激光-超声辅助磨削氮化铝表面改性机理

Aluminum Nitride Surface Modification Mechanism by Laser Ultrasonic-assisted Grinding

目的利用激光-超声辅助磨削技术(LUAG),研究氮化铝表面创成改性机理。方法通过分子动力学,从磨削力、原子相变和亚表面损伤深度方面,分析氮化铝表面材料去除的微观特性演变过程,对激光-超声双物理源条件下的单粒辅助磨削进行分子动力学(MD)模拟,对氮化铝分别进行传统磨削、激光辅助磨削、超声辅助磨削、激光-超声辅助磨削分子动力学分析,探讨不同工况下AlN的去除行为及损伤演化机制。结合LUAG过程中生成的氧化铝增强相,探明氮化铝表面力学性能提升原因。结果与传统磨削(TG)相比,LUAG过程的磨削力降低了50%,表面粗糙度Ra降低28.4%。AlN的表面硬度可达1298.6HV,相较于TG提高了25%。AlN表面摩擦磨损因数和亚表面损伤深度分别降低了50%和33%。结论LUAG生成的少量氧化铝被用作扩散强化的增强相,氧化铝相的生成实现了材料的弥散强化,填补了氮化铝原子间的空位以实现基体的材料硬化并提高耐磨性。该研究成果加深了人们对激光、超声波和磨粒加工耦合作用下材料去除和损伤的理解,同时促进和实现了氮化铝基底表面的高性能制造。

Aluminium nitride(AlN),as a covalently bonded compound with a fibrillar zincite-type crystal structure,has excellent properties such as super bandgap width(6.20 eV),high thermal stability(melting point of 3214℃),high breakdown field(1.2-1.4 mV/cm),and good ultraviolet penetration.Single-crystal AlN as an epitaxial substrate can significantly reduce the defect density in the device and effectively improve the performance of the device.In addition,aluminum nitride ceramics are versatile,mainly used in electronic heat dissipation,microwave communications,aerospace,heat exchangers,functional materials and other fields.However,the AlN meets the brittle fracture during the manufacture process and the using process.Therefore,a number of surface enhancement methods are applied in the machining of brittle materials,such as laser-assisted grinding(LAG),ultrasound-assisted grinding(UVAG),magnetic-field-assisted grinding(MFAG),chemical-mechanical polishing(CMP)process,and electrolytic internal dressing(ELID)grinding process.However,existing processing technologies are limited on improving mechanical properties and strengthening mechanisms of AlN ceramics.To fill these gaps,an efficient laser ultrasonic-assisted grinding(LUAG)was proposed and the molecular dynamic was applied,combining laser heating and ultrasonic vibration with abrasive grain processing technology.The AlN surface generation mechanism was investigated by LUAG.With the help of molecular dynamic,the microscopic material removal evolution process of AlN surface was studied from grinding force field,atomic phase transition,and subsurface damage depth field.The traditional grinding(TG),the LAG,the UVAG and the LUAG were used to machine the AlN surface.The specific AlN surface material removal mechanism and the surface material evolution mechanism were discussed respectively.The primary cause of the material transformation was that the stability of the transformed cubic AlN was smaller than the close-packed hexagonal AlN.The softened surface material caused by the high temperature and the high pressure resulted from the combination effect between the laser and ultrasonic.Meanwhile,the abrasive vibration of the wheel decreased the local high temperature region and formed a more uniform thermal distribution.To be specific,the laser energy is utilized to cause the atomic phase transition of the surface and the ultrasonic is used to decrease the surface material accumulation,which presents a smaller grinding force in LUAG processing technology.Therefore,the blank space is efficiently restrained.Furthermore,a small quantity of the generated Al2O3 is beneficial for the dispersion strengthening of the machined surface.It is the decreased grinding force that weakens the movement of the material dislocation.Compared to TG,LUAG produces 50%lower grinding forces and 28.4%lower surface roughness.The surface hardness of AlN is up to 1298.6HV,which is 25%higher than that of TG.The wear marks and subsurface damage depth on the surface of AlN are reduced by 50%and 33%,respectively.The small amount of alumina produced by LUAG is used as a reinforcing phase for diffusion strengthening to achieve material hardening and improve wear resistance of the substrate.The results of this research deepen the understanding of material removal and damage under the coupled effects of laser,ultrasonic,and abrasive processing while facilitating and enabling high-performance fabrication of AlN substrate surfaces.