DETONATION SPRAYED COATINGS OF (Ti, Cr)B₂–NiAlCr COMPOSITE MATERIALS
ІI. MECHANICAL AND TRIBOTECHNICAL PROPERTIES

Abstract

The mechanical and tribological properties of detonation sprayed coatings from composites in the (Ti, Cr)B₂–NiAlCr system were studied. The influence of various methods for the preliminary treatment of substrate surfaces and the refractory-to-metal ratio in the material to be sprayed on the adhesion strength, σad, of the coating to the substrate were analyzed. Spraying a sublayer had no significant effect on the adhesion of coatings. The adhesion strength σ_ad increased by 25–30% with the metal component content changing from 25 to 75%, while σ_ad = 120–145 MPa even at 25% NiAlCr. The hardness of the coatings is within rather narrow limits (HV_0.2 = 7–12 GPa), though the refractory-to-metal ratio varies over a wide range. The coatings containing a minimum amount of the metal component (25%) were predicted to have higher hardness, HV_0.2 = 10–12 GPa, despite the fact that it was almost half the hardness of a compact sintered material. At equal contents of the refractory and metal components, HV_0.2 = 9–10 GPa; for the material containing 75% of the metal component, HV_0.2 = 7–8 GPa. The tribotechnical properties of the coatings were studied in dry sliding friction conditions by ball-on-disk test. At the initial friction stage, high pressures appear 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 scraping 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%) ensures high abrasion resistance and adhesion.