Abstract
The effect of the third alloying elements of various intride fomer, such asl Ti, V, Nb, Ta, Cr, Mo or Al, on the surface hardening of Ni-7wt%Ti and Ni-20wt%Cr binary alloys has been investigated by PIN process under various conditions of nitriding temperature from 773 to 1073K and nitriding time at 10.8ks in N2+H2 mixed gas atmosphere of 800Pa.
The hardness and the thickness of nitrided layer of Ni ternary alloys were lager than these of Ni binary alloys at the same nitriding conditions, and the PIN treated Ni alloys showed far better wear resistance than untreated alloys. Among the alloying elemtn, Nb and Cr were beneficial for increasing the hardness and the thickness of nitrided layer for Ni-7wt%Ti and also Ti and Ta were beneficial for Ni-20wt%Cr. The maximum surface hardness Hv800-900 was obtained for Ni-7wt%Ti acontaining Nb and Cr, and Ni-20wt %Cr containing Ti and Cr, at nitriding temperature of 873-973K.
Transimission electron microscoyp and X-ray diffraction analysis revealed that the surface hardening of Ni ternary alloys was due to the mattix lattice strain in the nitrided layer. Moreover, the effect of the third alloying element was found to be the increase of the matrix lattice strain in the nitrided layer caused by a fine dispersion of nitride particles.
