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 filler granules with two metallic binders differing in the melting point. The infiltration resulted in a two-layer composite coating, with the layers being reinforced with the same filler but having  not the same binder compositions. The Fe–12.5% В–0.1% С alloy was used as filler and L62 copper-based alloy or hypoeutectic Fe–3.5% B–0.2% С alloy were binders. Quantitative metallography, energy-dispersive microanalysis, and microhardness measurements were employed to examine the structurization of interfaces between the boride filler and the molten binders. 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 the filler surface phases in the molten binders 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 binders 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.