纳米压入法点阵分析金属微观组织力学性能

Determination of mechanical properties of microstructure in metals based on grid nanoindentation

利用Berkovich金刚石压头对3种黄铜和2种碳钢共5种常见双相合金材料进行纳米压入法点阵实验,采用高斯混合模型(GMM)拟合实验数据的频率直方图,评估单相态的微观力学性能(压痕硬度H_(IT)、弹性模量E_(IT))和体积分数.结果表明:黄铜α相和β相的压痕硬度以及弹性模量差距较小,相界效应在频率直方图中没有显现,应采用双峰高斯模型对压痕硬度和弹性模量的频率直方图进行拟合.碳钢的相界效应不可忽略,应采用三峰高斯模型对点阵数据进行拟合.双峰或三峰高斯模型拟合得到的压痕硬度和弹性模量与独立纳米压痕实验结果接近.利用双峰高斯模型对微观力学性能参数(如弹性功W_(e)和总功W_(t)等)的频率直方图拟合得到的材料各相态体积分数与使用Image Pro-plus 6.0软件得到的体积分数f_(r)相近.大载荷下压痕实验得到的弹性模量E_(m)与点阵结果的加权平均值E_(ave)一致,压痕硬度有明显的压痕尺寸效应.

Grid nanoindentation tests under Berkovich diamond indenter were carried out on 5 common dual-phase alloys including 3 brasses and 2 carbon steels.Histogram data were fitted by gaussian mixture model(GMM)to estimate micromechanical properties including indentation hardness H_(IT),elastic moduli E_(IT) and volume fractions of individual phases.Phase interface effect(PIE)was little due to similar H_(IT) and E_(IT) between phaseαandβin brasses,so bimodal GMM was more applicable to fit the histogram of H_(IT) and E_(IT).Trimodal GMM was more suitable to fit histograms because of prominent PIE in carbon steels.Results obtained by trimodal and bimodal GMM corresponded well to the results of isolated nanoindentation tests.Histogram of mechanical property parameters(such as elastic work W_(e),total work W_(t) and so on)were fitted by bimodal GMM to estimate volume fractions of individual phases,which showed consistency with f_(r) obtained by Image Pro-plus 6.0.E_(IT)obtained by nanoindentation tests under large load was consistent with weighted average E_(ave) based on grid nanoindentation under small load.Indentation size effect was found in indentation hardness.