A new design of tungsten carbide tools with diamond coatings
- PDF / 1,728,703 Bytes
- 11 Pages / 612 x 792 pts (letter) Page_size
- 93 Downloads / 277 Views
MATERIALS RESEARCH
Welcome
Comments
Help
A new design of tungsten carbide tools with diamond coatings Volker Weihnacht, W. D. Fan, K. Jagannadham, and J. Narayan Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7916
C-T. Liu Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (Received 2 October 1995; accepted 10 April 1996)
We have designed tungsten carbide tools with a new binder, which makes them suitable for advanced diamond tool coatings. The new tool substrates, made of tungsten carbide and nickel aluminide as binder phase, are produced by sintering and hot isostatic pressing, and also by combustion synthesis. The high temperature strength of nickel aluminide is key to superior tool performance at elevated temperatures. More importantly, nickel aluminides reduce the formation of graphite and promote diamond growth during chemical vapor deposition. Diamond films are deposited on the new tool substrates to investigate the nucleation density, adhesion, and wear resistance. The diamond coatings are characterized by scanning electron microscopy and Raman spectroscopy. The graphitizing tendency due to cobalt in the tungsten carbide tools was found to be a limitation to improve adhesion of diamond films. The new tool substrates with nickel aluminide binder have been found to exhibit good adhesion and wear resistance. The implications of these results in advanced cutting tools are discussed.
I. INTRODUCTION
Low pressure synthesis of diamond films lends itself to applications ranging from microelectronics and electronics packaging to advanced tool coatings.1,2 The high hardness, wear resistance, and the high thermal conductivity of diamond are unique features favorable for the use of diamond as tool coatings. However, adhesion of diamond to the tool substrate is an important factor that determines the useful life of the tool coating. Diamond tool coatings using chemical vapor deposition (CVD) will become attractive and replace the costly polycrystalline diamond tools (PCD) only when the adhesion and wear resistance are improved to prolong the tool life. Toward this goal, several attempts are being made presently. One of the factors responsible for the poor adhesion of diamond is the formation of graphite film between the diamond and the tool substrate. In particular, the presence of graphitizing elements such as cobalt in the tungsten carbide tool substrate (WC–Co) is responsible for poor adhesion of diamond.3 While cobalt is an important binder that is responsible for the high toughness of the cutting edge of the tool, development of the CVD diamond coatings necessitates the removal of the cobalt layer near the surface to minimize the formation of graphite layers. Surface cleaning and etching of cobalt has been used extensively, resulting in partial enhancement of adhesion.4,5 In addition, multilayer diamond composite coatings have been developed, resulting in an order of magnitude improvement in the adhesion.6,
Data Loading...
