The Investigation Of Composition Design,Structure Stability And Mechanical Properties For Ti_(65-x)Ta₂₅Nb₁₀Zr_x Multi-component Refractory Alloys

Multicomponent alloys have attracted the continuous attention of materials workers because of their unique design concept and excellent properties.The design concept has changed the traditional single-principal matrix microalloying strategy.The nearly equal"multiple equality"makes multicomponent alloys often form a unique single-phase solid solution structure.The refractory multi-component alloys are composed of high-melting elements and have good high-temperature properties.They are potential materials that can replace traditional superalloys and become a current research hotspot.Most of the multi-component refractory alloys reported so far have a single-phase body-centered cubic(BCC)structure,while the research on mechanical properties mostly focuses on hardness and room temperature compressive properties,and there are few studies on tensile properties.Based on the empirical parameters and the calculation method of phase diagram,a multi-component refractory alloy Ti_(65-x)Ta₂₅Nb₁₀Zr_x(x=0,5,10,15,20)system was designed.The microstructure,local structure,mechanical properties,corrosion properties and phase stability of the alloy were investigated,and the influence of composition was analyzed.The results are as follows:(1)The phase formation law is consistent with the phase diagram calculation results.The five multi-component refractory alloys are single-phase body centered cubic structure in the as cast state.The alloy components after recrystallization after cold rolling are evenly distributed without obvious preferred orientation.The lattice constant increases with raising Zr concentration,and the grain size fall with raising Zr concentration.Compared with Zr0alloy,Zr20 alloy is increased by nearly 100%,which is related to the synergistic rapid diffusion caused by the addition of Zr.(2)The local structure and elastic properties of multi-component refractory alloys are investigated by DFT calculation.The results of ball-and-stick model,atomic radius,atomic displacement and atomic pair distribution function show that the distortion degree of the local structure of the alloy increases with the raise of Zr concentration.The calculation also shows that the alloy has high structural stability under external load.(3)The hardness,yield strength of the alloy elevate with the raise of Zr concentration,especially its tensile properties.The addition of Zr realizes the synchronous improvement of strength and plasticity.From Zr0 to Zr20 alloy,the hardness raise from 183Hv to 250Hv,the compressive yield strength raise from 452 MPa to 934 MPa,and the tensile yield strength raise from 476 MPa to 786 MPa.Zr5 alloy has the maximum fracture strain of17.7%,much higher than that of Zr0 alloy 4.35%.The hardness of each alloy is calculated by solution strengthening model.The results show that the contribution of Zr element to solution strengthening is much greater than that of other elements.In addition,corrosion experiments in 3.5 wt.%Na Cl solution showed that the alloys had good corrosion resistance.The results show that the corrosion resistance of refractory alloy is better than 304 stainless steel,and is equivalent to pure titanium and Ti6Al4V.(4)In this paper,the structural stability of the system alloy in the temperature range of500??800?was systematically studied.The experimental results of heat treatment under different conditions show that Zr0,Zr5 and Zr10 alloys still maintain their single-phase BCC structure in the temperature range of 500??800?.Zr15 alloy is single-phase at 800?and above,BCC2 phase begins to precipitate at 700?,and dual BCC phase structure at500?and 600?,that is,the matrix and Ta Nb enriched phases.Zr20 alloy has a large volume fraction of BCC2 phase at 800?,and it is still dual BCC phase in the range of 500??700?,which are Ta Nb enriched phase and matrix respectively.The microstructure stability of the alloy declining with the raise of Zr concentration,and the precipitation temperature of the second phase is directly proportional to Zr concentration.(5)CALPHAD method can effectively assist in alloy structure prediction,but it is not accurate enough to predict the phase decomposition temperature and phase composition in the medium temperature range,but it still has its reference significance.