Microstructure And Properties Of CrNbTiZrAlTa High-entropy Alloy

CrNbTiZr refractory high-entropy alloy has high melting point,good thermal stability,good room temperature and high temperature mechanical properties.CrNbTiZrAl_0.25high-entropy alloy is composed of disordered BCC phase and ordered Laves phase,with high yield strength and low plasticity.The addition of Ta can change the microstructure of High-entropy alloy,and then affect its properties.However,the study of Ta element on high-temperature oxidation resistance and corrosion resistance of refractory High-entropy alloy is less.In this paper,CrNbTiZrAl_0.25Ta_x（x=0,0.25,0.5,0.75,1）high-entropy alloy was prepared by vacuum arc melting furnace.The microstructure,room temperature mechanical properties,high-temperature oxidation resistance and corrosion resistance of the alloy were tested and analyzed by means of metallographic microscope,Diffractometer,field emission scanning electron microscope,universal compression tester,X-ray photoelectron spectrometer and other instruments.The crucial conclusions are as follows:（1）The phase structure of CrNbTiZrAl_0.25Ta_xhigh-entropy alloy is BCC+Laves phase.The BCC phase exhibits dendritic morphology,rich in Ta and Nb elements,and the Laves phase rich in Cr and Zr elements is distributed in the interdendritic region.（2）The room temperature mechanical properties of CrNbTiZrAl_0.25Ta_xhigh-entropy alloy are closely related to the Ta content.The compressive properties of the alloy increased first and then decreased with the increase of Ta content.When x≤0.5,the fracture strength and compressive strain of the alloy increase with the increase of Ta content;When x>0.5,the fracture strength and compressive strain of the alloy decrease with increasing Ta content.When x=0.5,the alloy exhibits the best mechanical properties at room temperature,with compressive fracture strength and compressive strain of 2005 MPa and 9.22%,respectively.（3）The oxidation resistance of CrNbTiZrAl_0.25Ta_x（x=0,0.5,1）high entropy alloy at 800,900,and 1000°C was studied.The oxidation kinetics curves all exhibit a parabolic shape and the variation pattern is consistent.As the temperature increases,the oxidation resistance of the alloy gradually decreases.The oxidation Reaction rate constant Kp of Ta0 alloy increases from36.80 mg²·cm^-4·h^-1at 800°C to mg²·cm^-4·h^-1at 1000°C.An increase in Ta content is beneficial for improving the oxidation resistance of the alloy.At 800°C,the oxidation rate constant Kp of the alloy decreased from 36.80 mg²·cm^-4·h^-1at Ta0 to 19.33 mg²·cm^-4·h^-1at Ta1.（4）XRD analysis indicates whether the oxidation products of CrNbTiZrAl_0.25Ta_x（x=0,0.5,1）at 800,900,and 1000°C are complex,including Al₂O₃、Ti O₂、Ta₂O₅、Zr O₂and Nb₂O₅.According to Gibbs free energy,Al₂O₃and Ti O₂are first generated during the oxidation process,and Cr Nb O₄is the most stable.（5）The electrochemical corrosion experiment shows that the corrosion resistance of CrNbTiZrAl_0.25Ta_xhigh-entropy alloy increases with the increase of Ta content,its self corrosion potential increases from-407.9 m V to-209.9 m V,and the self corrosion current density increases from 0.67μA/cm²reduced to 3.69×10-2μA/cm².（6）Electrochemical impedance spectroscopy（EIS）and X-ray photoelectron spectroscopy（XPS）analysis indicate that the passivation film exists in the form of Cr₂O₃、Cr（OH）₃、Nb O₂、Nb₂O₅、Ti O₂、Zr O₂、Al₂O₃and Al（OH）₃;The Ta element has two types of oxides:Ta O₂and Ta₂O₅.The passivation film of CrNbTiZrAl_0.25Ta_xhigh-entropy alloy becomes more and more stable,which increases the density of the passivation layer,thus improving the corrosion resistance of the metal.