Effects of Minor Yttrium Addition on Microstructure, Mechanical Properties and Hot Workability of Nb or V Containing TiAl Alloys

Abstract

The effect of 0.3 at.% yttrium addition on microstructure, mechanical properties and hot workability in Nb or V containing TiAl alloys was investigated. Four ingots with nominal compositions of Ti-43Al-9V, Ti-43Al-9V-0.3Y, Ti-45Al-5Nb and Ti-45Al-5Nb-0.3Y alloys were prepared by Induction Skull Melting. The results indicate a very strong effect of yttrium addition on the as-cast microstructures. The grain size and lamellar spacing of TiAl alloys with yttrium are significantly refined. The room temperature tensile properties of as-cast materials were improved by the addition of yttrium. The hot workability of these alloys was evaluated using a Gleeble-1500D thermo-simulation apparatus, canned forging and canned rolling processes. The simulation conformed that the TiAl alloys with yttrium have better hot workability. This is possibly caused by the initial fine microstructures and dynamic recrystallization induced by yttrium addition. The forged pancakes of Ti-43Al-9V0.3Y and Ti-45Al-5Nb-0.3Y alloys were produced on a 5000-ton press machine and the rolled sheets of Ti-43Al-9V-0.3Y alloy were fabricated using a two-high reverse mill. As-forged microstructure of Ti-45Al-5Nb-0.3Y alloy consists of major curved lamellae, broken lamellae and minor dynamic recrystallized grains. After heat treatment at 1150°C for 80min, extensive recrystallization occurred which resulted in near γ structure with fine γ grains of about 10pm, but rare remnant flat lamellae were retained. The compressive strength and strain were enhanced through heat treatment process. The microstructure of the rolled sheets of Ti-43Al-9V-0.3Y alloy showed obvious elongation in the rolling direction. Both tensile strength and plastic elongation of as-rolled material at room temperature and 700°C were greatly improved.