STRENGTHENING MECHANISMS OF A TI/TIB COMPOSITE PRODUCED BY SPARK PLASMA SINTERING AFTER HOT ROLLING

The Ti/TiB metal-matrix composite was obtained by spark plasma sintering at a temperature of 1000 °C. In the initial state, the Ti/TiB MMC microstructure consisted of TiB needle fibers unevenly distributed in the titanium matrix. SEM showed that the apparent diameter of the TiB fibers varied over a wide range: from tens to several hundreds of nanometers. The average TiB fiber diameter in the initial state is 163 ± 35 nm. Hot rolling caused the fragmented TiB fiber particles to align in the rolling direction. The apparent average length of the TiB fibers decreased from 8 ± 4 to 3.0 ± 1.2 μm, probably as a result of fiber breakage during deformation. It has been established that after hot rolling the composite has an increased yield strength and significantly improved ductility compared to the initial state: the hot-rolled sample failed at a compressive strain of 25 %, while the ductility for the initial state was 12 %. The yield strength was 930 and 1200 MPa for the initial and hot-rolled states. The predicted theoretical strength, calculated by summing the contribution of all hardening mechanisms, is 1946 MPa, which is higher than the experimental value of 1200 MPa. Dispersion strengthening by fragments of TiB fibers makes the most significant contribution to the overall strength of the composite (934 MPa or 50 %).

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