Study On Microstructure And Properties Of AlNbTiVZr System Lightweight Refractory High Entropy Alloy

As a new material,high entropy alloys（HEAs）have been widely used in aerospace,wear and corrosion resistant materials and other fields.With the increasing standard of living and the rapid development of modern science and technology,high entropy alloys with excellent high temperature properties have gradually come to the stage.Lightweight is one of the main problems restricting the application of refractory high entropy alloys.At present,most alloys such as NbMoTaW and HfNbTaTiZr still have problems of high density and low specific strength.Therefore,it is necessary to reduce the density of the alloy on the premise of meeting the excellent high temperature properties.Based on NbTiV medium entropy alloy system with high hardness and strength,refractory high entropy alloys with hard and brittle intermetallic compound phases are designed by adding Al and Zr elements,and the as-cast Al_0.5NbTiV₂Zr_x and Al_0.5Nb_0.5TiV₂Zr_x lightweight（refractory high entropy alloys）RHEAs were prepared by vacuum arc melting.The effects of Zr on microstructure and mechanical properties of the Al_0.5NbTiV₂Zr_x and Al_0.5Nb_0.5TiV₂Zr_x alloys were investigated,and the alloys with the best properties were selected.Based on the determination of Zr content,the content of Al and Ti elements were adjusted in turn.Through the characterization of microstructure and mechanical properties,the design of alloy composition with higher specific strength was completed.The strengthening mechanisms of the alloys were discussed,which can provide a theoretical basis for the design and application of lightweight refractory high entropy alloys.The effect of Zr on microstructure and mechanical properties of the Al_0.5NbTiV₂Zr_x and Al_0.5Nb_0.5TiV₂Zr_x alloys was investigated.The results show that with the increase of Zr,the volume fraction of the C14-Laves phase（enrich in Al and Zr）increases sharply,which leads to the decrease of the compressive yield strength of Al_0.5NbTiV₂Zr_xand Al_0.5Nb_0.5TiV₂Zr_xalloys at room temperature.The high temperature compression test results show that Al_0.5Nb_0.5TiV₂Zr_0.5alloy has better properties.After Zr content was determined,Al content was adjusted（atomic ratio0～1.0）,and its effect on microstructure and properties was investigated.The results show that Al can promote the formation of C14-Laves phase in Al_xNb_0.5TiV₂Zr_0.5alloys.As a hard intermetallic compound phase,the volume fraction of C14-Laves phase increases from 12.03%to 22.83%with the increase of Al content,and then decreases slightly to 20.31%.The density of the alloy is reduced by 11.2%.Hardness increased from 397.2 HV to 641.9HV.The compressive yield strength of Al_xNb_0.5TiV₂Zr_0.5alloys at room and elevated temperatures increases significantly in the range of 0～0.4 Al content,and decreases slightly after reaching the peak stress of Al0.8 alloy.The significant enhancement of its strength is related to the second phase strengthening caused by the increase of the volume fraction of C14-Laves phase.After the content of Al was determined,the content of Ti was adjusted（atomic ratio 0.4～2.0）,and its effect on the microstructure and properties was studied.The results show that Ti is one of the necessary components of the BCC matrix phase in the Al_0.8Nb_0.5Ti_xV₂Zr_0.5alloy.The addition of Ti increases the volume fraction of the BCC matrix phase from 63.48%to95.63%,reduces the density of the alloy by 6.1%,and makes the hardness,yield strength and compressive strain of the Al_0.8Nb_0.5Ti_xV₂Zr_0.5alloys increase first and then decrease.The strength and plasticity of the Al_0.8Nb_0.5Ti _1.2V₂Zr_0.5alloy are both excellent.The synergistic increase of yield strength and deformability is related to the serious lattice distortion and grain size reduction caused by solid solution of Ti atoms into the matrix.The results show that Al_0.5Nb_0.5TiV₂Zr_0.5,Al_0.8Nb_0.5TiV₂Zr_0.5and Al_0.8Nb_0.5Ti _1.2V₂Zr_0.5have the best mechanical properties.The specific yield strengths at 298 K are 257,312,336 MPa·cm3g-1,and 114,200,194MPa·cm³g^-1at 1073 K,respectively.The mechanical properties of the alloys are mainly affected by the second phase strengthening,solid solution strengthening and grain refinement strengthening.Adjusting the alloy composition with low density elements can effectively enhance the high temperature properties of the RHEAs and reduce density.The Al_0.8Nb_0.5Ti _1.2V₂Zr_0.5refractory high entropy alloy was designed and finally obtained in this paper,which has better room temperature and high temperature properties than the similar alloy and high entropy alloy materials reported in the current references,and it is expected to be used as structural materials in the field of high temperature materials in aviation and aerospace.