STRUCTURAL FEATURES OF THE Cr₃C₂–NiCr AND Ni–Cr–Fe–B–Si COATINGS PRODUCED BY MULTICHAMBER DETONATION SPRAYING

Abstract

The detonation spraying of coatings from fine composite materials is analyzed in the paper. The use of detonation coatings was found to improve the properties of machines and mechanisms and extend their life, while maintaining their functional performances over long-term operation. The structural features, strength, and fracture toughness of the coatings produced by multichamber detonation spraying from 75% Cr₃C₂ + 25% NiCr and Ni–Cr–Fe–B–Si (77–81.5% Ni, 10–14% Cr, 5–7% Fe, 2.0–2.3% B, 2.0–3.2% Si, 0.5% C) powder materials were examined. Changes in the detonation spraying parameters were proved to significantly affect the structure of the coatings: microhardness, phase composition, volume content of lamellae, sizes of grains and subgrains, phase formation, and dislocation density. The structural-phase state of the coatings was studied at all structural levels using a comprehensive approach, including light and scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The prospects of employing the multichamber detonation spraying method, ensuring the necessary combination of structural and phase parameters of the coating material with a simultaneous increase in their physical, mechanical, and operational properties, were demonstrated. A high level of strengthening and fracture toughness of the coatings was promoted by optimal structural and phase constituents: fine grain and subgrain structure, uniform distribution of nanosized strengthening particles, and uniform dislocation density. The improved fracture toughness of the coatings is due to the absence of extended structural zones of dislocation clusters. The gradient-free distribution of dislocation density prevents the formation of local internal stress concentrators in the resulting coatings.