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Numerical Investigation about Influence of WC Grain Distribution on Mechanical Properties of WC-Co Cemented Carbide

ABSTRACT Aiming at a finite element analysis approach for the estimation of mechanical properties in the real microstructure of WC -Co cemented carbide, the influences of WC grain distribution on the local deformation and mechanical behaviors were investigated in this research. Experimentally, two types of uniform alloy and nonuniform alloy with different WC grain sizes but same Co content, were designed and produced, and their hardness and microstructure were investigated by Vickers indentation test and SEM, respectively. The reconstruction of WC grain boundaries based on the SEM images was conducted to establish the finite element models of the real microstructures of WC grains and Co binder for the alloy. The mechanical properties, including E -modules, Poisson ratio and strength of the cemented carbide, were assessed, and the local deformation mechanisms were investigated by the finite element analysis (FEA). The FEA results show that the uniform alloy presents larger strength, which is consistent with the trend revealed by the measured hardness. Moreover, the FEA on the local deformation reveals that the more uniform stress distribution of the uniform alloy is the main mechanism for the enhancement in strength, and the stress concentration occurring at the WC/WC interfaces significantly deteriorates the mechanical behaviors.

KEY WORDS cemented carbide; mechanical properties; grain distribution; FEA

High Growth Rate Preparation of (lOO)-faceted Diamond Films by Microwave Plasma CVD

ABSTRACT: High quality (100)-faceted diamond films were deposited on silicon wafers by using a microwave plasma enhanced CVD reactor. The deposition rate was raised from 1 fim/h to 8.2 (i-m/h by increasing the CH4 concentration from 1% to 5%. The surface morphologies and qualities of deposited diamond films decreased with the increasing growth rate. Oxygen was added into the resource gases to improve the quality of diamond films under high growth rate. The value of FWHM (Full Width at Half Maximum) changes with the different concentration of oxygen. When the oxygen concentration was increased from 0.1% to 0.5%,the FWHM value of diamond film decreased. When the concentration was between 0.6% and 1.2%, the FWHM value of diamond film increased. And when the concentration was higher than 1.2% , the FWHM value of diamond film remained the same. Well faceted diamond films with pyramidal features were deposited when the flow rate of hydrogen was 300 cm3/min,the concentration of CH4 was 5% and the concentration of 02 was 0.5%.

KEYWORDS: microwave plasma; diamond film; CH4; 02; full width at half maximum

Effects of Y2O3 Addition on Microstructure and Properties of Ultrafine WC-6%Co Cemented Carbides

ABSTRACT The contents of Y203 and (Cr3C/VC/TaC) were doped as grain growth inhibitors in ultrafine WC-6%Co cemented carbides. The effects of Y203 on the microstructure, magnetic performance and mechanical properties of cemented carbides were researched. The microstructure and properties of the cemented carbide were measured by XRD detection, cobalt magnetic detection, coercive force test and other methods. Results show that Y203 can inhibit the grain growth .When adding 0.2%Y203(mass fraction), the alloy has the finest grain size and highest density, and the distribution of WC grain is uniform. Y203 can improve the magnetic properties of the alloys. The coercive forces of YG6 cemented carbides decrease and the magnetic saturation increase with the increase of the Y203 content, which shows that Y203 can reduce the carbon content of the alloy. At the same time, Y203 can improve the mechanical properties of the alloys. The hardness and TRS of WC-6%Co-0.8% (Cr3C/VC/raC)+0.2%TaC(mass fraction) cemented carbide are 94.1 HRA and 1 770 MPa, respectively.

KEY WORDS ultrafine cemented carbides; WC-6%Co; grain growth inhibitors; Y203

Effects of Molding Agents on Quality Control of Ultrafine Cemented Carbide

ABSTRACT: The influences of the sorts of molding agent and their adding manners on the quality control of ultrafine cemented carbide were researched with taking PEG and PW for example. The examinations of oxygen content, compacting force and microstructure of mixed powder show that the oxygen content of the mixed powder with adding PEG is higher than that of adding PW. Even the finer the grain is, the greater the difference is. The distribution uniformity of the molding agent added before wet milling is better than that of added after wet milling. PEG distributes more uniformly in the mixed powder than that of PW. Consequently it is the best for the molding agent to be added before wet milling, so that the distribution of the molding agent in the mixed powder is more uniform and the increase of oxygen content is a constant and in an acceptable level, which assures the quality of products.

KEY WORDS molding agent; ultrafine cemented carbide; distribution uniformity