Positron Annihilation Spectroscopy Study of Metallic Materials after High-Speed Cutting.

Jinquan Li,Pawel Horodek,Haolun Shen,Jian Cui,Krzysztof Siemek,Roman Laptev,Iurii Bordulev,Anton Lomygin

doi:10.3390/ma15031017

Abstract

During high-speed cutting, a white layer is often produced on the machined surfaces after mechanical machining, seriously affecting the mechanical properties. These properties are related to the material structure and the defects induced by cutting. However, there is a lack of research on the atomic-scale defects of the white layer. This paper studied the influence of cutting parameters, namely the feed rate, cutting speed and cutting depth, on atomic-scale defects induced by high-speed cutting in GCr15 steel. Positron annihilation studies showed typical plastically deformed or tempered carbon steel defects with additional vacancy cluster components. The quantity of these clusters changed with cutting parameters. Furthermore, significant changes were observed in the subsurface region up to 1 µm, occurring as a result of simultaneous phase transformations, deformation and thermal impacts. The predominant accumulation of only one type of atomic-scale defect was not observed.

Highlights

During the high-speed cutting process, a tool and a machined surface instantly collide at high speed, causing the temperature of the partial area to rise sharply
PALS and Doppler annihilation line broadening spectroscopy (DBS) spectra for GCr15 steel samples after high-speed cutting with different parameters, and two-dimensional CDBS spectra, are given in the Supplementary Materials
The component τA = 147 ± 2 ps is very close to the experimental values of positrons trapped by plastic deformation-induced defects [34]

Summary

Introduction

During the high-speed cutting process, a tool and a machined surface instantly collide at high speed, causing the temperature of the partial area to rise sharply. Under the action of the cutting edge of the tool, the surface layer of the machined material is subjected to the solid thermo-mechanical coupling effect, which gives rise to the deformed thermal layer on the machined surface This effect has a significant influence on the mechanical properties of the workpiece [1]. During the high-speed cutting process, for many metal materials, a layer that appears white under an optical microscope is produced on top of the degenerating layer, caused by the machining of the workpiece’s surface [2] This ultrafine-grain white layer has a surface hardness much higher than that of the matrix, ranging from 800 to 1200 HV, while its thickness ranges from 10 to 50 μm [3]. The high brittleness of the white layer may allow cracks to form, making it possible for the white layer to fall off and become a fatigue source, dramatically reducing the fatigue limit of the structure piece [4]

Methods

Results

Conclusion