Tentative Ni binary alloys containing nitride forming elements such as Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, Mn, Fe, Al and Si were nitrided by PIN process under the conditions of 873K, 10.8 ks, N2+H2 mixed gas atmosphere of 800Pa.
Surface hardening was observed in all Ni alloys used, however surface hardness were much different with depending on the kind of alloying elements and its contents. Maximum surface hardness were approximately Hv 550-800 for Ti, V, Nb and Cr containing alloys with more than 4, 4, 10 and 20wt%, respectively, and Hv 300-400 for Mo, Fe and Mn containing alloys more than 20, 30 and 30wt%, respectively, but Zr, Hf, Ta, Al and Si containing alloys were only slightly hardened as Hv 200-300. By using hardness increasing rate of each alloying elements, an equation to estimate the surface hardness of Ni alloy after PIN treatment was drawn and it was confirmed that there was a good agreement between measured and estimated hardness for various kinds of commercially used Ni alloys.
From results of EPMA and X-ray analyses, it was considered that surface hardening was due mainly to lattice strain of a matrix of nitrided layer caused by dispersive precipitations of fine nitrides of each alloying elements.