Study On Microstructure And Mechanical Properties Of High Entropy NbMoTaWZr_x Alloy

After the concept of high entropy alloy was put forward,many scientists began to study it.It is defined as an alloy with five or more principal element elements,and the content of each element is between 5%and 35%.Most of the crystal structures of the high entropy alloys are simple body-centered cubic crystals or face-centered cubic crystals,and some contain inter-metallic compounds.Refractory high entropy alloys are mainly composed of refractory metals,which usually exhibit high hardness,strength and low strain in mechanical properties.In order to solve the problem of high strength and low strain of refractory NbMoTAW high entropy alloy,this paper designed to add Zr element into NbMoTaW alloy by different proportion thro ugh the investigation and theoretical support of the existing research.In addition,NbMoTaWZrwas used as the basis for comparison and a control group was set for comparison.NbMoTaWZr0.5,NbMoTaWZr1.5 and NbMoTaWZr2 were used as the control group.In this paper,the hardness,room temperature yield strength,room temperature compressive strength,high temperature yield strength and high temperature compressive strength of the four-component high entropy alloy are compared,and the reasons for the different mechanical properties are analyzed from the microstructure and fracture morphology.In this paper,high entropy alloy smelting is carried out in a vacuum smelting furnace.The smelting process needs to be repeated 5 to 8 times to ensure sufficient smelting.After that,line cutting was used to prepare the preparation of test samples for each project.The yield strength,compressive strength and strain of four-component high entropy alloy at roomtemperature are tested by universal material testing machine.The micro structure and fracture of the alloy were observed by optical microscope and scanning electron microscope.The yield strength,comcompressive strength and strain of each component alloy at 900?,1000?,1100? and 1200? were tested by thermal simulation testing machine.The experimental results show that at room temperature,the compressive strength of NbMoTaWZr,NbMoTaWZr1.5 and NbMoTaWZr2 alloys with high entropy components are in the range of 1700MPa to 1800MPa,while the strain of NbMoTaWZr is 0.12.NbMoTaWZr1.5 and NbMoTaWZr2 are 0.25.Under high temperature,with the increase of temperature,the yield strength and compressive strength of the three decreased significantly,and the higher the temperature,the greater the decline range.The yield strength and compressive strength of NbMoTaWZr0.5 are higher than those of the other three components at room and high temperatures,but the yield strength should vary.Conclusion:The addition of Zr in NbMo TaW alloy has an obvious effect on improving the room temperature plasticity of NbMoTaW alloy.At the same time,it can maintain high yield strength and compressive strength at room temperature.However,the high entropy alloy will be softened at high temperature,which causes the high temperature compressive strength of the alloy to decline sharply.Zr atoms are dissolved into the matrix alloy during the smelting process,which can strengthen the alloy by solid solution.With the increase of Zr content,the overall strength of the alloy does not increase when the Zr atom cannot be further dissolved into the NbMOTAW lattice.At the same time,Zr is concentrated in the dendritic walls,which greatly improves the plasticity of the high entropy alloy.