Variable lattice expansion in martensitic stainless steel after nitrogen ion implantation

Similar to expanded austenite, expanded martensite could be formed in the surface region of martensitic stainless steel after energetic nitrogen ion implantation at elevated temperatures up to 400 °C, whereas a higher temperature of 420 °C leads to CrN precipitates in the steel matrix. The influence of the process conditions and the alloy composition on the lattice expansion is investigated. A variable, anisotropic lattice expansion normal to the surface of up to 3.5% was observed, generally larger for (1 1 0) planes than for (2 0 0) planes. The additional formation of a large number of point defects for some process conditions can be inferred from the missing correlation between the relative X-ray intensity and the layer thickness.