Mg_xTiAlFeNiCr(x=0.6～2.0)高熵合金微结构演变及耐蚀性

Phase evolution and corrosion resistance of Mg_xTiAlFeNiCr(x=0.6～2.0) high-entropy alloys

通过机械合金化方法制备了轻质MgxTiAlFeNiCr(x=0.6～2.0)高熵合金,研究了Mg含量、热力学参数、合金相结构间的关系。结果表明,Mg在体心立方(BCC)相中的固溶度较大,x=0.6～1.4、合金的热力学参数原子半径错配度d=8.68%～9.77%、混合熵ΔSmix为14.78～14.82 J/(mol·K),混合焓ΔHmix为-14.13～-6.76 kJ/mol时,合金为单相体心立方结构(BCC1)。x=1.6～1.8,d=10.0%～10.1%,ΔSmix=14.65～14.74J/(mol·K),ΔHmix=-5.40～-4.19kJ/mol时,合金由两种体心立方结构BCC1和BCC2组成。BCC2相比BCC1相的Mg含量更高,两相界面为半共格关系。MgxTiAlFeNiCr合金在3.5wt%NaCl溶液中具有良好的耐腐蚀性能。但随Mg含量增加,合金的耐蚀性下降。

The novel low density MgxT iAlFeNiCr(x=0.6~2.0)high-entropy alloys were prepared by mechanical alloying,the relation of Mg content,thermodynamic parameter and phase structure was researched.The results showed that the prepared high-entropy alloy powders were approximately spherical particles with a diameter about 3μm.The measurements of X-ray diffraction(XRD)and analyses of energy-dispersive X-ray spectrometry(EDS)revealed that Mg had a high solid solubility in BCC(body center cubic)lattice.The results of thermodynamic calculation showed that the alloys(x=0.6~1.4)had a single BCC1 phase when 8.68%≤δ≤9.77%(δwas atomic radii mismatches),14.78 J/(mol·K)≤ΔSmix≤14.82 J/(mol·K)(ΔSmix was mixing entropy)and-14.13 kJ/mol≤ΔHmix≤-6.76 kJ/mol(ΔHmix was mixing enthalpy).However,the alloys(x=1.6~1.8)consisted of BCC1 and BCC2 phases when 10.0%≤δ≤10.1%,14.65 J/(mol·K)≤ΔSmix≤14.74 J/(mol·K)and-5.40 kJ/mol≤ΔHmix≤-4.19 kJ/mol.When x≥2.0,Mg content exceeded the solid solubility of Mg in BCC1 and BCC2 lattices.As a result,Mg2.0 TiAlFeNiCr alloy contained the main phases BCC1 and BCC2 and the minor phases Mg and intermetallic compound.The lattice constant(a)of BCC1 and BCC2 were determined respectively to be 0.289 and 0.291 nm by the XRD measurement and high resolution transmission electron microscope(HRTEM)analysis.For BCC1 phase,Fe acted as a solvent element whereas Mg,Ti,Al,Ni and Cr behaved like solute elements.For BCC2,however,Cr acted as a solvent element whereas Mg,Ti,Al,Fe and Ni behaved like solute elements.Compared with BCC1,high Mg content was achieved in BCC2 phase.Moreover,BCC1 and BCC2 displayed a semicoherent interface.The Mgx TiAlFeNiCr(x=0.6~2.0)high-entropy alloys exhibited a good corrosion resistance in 3.5 wt%NaCl solution.But the corrosion resistance decreased with the increasing of Mg in the alloys.