粉末高温合金加工表面显微结构和力学性能变化研究

Microstructure and Mechanical Properties Transformation in the Machined Surface of Powder Metallurgy Superalloy Du Jin1,Zhang Jingjie1,Wang Liguo1

摘要:

在切削加工粉末高温合金过程中,合金已加工表面承受着严重的塑形变形会出现显微组织结构和力学性能的变化。已加工表面出现的白层体现着加工表面显微结构和力学性能的变化,对合金加工表面质量的影响至关重要。为了揭示粉末高温合金已加工表面显微组织结构和力学性能的变化,开展了切削速度对粉末高温合金FGH95已加工表面白层形成影响的研究。研究发现随着切削速度的提高,FGH95合金已加工表面出现的白层厚度增大。对加工表面进行显微观察发现在表面覆盖着一层致密的、无明显组织特征的白层结构。通过对加工前后材料的XRD测试分析得出FGH95粉末高温合金的基体材料以Ni基固溶体的形式存在,而已加工表面的显微组织结构则明显不同。这说明在切削过程中,粉末高温合金已加工表面发生了Ni基固溶体组织结构的变化。对加工表面进行晶粒度测量发现,切削速度越高晶粒细化现象越明显。对合金切削表面白层进行力学性能测试表明,白层的显微硬度随着切削速度的提高而增大；存在合金已加工表面白层中的残余应力为拉应力,且随着切削速度的提高而增大。粉末高温合金已加工表面显微结构和力学性能变化的研究可以明确合金表面完整性的形成机理,可为表面质量的预测和控制提供理论依据。

关键词:粉末高温合金;加工表面;相变;硬度测试;残余应力

Abstract:

During the machining of powder metallurgy (PM) superalloy parts, the machined surface undergoes severe plastic deformation which appears to be in the form of microstructure and mechanical properties transformation. White layer which is belong to the microstructure and mechanical properties transformation, usually generated on the machined surface during hard machining of PM superalloy, it has significant effect on the machined surface quality. The effect of cutting speed on the white layer formation has been successfully investigated in order to illustrate the microstructure and mechanical properties transformation in the machined surface of PM superalloy FGH95. White layer thickness on the machined surface increased with the increasing of cutting speed. The investigation results showed that machined surface exhibited densification with no obvious structural features characteristics. FGH95 superalloy bulk material existed in the form of Ni-based solid solution, while the microstructure of white layer was observed significantly different from bulk materials. It’s because of the transformation of microstructure presented in the form of Ni-based solid solution in FGH95 during the cutting process. The higher the cutting speeds more severe grain refinement, which will leads to higher values of hardness in white layer. Residual stresses in the machined surface of FGH95 were seems to be observed tensile in all cutting conditions and it was observed an increasing trend with respect to the increment of cutting speed. The microstructure and mechanical properties transformation in the machined surface of PM superalloy was revealed in order to identify the mechanism of machined surface integrity, it can be provide the theoretical basis for the controlling of machined surface quality.

Key words:powder metallurgy; machined surface; phase transformation; hardness measurement; residual stress