Effect of Zr on microstructure and mechanical properties of binary TiAl alloys

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 ofγphase significantly and the solubility values of Zr inγphase were 12.0%and 5.0%(molar fraction)in Ti43Al and Ti47Al,respectively.Zr-richγphase mainly formed throughβ→γin Ti43Al-xZr(molar fraction,%)andβ→α→γin 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.

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%-2.5at% 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 than2.5 at%,the microstructure shows equiaxed grains surrounded by y phase.Zr is a y stabilizer and promotes the β/y transition,resulting in the change of microstructure morphology.Zr reaches the maximum solid solubility(about 6.5 at%) in y 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 2.5at% Zr and the maximum compressive strain is 30.62%with addition of 0.5 at% Zr,improving by 9.24% and7.33%,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.