Key Engineering Materials Vols. 353-358

Abstract: With different heat treatment, the microstructure and mechanical properties of ZK60 magnesium alloy were investigated. It can be concluded that heat treatment has great effect on mechanical properties of ZK60. With artificial aging after extruding, the precipitation of the second phase from the supersaturated solid solution significantly improved mechanical properties. It can greatly increase yield strength of ZK60 alloy, while the tensile strength has little change. For the combination of solid solution strengthening and age hardening, two opposite factors must be considered. On one hand, the solid solution strengthening and the later precipitation strengthening is good for alloy’s strength; on the other hand, the properties decrease as the grains grew under high temperature for a long time during solution heating.

Abstract: The AZ31 Mg alloy was upseted from 250°C to 500°C. In optical microscopy, as the temperature increases, the volume fraction of deformation twin will reduce to a minium and vanish. Simultaneously, some small dynamically recrystallized grains were observed at the boundaries of origin grains and twins. When temperatures rise from 350°C to 500°C , the volume fraction and size of DRX grains increases .By the compression test of the upsetting proof samples, the compressive strength reach a maxium, and reduce during further rising temperatures.

Abstract: This paper describes abrasive belt grinding experiment method and studies grinding force alternation regular pattern and feature in the grinding magnesium alloy process, at the same time the induction is verified the grinding force linear regression pattern by survey the force effect elements in the experiment, finally summarizes the result of the magnesium alloy grinding experiment .

Abstract: The microstructure characteristic and wear behavior of the severe deformation surface constitution of Ti-4Al-2V alloy were studied in this paper. The results show that the wear resistance of the deformed surface is much better than that of the coarse grain surface. And the wear mechanism of the nanocrystalline surface is different from that of the coarse grain surface. The former is particle wear mechanism of harder material and the latter is adherence wear mechanism. The influence factors on the wear resistance of the nanocrystalline surface have been discussed.

Abstract: Chemical mechanical polishing (CMP) is a widely used technique to achieve high level of global and local planarity required in modern integrate circuit (IC) industries and hard disk manufacturing process, etc., which pleas for concentrate researches. The main purpose of the present research is in an attempt to express the counterintuitive experimental aftermath: the ‘negative’ pressure, i.e., a suction force occurred in conventional commercial CMP process. A preliminary two tiers wafer-scale flow model for CMP is presented considering the roughness as well as the elasticity of the bulk pad substrate. Numerical simulations were conducted to elucidate the contact pressure and flow pressure distributions. The results show that a divergence region appears near the leading edge, which contributes to the suction pressure. A stress-richened area near the edges will give rise to over polishing. The research aftermaths agree well with the experiments, that validate the proposed analysis to some extend. This will shed lights on the mechanism of CMP process, which for a long time is considered as a black art where empirical or semi-empirical data are dependent upon to optimize the CMP parameters.

Abstract: The cantilevers of atomic force microscope (AFM) are mounted under a certain tilt angle, which is commonly assumed to have negligible effect on friction measurements in AFM. We present a theoretical study of the effect of the tilt angle on AFM based friction measurements. A method for correcting the friction coefficient between sample surfaces and AFM tips is also presented to minimize the effects of the tilt. The frictional forces between a silicon tip and a silicon surface at tilt angles ranging from 5 degrees to 25 degrees were measured. The results show that the measured friction coefficient increases with the tilt angle effectively, whereas the variation range of the corrected friction coefficient is within 10%.

Abstract: This paper makes decomposition of the profile curve of rifle worn marks by the wavelet transform, which can make its complicated structure feature to be clear. By reconstruction, the noise in the process of collecting and distraction can be removed, which makes the calculated fractal dimension more reliable. The research shows that wavelet transforms of profile curves can not only describe the surface topography of rifle worn marks, but also exhibits its essence characteristics. The paper provides a new method of quantitative examination and classification identification for rifle worn marks.

Abstract: In this paper, the theory of fractal geometry was used to study the barrel-rifle surface topography and correlation dimension method was adopted to calculate the fractal dimensions of the projectile worn marks shot from the barrels with different worn. The study showed that the different wears of barrel-rifle surface resulted in different fractal dimensions of the projectile wear surface and there was a correlation between the fractal dimensions of the projectile wear surface and the change of the barrel rifle surface. Therefore, through the rifle marks on the projectiles, not only the wear of the barrel’s internal surface can be analyzed, but the gun life also can be further estimated. The paper provided a new tool for analyzing the barrel-rifle surface wear.

Abstract: This paper presents mainly the nonlinear dynamics of the mechanical system with sectional frictions and combination friction coefficients. It is clear that the nonlinear dynamic characteristics of mechanical systems with sectional frictions are quite different from those of classical machinery, and have more precise and valuable in many practical projects. The expressions of various nonlinear forces are given firstly and the approximation solutions of the system are found with asymptotic method in nonlinear theory, and the combination friction coefficients and damping coefficients of the materials are obtained. Then some nonlinear dynamic characteristics of the system with sectional frictions are also discussed. The results are very important for designers of these machines.

Abstract: This paper mainly focus on vibration friction and discuss the dynamic characteristics of the friction under the vibration working condition. It is rather valuable to study such a special kind of friction vibration in engineering. Many practical projects have already proved that under the vibration working condition, the friction force between workpieces can be reduced obviously. Wear and damage of the machine parts can be obviously decreaed.The work efficiency can be improved greatly. The Characteristic of friction under the vibration working condition is described in the paper firstly. Two fundamental experiments illustrate the basic features of vibration friction. With the nonlinear dynamics and tribology of vibration friction, some key machinery is introduced in the paper briefly. The study of vibration tribology is attracting more and more interest of investigators.