Fine-grained W-NiTi heavy alloys with enhanced performance

In this study, the effect of infiltration temperature and holding time on the microstructure, transformation behaviors and mechanical properties of W-NiTi heavy alloys prepared by infiltration and hot pressing were investigated by SEM, DSC and compression tests. It was found that the average W grain sizes of all the W-NiTi heavy alloys prepared at temperatures varied from 1350 to 1450 ℃ with different holding times were less than 5 µm. The average W grain size was found to increase with increasing sintering temperature and holding time. The morphology of W grain was still polygonal with less growth. The NiTi matrix in these alloys was observed to dissolve up to 8.75 wt% W, significantly less than that of conventional tungsten heavy alloys, which could suppress the growth of W grains and make W grains more stable in NiTi matrix than in NiFe or NiCu matrix. All the W-NiTi alloys exhibited reversible martensite transformation. The stable microstructure and the increasing bonding strength resulted in the increasing of the strength and ductility of the alloys with infiltration temperature and holding time in compression tests.