Influences of yttrium on microstructure and mechanical properties of NiAl-28Cr-5.5Mo-0.5Hf alloy

The influences of yttrium on the microstructure and mechanical properties of NiAl-28Cr-5 . 5Mo-0. 5Hf alloy were investigated by using SEM, XRD and compressive tests, respectively. The study indicates that the compressive strength and ductility of 0.05 % Y (mass fraction)-containing alloy are superior to those of other alloys at the strain rate of 1.94 x 10(-3) s(-1) over a range from room temperature to high temperature. It is also found that the microstructure of alloys is refined gradually with increasing Y content. This is reflected by more grain cells, finer spacing between Cr( Mo) fibers and smaller Cr( Mo) rods at the grain boundary. When 0.1% Y (mass fraction) and above are added to the matrix, tire yttrious compounds of Y2Ni17 and Al3Y form at the interfaces between NiAl and Cr(Mo) phases, which leads to the decrease of strength and ductility. Therefore, the proper addition of Y can improve the compressive strength and ductility of the alloy.