Basic Research for Development of New TiAl Base Alloys

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The effect of the Ti/Al retio, the addition of third elements (Cr, Hf and Nb) and the use of high purity base metals on mechanical properties of TiAl was studied at room teperature.1. Effect of the Ti/Al ratio : Strength of Ti-rich alloys was higher than than of Al-rich alloys. Fracture strain (ductility) in Ti-rich alloys was about 1.8 % which was larger than that in Al-rich a alloys being 0.6 % .2. Effect of third elements : (1) Cr ; Strength increased linearly with increasing Cr content. The alloy with 3 at.% Cr reached two times of that in a binary alloy. The Cr addition of 3 at.% to Ti-rich alloys improved ductility to 2.7 %. The Cr addition to Al-rich alloys lowered ductility.(2) Hg ; The effect of Hf addition on strength was similar to that in the Cr added alloys. The Hf addition up to 4 at.% to the Ti-rich alloys lowered ductility a little. The Hf eddition to Al-rich alloys decreased ductility to 0.8 %.(3) Nb ; Strength of the alloy with 3 at.% Nb increased to 2.5 times of that in a binary alloy. On the contrary. No strengthening effect was observed in Al-rich alloys. Ductility in Ti- and Al-rich alloys was decreased to 1/2 due to the Nb addition of 3 at.%.3. Effect of purity : The use of Ti with 99.91 % purity increased ductility to 2.7 % which has been the highest value in the binary alloys.