Structure And Properties Of Cr_xMoNbTiZr High Entropy Alloy

Refractory high-entropy alloys are a new type of high-entropy alloys in the past ten years,and their hardness and high-temperature stability have shown good properties.Nowadays,the research on high-entropy alloys mainly focuses on the 3D family system,and the research on refractory systems is relatively rare,while the exploration of refractory high-entropy alloys mainly focuses on mechanical properties and high-temperature stability.Corrosion resistance behavior and high temperature oxidation behavior are relatively less explored.These are an unavoidable part of material design,and it is very necessary to conduct systematic research.In this paper,Mo,Nb,Ti,Zr four elements with similar properties（atomic size,electronegativity,etc.）and infinite miscible are selected,and different proportions of classical alloying elements Cr are added,and a series of Cr_xMo Nb Ti Zr（x=0,0.5,1,1.5）high entropy alloys are prepared by arc melting.The influence of Cr content on the microstructure of Cr_xMo Nb Ti Zr alloys was explored by means of microstructure and morphology characterization technology,and the effect of Cr content on the microhardness of the alloy was studied.The results show that the increase of Cr content will make the alloy change from single-phase BCC structure to dual-phase BCC structure.With the increase of Cr content,Cr will segregate and further form Laves phase in Zr-rich phase;Strengthening,lattice distortion effect,Laves phase precipitation strengthening,and strengthening effect due to the increase of Cr content are enhanced.The hardness of Cr_xMo Nb Ti Zr alloy shows a trend of increasing with the increase of Cr content.The effect of Cr content on the corrosion resistance of Cr_xMo Nb Ti Zr alloys was characterized by electrochemical tests.It can be seen from the potentiodynamic polarization curve that in the 3.5 wt.%Na Cl saline environment,the E_Corr of the Cr_xMo Nb Ti Zr alloy shows a phenomenon of first decreasing and then increasing,and is always more negative than that of the Cr-free alloy.The increase of Cr content effectively reduces the alloy.The corrosion rate of Cr content increases but the pitting tendency increases,indicating that Cr content has a critical value on the corrosion resistance of the alloy,so as to balance its influence on the corrosion potential,corrosion current density and pitting resistance of the alloy;Cr content The corrosion morphology of the less two groups of alloys is shallow corrosion pits,and the two groups of alloys with more Cr content show obvious selective corrosion,and the corrosion area is the alloy interdendritic gray phase（Zr-rich phase）,Cr Mo Nb Ti Zr The corrosion is more dispersed,and the corrosion area of Cr_1.5Mo Nb Ti Zr is more dense and interconnected,dividing the unetched Mo-rich phase,which is caused by the intensified segregation of elements caused by the increase of Cr content.On the other hand,the distribution of Cr element is relatively more uniform,which is the main reason why the corrosion potential first decreases and then increases.The effect of Cr content on the high-temperature oxidation behavior of Cr_xMo Nb Ti Zr alloys was studied by weight gain method.The oxidation kinetics curve shows that an appropriate amount of Cr can enhance the oxidation resistance of the alloy at 600℃～800℃,and the Cr_1.5Mo Nb Ti Zr alloy has the best performance at 600℃.The analysis of corrosion products and cross-section morphology shows that the decrease of anti-oxidation performance at higher temperature is mainly caused by the catastrophic damage to the oxide film caused by the melting and evaporation of Mo oxide.In addition,after the surface oxide film is destroyed,the Zr-rich phase precipitates due to the increase of Cr content,and the oxidation rapidly diffuses into the alloy along the interdendritic layer,which is also an important reason for the decline of the oxidation resistance of this series of alloys.