Microstructure And Impact Energy Release Characteristics Of Ti-Zr-Ta Medium-Entropy Alloy

As a new type of damage material with both mechanical properties and reaction energy release characteristics,energetic structural material has broad application prospect in military field.High-entropy alloys composed of a variety of metal elements in equal or nearly equal ratios exhibit a series of excellent properties due to their simple solid solution structure,atomic chemical site occupancy disorder and nanostructured microstructure.Refractory high-entropy alloys composed of refractory metal elements have high strength and energy density,and are expected to be used as new energetic structural materials in the field of weapons.However,due to a large number of constituent elements and large difference in melting point between each element,it is difficult to prepare high-quality large-scale samples that meet application requirements.Compared with refractory high-entropy alloys,the medium-entropy alloy with fewer components and a lot of highly active elements has the potential to prepare large-scale energetic structural materials.In this paper,Ti-Zr-Ta medium-entropy alloy is taken as the research object,and Ti₂Zr Ta alloy is selected as the benchmark alloy.On this basis,composition design is carried out with reference to the calculated phase diagram acquired by Pandat.The effects of element content and heat treatment temperature on microstructure and mechanical properties were studied by XRD,SEM and quasi-static compression experiments.The effect of element content on impact energy release characteristics was studied by ballistic experiments,and the main conclusions are as follows:（1）Compared with the mixing entropy(ΔS_mix),effect of element content and element interaction on microstructure of Ti-Zr-Ta medium-entropy alloy is more significant.High mixing enthalpy(ΔH_mix)between Zr-Ta is the main reason for the phase separation of Ti-Zr-Ta medium-entropy alloy.However,Ti can achieve mutual solid solution with Zr and Ta at high temperature to form a single-phase BCC structure,so the addition of Ti element can inhibit the phase separation between Zr-Ta.Therefore,the higher Ti content,the easier alloy forms a single-phase solid solution structure.（2）The heat treatment temperature also has an important influence on microstructure of Ti-Zr-Ta alloy.Compared with 900℃equilibrium alloy,microstructure of Ti-Zr-Ta ternary alloy in 1200℃equilibrium state is more uniform.The area of single-phase region in the isothermal cross-sections obtained by heat treatment experiments at 900℃and 1200℃is relatively small compared with Pandat-calculated isothermal cross-sections,which indicates that Pandat-calculated phase diagrams overestimate the ability of Ti-Zr-Ta ternary alloy to form a single-phase BCC structure.（3）The element content has an important influence on mechanical property of Ti-Zr-Ta alloy.For Ti_xZr Ta（x=0.2,0.5,1.0,2.0,3.0）alloys,with the increase of Ti content,the yield strength first increases and then decreases,while the fracture strain shows an opposite trend.For Ti₂Zr_yTa（y=0.5,0.75,1.0,1.25,1.5）alloys,with the increase of Zr content,the yield strength increases,but the plasticity deteriorates.For Ti₂Zr Ta_z（z=0.5,0.75,1.0,1.25,1.5）alloys,with the increase of Ta content,the strength and plasticity first increased and then decreased.（4）The heat treatment temperature also has an important influence on mechanical propertiy of Ti-Zr-Ta alloy.Different heat treatment temperatures lead to different strengths and fracture strains.Compared with as-cast alloys,the strength and ductility after gas quenching at 900℃generally decrease,and it decreases more obviously after gas quenching at 1200℃.This may be caused by the grain growth during heat treatment.However,the change of heat treatment temperature does not affect overall trend of mechanical properties of Ti-Zr-Ta alloy.（5）The energy release mechanism of Ti-Zr-Ta medium-entropy alloy is mainly based on the oxidation reaction,so content of high oxidation active elements is the most critical factor affecting energy release efficiency.The Ti₂Zr Ta_0.5 alloy with Zr atoms accounting for 28.6%has an energy release rate of 17.4%.（6）The crushing behavior under impact load is another key factor affecting energy release characteristics.The more fully the alloy is broken,the higher the energy release efficiency.The Ti₂Zr Ta_0.75 alloy with excellent comprehensive mechanical properties has the most complete crushing.It’s quasi-static overpressure value generated after penetrating 27L airtight target box at 1300m/s can reach 0.227MPa,and energy release per unit mass can reach 1931J/g,showing good impact energy release characteristics.