than about 0.22 wt-%
and/or no greater than about 6 wt-%.
[0120] Embodiment 14 is the alloy of embodiment 13, wherein the
amount of zinc is about 0.22 wt-%.
[0121] Embodiment 15 is the alloy of embodiment 8, wherein the
amount of zinc is greater than about 0.5 wt-%.
[0122] Embodiment 16 is the alloy of any one of embodiments 1
through 7, comprising a substantial absence of zinc (e.g., less
than about 1 wt-%, 0.1 wt-%, 0.05 wt-%, etc).
[0123] Embodiment 17 is the alloy of any one of embodiments 1
through 16, comprising zirconium in an amount no less than about
0.3 wt-% and/or no greater than about 0.7 wt-%.
[0124] Embodiment 18 is the alloy of embodiment 17, wherein the
amount of zirconium is no greater than about 0.5 wt-%.
[0125] Embodiment 19 is the alloy of embodiment 18, wherein the
amount of zirconium is about 0.4 wt-%.
[0126] Embodiment 20 is the alloy of embodiment 17, wherein the
amount of zirconium is no less than about 0.5 wt-%.
[0127] Embodiment 21 is the alloy of embodiment 20, wherein the
amount of zirconium is about 0.6 wt-%.
[0128] Embodiment 22 is the alloy of any one of embodiments 1
through 15 comprising a substantial absence of zirconium (e.g.,
less than about 1 wt-%, 0.1 wt-%, 0.05 wt-%, etc).
[0129] Embodiment 23 is the alloy of any one of embodiments 1
through 22, wherein the magnesium is in an amount up to about 90
wt-%, as applicable.
[0130] Embodiment 24 is the alloy of embodiment 23, wherein the
magnesium is in an amount up to about 89.5 wt-%.
[0131] Embodiment 25 is the alloy of any one of embodiments 1
through 24, wherein the amount of yttrium is no less than about 4
wt-% and/or no greater than about 10 wt-%.
[0132] Embodiment 26 is the alloy of embodiment 25, wherein the
amount of yttrium is greater than about 4.5 wt-%.
[0133] Embodiment 27 is the alloy of embodiment 25, wherein the
amount of yttrium is less than about 7.7 wt-%.
[0134] Embodiment 28 is the alloy of any one of embodiments 26 and
27, wherein the amount of yttrium is no less than about 5 wt-%
and/or no greater than about 7 wt-%.
[0135] Embodiment 29 is the alloy of embodiment 28, wherein the
amount of yttrium is no less than about 5.5 wt-% and/or no greater
than about 6.7 wt-%.
[0136] Embodiment 30 is the alloy of embodiment 25, wherein the
amount of yttrium is no less than about 4 wt-%, as applicable.
[0137] Embodiment 31 is the alloy of embodiment 25, wherein the
amount of yttrium of yttrium no greater than about 6 wt-%.
[0138] Embodiment 32 is the alloy of any one of embodiments 30 and
31, wherein the amount of yttrium is about 5 wt-%.
[0139] Embodiment 33 is the alloy of embodiment 25, wherein the
amount of yttrium is no less than about 5.7 wt-%.
[0140] Embodiment 34 is the alloy of embodiment 25, wherein the
amount of yttrium is no greater than about 10 wt-%, as
applicable.
[0141] Embodiment 35 is the alloy of any one of embodiments 33 and
34, wherein the amount of yttrium is no less than about 6 wt-%
and/or no greater than about 10 wt-%, as applicable.
[0142] Embodiment 36 is the alloy of embodiment 35, wherein the
amount of yttrium is no less than about 6.7 wt-% and/or no greater
than about 9 wt-%.
[0143] Embodiment 37 is the alloy of any one of embodiments 1
through 36, wherein the amount of yttrium is greater than 3 wt-%,
as applicable.
[0144] Embodiment 38 is the alloy of any one of embodiments 1
through 36, wherein the amount of yttrium is greater than about 5.5
wt-%, as applicable.
[0145] Embodiment 39 is the alloy of any one of embodiments 1
through 38, wherein the rare earth element other than yttrium is
selected from a heavy rare earth element, a light rare earth
element, and combinations thereof, as applicable.
[0146] Embodiment 40 is the alloy of embodiment 39, wherein the
rare earth element other than yttrium is gadolinium, dysprosium,
erbium, and combinations thereof (e.g., heavy rare earth
elements).
[0147] Embodiment 41 is the alloy of embodiment 40, wherein the
rare earth element other than yttrium is gadolinium.
[0148] Embodiment 42 is the alloy of embodiment 39, wherein the
rare earth element other than yttrium is selected from neodymium,
lanthanum, cerium, and combinations thereof (e.g., light rare earth
elements).
[0149] Embodiment 43 is the alloy of embodiment 42, wherein the
rare earth element other than yttrium is neodymium.
[0150] Embodiment 44 is the alloy of embodiment 39, wherein the
rare earth element other than yttrium comprises a heavy rare earth
element and a light rare earth element.
[0151] Embodiment 45 is the alloy of embodiment 44, wherein the
light rare earth element comprises neodymium.
[0152] Embodiment 46 is the alloy of any one of embodiments 44 and
45, wherein the heavy rare earth element comprises gadolinium.
[0153] Embodiment 47 is the alloy of embodiment 39, wherein the
amount of the yttrium is greater than or equal to the amount of
rare earth element other than yttrium (e.g., REE less than or equal
to yttrium).
[0154] Embodiment 48 is the alloy of embodiment 39, wherein the
amount of yttrium is less than or equal to the amount of rare earth
element other than yttrium (e.g., REE is greater than or equal to
yttrium).
[0155] Embodiment 49 is the alloy of embodiment 39, wherein the
amount of yttrium is about equal to the rare earth element other
than yttrium (e.g., within about 5%, within about 10%, within about
20%, within about 25%, within about 33%, etc).
[0156] Embodiment 50 is the alloy of any one of embodiments 44
through 46, wherein the amount of the heavy rare earth element is
greater than the amount of light rare earth element.
[0157] Embodiment 51 is the alloy of any one of embodiments 44
through 46, wherein the amount of the heavy rare earth element is
less than the amount of light rare earth element.
[0158] Embodiment 52 is the alloy of any one of embodiments 50 and
51, wherein the amount of the heavy rare earth element is about
equal to the amount of yttrium.
[0159] Embodiment 53 is the alloy of embodiment 39, wherein the
amount of the rare earth element other than yttrium is no less than
about 0.1 wt-% and/or no greater than about 9 wt-%
[0160] Embodiment 54 is the alloy of embodiment 39, wherein the
amount of the rare earth element other than yttrium is no less than
about 4 wt-%.
[0161] Embodiment 55 is the alloy of embodiment 39, wherein the
amount of the rare earth element other than yttrium is no greater
than about 6 wt-%.
[0162] Embodiment 56 is the alloy of any one of embodiments 54 and
55, wherein the amount of the rare earth element other than yttrium
is about 5 wt-%.
[0163] Embodiment 57 is the alloy of embodiment 39, wherein the
amount of the rare earth element other than yttrium is no less than
about 4.5 wt-%.
[0164] Embodiment 58 is the alloy of embodiment 39, wherein the
amount of the rare earth element other than yttrium is no greater
than about 9 wt-%, as applicable.
[0165] Embodiment 59 is the alloy of any one of embodiments 57 and
58, wherein the amount of the rare earth element other than yttrium
is no less than about 5 wt-%.
[0166] Embodiment 60 is the alloy of embodiment 59, wherein the
amount of the rare earth element other than yttrium is no less than
about 5.5 wt-% and/or no greater than about 8 wt-%.
[0167] Embodiment 61 is the alloy of embodiment 39, wherein the
amount of the rare earth element other than yttrium is no greater
than about 2 wt-%.
[0168] Embodiment 62 is the alloy of embodiments 61, wherein the
amount of the rare earth element other than yttrium is about 1
wt-%.
[0169] Embodiment 63 is the alloy of embodiment 39, wherein the
amount of the rare earth element other than yttrium is no greater
than about 3.5 wt-%.
[0170] Embodiment 64 is the alloy of embodiment 63, wherein the
amount of the rare earth element other than yttrium is no greater
than about 3 wt-%.
[0171] Embodiment 65 is the alloy of embodiment 64, wherein the
amount of the rare earth element other than yttrium is less than
about 2.5 wt-%.
[0172] Embodiment 66 is the alloy of embodiment 39, wherein the
amount of the rare earth element other than yttrium is no less than
about 5 wt-%.
[0173] Embodiment 67 is the alloy of embodiment 39, wherein the
amount of the rare earth element other than yttrium is no greater
than about 7 wt-%.
[0174] Embodiment 68 is the alloy of any one of embodiments 66 and
67, wherein the amount of the rare earth element other than yttrium
is about 6 wt-%.
[0175] Embodiment 69 is the alloy of embodiment 39, wherein the
amount of the rare earth element other than yttrium is less than
about 5.5 wt-%.
[0176] Embodiment 70 is the alloy of embodiment 69, wherein the
amount of the rare earth element other than yttrium is less than
about 5 wt-%.
[0177] Embodiment 71 is the alloy of embodiment 70, wherein the
amount of the rare earth element other than yttrium is less than
about 4.5 wt-%.
[0178] Embodiment 72 is the alloy of embodiment 39, wherein the
amount of the rare earth element other than yttrium is less than
about 4 wt-%.
[0179] Embodiment 73 is the alloy of embodiment 72, wherein the
amount of the rare earth element other than yttrium is less than
about 3 wt-%.
[0180] Embodiment 74 is the alloy of any one of embodiments 1
through 73, wherein the amount of the rare earth element other than
yttrium is greater than about 3 wt-%, as applicable.
[0181] Embodiment 75 is the alloy of any one of embodiments 1
through 73, wherein the amount of the rare earth element other than
yttrium is greater than about 5.5 wt-%, as applicable.
[0182] Embodiment 76 is the alloy of any one of embodiments 53
through 62, wherein the rare earth element is a heavy rare earth
element.
[0183] Embodiment 77 is the alloy of embodiment 76, wherein the
heavy rare earth element is gadolinium.
[0184] Embodiment 78 is the alloy of any one of embodiments 53
through 56 and 66 through 73, wherein the rare earth element is a
light rare earth element.
[0185] Embodiment 79 is the alloy of embodiment 78, wherein the
light rare earth element is neodymium.
[0186] Embodiment 80 is the alloy of any one of embodiments 53
through 79, wherein the rare earth element other than yttrium
comprises only one rare earth element.
[0187] Embodiment 81 is the alloy of any one of embodiments 53 and
54, wherein the rare earth element is no less than about 5 wt-%
and/or no greater than about 8 wt-%.
[0188] Embodiment 82 is the alloy of any one of embodiments 81 and
66 through 68, wherein the rare earth element other than yttrium
comprises two or more rare earth elements other than yttrium.
[0189] Embodiment 83 is the alloy of embodiment 82, wherein the two
or more rare earth elements other than yttrium comprise a heavy
rare earth element and a light rare earth element.
[0190] Embodiment 84 is the alloy of embodiment 83, wherein the
light rare earth element comprises neodymium.
[0191] Embodiment 85 is the alloy of any one of embodiments 83 and
84, wherein the heavy rare earth element comprises gadolinium.
[0192] Embodiment 86 is the alloy of any one of embodiments 1
through 85, wherein the amount of the rare earth element alloy
component is greater than about 5 wt-% and less than about 16 wt-%,
as applicable.
[0193] Embodiment 87 is the alloy of embodiment 86, wherein the
amount of the rare earth element alloy component is no less than
about 9 wt-%, as applicable.
[0194] Embodiment 88 is the alloy of embodiment 86, wherein the
amount of the rare earth element alloy component is no greater than
about 13 wt-%, as applicable.
[0195] Embodiment 89 is the alloy of any one of embodiments 87 or
88, wherein the amount of the rare earth element alloy component is
no less than about 9.5 wt-% and/or no greater than about 12.7
wt-%.
[0196] Embodiment 90 is the alloy of embodiment 89 wherein the
amount of the rare earth element alloy component is no less than
about 10.5 wt-% and/or no greater than about 11.7 wt-%.
[0197] Embodiment 91 is the alloy of embodiment 86, wherein the
amount of the rare earth element alloy component is no less than
about 10 wt-%, as applicable.
[0198] Embodiment 92 is the alloy of embodiment 86, wherein the
amount of the rare earth element alloy component is no greater than
about 16 wt-%, as applicable.
[0199] Embodiment 93 is the alloy of any one of embodiments 91 and
92, wherein the amount of the rare earth element alloy component is
no less than about 10 wt-% and/or no greater than about 15.7
wt-%.
[0200] Embodiment 94 is the alloy of embodiment 93, wherein the
amount of the rare earth element alloy component is no less than
about 11 wt-% and/or no greater than about 14.7 wt-%.
[0201] Embodiment 95 is the alloy of any one of embodiments 88 and
90, wherein the amount of the rare earth element alloy component is
no less than about 10.5 wt-% and/or no greater than about 13.7
wt-%.
[0202] Embodiment 96 is the alloy of embodiment 95, wherein the
amount of the rare earth element alloy component is no less than
about 11.5 wt-% and/or no greater than about 12.7 wt-%.
[0203] Embodiment 97 is the alloy of embodiment 86, wherein the
amount of the rare earth element alloy component is no greater than
about 14 wt-%, as applicable.
[0204] Embodiment 98 is the alloy of any one of embodiments 87 and
97, wherein the amount of the rare earth element alloy component is
no less than about 9 wt-% and/or no greater than about 14 wt-%.
[0205] Embodiment 99 is the alloy of embodiment 98, wherein the
amount of the rare earth element alloy component is no less than
about 10 wt-% and/or no greater than about 13 wt-%.
[0206] Embodiment 100 is the alloy of embodiment 86, wherein the
amount of the rare earth element alloy component is no greater than
about 13 wt-%, as applicable.
[0207] Embodiment 101 is the alloy of any one of embodiments 86 and
100, wherein the amount of the rare earth element alloy component
is no less than about 5.7 wt-% and/or no greater than about 12.5
wt-%.
[0208] Embodiment 102 is the alloy of embodiment 101, wherein the
amount of the rare earth element alloy component is no less than
about 6.7 wt-% and/or no greater than about 11.5 wt-%.
[0209] Embodiment 103 is the alloy of embodiment 86, wherein the
amount of the rare earth element alloy component is no greater than
about 15 wt-%, as applicable.
[0210] Embodiment 104 is the alloy of any one of embodiments 86 and
103, wherein the amount of the rare earth element alloy component
is no less than about 5.7 wt-% and/or no greater than about 14.5
wt-%.
[0211] Embodiment 105 is the alloy of embodiment 104, wherein the
amount of the rare earth element alloy component is no less than
about 6.7 wt-% and/or no greater than about 13.5 wt-%.
[0212] Embodiment 106 is the alloy of embodiment 86, wherein the
amount of the rare earth element alloy component is no greater than
about 11 wt-%, as applicable.
[0213] Embodiment 107 is the alloy of any one of embodiments 87 and
106, wherein the amount of the rare earth element alloy component
is about 10 wt-%.
[0214] Embodiment 108 is the alloy of embodiment 86, wherein the
amount of the rare earth element alloy component is greater than
about 6 wt-%.
[0215] Embodiment 109 is the alloy of any one of embodiments 86
through 94, 100 through 102, 106, and 107, wherein the rare earth
element is a heavy rare earth element.
[0216] Embodiment 110 is the alloy of any one of embodiments 86
through 90, 95, 96, and 103 through 105, wherein the rare earth
element is a light rare earth element.
[0217] Embodiment 111 is the alloy of any one of embodiments 86
through 90 and 94 through 99, wherein the rare earth element
comprises a heavy rare earth element and a light rare earth
element.
[0218] Embodiment 112 is the alloy of any one of embodiments 1
through 111 wherein the amount of at least one of the yttrium and
the rare earth element is greater than the amount corresponding to
one-half the respective solid solubility in magnesium, as
applicable.
[0219] Embodiment 113 is the alloy of any one of embodiments 1
through 112 comprising a substantial absence of scandium (e.g.,
less than about 1 wt-%, 0.1 wt-%, 0.05 wt-%, etc).
[0220] Embodiment 114 is the alloy of any one of embodiments 1
through 113 comprising a substantial absence of calcium (e.g., less
than about 1 wt-%, 0.1 wt-%, 0.05 wt-%, etc).
[0221] Embodiment 115 is the alloy of any one of embodiments 1
through 114 comprising a substantial absence of indium (e.g., less
than about 1 wt-%, 0.1 wt-%, 0.05 wt-%, etc).
[0222] Embodiment 116 is the alloy of any one of embodiments 1
through 115 wherein the alloy comprises a balance of magnesium.
[0223] Thus, embodiments of the MAGNESIUM AND RARE EARTH ELEMENT
ALLOY are disclosed. All references and publications cited herein
are expressly incorporated herein by reference in their entirety
into this disclosure, except to the extent they may directly
contradict this disclosure. Although specific embodiments have been
described herein, it will be appreciated by those of ordinary skill
in the art that a variety of alternate and/or equivalent
implementations can be substituted for the specific embodiments
described without departing from the scope of the present
disclosure. This application is intended to cover any adaptations
or variations of the specific embodiments discussed herein.
Therefore, it is intended that this disclosure be limited only by
the claims and the equivalents thereof. The disclosed embodiments
are presented for purposes of illustration and not limitation.
* * * * *