耐高温氧化Fe-Cr-Ni中熵合金氧化层的微结构与力学性能分布

Microstructure and Micro-mechanical Distribution of Oxide Layer Formed on Fe-Cr-Ni Medium Entropy Alloy with Excellent High-temperature Oxidation Resistance

目的开发有优异抗高温氧化性的低成本Fe-Cr-Ni中熵合金,研究其高温氧化层微结构与力学性能分布。方法通过连续氧化增重试验研究了Fe-Cr-Ni中熵合金在1150~1240℃空气中的氧化动力学,结合SEM、EDS、XRD、XPS等分析技术与微米划痕试验,对经1150℃氧化4 h后的氧化层形貌、成分、相分布与微米力学性能分布进行了分析。结果Fe-Cr-Ni中熵合金在空气中高温氧化增重遵循抛物线规律,氧化激活能为417.64 kJ/mol,抗氧化性优异;经1150℃氧化4 h后,Fe-Cr-Ni中熵合金氧化层形成双层结构,外层主要由致密的Mn(Fe/Cr)_(2)O_(4)尖晶石氧化物、Fe_(2)O_(3)和少量MnO_(2)组成,内层由致密且连续的Cr_(2)O_(3)组成,在基体与氧化层界面弥散分布着SiO_(2)内氧化物颗粒。氧化层的力学分布特征体现了其分层结构,外层与内层的结合力约为10 N,氧化内层与基体的结合性好,结合力约为24 N。随着划痕深度的增加,压头从氧化层表面划动至基体,塑性变形比例逐层降低,断裂韧性则随着划痕深度的增加逐层增大。结论开发的低成本Fe-Cr-Ni中熵合金具有优异的耐高温氧化性能,经高温氧化后在表面形成致密的氧化层有效阻碍了O^(2-)的向内扩散和合金元素的向外扩散,同时SiO_(2)内氧化物颗粒增加了氧化层与基体的结合力,这是Fe-Cr-Ni中熵合金具有优异抗氧化性的重要原因。

This work aims to develop a low cost Fe-Cr-Ni medium entropy alloy with excellent high temperature oxidation resistance,and then,the microstructure and micro-mechanical distribution of oxide layer formed on Fe-Cr-Ni medium entropy alloy were studied.The oxidation kinetics in the air at 1150-1240℃was obtained by continuous oxidation and weight gain experiment.The morphology,composition and phase composition of the oxide film oxidized at 1150℃for 4 h were analyzed by SEM,EDS,XRD and XPS techniques.The micro-mechanical distribution of oxide layer was studied by micro-scratch method.The result show that,the oxidation resistance of Fe-Cr-Ni medium entropy alloy is excellent with a high oxidation activation energy that is 417.64 kJ/mol.The weight gain at high temperature in air follows a parabolic rule.After being oxidized at 1150℃for 4 h,the entropy alloy oxide film of Fe-Cr-Ni formed a double-layer structure.The outer oxide layer was mainly composed of dense Mn(Fe/Cr)_(2)O_(4)spinel,Fe_(2)O_(3) and a small mount MnO_(2) oxides,the inner oxide layer was composed of dense and continuous Cr_(2)O_(3).Meanwhile,internal oxide particles SiO_(2)were dispersed at the interface between the matrix and the oxide film.The micro-mechanical distribution characteristics of the oxide layer reflect its layered structure,the binding force between the outer oxide layer and the inner oxide layer is about 10 N,while the binding force between the inner oxide layer and the matrix is about 24 N.With the increase of scratch depth,the indentation moves from outer oxide layer to matrix,the plastic deformation ratio decreases,while the fracture toughness increases from outer oxide layer to matrix.The developed low cost Fe-Cr-Ni medium entropy alloy really show an excellent high temperature oxidation resistance.After high temperature oxidation,the dense oxide layer formed on the surface effectively hinders the inward diffusion of O_(2)‒and the outward diffusion of alloying elements.Meanwhile,the internal oxide particles in SiO_(2)increase the binding force between the oxide layer and matrix,this is an important reason for the excellent oxidation resistance of the entropy alloy in Fe-Cr-Ni.The dense and continuous Cr_(2)O_(3)layer effectively impedes the growth of the oxide layer,while the internal oxide particles SiO_(2)increase the binding force between the oxide film and the matrix,which is an important reason for the excellent oxidation resistance of Fe-Cr-Ni MEA.