Thermal oxidation behavior of WC–Co hard metal machining tool tip scraps

Abstract

The thermal oxidation behavior of scraps of WC–Co hard metal machining tool tips, which have worn in high speed machining of metals or alloys, is investigated with a view toward recycling WC–Co tool tip scraps into W and Co resources. Oxidation is a preliminary process in eco-friendly dry recycling of scraps including rare metals. High oxidation rate of the WC–Co tool tip scraps is achieved when they are fragmented into many pieces to avoid the resistance to oxidation of a protective CrAlN coating. WC–Co compound scrap is oxidized to WO3 and CoWO4 with a weight gain of 20% compared to its initial weight during isothermal oxidation at 900°C. It experiences a large volume expansion of more than 200%, producing a porous microstructure. Fragmented WC–Co scraps are oxidized in a parabolic-like behavior, whereas the initial gradual oxidation of mechanically untreated WC–Co scraps is followed by a rapid oxidation after 1.5h due to the breakdown of the CrAlN coating.