Titanium alloys
Provided herein are titanium alloys that can achieve a combination of high strength and high toughness or elongation, and a method to produce the alloys. By tolerating iron, oxygen, and other incidental elements and impurities, the alloys enable the use of lower quality scrap as raw materials. The alloys are castable and can form α-phase laths in a basketweave morphology by a commercially feasible heat treatment that does not require hot-working or rapid cooling rates. The alloys comprise, by weight, about 3.0% to about 6.0% aluminum, 0% to about 1.5% tin, about 2.0% to about 4.0% vanadium, about 0.5% to about 4.5% molybdenum, about 1.0% to about 2.5% chromium, about 0.20% to about 0.55% iron, 0% to about 0.35% oxygen, 0% to about 0.007% boron, and 0% to about 0.60% other incidental elements and impurities, the balance of weight percent comprising titanium.
1. A method for casting a titanium alloy article of manufacture comprising the steps of:
(a) forming a melt having a Scheil freezing range less than about 200° C., and a β-phase transus temperature in a range below 900° C., said melt comprising, by weight, about 4.0% to about 5.5% aluminum (Al), 0% to about 1.0% tin (Sn), about 2.5% to about 3.5% vanadium (V), about 1.0% to about 2.0% molybdenum (Mo), about 1.0% to about 2.0% chromium (Cr), no more than about 0.35% oxygen (O), no more than about 0.55% iron (Fe), no more than about 0.2% other incidental elements and impurities, and the balance of weight percent comprising titanium (Ti);
(b) casting from said melt a cast alloy casting having said β phase transus temperature;
(c) annealing said as cast alloy casting above the β phase transus temperature to form an annealed cast alloy casting characterized as having a single phase microstructure of β-phase with a body centered cubic crystal structure; and
(d) cooling said annealed cast alloy casting from the β-phase at a cooling rate between 0.03° C. per second to 10° C. per second from at or above the β transus temperature to form, by nucleation and growth, fine α-phase laths with a basketweave morphology in the β-phase and to limit the formation of detrimental grain boundary α-phase lamellae.
2. The method of claim 1 , wherein said melt includes at least 25% by weight of a recycled starting material of a titanium (Ti) based alloy wherein said recycled material includes, nominally by weight, about 6% by weight aluminum (Al) and about 4% by weight vanadium (V).
3. The method of claim 1 further including the step of subjecting the cast alloy casting of step (b) to hot isostatic pressing prior to step (c).
4. The method of claim 1 , wherein step (d) includes cooling the as cast alloy casting step (d) with a gas.
5. The method of claim 1 wherein the β transus temperature of step (a) is 825° C. to 900° C.
6. The method of claim 1 wherein the melt of step (a) has a normalized coarsening rate constant (Kα) less than below about 4×10 −19 m 2* mol/J*s.
7. The method of claim 1 wherein the melt has a coarsening rate constant (Kα), said constant (Kα) located at approximately a nose temperature of a C-curve of a time-temperature transformation diagram of said melt.
8. The method of claim 1 wherein the laths are no more than about 100 microns.
9. A titanium alloy article manufacture in accord with the method of claim 1 .
10. A method for casting a titanium alloy article of manufacture comprising steps of:
(a) forming a melt having a Scheil freezing range less than about 200° C., and a β-phase transus temperature in a range below 900° C., said melt consisting essentially of, by weight, 3.0% to 5.6% aluminum (Al), 3.6% vanadium (V), 4.0% molybdenum (Mo), 1.9% chromium (Cr), 0.15% oxygen (O), 0.38% iron (Fe), 0.51% zirconium (Zr), no more than 0.2% other incidental elements and impurities, and the balance of weight percent comprising titanium (Ti);
(b) casting from said melt a cast alloy casting having said β phase transus temperature;
(c) optionally subjecting the cast alloy of step (b) to hot isostatic pressing prior to step (d);
(d) annealing said as cast alloy casting above the β phase transus temperature to form an annealed cast alloy casting characterized as having a single phase microstructure of β-phase with a body centered cubic crystal structure; and
(e) cooling said annealed cast alloy casting from the β-phase at a cooling rate between 0.03° C. per second to 10° C. per second from at or above the β transus temperature to form, by nucleation and growth, fine α-phase laths with a basketweave morphology in the β-phase and to limit the formation of detrimental grain boundary α-phase lamellae.
11. A titanium alloy article in accord with claim 10 .