Phase composition and morphology as a function of depth for boride coatings grown on Fe-Ni alloys

Two Fe-Ni alloys very differing in Ni content, Fe64Ni36 and Fe20Ni80, were borided at 850°C for 8 h using a high boron potential powder medium. On both alloys ~150 μm thick boride coatings grew in the form of two stratified sublayers of different thickness depending on the Ni content of the metal substrate. The outer sublayer mainly consisted of a ternary (Fe,Ni)B compound with small amounts of Ni borides in its outermost region, the inner by a ternary (Fe,Ni)2B compound. It is shown and explained how the same (Fe,Ni)B compound could form on both high-Ni alloys in spite of the considerable difference in Ni content.