Fabrication, microstructure and mechanical properties of W-NiTi composites

New two-phase tungsten-based composites containing 88 wt% tungsten powders and 12 wt% nearly equiatomic NiTi alloy deforming by martensite variant detwinning were fabricated by infiltration and hot pressing in this study. The change of Ti/Ni ratio in NiTi mater alloy and the effect of addition of Nb element on the microstructure, martensitic transformation and mechanical properties of W-NiTi composites were investigated by comparison of W-Ni50Ti50, W-Ni44Ti56, W-Ni42Ti58 and W-Ni42Ti53Nb5 composites. The results showed that brittle Ni3Ti formed in the W-Ni50Ti50 and W-Ni44Ti56 composites and brittle Ti2Ni formed in the W-Ni42Ti58 composites while no brittle intermetallics formed in the W-Ni42Ti53Nb5 composite. The W-Ni42Ti53Nb5 composite exhibited the sharpest martensitic transformation with the largest transformation enthalpy among the four different composites. The W-Ni42Ti53Nb5 composite exhibited a double-yielding phenomenon under compression with an ultimate compressive strength of 3820 MPa and a deformation of 50.4%. In-situ synchrotron high-energy Xray diffraction measurements revealed the first yielding was caused by the martensite reorientation of the NiTi matrix and the second was due to the commencement of massive plastic deformation of the reoriented martensite and is also attributed to the microscopic internal fracturing of the W particles. (C) 2016 Elsevier B.V. All rights reserved.