Tivcunial Amorphous Matrix/ultrafine-grained Composites Reinforced By Crystallized β-Ti(V) Phase Synthesized By Spark Plasma Sintering

Composites based on bulk amorphous alloys (CBBAAs) always show excellentmechanical properties of high hardness and strength. This can meet the development of thediversity and complexity in space flight. In previous work of our research group,Ti66Nb13Cu8Ni6.8Al6.2ultrafine-grained composites (UFGCs) with high strength up to2415MPa and distinct plasticity of32.6%have been successfully synthesized by spark plasmasintering (SPS) and crystallization of amorphous phase. In this paper, based on the binaryphase graph of Ti-V, alloy compositions have been designed as Ti66V13Cu8Ni6.8Al6.2(V13) andTi58V9Cu812.6Ni10.7Al9.7(V9) through using Vanadium instead of Niobium element. Ti-basedCBBAAs were fabricated by mechanical alloying (MA) and subsequently SPS. The aim ofthis work is to investigate phase evolution of the synthesized Ti-based glassy alloy powdersand effects of consolidation parameters on microstructure and mechanical properties of thefabricated alloys.Firstly, the V13and V9amorphous powders with particle size of30μm and20μm weresynthesized by MA after40h and35h milling, respectively. The glass transition temperatures(Tg), crystallization temperatures (Tx), peak crystallization temperatures (Tp), the supercooledliquid regions (Tx) and the crystallization enthalpy (Hx) of the two amorphous powders are720K,770K,788K,50K,28.4J/g and744K,807K,822K,63K and28.2J/g,respectively.Subsequently, V13amorphous powder was consolidated into Ti-based CBBAAs by SPSin the Txor above Txunder500MPa or50MPa. The relative densities, microhardnesses,and volume fractions of crystallization phases in the composites consolidated in the Txunder500MPa exhibit increased tendency with the increasing sintering temperature. When thesintering temperature is753K, the relative density and microhardness is up to98.7%and8.18GPa, respectively. The microstructures of all alloys consolidated above Txunder50MPaconsist of ductile β-Ti phase and brittle (Cu，Ni)-Ti2phase. The relative densities of all alloysare above97%, up to nearly full density. Under heating to a given sintering temperature, thelattice parameters of the β-Ti phases in the consolidated alloys increase with the increasedheating rate. Besides, the microstructures and volume fractions of the β-Ti phases are mainly relevant to the sintering temperature. At the same time, the plasticity of the UFG alloys is attributed to the continuous or isolated distribution of β-Ti phase. Under heating to1173K at205K/min and holding for5minutes, the consolidated alloy has ultimate fracture strength of2213MPa. Under heating to1310K at96K/min and holding for10minutes, the consolidated alloy has a fracture strain of14.2%.V9amorphous powder was consolidated into Ti-based CBBAAs by SPS in the ΔTx or above Tx under500MPa or50MPa. The relative densities, microhardnesses, and volume fractions of crystallization phases in the composites consolidated in the ΔTx exhibit increased tendency with the increasing sintering temperature. When the sintering temperature is803K, the relative density, microhardness and fracture strength is up to99.7%,10.1GPa and799MPa. The microstructures of alloys consolidated above Tx under50MPa consist of ductile β-Ti phase and brittle (Cu, Ni)-Ti2phase. The relative densities of all alloys are above97.9%. The effects of consolidation parameters on lattice parameters, volume fractions of the β-Ti phases and microstructures of the consolidated alloys are in accordance with the results of those of the consolidated V13alloys. However, all the consolidated V9alloys exhibit no plasticity due to the continuous distribution of the brittle phase. Under heating to1173K at164K/min and holding for5minutes, the consolidated alloy has ultimate fracture strength of2160MPa.