US20130139933A1

US20130139933A1 - Method for enhancing mechanical strength of a titanium alloy by aging

Info

Publication number: US20130139933A1
Application number: US13/706,377
Authority: US
Inventors: Chien-Ping Ju; Jiin-Huey Chern Lin
Original assignee: National Cheng Kung University NCKU
Current assignee: National Cheng Kung University NCKU
Priority date: 2011-12-06
Filing date: 2012-12-06
Publication date: 2013-06-06
Also published as: WO2013086010A1; TW201331380A

Abstract

A titanium-molybdenum alloy having α″ phase as a major phase is subjected to an aging treatment, so that yield strength of the aged alloy is increased by 10% to 120% with elongation to failure thereof being not less than about 5.0%.

Description

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

The present patent application claims the benefit of U.S. provisional patent application No. 61/567,170, filed Dec. 6, 2011, the contents of which are hereby incorporated by reference in their entireties.

FIELD OF THE INVENTION

The present invention is related to a method for enhancing mechanical properties of a titanium-molybdenum alloy having α″ phase as a major phase by aging, and in particular to a method for enhancing mechanical properties of a medical implant of a titanium-molybdenum alloy by aging.

BACKGROUND OF THE INVENTION

Titanium and titanium alloys have been popularly used in many medical applications due to their light weight, excellent mechanical performance and corrosion resistance. The relatively low strength commercially pure titanium (c.p. Ti) is currently used as dental implant, crown and bridge, as well as denture framework. Other examples for use of commercially pure titanium include pacemaker case, heart valve cage and reconstruction devices. Nevertheless, due to its relatively low strength, c.p. Ti may not be used for high load-bearing applications.
The most widely-used titanium alloy for load-bearing applications is Ti-6Al-4V alloy (the “work-horse” titanium alloy). With a much higher strength than c.p. Ti, Ti-6Al-4V alloy has been widely used in a variety of stress-bearing orthopedic applications, such as hip prosthesis and artificial knee joint. Nevertheless, studies indicated that release of Al and/or V ions from Ti-6Al-4V might cause long-term health problems (Rao et al. 1996, Yumoto et al. 1992, Walker et al. 1989, McLachlan et al. 1983). Its poor wear resistance could further accelerate the release of such harmful ions (Wang 1996, McKellop and RoKstlund 1990, Rieu 1992).
Compared to conventional 316L stainless steel and Co—Cr—Mo alloy, titanium and titanium alloys have much lower elastic modulus values. The lower elastic modulus allows the titanium/titanium alloy to more closely approximate the stiffness of bone for use in orthopedic devices compared to alternative stainless steel and cobalt-chrome alloys in orthopedic implants. Thus, devices formed from the titanium alloy produce less bone stress shielding and consequently interfere less with bone viability.
It should be noted that, although the elastic modulus values of c.p. Ti and Ti-6Al-4V alloy (about 110 GPa) are much lower than the popularly-used 316L stainless steel and Co—Cr—Mo alloy (200-210 GPa), the modulus values of c.p. Ti and Ti-6Al-4V alloy are still much higher than that of the natural bone (for example, only about 20 GPa for typical cortical bone). The large difference in modulus between natural bone and implant is one major cause for the well-recognized “stress-shielding effect.”
More recently an Al and V-free, high strength, low modulus α″ phase Ti—Mo based alloy system (typically Ti-7.5M) has been developed in the present Inventors' laboratory (U.S. Pat. No. 6,726,787 B2), which demonstrates excellent mechanical properties and biocompatibility, and has a great potential for use as orthopedic or dental implant material.
Biocompatibility of this α″ type Ti-7.5Mo alloy was confirmed through cytotoxicity test and animal implantation study. The cell activity of this alloy is similar to that of Al₂O₃(control). Animal study indicates that, after 6 weeks of implantation, new bone formation is readily observed at alloy surface. It is interesting to note that, after 26 weeks, the amounts of new bone growth onto the surface of Ti-7.5Mo implants at similar implantation site are dramatically larger than that of Ti-6Al-4V implant, indicating a much faster healing process.
U.S. Pat. No. 6,726,787 B2 provides a process for making a biocompatible low modulus high strength medical device from a titanium alloy, which comprises preparing a titanium alloy having a composition consisting essentially of at least one isomorphous beta stabilizing element selected from the group consisting of Mo, Nb, Ta and W; and the balance Ti, wherein said composition has a Mo equivalent value from about 6 to about 9; casting or metal working the titanium alloy to form a work piece; and quenching the work piece which is the resulting hot cast having a temperature higher than 800° C. at a cooling rate greater than 10° C. per second, or heating the work piece resulted from said metal working to a temperature higher than 800° C. and quenching the work piece having a temperature higher than 800° C. at a cooling rate greater than 10° C. per second, so that the cooled work piece contains an α″ phase as a major phase, and can be used as a medical device which is biocompatible, and has a low modulus and high strength.
In this invention, said Mo equivalent value, [Mo]eq, can be represented by the following equation: [Mo]eq=[Mo]+0.28[Nb]+0.22[Ta]+0.44[W], wherein [Mo], [Nb], [Ta] and [W] are percentages of Mo, Nb, Ta and W, respectively, based on the weight of the composition.
A typical quenching method used in the process of the present application is water quenching; however, any methods known in the art which have a cooling rate greater than 10° C., preferably 20° C., per second, can also be used.
U.S. Pat. No. 6,409,852 and U.S. Pat. No. 6,726,787 disclosed a titanium alloy composition and a method for preparing a titanium alloy having α″ phase as a major phase.
One disadvantage for an α″ phase titanium alloy is that the alloy generally has a relatively low strength (e.g., compared to Ti-6Al-4V ELI).

SUMMARY OF THE INVENTION

A primary objective of the present invention is to provide an article made of a titanium-molybdenum alloy with enhanced mechanical properties.
Another primary objective of the present invention is to provide a method for enhancing mechanical properties of a titanium-molybdenum alloy having α″ phase as a major phase by aging.
In order to accomplish the aforesaid objective, a method for enhancing mechanical properties of a titanium-molybdenum alloy having α″ phase as a major phase by aging disclosed in the present invention comprises providing an article of a titanium-molybdenum alloy having α″ phase as a major phase; and aging said article, so that yield strength of said aged article is increased by 10% to 120%, based on the yield strength of said article, with elongation to failure of said aged article being not less than about 5.0%.
Preferably, the yield strength of said aged article is increased by at least 20%, preferably at least 50%, and more preferably at least 75%, based on the yield strength of said article, with elongation to failure of said aged article being not less than about 7.0%.
Preferably, the titanium-molybdenum alloy consists essentially of 7-9 wt % of molybdenum and the balance titanium. More preferably, the titanium-molybdenum alloy consists essentially of about 7.5 wt % of molybdenum and the balance titanium.
Preferably, the article provided is an as-cast article.
Preferably, the article provided is a hot-worked or cold-worked article.
Preferably, the article provided is a solution-treated article.
Preferably, the article provided is a hot-worked and then solution-treated article.
Preferably, the article provided is a cold-worked and then solution-treated article.
Preferably, the article provided is a solution-treated and then cold-worked article.
Preferably, the article provided is an as-cast and then cold-worked article.
Preferably, said aging is conducted at a temperature of 150-850° C., more preferably 200-800° C., and most preferably 250-750° C.
Preferably, said aging is conducted for a period of time depending on the temperature as follows:

250° C.: >5 m; preferably >15 m; more preferably >30 m;
350° C.: >5 m; preferably >10 m; more preferably >15 m;
400° C.: >1 m; preferably >5 m; more preferably >5 m and <960 m; most preferably >5 m and <480 m;
450° C.: >1m; preferably >3 m; more preferably >3 m and <960 m; most preferably >3 m and <480 m;
500° C.: >30 m; preferably >60 m; more preferably >120 m;
550° C.: >15 m; preferably >30 m; more preferably >60 m;
600° C.: >5 m; preferably >15 m; more preferably >30 m;
650° C.: >1 m; preferably >5 m; more preferably >15 m;
700° C.: >1 m; preferably >3 m; more preferably >10 m;
750° C.: >1 m; preferably >3 m; more preferably >5 m.

DETAILED DESCRIPTION OF THE INVENTION

It is discovered by the present inventors that an appropriate aging treatment can effectively increase the mechanical strength of α″ phase titanium alloy. To the knowledge of the present inventors, aging treatment has never been taught or tested to increase the mechanical strength of a titanium alloy having an α″ phase with an orthorhombic crystal structure.
It is further discovered by the present inventors that, with an appropriate aging treatment process (with specific aging temperature and time ranges), the strength of α″ phase Ti alloys (particularly Ti—Mo based α″ phase Ti alloys) can be dramatically increased while other important properties (e.g., a reasonable elongation) of the alloys are maintained.
It is further discovered that the appropriate aging temperature/time ranges generally correspond to the ranges, in which the formation of hard, brittle omega phase is largely avoided.
It is further discovered that a mild aging treatment (with a temperature lower than about 250° C. and time less than about 30 m) can significantly increase the strength level while maintaining low modulus and reasonable elongation values of the alloy.
The α″ phase Ti-7.5Mo alloy samples for aging treatment may be prepared from directly casting the alloy into a mold from the molten state, from solution-treating (heated to beta-phase regime) a cast alloy followed by fast cooling, e.g., water quenching, or from solution-treating a mechanically or thermomechanically worked (e.g., through rolling, drawing, forging, extrusion, etc. at a room temperature or a high temperature) alloy followed by fast cooling, e.g. water quenching. The aging treatment can also be directly conducted on a mechanically or thermomechanically worked (e.g., through rolling, drawing, forging, extrusion, etc. at a room temperature or a high temperature) alloy followed by water quenching without first solution-treating said alloy.

EXPERIMENTAL EXAMPLES

Terminology:

AC: As-cast;
ST: Solution-treated at 900° C. for 5 min followed by water quench;
A: aged (Note: Aging was carried out in a quartz tube, which had been evacuated, followed by purging with inert (argon) gas. All aged samples were air-cooled to room temperature from the aging temperature.)
HR: Hot-rolled (Samples are heated to 900-1000° C. then taken out of furnace for rolling by about 65% reduction in thickness);
CR: Cold-rolled (Samples at room temperature are directly rolled at room temperature).

Preparation of α″ Phase Binary Ti—Mo Alloys:

The various Ti alloys were prepared from grade-2 commercially pure titanium (c.p. Ti) bars (Northwest Institute for Non-ferrous Metal Research, China) and molybdenum wire of 99.95% purity (Alfa Aesar, USA) by using a commercial arc-melting vacuum-pressure type casting system (Castmatic, Iwatani Corp., Japan). Prior to melting/casting, the melting chamber was evacuated and purged with argon. An argon pressure of 1.5 kgf/cm2 was maintained during melting. Appropriate amounts of metals were melted in a U-shaped copper hearth with a tungsten electrode. The ingots were re-melted at least three times to improve chemical homogeneity of the alloys. After each melting/casting, the alloys were pickled using HNO₃/HF (3:1) solution to remove surface oxide.
Prior to casting, the alloy ingots were re-melted again in an open-based copper hearth in argon under a pressure of 1.5 kgf/cm². The difference in pressure between the two chambers allowed the molten alloys to instantly drop into a graphite mold at room temperature. This fast cooling process generates a cooling rate of the alloy that is sufficient to form an α″ phase. Some of these as-cast alloy samples directly underwent cold working treatment to obtain a desired shape/thickness. Other cast samples, to further improve structural uniformity, were solution-treated to a beta phase regime (about 900-1000° C.), followed by fast cooling (water quenching) to transform the beta phase into α″ phase again. Thus obtained α″ phase alloys then underwent cold working treatment to obtain a desired shape/thickness. The XRD results confirm that the fast-cooled (water-quenched) samples have α″ phase as a major phase.

X-Ray Diffraction

X-ray diffraction (XRD) for phase analysis was conducted using a Rigaku diffractometer (Rigaku D-max IIIV, Rigaku Co., Tokyo, Japan) operated at 30 kV and 20 mA with a scanning speed of 3°/min. A Ni-filtered CuKα radiation was used for the study. A silicon standard was used for the calibration of diffraction angles. The various phases were identified by matching each characteristic peak in the diffraction patterns with JCPDS files.

Tensile Testing

A servo-hydraulic type testing machine (EHF-EG, Shimadzu Co., Tokyo, Japan) was used for tensile tests. The tensile testing was performed at room temperature at a constant crosshead speed of 8.33×10−6 m s−1. The average ultimate tensile strength (UTS), yield strength (YS) at 0.2% offset, modulus of elasticity (Modulus) and elongation to failure (Elongation) were taken from five tests under each process condition.

Cold Rolling (Rolling Conducted at Room Temperature)

Cold rolling was conducted by using a two-shaft, 100 ton level rolling tester (Chun Yen Testing Machines Co., Taichung, Taiwan). After each pass, the thickness of the samples was reduced by about 5-15% from the last pass.

TABLE 1

Tensile properties of Ti-7.5Mo alloy under different aging conditions.
(All α″ phase Ti-7.5Mo alloy samples for aging treatment are prepared
directly from a fast-cooling casting process)

				Elonga-
Aging condition		UTS	Modulus	tion
(Temp/Time)	YS (MPa)	(MPa)	(GPa)	(%)

As-cast	540	879	80	29.1
AC-A (350° C./30 min)	639	892	74	18.9
AC-A (350° C./480 m)	728	1227	70	12.7
AC-A (400° C./30 m)	918	1111	106	11.2
AC-A (400° C./480 m)	990	1409	81	3.6
AC-A (450° C./15 m)	909	1123	98	11.1
AC-A (450° C./30 m)	973	1133	101	10.6
AC-A (450° C./480 m)	1025	1469	80	3.5
AC-A (500° C./15 m)	1291	1414	125	2.0
AC-A (500° C./30 m)	1239	1352	120	1.8
AC-A (550° C./5 m)	1399	1455	124	1.5
AC-A (550° C./10 m)	1403	1472	132	1.3
AC-A (550° C./15 m)	1317	1498	117	1.4
AC-A (550° C./30 m)	1133	1280	125	2.4
AC-A (550° C./60 m)	1119	1409	116	2.2
AC-A (550° C./240 m)	1021	1144	114	4.6
AC-A (550° C./480 m)	936	1112	130	7.8
AC-A (550° C./480 m)	917	1110	118	6.0
AC-A (600° C./30 m)	1049	1221	115	3.4
AC-A (600° C./480 m)	1035	1135	87	8.8
AC-A (650° C./15 m)	921	1037	120	13.4
AC-A (650° C./30 m)	927	1035	118	12.2
AC-A (650° C./60 m)	811	946	116	15.0
AC-A (650° C./480 m)	971	1035	85	11.0
AC-A (650° C./480 m)	758	830	106	21.0
AC-A (650° C./480 m)	725	878	113	19.7
AC-A (700° C./30 m)	827	907	114	14.7
AC-A (750° C./15 m)	810	935	123	14.6
AC-A (750° C./30 m)	912	1002	116	11.4
AC-A (750° C./60 m)	916	1064	104	11.4
AC-A (550° C./15 m) followed	911	1048	127	11.3
by A (750° C./60 m)
(two-step aging)

TABLE 2

Tensile properties of aged Ti-7.5Mo alloy under different
aging conditions.
(All α″ phase Ti-7.5Mo alloy samples for aging
treatment are prepared by solution
treatment followed by water quenching)

				Elonga-
		UTS	Modulus	tion
Aging condition (Temp/Time)	YS (MPa)	(MPa)	(GPa)	(%)

As solution-treated	427	845	72	31.3
ST-A (350° C./30 m)	624	885	73	20.3
ST-A (350° C./45 m)	639	893	73	21.0
ST-A (350° C./60 m)	677	901	76	18.0
ST-A (350° C./120 m)	734	943	87	18.0
ST-A (350° C./240 m)	801	973	87	15.0
ST-A (350° C./480 m)	811	1031	94	13.0
ST-A (350° C./30 m)	804	965	99	18.3
ST-A (400° C./30 m)	963	1127	101	7.3
ST-A (400° C./240 m)	925	1143	104	5.0
ST-A (450° C./15 m)	916	1110	102	6.2
ST-A (450° C./30 m)	1002	1137	106	6.4
ST-A (450° C./240 m)	983	1083	106	3.0
ST-A (500° C./30 m)	1291	1371	125	1.2
ST-A (500° C./60 m)	1002	1098	118	2.1
ST-A (500° C./240 m)	872	983	110	5.0
ST-A (550° C./30 m)	1068	1213	118	4.2
ST-A (550° C./60 m)	902	1013	108	7.0
ST-A (550° C./240 m)	824	904	104	13.0
ST-A (600° C./30 m)	904	1074	110	7.2
ST-A (600° C./60 m)	827	931	104	9.7
ST-A (600° C./240 m)	768	863	102	12.0
ST-A (650° C./30 m)	866	975	110	13.9
ST-A (650° C./60 m)	795	929	104	14.4
ST-A (650° C./120 m)	717	869	102	16.7
ST-A (650° C./240 m)	730	885	107	16.0
ST-A (650° C./60 m)	856	975	109	11.0
ST-A (650° C./120 m)	815	911	104	14.4
ST-A (500° C./30 m) + A	872	993	108	9.1
(650° C./30 m)
(two-step aging)
ST-A (450° C./30 m) + A	884	1030	101	8.3
(650° C./5 m)
(two-step aging)
ST-A (650° C./30 m) + A	834	982	102	15.0
(450° C./30 m)
ST-A (650° C./480 m)	694	823	109	20.8
ST-A (750° C./60 m)	813	978	113	14.0

TABLE 3

Tensile properties of Ti-7.5Mo alloy under different aging conditions.
(All α″ phase Ti-7.5Mo alloy samples for aging treatment are
prepared by solution treatment, followed by
cold rolling with 50% reduction in thickness.

			Modu-
	YS	UTS	lus	Elonga-
Aging condition (Temp/Time)	(MPa)	(MPa)	(GPa)	tion (%)

ST-CR 50% (no aging)	904	1149	64	20.5
ST-CR 50%-A (200° C./15 m)	1013	1193	66	14.6
ST-CR 50%-A (200° C./30 m)	919	1213	67	5.3
ST-CR 50%-A (250° C./30 m)	1006	1237	68	4.2
ST-CR 50%-A (250° C./240 m)	1044	1236	68	1.8
ST-CR 50%-A (350° C./30 m)	997	1263	76	0.7
ST-CR 50%-A (350° C./240 m)	731	1086	74	3.1

Results: Aging conditions of 200° C. for 15 minutes will enhance the yield strength (YS) of the cold-rolled α″ phase Ti-7.5Mo alloy by about 12% with the elongation to failure still being maintained at 14.6%. It can been from Table 3 that, for these cold-rolled samples, the period of time for aging is preferably no longer than 30 minutes for keeping the elongation to failure not less than 5% with the aging temperature being lower than 350° C.

TABLE 4

Tensile properties of Ti-7.5Mo alloy under different aging conditions.
(All α″ phase Ti-7.5Mo alloy samples for aging treatment are prepared by
hot rolling by 65% reduction in thickness followed by solution treatment)

		UTS	Modulus	Elongation
Aging condition (Temp/Time)	YS (MPa)	(MPa)	(GPa)	(%)

HR-ST-A (250° C./15 m)	463	784	86	24.3
HR-ST-A (250° C./30 m)	514	830	82	29.5
HR-ST-A (250° C./60 m)	496	800	81	26.8
HR-ST-A (250° C./240 m)	520	848	92	25.4
HR-ST-A (350° C./15 m)	664	869	95	12.2
HR-ST-A (350° C./30 m)	694	906	93	12.7
HR-ST-A (350° C./60 m)	705	900	98	11.8
HR-ST-A (350° C./240 m)	686	957	95	17.0
HR-ST-A (450° C./15 m)	791	1000	95	9.8
HR-ST-A (450° C./30 m)	882	1075	94	5.5
HR-ST-A (450° C./60 m)	941	1193	104	3.2
HR-ST-A (450° C./240 m)	1060	1178	125	0.5
HR-ST-A (550° C./15 m)	1087	1154	116	0.2
HR-ST-A (550° C./30 m)	1085	1150	113	0.8
HR-ST-A (550° C./60 m)	1028	1153	127	0.8
HR-ST-A (550° C./240 m)	888	1032	125	3.9
HR-ST-A (650° C./15 m)	865	1048	106	7.9
HR-ST-A (650° C./480 m)	694	823	108	20.8
HR-ST-A (750° C./15 m)	871	1042	108	13.5
HR-ST-A (750° C./60 m)	813	978	113	14.0
HR-ST-A (550° C./15 m) + A	882	1085	107	11.6
(750° C./15 m)
(two-step aging)
HR-ST-A (500° C./480 m) + A	897	1136	112	13.4
(750° C./15 m)
(two-step aging)

TABLE 5

Comparison in tensile properties among selected aged Ti-7.5Mo alloy
and popularly-used commercially pure titanium and Ti-6AI-4VELI.

		UTS	Modulus	Elongation
Material	YS (MPa)	(MPa)	(GPa)	(%)

c.p. Ti (Grade 2)	235	345	100	20
c.p. Ti (Grade 4)	483	550	100	15
Ti-6AI-4V (ELI)	795	860	114	10
(ASTM F136)
AC-A (450° C./30 m)	973	1133	101	10.6
AC-A (600° C./480 m)	1035	1135	87	8.8
ST-A (650° C./30 m)	866	975	110	13.9
ST-CR 50%-A	1013	1193	66	14.6
(200° C./15 m)

Summary of the Results:

(1) Aging treatment can significantly increase the strength level of Ti-7.5Mo alloy. For example, at comparable modulus and elongation levels, the YS and UTS values of Ti-7.5Mo samplecoded “AC-A(450° C./30 m)” are higher than those of Ti-6Al-4V(ELI) (ASTM F136) by 22% and 32%, respectively. The YS and UTS values of Ti-7.5Mo sample coded “AC-A(600° C./480 m)” are higher than those of Ti-6Al-4V(ELI) (ASTM F136) by 30% and 32%, respectively.
(2) A mild aging treatment (with a temperature lower than about 250° C. and time less than about 30 m) can significantly increase the strength level while maintaining low modulus and reasonable elongation values of the alloy. The YS and UTS values of Ti-7.5Mo sample coded “ST-CR 50%-A (200° C./15 m)” are higher than those of Ti-6Al-4V (ELI) (ASTM F136) by 27% and 39%, respectively, while maintaining an elongation higher than Ti-6Al-4V (ELI) (ASTM F136) by 46% and a modulus lower than Ti-6Al-4V (ELI) (ASTM F136) by 42%. These data result in amazing YS/Mod and UTS/Mod ratios (important performance indices for orthopedic implants) which are higher than Ti-6Al-4V (ELI) (ASTM F136) by 120% and 140%, respectively.
(3) The best aging temperature range: 150-850° C.; preferably 200-800° C.; more preferably 250-750° C.;
(4) The best aging time range: depending on aging temperature, as follows:
250° C.: >5 m; preferably >15 m; more preferably >30 m;
350° C.: >5 m; preferably >10 m; more preferably >15 m;
400° C.: >1 m; preferably >5 m; more preferably >5 m and <960 m; most preferably >5 m and <480 m;
450° C.: >1 m; preferably >3 m; more preferably >3 m and <960 m; most preferably >3 m and <480 m;
500° C.: >30 m; preferably >60 m; more preferably >120 m;
550° C.: >15 m; preferably >30 m; more preferably >60 m;
600° C.: >5 m; preferably >15 m; more preferably >30 m;
650° C.: >1 m; preferably >5 m; more preferably >15 m;
700° C.: >1 m; preferably >3 m; more preferably >10 m;
750° C.: >1 m; preferably >3 m; more preferably >5 m.

Claims

1. A method for enhancing mechanical strength of an article of a titanium alloy by aging comprising providing an article of a titanium-molybdenum alloy having α″ phase as a major phase; and aging said article, so that yield strength of said aged article is increased by 10% to 120%, based on the yield strength of said article, with elongation to failure of said aged article being not less than about 5.0%.

2. The method of claim 1, wherein the yield strength of said aged article is increased by at least 20%, preferably at least 50%, and more preferably at least 75%, based on the yield strength of said article, with elongation to failure of said aged article being not less than about 7.0%.

3. The method of claim 1, wherein the titanium-molybdenum alloy consists essentially of 7-9 wt % of molybdenum and the balance titanium.

4. The method of claim 3, wherein the titanium-molybdenum alloy consists essentially of about 7.5 wt % of molybdenum and the balance titanium.

5. The method of claim 1, wherein the article provided is an as-cast article.

6. The method of claim 1, wherein the article provided is a hot-worked or cold-worked article.

7. The method of claim 1, wherein the article provided is a solution-treated article.

8. The method of claim 1, wherein the article provided is a hot-worked and then solution-treated article.

9. The method of claim 1, wherein the article provided is a cold-worked and then solution-treated article.

10. The method of claim 1, wherein the article provided is a solution-treated and then cold-worked article.

11. The method of claim 1, wherein the article provided is an as-cast and then cold-worked article.

12. The method of claim 1, wherein said aging is conducted at a temperature of 150-850° C.

13. The method of claim 12, wherein said aging is conducted at a temperature of 200-800° C.

14. The method of claim 13, wherein said aging is conducted at a temperature of 250-750° C.

15. The method of claim 14, wherein said aging is conducted for a period of time depending on the temperature as follows:

250° C.: >5 m; preferably >15 m; more preferably >30 m;

350° C.: >5 m; preferably >10 m; more preferably >15 m;

400° C.: >1 m; preferably >5 m; more preferably >5 m and <960 m; most preferably >5 m and <480 m;

450° C.: >1m; preferably >3 m; more preferably >3 m and <960 m; most preferably >3 m and <480 m;

500° C.: >30 m; preferably >60 m; more preferably >120 m;

550° C.: >15 m; preferably >30 m; more preferably >60 m;

600° C.: >5 m; preferably >15 m; more preferably >30 m;

650° C.: >1 m; preferably >5 m; more preferably >15 m;

700° C.: >1 m; preferably >3 m; more preferably >10 m;

750° C.: >1 m; preferably >3 m; more preferably >5 m.