Structure and Properties of Diamond Grits Coated with Corundum Micron Powders

Abstract: Diamond is widely applied in cutting and grinding tools as the hardest and anti-wear material. Coating diamond surface with suitable materials is an effective method to improve the adhesion between diamond and matrix. Corundum-coated diamond, a new kind of diamond abrasive is developed for resin bond grinding applications. Diamond grits are coated with the corundum micron powders by the binding of a kind of vitreous material. The very rough and spiny morphology of the coated grit gives outstanding bond retention in resin matrix and avoids the premature loss of diamond from tools. The strength and oxidation resistance of diamond grits improve due to the coating protection effect. Industrial test results show that the grinding efficiency with an abrasive wheel made with corundum-coated diamond grits increases by more than 30% and the life of the wheel increases by 30~35%. Introduction Diamond grits give superior cutting performance for machining of rock and other nonferrous materials. The great attentions have been focused on the wear of diamond-segmented tools and the choice of bond type [1-4]. However, the waste of expensive grits associated with premature loss from tools is unexpected for toolmakers and users. One effective way to improve the adhesion between diamond and matrix is to coat diamond surface with suitable materials. Two types metals are usually selected as coating materials. One is carbide-forming metal as titanium, tungsten etc, which can form chemical bond between diamond and metal matrix [5-9]. Diamond grits coated with above materials have been developed for metal bond tools. The other is the metal such as nickel or copper. The thick coating layer of the metal assists the retention of diamond grits by keying into the bond. Cu, Ni-coated diamond grits are suitable for resin bond application. The metal coating, like Cu or Ni, can mechanically grip the friable grit to reduce its pullout and improve the adhesive strength between the grit and resin bond, thereby increasing the tool life greatly. However, designed for resin bond grinding wheels, the irregular friable grit is necessary for self-sharpening ability, which ensures the presence of new sharp cutting edges and keeps free cutting. The thick tough coating lowers the grit friability and cutting efficiency. The aim of this paper is to seek a suitable coating material that possesses the advantages of Cu or Ni coating and has no hurts to self-sharpening property. A new method has been developed to coat diamond with corundum micron powders, which are of low toughness and high strength. It is hoped that the new coating can meet all above-mentioned requirements. The coating process and the properties of corundum-coated diamond are introduced in this paper. Experimental Coating Process. Diamond grits were mixed with fine borosilicate glass powders; a thin layer of glass powders homogeneously bound on diamond surface, and then covered with corundum micro-powders. Various sizes of corundum micro-powders were selected to determine the effect of corundum particles on the coating properties. Table1 shows the range of glass compositions. The Key Engineering Materials Online: 2003-09-15 ISSN: 1662-9795, Vol. 250, pp 94-98 doi:10.4028/www.scientific.net/KEM.250.94 © 2003 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-13/03/20,20:10:19) Key Engineering Materials Vols. 95 covered diamond grits were sintered at 800 for 1h, then the corundum-coated diamond was obtained. The phase composition of corundum-coated diamond was investigated by D/max-rB diffractometer using CuKα radiation. The compressive strength of the grits was measured by a single grit method. Thermogravimetry analysis (TGA) was used to measure the temperature under which oxidation took place on the coated grits. Table 1 The composite scope of vitreous bond [wt%] SiO2 B2O3 Al2O3 Li2O Na2O K2O MgO CaO ZnO 48~100 5~45 1~15 0~18 0~18 0~20 0~12 0~16 0~18 Results and Discussion Morphology and Phase Composition of Corundum-Coated Diamond. The morphology of coated diamond grits is shown in Fig.1. The original shape and surface texture of diamond grits can not be seen due to the corundum coating, and the very rough, spiny and nodular surface presents. Therefore, when the grits with the corundum coating are used in resin bond tools, excellent bond retention and long tool life may be expected. Fig.1 The morphology of corundum-coated diamond 30 35 40 45 50 55 60 65 70 75 80 0 500