This article, by Y. Li, H. Jiang, F. Wu and H. Li, describes the development of a new matrix of nanocrystalline Ni-Co alloy for the production of higher quality diamond tools. Containing about 8.5% Co and possessing colony-like morphology with a grain size of approximately 15 nm, the alloy is pulse plated by adding appropriate amounts of non organic grain size refiner Co and less amount of organic refiner saccharin to the electrolytic solution which was developed to produce pure nanocrystalline nickel deposit, a potential upgrading substitute for conventional polycrystalline matrix material. Compared with the pure nano-nickel, the Ni-Co deposit has a similar hardness but substantially higher tensile strength, which should be attributed to the remarkably reduced amount of saccharin (also responsible for introduction of sulphur and carbonate into the grain boundaries and reduction of the deposit strength and ductility) needed to produce a nanocrystalline structure. Performance testing of the diamond tools shows that the average service life is 15.5% higher than that for the pure nano-Ni samples.

Electroplating of diamond tools has become an accepted industrial production technique because electroplated composites have very good bonding characteristics [1-6]. The tools are made under normal temperature so that diamond grains suffer no loss from high temperature and can be retained tightly in the matrix. Moreover, the manufacturing technique is rather simple and does not require a great deal of investment in equipment. As a result, it has been used to produce many different kinds of electroplated diamond tools with complex shapes and high precision including hand and machine files, hones, cut-off discs, dressing tools, grinding wheels and geological drilling bits. These tools are in great demand for processing advanced materials such as grinding and machining superalloys and high-tech ceramics, metalworking hardened steel, bi-metals or metal matrix composites, sawing or drilling stone and concrete from huge quarries, shaping wood and laminates, grinding glass, etc. [1-6]. The industry has strict requirements on matrix materials for use in diamond tool fabrication because of diamond’s unique surface properties (e.g., bad wettability), i.e., diamond grains only adhere to the matrix by mechanical interlocking, rather than chemical bonding [4, 7]. They tend to fall off easily, therefore, the matrix must be of not only of high hardness and wear resistance to retain and mechanically impregnate diamond grains, but also be of enough toughness to ensure that the tools are able to bear heavy impact during operation. If the matrix is too brittle, it may break into pieces and drop out of the substrate. We developed a simple approach to producing better diamond tools at lower cost and with higher productivity by introducing nanocrystalline matrix of nickel deposit pulse-plated from modified Watts-type bath [8]. Indeed, nanocrystalline electrodeposits are chosen as the matrix of diamond tools due to: (1) their unusual wear resistance; (2) no problems caused by low thermal stability of nanocrystalline materials. In fact, because of the low thermal stability of diamond itself, diamond tools can be used only when water serves as a cooling medium. In spite of its desirable microhardness, the nano-nickel matrix is still not satisfactory in terms of embrittlement that results from the high addition of grain size refiner, i.e. saccharin, which is widely believed to be responsible for the embrittlement of nanocrystalline Ni and nickel alloys deposits [9, 10]. Therefore, non-organic refiner cobalt is introduced in the hope to reduce saccharin addition. This article details the fabrication technique of the new diamond tools and their performance and gives information about the nanocrystalline Ni-Co deposit composition, microstructure, hardness and tensile strength.

Conclusion

Electroplated diamond tools with a new matrix of nanocrystalline Ni-Co alloy deposit have been fabricated, and the performance testing shows that their average service life is 15.5% higher than that for the pure nano-Ni samples. This better performance might be the result of tighter impregnation of diamond in the matrix which possesses higher wear resistance (higher tensile strength and higher ductility in spite of the close hardness) and better wetting and bonding abilities with diamond particles.