Experimental investigation on induction brazing of diamond with Ni-Cr hardfacing alloy under argon atmosphere

In recent years direct brazing of a monolayer of diamond crystals on a steel substrate with active filler metals has gained tremendous importance in the industry, with a view to developing tools which can out-perform the conventional galvanically bonded diamond tools. An existing proprietary process uses a specially prepared Ni-Cr filler metal to facilitate its application on a steel substrate. The brazing is done either in a vacuum or a dry hydrogen furnace. The present study has shown that a commercially available Ni-Cr hardfacing alloy, flame-sprayed on a steel substrate with an oxyacetylene gun, could be used for direct brazing of diamond particles. Induction brazing was carried out in an argon atmosphere only for short durations. During brazing under such conditions, the chromium present in the alloy segregated preferentially to the interface with diamond to form a chromium-rich reaction product promoting the wettability of the alloy. It has been further revealed that under a given set of brazing conditions, the wettability of the Ni-Cr hardfacing alloy towards diamond grits primarily depended on its layer thickness. Such dependence resulted in significant variation of topographical features of the tool and its wear mode in simulated grinding tests.