CrAlN硬质刀具涂层的相结构稳定性及其热分解机制

Phase structure stability and thermal decomposition mechanism of CrAlN hard cutting tool coating

采用基于密度泛函理论的第一性原理计算方法,从理论上系统研究不同Al固溶浓度x(x=0~1)下面心立方(FCC)结构Cr1-xAlxN硬质刀具涂层的微观几何构型、相结构稳定性及其热分解机制,并从电子结构角度对其稳定性起源进行分析。结果表明:随着Al固溶浓度增大,FCC-Cr1-xAlxN晶胞逐渐收缩,而其晶格畸变程度却先增大后减小,且当Al浓度x为0.5~0.75时,FCC-Cr1-xAlxN晶格畸变较为严重,为析出密排六方(HCP)结构的Al N化合物提供源动力;随着Al固溶浓度增大,FCC-Cr1-xAlxN相结构稳定性逐渐降低,且其极易按FCC-Cr1-xAlxN→(FCC-Cr N)+(HCP-Al N)→(HCP-Cr2N)+N2+(HCP-Al N)的路径进行分解,计算结果与实验保持一致;Al固溶致使FCC-Cr1-xAlxN相结构稳定性降低的内在原因在于Cr1-xAlxN晶胞中Cr—N共价键作用随Al固溶度的增大而逐渐减弱。

Using first-principles calculations method based on density functional theory,the microscopic geometric configurations,phase structure stability and thermal decomposition mechanism of the face-centered cubic(FCC) Cr1-xAlxN(x=0~1) hard cutting tool coating with different aluminum solution concentrations were systematically studied.The origin of phase structure stabilities were also analyzed from the perspective of electronic structures.The results show that the crystal cell of FCC-Cr1-xAlxN gradually contracts with the increase of Al solid solubility,while the magnitude of lattice distortion becomes large firstly,and then becomes small.The magnitude of lattice distortion is the largest when the Al concentration x is 0.5-0.75,which provids the driving force for the precipitation of hexagonal close-packed(HCP) Al N compound.The calculations of cohesive energy and decomposition enthalpy reveal that the phase structure stability of FCC-Cr1-xAlxN is gradually weakened with the increase of Al solid solubility,and it is likely to decompose according to the paths of FCC-Cr1-xAlxN→(FCC-Cr N)+(HCP-Al N)→(HCP-Cr2N)+N2+(HCP-Al N).The analysis of electronic structures indicates that the intrinsic reason of the weakened phase structure stability of FCC-Cr1-xAlxN with Al solid solution should be attributed to the weakened covalent bond strength between Cr and N in Cr1-xAlxN crystal cell with the increase of Al solid solubility.