表面宏观残余应力测试实验

介绍一例用X-射线衍射法(sin2ψ法)测定材料表面宏观残余应力的实验,可使学生掌握一种实用测试方法的同时。

45~#钢表面激光熔覆自熔性镍基碳化钨粉末

目的提高45#钢的表面性能。方法利用IPG光纤激光加工系统,采用不同的工艺参数在45#钢表面激光熔覆自熔性镍基碳化钨粉末,对熔覆层的宏观表面(平整度、表面硬度、裂纹情况)及金相组织、显微硬度分布进行对比分析。结果在激光功率为1200 W、扫描速度为2 mm/s、送粉电压为7 V时,获得的熔覆层宏观表面相对平整光滑,平均洛氏硬度约是基体的2.5倍。由微观组织分析得知,熔覆层及界面处无裂纹、气孔等缺陷,熔覆层中上部组织晶粒细小,沿熔覆层与基体交界处向外,晶粒呈现柱状晶及等轴晶,组织性能良好,基体与熔覆层间冶金结合比较牢固。熔覆层显微硬度分布比较均匀,并且与基体相比提高了约1.5倍。结论 45#钢表面机械性能得到提升,在其表面激光熔覆自熔性镍基碳化钨粉末具有可行性和研究价值。

激光熔覆原位自生碳化钨陶瓷涂层的研究

使用IPG光纤激光器YLR-3000激光加工系统,在45钢表面通过激光熔覆自熔性碳化钨陶瓷涂层,提高熔覆层组织和性能。对涂层的硬度和显微组织进行分析。结果表明:激光功率1200 W、扫描速度2 mm/s、送粉电压7 V时,熔覆层的平均洛氏硬度约是基体平均硬度的2.6倍;熔覆层及界面处无裂纹、气孔等缺陷,熔覆层中上部的晶粒细小,沿熔覆层与基体交界处向外晶粒呈现柱状晶及等轴晶,组织性能良好,基体与熔覆层间冶金结合牢固。

4 in InSb晶片加工技术研究

在红外探测领域,InSb材料已经大规模地被用于制造3~5μm波长范围的焦平面阵列探测器。对更大规模、更高性能探测器的需求日益增长,而该类探测器需要在更大尺寸、更高质量的晶片上制备。所以,对4 in InSb晶片加工技术进行了研究。通过优化研磨、抛光工艺参数,最终获得总厚度偏差小于等于10μm、翘曲度小于等于20μm、表面粗糙度小于1 nm、表面质量优的4 in InSb晶片,提高了加工效率,能够满足大规模高质量红外焦平面探测器的使用需求。

Design of a device for precision shaping of grinding wheel macro-and micro-geometry

The selected modifications to the construction of grinding wheels were described which facilitate an increase in the material removal rate （grinding wheels with conic chamfer and grinding wheels with microdiscontinuities on the active surface）. Using these background details, a suggested thesis was put forward regarding the need to develop a device which will allow for the shaping of the macrogeometry of the grinding wheel （cylindrical and conical surfaces） and the microdiscontinuities within the dressing operation simultaneously. The device was presented and prepared in two functional variants （horizontal and vertical mounting of the motor）, then a prototype was described. An example of the grinding wheel active surface, shaped by using this device, was also presented. The theoretical analysis and experimental verification performed determine that the error of shaping the conic chamfer angle within the range of 0-1.5°, using the developed device, is approximately ±3%.

A novel method to improve interfacial bonding of compound squeeze cast Al/Al-Cu macrocomposite bimetals:Simulation and experimental studies

A facile and innovative method to improve bonding between the two parts of compound squeeze cast Al/Al-4.5 wt.%Cu macrocomposite bimetals was developed and its effects on microstructure and mechanical properties of the bimetal were investigated.A special concentric groove pattern was machined on the top surface of the insert(squeeze cast Al-4.5 wt.%Cu) and its effects on heat transfer,solidification and distribution of generated stresses along the interface region of the bimetal components were simulated using ProCAST and ANSYS softwares and experimentally verified. Simulation results indicated complete melting of the tips of the surface grooves and local generation of large stress gradient fields along the interface. These are believed to result in rupture of the insert interfacial aluminum oxide layer facilitating diffusion bonding of the bimetal components. Microstructural evaluations confirmed formation of an evident transition zone along the interface region of the bimetal. Average thickness of the transition zone and tensile strength of the bimetal were significantly increased to about 375 μm and 54 MPa, respectively, by applying the surface pattern.The proposed method is an affordable and promising approach for compound squeeze casting of Al-Al macrocomposite bimetals without resort to any prior cost and time intensive chemical or coating treatments of the solid insert.

Micro-and macro-fractures of coarse granite under true-triaxial unloading conditions

We studied the mechanical behavior of rock under different boundary conditions, based on the fractal characteristics of fractures in terms of microscopic and macroscopic investigations. Three rectangular granite specimens of similar dimensions were tested by a triaxial rock testing machine under uniaxial compression （UC）, confined compression （CC） and true-triaxial unloading conditions （RB） under rock burst boundary conditions. The failure processes of these specimens were investigated via examinations of their fracture behavior on a macro-scale by laser profilometers and on a micro-scale by a scanning electron microscopic （SEM） imaging technique. The SEM images, showing the spailing features of RB frag- ments, are compared with the grain dislocations under UC and CC conditions. Based on a variogram method, two fractal parameters, i.e., fractal dimensions （Dr^d） and the scale dependent fractal parameter Kv, were induced to present the surface roughness of scanning profiles in all directions. The fitted ellipses of Dr^d distribution show that RB surface has the smallest eccentricity, followed by the CC surface, while the UC surface had the largest eccentricity. As a result of this assessment, we conclude that rocks are affected by shear traction in an intermediate stress direction, which will cause fractures generated during rock bursts to twist rather than to tilt as shown in the uniaxial compression and the confined compres- sion tests.