Detonation-Sprayed Coatings of (Ti, Cr)B2–NiAlCr Composite Materials II. Mechanical and Tribotechnical Properties

Abstract

The mechanical and tribotechnical properties of detonation-sprayed coatings produced from (Ti, Cr)B2–NiAlCr composites were studied. The influence of various preliminary substrate treatment methods and refractory-to-metal ratio in the spray material on the coating–substrate adhesion strength, σad, was analyzed. Spraying a sublayer had no significant effect on the coating adhesion strength. The adhesion strength σad increased by 25–30% with the metal content changing from 25 to 75%, while σad = 120–145 MPa even at 25% NiAlCr. The hardness of the coatings changed within rather narrow limits (HV0.2 = 7–12 GPa), but the refractory-to-metal ratio varied over a wide range. The coatings containing a minimum amount of the metal component (25%) were predicted to have higher hardness, HV0.2 = 10–12 GPa, though it was almost half the hardness of the sintered compact material. At equal contents of the refractory and metal components, HV0.2 = 9–10 GPa; for the material containing 75% of the metal component, HV0.2 = 7–8 GPa. The tribotechnical properties of the coatings were studied in dry sliding friction conditions with ball-ondisk tests. At the initial friction stage, high pressures appeared in the contact zone (P ≥ 500 MPa). Therefore, in addition to high hardness, the coatings should have high strength. At 50–75% (Ti, Cr)B2, besides abrasion processes, brittle fracture and spalling of the coatings occurred. The best characteristics were shown by the coating produced from the material containing 25% (Ti, Cr)B2. Since the (Ti, Cr)B2 particles are fine, wetted well by the NiAlCr alloy, and uniformly distributed over the starting material and associated coating, even their relatively low content (25%) promotes high abrasion resistance and adhesion.