Preparation And Mechanical Properties Of ODS-NbTaTiV Refractory High-Entropy Alloy

Due to the high strength,hardness and excellent high-temperature mechanical properties,the refractory high-entropy alloys have great potential for application in the field of high temperature structural materials.The dispersed nanoparticles obtained by the oxide dispersion strengthening method have good resistance to high temperature softening and little influence on the plasticity of the alloy while improving the room/high temperature strength of the material.In this thesis,ODS-NbTaTiV refractory high-entropy alloys were prepared by powder metallurgy methods,and the main conclusions are as follows:（1）The effect of sintering temperature on Y₂O₃ reinforced NbTaTiV refractory high-entropy alloys was studied.It was found that the alloy is mainly composed of a matrix phase of BCC structure,in which submicron Ti-（O,N）particles and nanometer Y-Ti-O particles are dispersed.The grain size and mechanical properties of the alloy increased with the increase of sintering temperature.The alloy sintered at 1500°C has the largest grain size and the highest yield strength and fracture strain of 0.77μm,1626.4MPa and 22.1%,respectively,and still retains a yield strength of 482 MPa when compressed at 1000°C.（2）The effect of Y₂O₃ content on ODS-NbTaTiV refractory high-entropy alloys was studied.It was found that with the increase of Y₂O₃content,the strength of the alloy increased,but the grain size decreased.When the Y₂O₃ content increased to 3 wt.%,nano-Y₂O₃ particles appeared in the alloy.3 wt.%-NbTaTiV alloy has the smallest grain size and the highest yield strength,which are 0.64μm and 1865.6 MPa,respectively.The improvement of alloy strength is mainly attributed to the dispersion strengthening of submicron Ti-（O,N）particles and nano-Y-Ti-O/Y₂O₃particles and the fine-grain strengthening induced by ultrafine grains.（3）The effect of sintering temperature on Al₂O₃ reinforced NbTaTiV refractory high-entropy alloys was studied.It was found that the grain size and mechanical properties of the alloy increased with the increase of sintering temperature.The alloy is mainly composed of a matrix phase of BCC structure,in which submicron Ti-（O,N）particles are dispersed.The alloy sintered at 1600°C had the highest yield strength and compressive strength,2075.0 MPa and 2799.6 MPa,respectively,and still maintained a yield strength of 690.4 MPa when compressed at 1000°C.The improvement of the alloy’s yield strength is mainly attributed to the dispersion strengthening of submicron Ti-（O,N）particles and the solid solution strengthening of Al.