Effect of Zr on microstructure and mechanical properties of binary TiAl alloys
(School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China)
Abstract: Ti43Al and Ti47Al alloys with different contents of zirconium were prepared by non-consumable vacuum arc melting furnace. The microstructure and mechanical properties were investigated. The results showed that Zr had no obvious effect on microstructure morphology of Ti43Al, while that of Ti47Al was modified from dendrites into equiaxed grains. The addition of Zr could refine the grains. Zr promoted the formation of γ phase significantly and the solubility values of Zr in γ phase were 12.0% and 5.0% (molar fraction) in Ti43Al and Ti47Al, respectively. Zr-rich γ phase mainly formed through β→γ in Ti43Al-xZr (molar fraction, %) and β→α→γ in Ti47Al-xZr (molar fraction, %). Fine-grain strengthening and solution strengthening were beneficial to improving the compressive strength while severe micro-segregation was detrimental to compressive properties. Large solubility of Zr was bad for ductility of alloys as well. The maximum compressive strengths of Ti43Al-xZr and Ti47Al-xZr were 1684.82 MPa (x=5.0%) and 2158.03 MPa (x=0.5%), respectively. The compressive strain fluctuated slightly in Ti43Al-xZr and reached the maximum value of 35.24% (x=0.5%) in Ti47Al-xZr. Both alloys showed brittle fracture.
Key words: TiAl binary alloy; zirconium; microstructure evolution; phase transformation; compressive properties