Microstructure and mechanical properties of Ti43Al6Nb alloys with different zirconium contents

Ti43Al6Nb-xZr alloys with different additions of zirconium were prepared by vacuum arc melting furnace. The microstructure and compressive properties at room temperature (RT) were investigated. The microstructure shows dendrites with addition of 0 at%–2.5 at% Zr, and the dendrites are refined with the primary dendrite arms spacing decreasing from 222.64 μm (0 at% Zr) to 92.57 μm (2.0 at% Zr). With Zr addition more than 2.5 at%, the microstructure shows equiaxed grains surrounded by γ phase. Zr is a γ stabilizer and promotes the β/γ transition, resulting in the change of microstructure morphology. Zr reaches the maximum solid solubility (about 6.5 at%) in γ phase with addition of 2.5 at% Zr; moreover, γ phase increases in quantity, bringing about severe micro-segregation. With addition of Zr, the remained β phase turns into ω phase with B82 structure. Ti43Al6Nb-xZr alloys show brittle fracture. The maximum compressive strength is 2161.69 MPa with addition of 2.5 at% Zr and the maximum compressive strain is 30.62% with addition of 0.5 at% Zr, improving by 9.24% and 7.33%, respectively. The improvement of compressive strength results from fine-grain strengthening and solution strengthening. Severe micro-segregation is bad for compressive strength, and large solubility of Zr is detrimental to ductility.