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

Abstract

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 ≈10% by sintering at 1450 °C, whereas sintering at 1500 °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.

Sinterability and microstructure evolution of powder metallurgy processed titanium aluminides

“…The powder mixtures were uniaxially pressed into cylinders with 8.1 mm diameter and 5.5 mm height in a single action die with a pressure of approximately 380 MPa. Sintering was conducted in a tubular furnace under an argon atmosphere at 1300°C and 1400°C for 2 h. Density measurements using Archimedes’ Principle were carried out according to ASTM B962 [20]. To close surface porosity, the specimens for density measurements were oil-impregnated on a Petri dish at 82°C ±5 for 4 h.…”

“…Therefore, investigating the effects of aluminium content in the sinterability of titanium aluminides is of great importance to enable a possible reduction of production costs by the blended elemental powder approach. Reports of different titanium aluminide alloys with small additions of elemental aluminium typically describe less densification than their pre-alloyed counterpart [19,20]. However, a study systematically varying the Al content focused on sinterability and phase formation for the press and sinter technique is still missing.…”