Diffuser with improved erosion resistance

A diffuser for a centrifugal compressor in a gas turbine engine, the diffuser comprising a diffuser ring for surrounding a periphery of the compressor, the diffuser ring being made from one of iron based and nickel based metal and defining an inner surface adapted to extend adjacent the periphery of the compressor and an opposed outer surface, the diffuser ring including a series of bores defined therethrough from the inner surface to the outer surface to receive and direct air exiting the compressor, each bore being defined by a respective erosion resistant surface consisting of a surface boride layer formed of borides of the diffuser ring metal obtained through reaction of the diffuser ring metal with a boronizing agent including about 50% by weight of a mix of boron fluoride and silicon carbide.