Microstructure and tensile properties of TiNbZr alloy-based metal-matrix composites, reinforced with borides

The TiNbZr/(TiNbZr)B metal-matrix composites with different amounts of TiB2 (0.2, 2, 0.7 and 4 wt. %) were produced vacuum arc melting in a high purity argon atmosphere. The initial microstructure of the synthesized composites was composed of bcc TiNbZr matrix and needle-like monoborides (Ti, Nb) B with the average thickness of 0.2, 0.4, 0.9 and 2.0 µm, respectively. EBSD analysis suggested microstructure refinement with an increase in the amount of borides: the grain size in the TiNbZr matrix was found to be: 180 µm, 130 µm, 65 µm, and 50 µm for the four conditions, respectively. Sections with equiaxed ω phase particles measuring∼10 nm in diameter were found in the microstructure of composites of all states. The composite with 0.2 wt. % TiB2 showed the lowest value of the yield strength 690 MPa and the highest elongation∼20 %. The highest strength properties were attained in the composite with 4 wt. % TiB2 in which the yield strength reached 900 MPa with, however, ductility only 0.5 %.