Interface Bonding Between Ti-Coated CBN and Vitrified Bond

The metallization of cubic nitride boron (cBN) surface can improve the bonding between cBN and other substrates. An effective way of metallization is to coat cBN with the metal titanium. The homogeneous titanium coating on cBN surface was obtained through vacuum slow vapor deposition (VSVD) technique in this present work. X-ray diffraction (XRD) was carried out to analyze the interface structure of Ti-coated cBN deposited at the different temperatures. Ti-coated cBN composites bonded with SiO2-R2O-B2O3 vitrified bond were prepared by hot-press sintering method. The composition was investigated by the mean of electron dispersive spectrum (EDS) and the bending strengths were measured using three-point bending experiment. The results showed that the reaction between the metal Ti and cBN occurred at the deposition temperatures of 600~950°C during depositing process. The resultant was TiN which grew on cBN surface below 800°C but borides of titanium including TiB and TiB2 formed at above 800°C. The coating consisting of these compounds not only protected cBN from corrosion during sintering process, but also realized the strong bonding between the cBN grit and the bond. The latter was confirmed by the result that the bending strength of Ti-coated cBN composite increased evidently in comparison with that of uncoated cBN. The theoretic calculation according to composite materials strength model showed that the interface bonding strength between cBN and the vitrified bond increased by 20 MPa owing to the coating at the deposition temperature of 800°C. Introduction Cubic BN (cBN) is considered as the excellent tool material to machine ferrous metals. The porous vitrified bond cBN composites have a great potential in high effective and high speed super finishing on the numerical control grinding machines. The considerable attentions have been focused on the manufacture process and the properties of the composites [1-5]. The protection of B2O3 film on cBN surface results in high thermal stability of cBN crystal. However the film dissolves into alkali vitrified bond and the cBN crystal decomposes in presence of oxygen or water during hot-press sintering process. The reactions formulas are as follows: 4BN+2Na2O·K2O+3O22Na2O·K2O·B2O3+2N2 2BN+Na2O·K2O+3H2ONa2O·K2O·B2O3+2NH3 As a result, the cBN crystal is corroded acutely and the edges and corners as cutting edges become smooth and blunt. The gases releasing from the interface between cBN and the bond form many holes that cause the cBN grits to separate easily from vitrified matrix. In addition, due to the corrosion cBN grits become smaller, moreover, excessive corrosion pits on the original flat planes lead to the decrease of the cBN compressive strength. Coating cBN with suitable materials on the surface is an effective way to solve the above problems. In this paper Ti-coated cBN grits were prepared using vacuum slow vapor deposition technique [6-7] and used to fabricate vitrified bond cBN composites. XRD, EDS and mechanical properties measurement were carried out to investigate Ti coating/cBN interfacial reaction process, interfacial composition of Ti-coated cBN/bond and the effects of Ti coating on interface bonding between Ti-coated cBN and vitrified bond. Key Engineering Materials Online: 2004-03-15 ISSN: 1662-9795, Vols. 259-260, pp 14-18 doi:10.4028/www.scientific. net/KEM.259-260.14 © 2004 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-13/03/20,19:03:34) Journal Title and Volume Number (to be inserted by the publisher) 15