Sliding-wear evaluation of boronized austenitic alloys

Abstract

The reaction zone produced on a series of austenitic alloys by boronizing at 950°C consists of two distinct layers, an outer layer of M B phase and an inner, M₂B compound. Beneath the boride layers, appreciable quantities of chromiumrich boride form at grain boundaries, giving an irregular, or ‘toothed’ interface. The dry lvear behaviour of boronized samples exhibits a transition from mild to severe wear, once the load applied to the specimen exceeds a critical value. The transition marks the point where stresses developed by the applied load are sufficient to deform the substrate and thence to promote mechanical instability of the boride coating. Little difference between the wear characteristics of M B and M₂B was observed, but a toothed structure appears beneficial, because it increases substrate rigidity and enhances adhesion between boride and metal. Comparison with wear data for untreated austenitic alloys shows that boronizing substantially improves tribological properties, provided that the structure and properties of the core material are not adversely affected by the treatment.