Microstructure And Mechanical Property Of TiB₂-Based Ceramic Composite Fabicated By Spark Plasma Sintering

In order to explore the effect of compounded metal binder and amorphous binder on the densification behavior, microstructure and mechanical properties of Ti B2 ceramics materials, Fe-25Ni-6.3Ti-10.7Al(wt.%) compounded metal and Ti-25Al-10Nb-3V-1Mo-0.2B(at.%)/ Ti-46.5Al-3Nb-2Cr-0.2W-0.2B(at.%) alloy compositions in this paper were chosen as compounded metal binder and amorphous binder, respectively. On the one hand, the Ti B2-5 wt %(Fe–Ni–Ti–Al) blended powders were fabricated by mechanical alloying(MA) with one-step method. Fe, Ni, Ti and Al are uniformly distributed in the Ti B2 ceramics powder after 8h milling, and Ti B2 grains have also been refined after milling. On the other hand, the Ti B2-5 wt %(Ti-Al-Nb-V-Mo-B) and Ti B2-5 wt %(Ti-Al-Nb-Cr-W-B) blended powders were fabricated by MA with a two-step method. Firstly, the amorphous composite powder Ti Al Nb VMo B(A) and Ti Al Nb Cr WB(B) were prepared by MA of respective element powders after 70 h milling, and the powders A and B contain the β-Ti/Ti3Al/amorphous phase and the Ti Al/Ti3Al/ amorphous phase respectively. Secondly, the Ti B2-5 wt %(Ti-Al-Nb-V-Mo-B) and Ti B2-5 wt %(Ti-Al-Nb-Cr-W-B) blended powders were prepared by wet ball-milling.Comparing the change of shrinkage displacement of pure Ti B2 and Ti B2-5 wt %(Fe–Ni–Ti–Al), the addition of Fe Ni Ti Al compounded metal binder into Ti B2 can facilitate sintering of the Ti B2 ceramics. As the sintering temperature exceeds 1300 °C, the relative density does not significantly change. Alumina particles and austenite(Fe–Ni–Ti) metallic binder distributed homogeneously in the grain boundary of Ti B2 can inhibit the growth of the Ti B2 grains when the sintering temperature is below 1300 °C. The density and particle size of Ti B2 greatly influence the mechanical behavior of Ti B2–5 wt %(Fe–Ni–Ti–Al) composites. The specimen sintered at 1300℃ has the highest microhardness of 21.1 ± 0.1 GPa with an elastic modulus of 461.4 GPa. The content of secondary borides(M2B, being M = Fe, Ni), which are more brittle than Ti B2 particles, can also influence the fracture toughness. The specimen sintered at 1500 °C has the highest fracture toughness of 6.16 ± 0.30 MPa?m1/2 with the smallest M2 B phase.The densification process of Ti B2-5 wt %(Ti-Al-Nb-V-Mo-B) and Ti B2-5 wt %(Ti-Al-Nb-Cr-W-B) blended powders mainly have two stages: ① The densification at low temperature(<600℃) because of the viscose flow of amorphous powder in supercooled liquid region;② The common densification at 870~1500℃ due to the softening of the binders in materials. As the sintering temperature exceeds 1300 °C, Ti Al decomposes into active Ti and Al,and they will form Ti(O,C,N) and Al2O3 with C, N, O impurities in the powders. When the sintering temperature locates at 1200~1500℃,The fracture toughness of Ti B2-5 wt %(Ti-Al-Nb-V-Mo-B) materials(TA) and Ti B2-5 wt %(Ti-Al-Nb-Cr-W-B) materials(TB) are 8.05~10.31 MPa·m1/2 and 7.24~9.40 MPa·m1/2, respectively. The TA specimens have superior fracture toughness with more content of Ti(O,C,N), which has better plastic deformation capacity. Because of the existence of crack deflection and crack bridging caused by the reinforcement phase of Ti(O,C,N), Ti Al and Al2O3 in ceramic matrix, the two kinds of ceramic composite materials have good toughening effect.The amorphous binders have viscous flow behavior in supercooled liquid region. This accelerates densification process of the Ti B2 ceramics powders at low temperature(< 600 ℃), and thus the density and mechanical property of Ti B2-based ceramic composites.