Sintering and Creep Resistance of Powder-Metallurgy-Processed Ti-(43-47)Al-5Nb-0.2B-0.2C

The effect of Al variations in the sintering behavior and creep resistance is investigated in powder-metallurgy-processed titanium aluminides based on the alloy TNB-V5 (Ti-45Al-5Nb-0.2B-0.2C at%). Two compositions are prepared with Al-contents of 43 and 47 at%, varying Al-content by +/- 2 at% relative to the reference material TNB-V5. Specimen preparation is conducted by metal injection molding using feedstock prepared with mixtures of prealloyed and elemental powders. The sinterability of alloys with addition of elemental powders decreases in comparison to the reference material, according to dilatometry experiments. However, in experiments with the sintering furnace, it is possible to obtain porosity with values of approximate to 10% by sintering at 1450 degrees C, whereas sintering at 1500 degrees C decreases the porosity to less than 1% in case of 43 at% and 45 at% of Al. Even though the alloy containing 47 at% Al shows higher porosity of about 7%, the creep resistance is superior to 43 at% Al, which can be attributed to a larger colony size. In tensile tests at room temperature, the effect of porosity is very detrimental leading to significantly reduced tensile strength and total elongation. Nevertheless, in compressive creep tests, the effect of porosity is secondary to colony size.