Abstract
Air plasma spray coatings of three different WC-12%Co powders based on the powder manufacturing methods were conducted. Mixed powders composed of S&F (Sintered and Crushed) WC-l2%Co which revealed the best wear resistance in this study and NiCrSiB with different ratio(25:75(B1), 50:50(B2), 75:25(B3)) were also evaluated. The best wear resistance of S&F WC-l2%Co coating was mainly due to its high hardness related with large amount of homogeneously and/or uniformly distributed total carbides and low porosity. The wear resistance of blend coatings increased with increasing WC-l2%Co weight percent but was not noticeably improved compared to that of WC-12%Co coatings. The dominant wear mechanisms of WC-12%Co coatings were combined actions of adhesive wear. carbide particle fragmentation, and tribo-film formation by material transfer on which fatigue crack formed and propagated under repeated loading leading to delamination. In the case of blend coatings, the dominant mechanism of Bl and/or B2 coating was observed to be the following sequence : abrasive wear(ploughing or scratching) in the soft NiCrSiB coating $layers{\rightarrow}carbide$ extrusion and $fragmentation{\rightarrow}crack$ formation and propagation at the rear of abrasive $mark{\rightarrow}$separation of coating layers and delamination as well as adhesive wear (adhesion). But, B3 coating which contained the 75wt% of WC-12%Co showed both the wear mechanism of B1 and/or B2 coating and that of WC-12%Co coating.