Investigation of the microstructure evolution and mechanical properties of cast Ti-47Al-2Cr-2Nb alloy during ultra-high pressure heat treatment

TiAl alloy is a high-temperature and lightweight material with superior properties, which has been widely used in aerospace industry. and casting is an economical method for its production. However, casting defects has hindered its direct applications in aerospace turbine blades. To minimize casting defects and achieve alloy strengthening, this paper proposed a novel single heat treatment process under ultra-high pressure (UHP) to regulate the microstructure and mechanical properties of the Ti-47Al-2Cr-2Nb alloy. The results indicated that the microstructure achieved overall grain refinement, high temperature and ultra-high pressure stresses jointly induced the gamma ->alpha 2 phase transformation. After the UHP heat treatment, the hardness of the alloy increased from 287HV to 381HV, and the yield strength and ultimate strength increased by 53 % and 20 %, respectively, without significantly affecting the strain to fracture. Based on the phase transformation behavior and strengthening mechanism, these enhancements in mechanical properties were mainly attributed to the precipitation strengthening of alpha 2 grains and the reduction of lamellar thickness. This suggested that UHP heat treatment was an effective method to improve cast TiAl alloys.