Two-Layer Composite Coatings Reinforced with Iron Borides

Abstract

The furnace infiltration technique was proposed to produce two-layer macroheterogeneous composite coatings. The technique involved consecutive infiltration of hard alloy reinforcement granules with two metallic matrices differing in the melting point. The infiltration resulted in a twolayer composite coating, with the layers being strengthened with the same reinforcement but not having the same matrix compositions. The Fe–12.5% B–0.1% C alloy was used as the reinforcement and the L62 copper-based alloy or hypoeutectic Fe–3.5% B–0.2% C alloy was the matrix. Quantitative metallography, energy-dispersive microanalysis, and microhardness measurements were employed to examine the structurization of interfaces between the boride reinforcement and the molten matrices. Furnace infiltration ensured virtually defect-free structure of the two-layer composite coating, with porosity not exceeding 5 to 7%. This was achieved through the dissolution of reinforcement surface phases in the molten matrices during infiltration without forming brittle intermetallic phases at the interfaces. The intensity of contact interaction processes at the interfaces between iron borides and iron- and copper-based matrices was compared. The mechanical and performance properties of the composite coating layers were studied. The combination of two layers prevented the delamination of the composite coatings under nonuniform distribution of temperatures, stresses, and strains. This determines the prospects of using the proposed technique for surface strengthening of aerospace engineering parts.