SPS Fabrication And Mechanical Behavior Of TiNbCuNiAl Composites Reinforced By Minor Ceramic Phase

Bulk amorphous alloys （BAAs） usually fail without plasticity because of theirsingle-phase microsctructure. This limits their application as structural materials. Tocircumvent the plasticity of BAAs, second phases with different scales and shapes areintroduced to synthesize bulk amorphous matrix composites （BAMCs） or ultrafine-grainedcomposites （UFGCs）. In this paper, mechanical alloying was used to synthesizeTi₆6Nb₁3Cu₈Ni_6.8Al_6.2amorphous powders with minor B/C additions, and subsequently SPSwere applied to fabricate Ti-based BAMCs or UFGCs.Minor B/C additions accelerate the amorhization of Ti66Nb13Cu8Ni6.8Al6.2（（Ti）） alloypowder during mechanical alloying, and cause improvement in glass forming ability andthermal stability and decrease in the particle size of the synthesized amorphous alloy powders.The mixed powders with0.3wt.%B₄C (（Ti）₁B_1.2C_0.3),0.2wt.%B₄C+0.1wt.%C(（Ti）₁B_0.8C_0.7) and2wt.%B （（Ti）1B10.3） contain abundant amorphous phase after a millingtime of40,40and35h respectively, and corresponding particle sizes are35,40and20μm,respectively. The ΔHxof the three group powders are37.1,31.3and11.2J/g, respectively.The ΔTxfor the （Ti）₁B_1.2C_0.3and （Ti）₁B_0.8C_0.7amorphous powders are112and102K,28and18K larger than that of the amorphous powder without addition, respectively. This providesthe possibility of preparing plasticity-enhanced Ti-based BAMCs or UFGCs by powdermetallurgy.Ti-based BAMCs with in-situ precipitated β-Ti phase were fabricated through SPS athigh pressure and low sintering temperature. The influences of sintering temperature, holdingtime and minor B, C addition on microstructure and mechanical property of the consolidatedBAMCs were studied. During sintering process, minor B and C small atoms are helpful forstabilizing its amorphous structure while the amorphous powder is densifying. The Ti-basedBAMC consolidated from the （Ti）₁B_0.8C_0.7amorphous powder at743K and holding for10min by30K/min under500MPa contains amorphous phase with a volume fraction of55.2%,and has a relative density of98.1%and a fracture stress of833.1MPa, respectively.Ti-based UFGCs with β-Ti matrix and （Cu, Ni）-Ti₂as second phase were fabricated bySPS and crystallization of amorphous phase at high temperature and low pressure. The effects of heating rate, sintering temperature, holding time and minor B, C addition onmicrostructure and mechanical property of the consolidated Ti-based UFGCs were studied.The plasticity for the （Ti）₁B_1.2C_0.3and （Ti）₁B_0.8C_0.7UFGCs increases with the increasingholding time, and the plastic strain for the （Ti）1B0.8C0.7UFGCs is twice than that of the（Ti）1B1.2C0.3UFGCs sinteded at the same condition. The UFGCs consolidated from the（Ti）1B0.8C0.7amorphous powder at1223K and holding for15min by160K/min haveexcellent fracture stress and plasiticity,1958MPa and15.3%, respectively.Different volume frations of TiC or TiB₂were added into （Ti）₁B_0.8C_0.7amorphous alloypowder by SPS and cystallziation of amorphous phase. Among the Ti-based UFGCsconsolidated from the （Ti）₁B_0.8C_0.7amorphous alloy powder with ex-situ TiC or TiB₂particles,no reactions are observed to occur between the ex-situ TiC particle and the UFGCs matrix;the ex-situ TiB₂particles greatly change the interface between the TiB2particle and the matrix.The fracture stress increases with the increasing volume fraction of the ex-situ TiC or TiB2particles.In summary, three amorphous alloy powders with minor B and C additions weresynthesized by mechanical alloying, and subsequently Ti-based BAMCs and UFGCs weresuccessfully fabricated through precise control of sintering parameters by SPS andcrystallization of amorphous phase. Therefore, the method was developed that powdermetallurgy technology can fabricate composites based on BAAs. Meanwhile, the fabricatedcomposites have new structures and excellent mechanical properties.