Preparation and properties of VC + Ni cermets with controlled carbon-to-metal ratio
- PDF / 3,385,986 Bytes
- 11 Pages / 594 x 774 pts Page_size
- 87 Downloads / 136 Views
m majority of cutting tool inserts are fabricated from cemented carbides which contain a hard abrasionresistant carbide dispersed in a relatively soft matrix to achieve both good abrasion resistance and fracture toughness. Over the years, considerable research effort has gone into understanding the role of microstructural features such as carbide grain size and distribution, binder content, mean-free-path, and so forth in controlling the mechanical behavior of these cermets. However, these efforts have not been accompanied by a parallel effort to develop an understanding of the relationship between the fundamental properties of the constituent phases and overall performance of a cermet system. Consequently, no guidelines that would be useful in developing new and improved cutting tool materials have been developed. To do so, it is necesary to investigate m o d e l cemented carbide systems, where selected properties of the carbide phase, the binder phase, and the carbide/binder interface can be systematically and independently varied in a controlled manner and their influence on the mechanical properties of the cermet examined. One of the fundamental properties of the carbide phase is its cleavage energy. Prior work at Martin Marietta Laboratories has shown that the cleavage energy of VC x can be changed in a controlled manner by varying the carbon-to-metal ratio, x. 1,2The nominally cubic phase field in VC extends from VC0.75 to VC0.89 below 1000 ~ but within this range longrange ordering in the carbon sublattice has been R. K. VISWANADHAM, formerly with Martin Marietta Laboratories, Baltimore, is now Staff Research Engineer, Materials Research, Reed Rock Bit, P.O. Box 2119, Houston, TX 77001. W. PRECHT is with Martin Marietta Laboratories, 1450 S. Rolling Road, Baltimore, MD 21227. Manuscript submitted July 16, 1979.
demonstrated for particular compositions. DeNovian e t X-ray studies, determined a cubic superlattice near VsC 7, and Venables e t a l 4 using electron microscopy and diffraction, determined a trigonal structure near V6C 5. The different ordered arrangements are induced by the electronic structure to optimize the bond energy between all neighboring metal atoms. 5 The electronically-induced ordering effects that occur in VC have an important influence on the mechanical properties of the material. It has been demonstrated that the ductile-brittle transition temperatures of V6C 5 and VsC 7 are determined by the temperature at which the materials disorder. 6 The electronic effects that control the high temperature mechanical properties of VC monocrystals also control their properties at ambient temperature. The fracture surface energy as a function of the carbon-to-metal ( C / M ) ratio has been measured in VC and shows a maximum at VCo.s4. To determine whether the cleavage energy of the carbide is an important parameter in determining the mechanical behavior of cermets, a cermet system must be selected where VC x is the hard phase and x can be varied in a controlled manner without drastically altering t
Data Loading...
