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Friction and Wear Behaviors of Hard-brittle Tool Materials at Elevated Temperatures

Author: ZhangHui
Tutor: DengJianXin
School: Shandong University
Course: Mechanical Manufacturing and Automation
Keywords: Hard and brittle tool Friction properties Wear mechanism High temperature
CLC: TG711
Type: PhD thesis
Year: 2011
Downloads: 433
Quote: 1
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Abstract

The advanced processing technology for dry cutting, high-speed cutting and hard cutting difficult materials can achieve efficient, clean processing is an important development direction of modern machining technology. Dry cutting, high speed cutting and hard cutting process, cutting heat generated a large amount of high cutting temperature, increased tool wear, friction and wear properties of the high temperature of the tool material put forward higher requirements. This paper systematically studied the high-temperature friction and wear characteristics of three typical hard and brittle tool materials (PCD tool of Al2O3/TiC ceramic cutting tools and carbide cutting tools), reveals the high temperature friction and wear mechanisms of hard and brittle tool materials for the design of the tool material and Choose provide a theoretical basis. Based on the tribology theory, hard and brittle tool materials friction coefficient and wear rate variation with temperature. The use of the Gibbs free energy function method of PCD cutting tool materials, of Al2O3/TiC ceramic tool materials and carbide tool material of each component may occur chemical reaction carried out thermodynamic calculations, from the theoretical analysis of the individual components may occur reaction of its oxidation products. The calculation results show that: the diamond grains of the PCD tool material at high temperatures may occur oxidation and graphitized binder phase Co generated by the oxidation reaction may occur Co3O4; Al2O3/TiC TiC ceramic tool materials may be oxidized TiO2; hard alloy of WC, Co, TiC may be oxidized to generate WO3, Co3O4 and TiO2. Three hard and brittle tool material at high temperature friction and wear characteristics of the material composition, microstructure, mechanical properties and test conditions (temperature, speed, load) hard and brittle tool materials friction coefficient and wear rate of the system. The results show that: the coefficient of friction of the PCD tool material increased with increasing temperature from 200 ° C to 600 ° C range, at 700 ℃ decreased. Ceramic Al2O3/TiC tool material friction coefficient with increasing temperature in the range of 200 ° C to 500 ° C increased the coefficient of friction began to fall in the range of 600 ° C to 800 ° C; wear rate increased with increasing temperature, its magnitude as 10-7 mm3 / (Nm). CARBIDE friction coefficient within the range of from 200 ° C to 600 ° C as the temperature rises and decreased; wear rate increases as the temperature rises, the magnitude of 10-6 mm3 / (Nm). Which, under the same conditions fine grain cemented carbide wear rate of about 50% of the coarse grain cemented carbide, TiC and TaC Add the wear resistance of carbide cutting tools also significantly increased. The three-dimensional morphology of the three kinds of hard and brittle tool worn surface, the cross-sectional profile and surface roughness has been systematically studied, compared to the wear scar morphology of different materials under different conditions, the cross-sectional contour and surface roughness evolution. The results showed that: the PCD tool wear scar cross-sectional contour is not obvious, depth range and its surface roughness is in the same order of magnitude. As the temperature increases, the depth of the wear scar cross-sectional profile of the ceramic tool material gradually increased to 800 ° C when the maximum depth is about 1.0μm. Carbide cutting tools material wear scar depth of the cross-sectional profile with temperature is significantly increased, especially at 600 ° C when the increase is very significant, wherein the of Al carbide material grinding marks the innermost reaches about 4.0μm. Three kinds of hard and brittle tool worn surface chemical reaction products generated temperature and composition. The study found that PCD tool material Co at 600 ° C oxidation generates C0304 started at 700 ℃ diamond graphite, binder phase Co and O2 in the air has a role in promoting the diamond graphitization: of Al2O3/TiC ceramic tool material in 600 ° C when a slight oxidation at 800 ℃ oxidation phenomenon is more obvious, the main oxidation product is TiO2; carbide tool material is slightly oxidized at 500 ℃ oxidation at 600 ℃, the main oxidation products by Oxidation of WC and Co, W03 and C03O4. Hard and brittle tool materials wear a comprehensive analysis of the surface morphology, surface composition, on the evolution of the hard and brittle tool materials wear and wear mechanism. : PCD tool material below 600 ℃ mainly adhesive wear, oxidation wear and graphitization of diamond began to appear in the 600 ° C, at the same time due to the loss of thermal expansion mismatch and Co, between the diamond grains and grain interior large the cracks. Ceramic tool material wear in Al2O3/TiC form with increasing temperature at 200 ° C to 500 ° C within a large loss by a single grain peeling gradually evolved into materials, oxidation wear after 600 ° C, 800 ° C when increasing oxidation wear. Carbide Tool Material 400 ° C or less, the main wear mechanism is the precipitation of the binder phase of Co and WC grain defects and the occurrence of cracks, and thus lead to the WC particles are pulled out from the friction surface and breakage. 500 ℃, the carbide tool material beginning of oxidation wear, the 600 ℃ wear surface oxide film composed by oxidation wear products began to appear. The grain refinement TiC and TaC Add to increase the wear resistance and oxidation resistance of carbide cutting tools. Oxidation wear appears to increase the amount of abrasion of the material at the same time due to the strength of the oxide, the lower the hardness, the friction surface has played a certain lubricating action, so that the coefficient of friction at high temperatures decreases.

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