Effect of Sn Addition on Densification and Mechanical Properties of Sintered TiAl Base Alloys

High Nb containing TiAl alloys (TiAl-Nb) are a new generation of materials for high temperature structural applications because of their low density, high strength and corrosion resistance at elevated temperatures. The alloys can be processed by powder metallurgy (PM) which have more advantages including low cost-effectiveness, near net forming for complex parts with fine grain size and uniform microstructure. However, the alloy powders are difficult to achieve full densification due to their lower sintering activity, which impairs the mechanical performance of sintered parts. The present work focuses on the densification performance of TiAl-Nb alloy powders with 1% Sn (atomic fraction) as sintering aids. The effects of Sn addition on the sintering densification process, microstructure and mechanical properties of sintered alloys were investigated. The results show that 1% Sn addition can significantly reduce the sintering densification temperature of alloy powders, and increase the relative density and linear shrinkage of sintered parts. This contributes to control microstructure grain size and improve the comprehensive properties. Sintered with 1500 degrees C for 2 h, 1% Sn containing TiAl-Nb base alloys show the best densification performance, with the relative density of 99.1% and linear shrinkage of 9.3%. The alloy samples exhibit fine and uniform full lamellar microstructure, and alpha(2)/gamma lamellar colonies are sized about 40 similar to 60 mu m. Sn mainly dissolved into phase, leading to the enhancement of axial ratio c/a and unit cell volume. The sintered TiAl-Nb-1Sn samples have been found to possess superior room-temperature mechanical properties, with a Rockwell hardness of 50.1 HRC, a compressive strength of 2938 MPa, a yield strength of 680 MPa, and a compression ratio of 29.1%, which is obviously higher than those of TiAl-Nb alloys.