Evaluation of microstructural changes by X-ray diffraction peak profile and focused ion beam/scanning ion microscope analysis

摘要

Microstructure in subsurface is investigated to understand the effect of cryogenic coolant in hard machining of hardened AISI 52100 bearing steel. The cutting experiments were performed under dry and cryogenic cooling conditions using cubic boron nitride (CBN) tool inserts. The change in the microstructure was analyzed at varying of the tool shape and cutting speed for different initial hardness of the workpiece. The machined surfaces and subsurface were analyzed by several investigation techniques. The affected layer depth was observed with a scanning electron microscope (SEM), while the phase composition was analyzed by X-ray diffraction (XRD). The grain size has been directly measured with a focused ion beam and scanning ion microscope (FIB-SIM) and compared with an indirect method of analysis: X-ray diffraction peak profile (XDPP). The experimental results show that the microstructural phase strongly depends on the cutting process parameters. Furthermore, when the cryogenic cooling is applied, martensitic structure disappears in some cases. The grain size on the machined surfaces is also influenced by the material properties and the process parameters. In addition, it is demonstrated that the XDPP indirect method for grain size analysis is a valid alternative to the direct method.