SPUTTERING, DEPOSITION, AND DIFFUSION IN ION-NITRIDING OF AN AUSTENITIC STAINLESS-STEEL

The surface of a commercial austenitic 18-8 stainless steel ion nitrided at 400-degrees-C, 450-degrees-C, and 550-degrees-C was examined by scanning electron microscopy, energy-dispersive X-ray analysis and electron probe microanalysis. Non-metallic inclusions in the steel, particularly oxides, were not much affected by sputtering so they remained on the surface of the specimens, and were covered with deposit. A surface layer, 5-10-mu-m thick, was sputtered by ion-nitriding at 400-degrees-C for 40 h (5 cycles of 8 h) and 550-degrees-C for 4 h in an N2-H2 atmosphere at a pressure of 6.67 x 10(2) Pa. A layer 0.2-mu-m thick was deposited at 400-degrees-C for 4 h and a layer about 2-mu-m thick was deposited at 400-degrees-C for 40 h (5 cycles of 8 h) and 550-degrees-C for 4 h. Cracks were observed in the layers deposited onto non-metallic inclusions at 400-degrees-C and 450-degrees-C. The cracks lower the corrosion resistance of the nitrided layer.