基于分子动力学的GaN纳米磨削亚表面损伤形成机制

Formation Mechanism of Subsurface Damage of GaN During Nano-Grinding Based on Molecular Dynamics

纳米磨削技术是实现Ga N晶体低损伤加工的超精密加工方法之一,但纳米磨削过程中Ga N的亚表面损伤形成机制仍不清楚。同时,磨削深度作为典型的工艺参数之一,其对Ga N亚表面损伤的影响也鲜有报道。通过分子动力学模拟来研究Ga N纳米磨削过程中的亚表面损伤形成机制以及磨削深度对亚表面损伤的影响。结果表明,Ga N亚表面存在间隙原子、空位缺陷、原子团簇、位错、堆垛层错和结构相变等缺陷。位错的伯氏矢量方向主要为■、■,相变由六方纤锌矿结构向立方闪锌矿结构和非晶结构转变。磨削深度由0.5nm增加到2.0nm时,切向磨削力由26N增加到182N,法向磨削力由148N增加到305N,并且位错线长度由6.5nm增加到18.2nm,亚表面损伤层深度由1.7nm增加到4.1nm。位错滑移和结构相变是Ga N纳米磨削过程中的主要塑性变形机制。由于磨削深度的增加导致磨削力增大,使得磨削接触区的磨削热量和能量升高,因此Ga N塑性变形程度随磨削深度的增加而增大。

Nano-grinding technology is one of the ultra-precision machining methods to realize low damage machining of gallium nitride(GaN)crystal,but the formation mechanism of sub surface damage for GaN during nano-grinding is still unclear.Meanwhile,as one of the typicalprocess parameters,the effect of grinding depth on the subsurface damage of GaN has been rare ly reported.The formation mechanism of subsurface damage and the effect of grinding depth onsub surface damage during nano-grinding of GaN were studied by molecular dynamics simulation.The results show that there are defects such as interstitial atoms,vacancy defects,atomic clusters,dislocations,sta cking faults and structural phase transition on the GaN subsurface.The dire ctions of the Burgersvector of the dislocations are mainly■and■,and thephase tr ansition changes from hexagonal wurtzite structure to cubic sphalerite structure and amorpho usstructure.When the grinding depth increases from 0.5 nm to 2.0 nm,the tangential grindingforce enhances from 26 N to 182 N and the normal grinding force enhances from 148 Nto 305 N,the length of dislocation line increases from 6.5 nm to 18.2 nm and the depth of subsurfaceda mage layer increases from 1.7 nm to 4.1nm.Dislocation slip and structural phase transiti onare the main plastic deformation mechanisms during nano-grinding of GaN.The increas eof grinding depth causes the increase of grinding force,which increases the grinding heat and energyi n thegrinding contact area.Therefore,the plastic deformation degree of GaN i ncrea-seswith the increase of grinding depth.