Research On Laser-assisted Machining Property Of Magnesium Aluminate Spinel

Magnesium aluminate spinel is a typical hard and brittle transparent ceramic material.With the perfection of sintering techniques and the increasing demand for application for spinel,the research on its processing technology is urgently needed.At present,grinding and polishing are mainly used to process magnesium aluminate spinel,but it is difficult to process parts with complex surfaces.In addition,abrasive machining processes always bring sub-surface damages on hard and brittle materials.To solve these problems,laser-assisted turning technology is considered to be applied on machining spinel.Nevertheless,the mechanical properties and material removal mechanism of magnesium aluminate spinel under high temperature environment are still waiting to be investigated.In this paper,the effects of high temperature environment on the material removal mechanism and damage mechanism of spinel are studied through a comprehensive study of theoretical analysis,simulation and experimental work.The micro-hardness and the critical depth of ductile–brittle transition of spinel within high temperature environment are determined.The feasibility of two laser-assisted mechanisms,which are the laser ablation-induced thermal cracking and material softening induced by laser heating,are explored.The research work in this paper can lay a solid foundation for laser assisted turning.The hardness values of magnesium aluminum spinel material at elevated temperature are firstly measured through a series of high-temperature Vickers indentation tests.Then scratching experiments at high temperature are conducted to observe the surface morphology of the ductile-brittle transition area,analyze the damage mechanism of the magnesium aluminate spinel,and investigate the trend of ductile-brittle transition depth at high temperature.The distribution model of laser power absorption on the magnesium aluminate spinel surface is established.By establishing the laser scanning model,the effects of laser power,scanning speed,defocus amount and the distance between the laser spot center and the heating distance of laser spot prior to machining on the resultant laser induced temperature field are systematically studied.This part of work provides a guidance for the subsequent selection of proper laser parameters.The laser-assisted machining system is estabilished in the final part of this paper.The feasibility of inducing controllable surface and subsurface damages by laser ablation is evaluated,including the applicability of black-body coating and the impact of laser parameters.Secondly,the possibility of achieving material softening effect through laser irradiation is discussed.The effects of laser-assisted heating on the material removal mechanisms of the ductile domain and brittle domain are studied through a group of orthogonal laser-assisted scratching experiments.The improvement of critical scratching depth of ductile-to-brittle transition are studied by adjusting different laser-assisted parameters.These results provide experimental foundation on selecting reasonable laser parameters in the laser-assisted turning on spinel.