Design of Ultra-Strong As-Cast Titanium Alloy at 600 degree celsius by Using Cluster Formula

A Ti-5.4Al-6.4Zr-6.2Sn-0.4Mo-1.6W-0.4Nb-3.2Ta-0.5Si alloy is designed following cluster formula approach that achieves a strength level of 1 GPa at 600 degree celsius in the as-cast state, superior to any existing high-temperature Ti alloys. Its composition is formulated by 17 basic units, alpha-{[Al-Ti12](AlTi2)}12 + beta-{[Al-Ti12Zr2](Mo0.125Nb0.125Ta0.5W0.25Sn1.5Si0.5)}5, each unit covering a nearest-neighbor cluster plus a few next-neighbor glue atoms. This design is on the basis of the composition formula of Ti65 alloy, with an enhanced beta stability via more Zr, Mo, Nb, Ta, W, Sn, and Si co-alloying. Upon copper-mold pour casting, this alloy shows a good microstructure stability. In tensile testing below at 650 degree celsius, its alpha plates thickness is nearly at the same level of 0.2 mu m, which is much smaller than 0.7-0.8 mu m of Ti65 at the same condition. The changes in volume fraction of beta phase are increased by 86%, much less than by 105% in Ti65. Its room-temperature strength reaches the ultra-high-strength level, with an ultimate tensile strength of 1328 MPa and a yield strength of 1117 MPa, with a moderate elongation of 3.8%. At 600 degree celsius, its ultimate tensile strength of 1017 MPa and yield strength of 936 MPa are superior to those of any existing high-temperature Ti alloys, with an elongation of 7.2%. At 650 degree celsius, its ultimate tensile strength of 848 MPa still maintains a high level.