fcc/L1_(2)共格高熵合金Al_(0.1)CoCrFeNiTi_(0.1)热压缩PLC变形行为

Deformation Behavior of fcc/L1_(2) Coherent High-Entropy Alloy Al_(0.1)CoCrFeNiTi_(0.1) Under Hot Compression PLC

采用真空感应熔炼(VIM)的方法,结合特定的热处理工艺,制备具有fcc/L1_(2)两相共格的Al_(0.1)CoCrFeNiTi_(0.1)高熵合金,在宽温度(298~973 K)内进行系统的准静态单轴恒温压缩试验。使用SEM和XRD测试方法对高熵合金微观结构、形貌进行观察;根据热力学和晶体学理论计算fcc固溶体相和L1_(2)相纳米沉淀相的晶格参数和热力学参数,并解释其形成原因;通过Image J图像处理软件自动统计L1_(2)相在晶内和晶界处的尺寸、间距以及体积分数。结果表明:L1_(2)相与fcc相晶格常数和晶面间距的比值分别约为1.008和0.605;该高熵合金的平均原子半径δ=3.507%;平均混合熵ΔS_(mix)=14.8821 J/(kJ·mol);平均混合焓ΔH_(mix)=-6.848 kJ/mol;价电子浓度VEC=8.0238;由EDS能谱分析得到L1_(2)沉淀相粒子化学式为(Fe,Co,Ni)3(Al,Ti,Cr);热压缩变形过程中,在同一温度下的初始应变阶段,随着应变的增大,锯齿屈服(PLC)强化现象的A型锯齿波逐渐消失;而当温度高于873 K,应变大于0.213时,则有B型锯齿波出现。这主要与合金各阶段的变形机制有关。

Al_(0.1)CoCrFeNiTi_(0.1) high-entropy alloy with fcc/L1_(2) two-phase coherence was prepared by vacuum electromagnetic suspension melting(VIM)method combined with specific heat treatment process and the quasi-static uniaxial constant temperature compression test of the system was carried out in a wide temperature(298-973 K).The microstructure and morphology of high-entropy alloys were observed by SEM and XRD.At the same time,the lattice parameters and thermodynamic parameters of the fcc solid solution phase and the L1_(2) phase nanoprecipitation phase were calculated according to the thermodynamic and crystallographic theories,and the reasons for their formation were explained.In addition,the size,spacing and volume fraction of the L1_(2) phase within the crystal and at the grain boundary were automatically counted by Image J image processing software.The results show that the ratios of L1_(2) phase to fcc phase in lattice constant and interplanar spacing are about 1.008 and 0.605,respectively.The average atomic radius of the high-entropy alloyδ=3.507%;the average mixing entropyΔS_(mix)=14.8821 J/(kJ·mol);average mixing enthalpyΔH_(mix)=-6.848 kJ/mol;the valence electron concentration VEC=8.0238;the chemical formula of L1_(2) precipitated phase particles obtained by EDS analysis is 3()Fe,Co,Ni Al,Ti,Cr().In the process of thermal compression deformation,at the initial strain stage and at the same temperature,with the increase in strain,the A-type sawtooth wave of the PLC sawtooth yield strengthening phenomenon gradually disappears;while when the temperature is greater than 873 K and the strain is greater than 0.213,a B-type sawtooth wave appears.This is mainly related to the deformation mechanism of the alloy at each stage.