Sand erosion performance of CVD boron carbide coated tungsten carbide

The erosion performance and the interaction between the micro-mechanisms of erosion and the microstructure of a chemical vapour deposited baron carbid e coating are presented. Samples were tested using both water-sand slurry a nd air-sand jet impingements at 90 degrees incidence. Tests used angular qu artz sand with a mean diameter between 135 and 135 mu m and jet impingement velocities between 16 and 268 m s(-1). The chemical vapour deposition (CVD ) baron carbide coatings were 15-20 mu m thick and deposited on a range of substrates of sintered tungsten carbide with 6 to 15 wt.% metal binder. The results, relative to the erosion resistance of the uncoated substrates, sh ow the coatings to have higher resistance (10 times) under lower energy imp acts but similar resistance at higher energy impacts. The sintered baron ca rbide had a similar erosion resistance to that of sintered tungsten carbide except at high energy impacts where it outperforms tungsten carbide and CV D boron carbide by a factor of 2, The performance of these coatings against erodent mass and impact energy are discussed and related to the nano and m icro brittle fracture mechanisms identified by detailed microscopy and pred icted by Hertzian cone crack theory. Partial concentric spalling of the coa ting was also evident in regions where circular Hertzian surface cracks are present. These erosion mechanisms, primarily nano-chipping and crack propa gation, are also related to the microstructure and composition identified b y XRD analysis and Raman spectroscopy. These results, in conjunction with f racture toughness and micro-hardness measurements, suggest that the coating composition is not pure B13C2 but has less erosion resistant forms of boro n carbide present such as B50C2. (C) 1999 Elsevier Science S.A. All rights reserved.