Boride surface modifications

Boronising is a thermochemical heat treatment technique whereby boron is diffused into and combines with a metal substrate forming a hard metal boride layer at and adjacent to a component surface. Such layers are resistant to abrasive and adhesive wear and exhibit marked resistance to attack by HCl. Commercial boronising of steels is confined to the pack (or paste) technique (s). These frequently result in a dual phased layer of FeB and Fe2B. The disparities in the coefficients of thermal expansion of the two phases produces residual tensile stresses in the exterior FeB, which causes exfoliation under mechanical loading. It is therefore desirable to obtain a monophased layer of Fe2B. Conventionally, this has normally been satisfactorily accomplished, in the case of engineering steels, by a subsequent diffusion treatment at about 9000C. An alternative is to boronise using plasma or gaseous media, which in principle, allows a broader range of boron potential, facilitating the production of monophased layers