Grindability of high-temperature alloy with ceramic alumina wheels

The grindability of high-temperature alloy by using ceramic alumina wheels is studied on the basis of extensive analysis of the grinding force, grinding temperature, surface roughness and topography of ground surfaces, residual stress, hardness distribution of surface layer, and morphology of the surface layer from a metallographic point of view. The grinding burn mechanism of high-temperature alloy is unveiled and the feasible grinding parameters to avoid burning are analyzed. Some conclusions are obtained as follows. Increasing the grinding depth or the wheel velocity makes grinding temperature and residual tensile stress of the surface rise, which deteriorates the surface topography. Appropriate liner velocity of the wheel is 18–22 m/s and the depth of grinding should not exceed 0.02 mm in grinding GH2132 alloy with ceramic alumina wheels to assure the surface quality. When a _p increases enough to cause grinding burn, the strengthening effect of particles γ′ in γ base decrease and the micro-hardness of the surface is obviously lower than that of the base material, which deteriorates the mechanical properties and heat resistance of GH2132 alloy. Results provide a theoretical and experimental basis for technical optimization in the grinding of high-temperature alloy with high efficiency and high quality.     

Tribological characteristics in high-speed grinding of alumina with brazed diamond wheels

In this work, two brazed diamond wheels fabricated by brazing in vacuum were used to grind alumina at different grinding speeds. During the process, the horizontal and vertical grinding forces were measured by a force measurement device. The grinding forces, specific grinding energy, and friction in grinding of alumina at low and at high speeds were investigated. The results show that the friction coefficient decreases with the increase of the grinding speed and also relates to the grinding mode. A nearly proportional relationship between grinding power per unit width (P _m ) and the rate of plowed surface area generated per unit time per unit width (S _w ) reveals the effects of friction in grinding and most of the grinding energy is expended by friction. The surface energy per unit area generated by plowing friction (J _s ) for high-speed grinding is found to be lower than for low-speed grinding.     

Photoresist for photochemical machining of alumina ceramic

The applicability of a cyclized polybutadiene rubber as a resist material for photoetching of alumina ceramic in phosphoric acid was studied. Stencil breakdown, change in the stencil thickness during etching, and etch factor were measured. It was found that this material post-baked at temperatures as high as 300°C for 30 min provided good resistance to severe attack by the acid at temperatures of up to 300°C. The effects of post-bake temperature, of etching temperature, of etching time, and of original slot width on etch factor are discussed.     

Biocompatible alumina ceramic for total hip replacements

Abstract

Their resistance to wear and biocompatibility make ceramics ideal materials for medical applications, such as implants. For over 30 years, pure alumina has been the dominant material for ceramic hip prostheses. Interest in alumina hip prostheses continues to grow, due to the relatively short life of polymer/metal prostheses, mainly resulting from osteolysis and aseptic loosening caused by polymer wear debris. Since its introduction by Boutin in the 1970s, substantial improvements have been achieved in the microstructure of medical grade alumina by improving purity and processing to give complete densification and fine, uniform grain sizes. A brief review is given of the types of alumina used in total hip replacement, the development of medical grade alumina, and methods of in vivo and in vitro investigation of alumina prostheses, with a focus on current knowledge of the damage observed on alumina prostheses. Particular attention is paid to wear mechanisms and the influence of materials properties on wear behaviour. A region of relatively severe wear, known as stripe wear, is widely observed on retrieved alumina hip prostheses. This type of wear can now be replicated in vitro in joint simulators by the introduction of a 'microseparation' motion during the test cycle. Finally, the future of ceramic hip prostheses and development of the next generation of ceramics for hip prostheses is discussed.     

基于ANSYS的低压铸造铝合金轮毂的优化设计

本文对低压铸造铝合金轮毂的参数化设计进行了研究及分析,以16× 6.5J为应用实例,按照轮辋的国家标准,建构了车轮的Pro/Engineer实体模型,并将模型导入ANSYS,进行强度分析与优化设计.优化结果表明,车轮的重量有了显著的减少,车轮的最大应力接近材料的许用应力,且分布更合理.     

普通高速钢刀具加工高温合金零件

介绍普通高速钢立铣刀加工GH864高温合金时的切削特点 ,分析加工中的磨损机理 ,通过改变刃磨角度 ,选取了合理的几何参数 ,并给出切削用量     

A comparative study of residual stress and affected layer in Aermet100 steel grinding with alumina and cBN wheels

Residual stresses induced by finish machining processes have significant effect on fatigue strength of ultra-high strength steel in large structures. In this study, an experimental investigation was carried out to explore the residual stress and affected layer in grinding Aermet100 by using a resin bond white alumina (WA) wheel and cubic boron nitride (cBN) wheel, respectively. The grinding force and temperature were measured, and then the affected layer of residual stress, microhardness, and microstructure by a WA and a cBN wheel was obtained. The comparisons of surface residual stress studies and thermal–mechanical coupling mechanism on the affected layer were discussed in light of the current understanding of this subject. Experimental results show that grinding with cBN wheel can provide compressive residual stress and a smaller affected layer owing to its better thermal conductivity; the coupling effect of wheel speed and grinding depth plays a more significant role on surface residual stress; when grinding with parameters v _w?=?18 m/min, v _s?=?14 m/s, and a _p?=?0.01 mm, compressive residual stress and hardening effect appeared on ground surface, and the depth of residual stress layer is 40~50 μm; the depth of hardened layer is 30~40 μm and the depth of plastic deformation layer is 5~10 μm.     

Robust design and optimisation of aerospace alloy grinding by different abrasive wheels

Grinding operations are widely used for aerospace materials. The quality and economy of grinding depend on the adequate selection of grinding conditions for the materials to be ground. This paper presents a robust experimental research of grinding wheel performance using experimental signal-to-noise ratio (SNR) designs and multi-objective optimisation methods. Combining orthogonal design and SNR can solve many issues of comprehensive assessments based on different characteristics. The assessment of grinding performance takes account of grinding control parameters as the inputs and the roughness, grinding ratio, grinding forces and temperature as the outputs. The optimisation of conventional and superabrasive grinding processes was based on a single-objective or multi-objective optimisation, where a ranking measure method was employed with weighted factors based on a performance index scoring system. The selection of weighted factors depends on different quality and economic requirements. An appropriate strategy was developed for grinding nickel-based aerospace alloys with different wheels.     

Experimental analysis on Nd:YAG laser micro-turning of alumina ceramic

Laser micro-turning is a micro-machining strategy to machine cylindrical workpiece of hard-to-process materials such as ceramics. Laser micro-turning method is in high demand in the present high-precision manufacturing industries because of its wide and potential uses in various engineering fields such as automobile, electronics, aerospace, and biomedical applications, etc. In the present research, the experimental analysis of Nd:YAG laser micro-turning of cylindrical-shaped ceramic material has been made to explore the desired laser output responses, i.e., depth of cut and surface roughness by varying laser micro-turning process parameters such as lamp current, pulse frequency, and laser beam scanning speed. Single laser beam has been utilized for successful micro-turning operation. Experimental results revealed that the laser machining process parameters have great influences for achieving desired laser micro-turned depth and surface roughness characteristics during laser micro-turning of alumina ceramics. SEM and optical photographs have also been analyzed for better understanding of the laser micro-turning process for different parametric settings.     

Wear behaviour of alumina based ceramic cutting tools on machining steels

The advanced ceramic cutting tools have very good wear resistance, high refractoriness, good mechanical strength and hot hardness. Alumina based ceramic cutting tools have very high abrasion resistance and hot hardness. Chemically they are more stable than high-speed steels and carbides, thus having less tendency to adhere to metals during machining and less tendency to form built-up edge. This results in good surface finish and dimensional accuracy in machining steels. In this paper wear behaviour of alumina based ceramic cutting tools is investigated. The machining tests were conducted using SiC whisker reinforced alumina ceramic cutting tool and Ti[C,N] mixed alumina ceramic cutting tool on martensitic stainless steel-grade 410 and EN 24 steel work pieces. Flank wear in Ti[C,N] mixed alumina ceramic cutting tool is lower than that of the SiC whisker reinforced alumina cutting tool. SiC whisker reinforced alumina cutting tool exhibits poor crater wear resistance while machining. Notch wear in SiC whisker reinforced alumina cutting tool is lower than that of the Ti[C,N] mixed alumina ceramic cutting tool. The flank wear, crater wear and notch wear are higher on machining martensitic stainless steel than on machining hardened steel. In summary Ti[C,N] mixed alumina cutting tool performs better than SiC whisker reinforced alumina cutting tool on machining martensitic stainless steel.     

Modeling and microstructural modification of alumina ceramic for improved tribological properties

Very simplified models were deduced for identifying important factors influencing friction and wear of ceramics in unlubricated sliding contact. Based on the theoretical predictions, laser surface alloying was used for modifying alumina ceramic by adding hafnia. Tribological tests were run on the modified ceramic, monolithic alumina and two different cutting ceramics on the base of alumina under conditions of unlubricated reciprocating sliding motion against Al₂O₃ balls. The friction coefficient and linear wear of the sliding pairs were substantially reduced and the transition from mild to severe wear shifted to higher applied surface pressure for the microstructurally modified ceramic compared with the monolithic alumina or the cutting ceramics, respectively.     

Improved performance of grinding wheels in machining plastic steel and alloy blanks

Formulas are proposed for the forces required to rupture the bonds between metal buildup and the abrasive grains of a grinding wheel. The most effective methods of reducing wheel deterioration due to metal buildup are established.     

牙科烤瓷合金的发展现状及趋势

现代口腔修复技术的发展和"绿色修复"概念的提出就要求口腔修复材料应具有良好的综合机械性能和优良的生物安全性能.本文根据临床口腔修复的基本要求,从生物安全性和金瓷结合性的基本角度出发,对现有的几大类牙科烤瓷修复合金进行了全面的总结.概述了各类合金的主要成分、元素作用、性能特点厦应用现状,并讨论了目前我国烤瓷修复的基本状况和存在的问题,从口腔修复学发展方向和我国的国情出发,提出了我国烤瓷合全的发展方向.     

Fabrication and performance of porous metal-bonded CBN grinding wheels using alumina bubble particles as pore-forming agents

Porous metal-bonded cubic boron nitride (CBN) composite blocks and grinding wheels were fabricated using alumina bubble particles as pore-forming agents and Cu-Sn-Ti alloy as bonding material. The influence of the porosity on the mechanical strength of the porous composite blocks was examined by means of three-point bending tests. The microstructure of the blocks fracture surface was characterized. The grinding performance of the porous metal-bonded CBN wheels was investigated and compared with the vitrified CBN wheel. Results show that the bending strength of the porous metal-bonded blocks is varied from 51 to 103 MPa when the porosity is changed from 8 to 45 %. High blocks strength is mainly attributed to the firm bonding formed at the sintering interface of Cu-Sn-Ti/CBN grain and Cu-Sn-Ti/alumina particles. Porous metal-bonded CBN wheels exhibits good grinding performance during grinding nickel superalloy due to the abundant chip storage space.     

High-energy metal ion implantation for reduction of surface resistivity of alumina ceramic

In this work, the possibility to increase the surface conductivity of ceramic insulators through their treatment with accelerated metal ion beams produced by a MevvaV.Ru vacuum arc source is demonstrated. The increase in surface conductivity is made possible due to experimental conditions in which an insulated collector is charged by beam ions to a potential many times lower than the accelerating voltage, and hence, than the average beam ion energy. The observed effect of charge neutralization of the accelerated ion beam is presumably associated with electrons knocked out of the electrodes of the accelerating system of the source and of the walls of the vacuum chamber by the accelerated ions.     

Surfaces ground by standard wheels and wheels with graduated grain sizes

A second-order orthogonal experiment design is used to establish how the grinding conditions affect the roughness of surfaces ground by standard wheels and wheels with graduated grain sizes.     

Sliding wear behaviors of in situ alumina/aluminum titanate ceramic composites

In situ alumina/aluminum titanate ceramic composites were prepared by spark plasma sintering with two kinds of alumina/titania powders, which are microsized irregular particles (referred to M powder) and microsized spherical particles composed of nanosized grains (referred to N powder). The phase constitution and microstructures of the powders and as-prepared ceramic composites were characterized by using X-ray diffractometer (XRD) and scanning electron microscope (SEM). The sliding wear behaviors of two alumina/aluminum titanate ceramic composites were investigated by ball-on-disc wear test with varied normal loads. The worn surfaces of ceramic composites and counterpart Si₃N₄ balls were characterized by using SEM equipped with X-ray energy dispersive spectroscopy (EDS). The results showed that the wear volume of two ceramic composites increased with increasing the normal load. Under the same normal load, the wear volume of N composite (obtained from the N powder) was higher than that of M composite (obtained from the M powder). Two different behaviors were identified: N composite showed intergranular fracture and grain pull-out; however, the surface reaction layer formed in M composite presented plastic deformation. The different behaviors are controlled by two different mechanisms, brittle fracture mechanism for N and tribochemical reaction mechanism for M. The different wear behaviors for the two ceramic composites were discussed in detail.