Ni-2V, Ni-5V, Ni-12V, Ni-10Cr, Ni-20Cr, andNi-3Nb alloys were carbonitrided inC3H6 and NH3 gasmixtures (bal. H2) over the range700-1000°C. Carbonitridation of Ni-12V and Ni-20Cr inC3H6/NH3/H2(1.5/1.5/97 v/o) and (1.5/10/88.5 v/o) produced duplexsubscales consisting of near-surface nitrides with underlying carbides. Growth of each zone obeyedthe parabolic rate law under most conditions. Thepresence of carbon generally did not effect the depth ofthe nitride zones compared to nitriding the alloys in NH3/H2 (10/90 v/o).However, at 700°C, the nitride zones weredeeper in the carbonitrided Ni-V alloys and Ni-20Cr. Thepresence of nitrogen generally increased the depth of the carbide zones in Ni-12V andNi-20Cr compared to carburizing these alloys inC3H6/H2 (1.5/98.5 v/o).VN, CrN, and NbN formed in Ni-V, Ni-Cr, and Ni-Nballoys, respectively, whereas the underlying carbidelayers contained V4C3 in Ni-12V,Cr3C2 above a zone ofCr7C3 in Ni-20Cr, and NbC inNi-3Nb. The solubilities and diffusivities of nitrogenand carbon in nickel were determined. Nitrogen andcarbon each exhibited retrograde solubility withtemperature in pure Ni in both carbonitridingenvironments. Nitrogen diffusion in nickel was generallylower in each carbonitriding mixture compared tonitrogen diffusion in a nitriding environment, except at700°C when nitrogen diffusion was higher. Carbon diffusion in nickel was generally higherin the carbonitriding environments compared to carbondiffusion in a carburizing environment.