摘要
Phase field models were established to simulate the grain growth of a nanostructured AZ31 magnesium alloy,which contain spherical particles of differing sizes and volume fractions, under realistic spatial and temporal scales.The effect of the second phase particles on the nanostructure evolution was studied. The simulated results were compared with those of the conventional microstructured alloy.The expression of the local free energy density was improved by adding a second phase particle term. The right input parameters were selected for proper physical meaning. It was shown that the rules that govern the pinning effect of the second phase particles during the grain growth were different for the nanostructure and microstructure. There was a critical particle size value that affected the grain growth within the nanostructure. If the particle size was lower than the critical value, the pinning effect on grain growth increased with decreasing particle size. When the particle size was greater than the critical value, the particles had almost no pinning effect.However, in the conventional microstructured material,the larger particle size resulted in an enhanced pinning effect during grain growth for particle sizes smaller than 1 μm. The effect was reversed when the particle size was larger than the critical value. For the nanostructure, the critical value was200 nm when the particle content was 10 v.%, and the critical value decreased when the content increased. When the particle size was 30 nm, the particle pinning effect on the grain growth increased for increasing particle content.
本文建立了一个真实时空的相场模型模拟,研究了含不同尺寸和体积分数的球形第二相颗粒的纳米结构AZ31镁合金的晶粒生长过程;第二相颗粒对单相合金系统晶粒组织演化和生长动力学的影响;并将模拟结果与微米晶结构镁合金的模拟结果相比较.通过在自由能密度函数的表达式中增加第二相颗粒的表达来改进模型.模拟结果表明:纳米晶组织中第二相粒子对晶粒长大的钉扎作用,与对微米晶组织下的作用有很大区别.纳米结构中,第二相颗粒对晶粒长大影响存在一个粒子尺寸的临界值,当第二相颗粒体积分数为10%时,粒子尺寸的临界值为200 nm,随粒子含量增加,临界尺寸值将减小.另一方面,粒子含量越大对晶界钉扎作用越大,晶粒平均尺寸越小.该研究将为选择复合加入和原位合成的方法在AZ31镁合金中引入第二相颗粒的实验研究提供显微组织设计的理论指导.
基金
supported by the National Natural Science Foundation of China(U1302272)
