Investigation of indentation response, scratch resistance, and wear behavior of tungsten carbide coatings fabricated by two-step interstitial carburization on tungsten

In the present study, we fabricated tungsten carbide (WC) coatings on tungsten using a recently proposed two-step interstitial carburization method and systematically investigated their mechanical behavior, including their responses to indentation, scratch, and wear. The coatings comprised WC and a very small amount of W₂C dispersed at the coating–substrate interface. The volume fraction of the carbide phases nearly reached 100 %, and the grain size of WC increased with increasing distance from the surface, thus exhibiting a distinct gradient microstructure with columnar WC grains. Indentation experiments on the coating surface showed that the coating attained a hardness of 25 GPa and cracks were generated when the indentation load exceeded 5 N. The fracture toughness of the coating was estimated to be 2.5 MPa m^1/2. The response of the coating to scratching was not sensitive to the scratching speed, and an increase in the scratching speed did not alter the geometry of the grooves, but it resulted in an earlier occurrence and a higher density of cracks; further, it leads to increased acoustic emission. Delamination of the coating did not occur when the normal load was in the range of 0–100 N, indicating that the adhesion strength of the coating was greater than 100 N. We studied the wear behavior using a ball-on-disc tribometer and found that the WC coatings exhibited extraordinarily high wear resistance, and both abrasive wear and adhesive wear mechanisms acted concurrently during wear. Therefore, we verified that the WC coatings prepared by interstitial carburization have a high hardness and excellent scratch and wear resistance.