Effect of two-step pretreatment on cobalt contents and surface roughness of tungsten carbide substrate prior to diamond coating

Abstract

Cemented tungsten carbide is the most widely used material for cutting tools. Due to extreme demands higher tool life several types of coating have been introduced to prolong the service time which include diamond coating. However cobalt binder in tungsten carbide prevents diamond to adhere well on the substrate and its content at the outer surface should be reduce to below 1%. Single step and two-step pretreatments have been studied by many researchers. But to date poor adhesion of diamond coating still an issue. In this work a two-step pretreatment was used to etch tungsten carbide with 6% cobalt (WC-6% Co) at the surface of the substrate in order to solve poor adhesion problem. First step with Murakami's reagent (2, 3, 6, and 20 minutes) and the second step of the process were carried out by etching in a solution of hydrochloric acid (30, 45, and 60 seconds) or a solution of sulfuric acid (10 seconds). The effect of them on Co cemented tungsten carbide samples in term of surface morphology, surface roughness, and cobalt removal from the surface were examined. It is found the longer Murakami etching time produces a slightly rougher surface than the shorter exposing time. Both acid solutions were used in the second pretreatment step able to reduce cobalt content to below 1% at all conditions regardless of etching time. The best combination of pretreatment process is 20 minutes Murakami etching and 45 seconds exposure time of hydrochloric acid that yields the higher surface roughness and the lowest cobalt content on the substrate surface.