The effects of nitrogen implantation conditions (ion energy, dose rate, and processing time) on the thickness and wear behavior of N-rich layers produced on 304 stainless-steel surfaces are examined. Surfaces implanted at elevated temperatures ( ~400°C) with 0.4 to 2 keV nitrogen ions at high dose rates (1.5 to 3.8 mA/cm 2 ) are compared to surfaces implanted at higher energies (30 to 60 keV) and lower current densities (0.1 to 0.25 mA/cm 2 ). The most wear-resistant surfaces are observed when the implanted-ion energy is near 1 keV and the dose is very large (>2xl0 19 ions/cm ). Typically, surfaces implanted under these optimum conditions exhibit load-bearing capabilities at least 1000 times that of the untreated material. Some comparisons are also made to surfaces processed using conventional plasma-nitriding. Samples treated using either process have wear-resistant surface layers in which the nitrogen is in solid solution in the fee phase. It is argued that the deep N migration ( >l\x,m) that occurs under low-energy implantation conditions is due to thermal diffusion that is enhanced by a mechanism other than radiationinduced vacancy production.
General analytical expressions for multiphase diffusion under nonsteady-state conditions, which treats the special degenerative case of steady-state diffusion, are developed. The validity of these solutions is examined by application to multiphase layer growth in the Zr-0 and Fe-N systems. The analytical solutions examined include closed-form error function solutions and steady-state approximations to the solutions developed by Wagner. The solutions are general and can accommodate solubility ranges in all phase layers as well as terminal solubilities in the end member phases of the diffusion couple. In diffusion couples where the end member phases have finite, terminal solubilities and where these terminal phases have diffusivities greater than in the intermediate phases (which is common in many metal-interstitial phases), closed-form error function solutions are particularly useful in determining chemical diffusivities from simple intermediate phase layer growth measurements.
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