Abstract This work reports an experimental investigation on the thermodynamic and kinetic view-point of the nitrided layer growth behavior, carried out separately at ferrite and austenite phase grains, for the UNS S32750 super duplex stainless steel (SDSS). For this purpose, and motivated by the DSSs distinct behavior showing formation of two- or single-phase nitrided layers, which apparently depend on the steel substrate chemical composition, two series of treatment were studied here, one varying the nitriding temperature on the 300-450 °C range for 4 h time, and other one varying the time on the 2-8 h range at 350 °C. Microstructural characterization of studied layers by means of SEM and EDS analysis, XRD and microhardness measurements showed precipitation-free nitrogen-expanded austenite layer formation on both steel phases for all samples treated up to 400 °C. The nitriding kinetics study showed that the layer thickness on both steel phases is proportional to the square root of the treatment time and follows an Arrhenius law for the studied treatment temperatures. The nitrogen diffusion activation energy, separately determined from the layer growth on each steel phase, was 115±3.2 and 120±5.4 kJmol-1, for austenite and ferrite grains, respectively.

Corpos-de-prova de zircônia parcialmente estabilizada com ítria foram moldados por prensagem uniaxial, sinterizados e nitretados em plasma de micro-ondas à pressão atmosférica. A camada de ZrN sobre zircônia formou-se a uma taxa de 4 µm.min-1, podendo atingir uma espessura de 500 µm. As amostras foram caracterizadas por meio de medidas de dureza e resistência ao desgaste. A superfície nitretada apresentou dureza superior e resistência ao desgaste similar ao substrato de zircônia.

Samples of yttria partially-stabilized zirconia were molded by uniaxial pressing, sintered and nitrided in an atmospheric pressure microwave plasma. This procedure leads to the formation of a ZrN layer whose growth rate and thickness reached 4 µm.min-1 and 500 µm, respectively. The samples were characterized by means of hardness and wear resistance tests. The nitrided surface exhibits superior hardness and wear resistance similar to that of the zirconia substrate.