The aim of this work was to study the influence of varying nitrogen potential during plasma nitriding of stainless steel ISO 5832-1. The control of nitrogen potential was achieved by pulsing the nitrogen flow for different times (01/19, 02/18, and 05/15), where the numbers represent the time (in minutes) of nitrogen flow on/off, thus creating an intermittent flow of nitrogen during the treatment. For all tested conditions - continuous and pulsed flow of nitrogen - the treatment temperature was kept at 425ºC during 2 and 8 hours. Specimens were characterized by means of X-ray diffraction, scanning electron microscopy, optical microscopy, energy-dispersive X-ray spectroscopy, and nanohardness. Results showed that the layer thickness increases with the increase of total treatment time, and decreased for shorter times of pulsed nitrogen flow. Smaller expansion of the austenite phase, as well as less precipitation of chromium nitrides, were also observed for shorter times of pulsed nitrogen flow. Hence, the use of intermittent nitrogen flow appears to be an efficient approach in order to control the nitrogen concentration within the layer, reducing its brittleness.

A produção de revestimentos soldados permite a proteção de componentes respeitando suas propriedades estruturais e em simultâneo otimiza a resistência ao meio. Avanços significativos podem ser conseguidos se for possível usufruir materiais com propriedades mais nobres mas tipicamente associadas a baixa. Procedimentos de síntese de aluminetos in-situ por plasma com arco transferido utilizando misturas de pós e as características dos revestimentos obtidos são revisados. É feita a análise de revestimentos obtidos pela síntese simultânea de uma camada de alumina(Al2O3) e da camada de aluminetos de ligação com o substrato metálico. Estes revestimentos apresentam um gradiente de propriedades severo, apresentando um diferencial na produção de sistemas de materiais com potencial para operar em condições de elevada agressividade. Os materiais foram sintetizados durante a deposição de misturas de pós de quartzo e de alumínio com composição química pré-determinada sobre liga de NiCr2%Nb e aço AISI 1020. A estratificação dos revestimentos é destacada e sua microestrutura analisada. Avaliação preliminar do desempenho ao desgaste e sua correlação com revestimentos de superligas de Co mostrou que a perda de massa em deslizamento abrasivo foi reduzida em até 5x.

Hardfacing allows to protect components with coatings exhibiting very distinct properties from those of the substrate. This procedure maintains the structural properties of the substrate and optimizes resistance of the surface to the working environment. A step towards enhanced performance of components can be achieved if high hardness and chemical inertia, low weldability materials can be used. In-situ aluminide processing, involving the development of aluminide during the deposition by Plasma Transferred Arc of powder mixtures is reviewed. Analysis of coatings exhibiting a gradient of properties obtained by the in-situ synthesis of an alumina and an aluminide bond-layer was carried out. The synthesis of the different layers occurred during the deposition of a mixture of quartz and Al powders on a steel and a Ni based substrates. The main features of the layered coatings are described and their microstructure analyzed. Preliminary results of abrasive sliding wear tests showed a 5x reduction in mass loss compared to the behavior of Co-based coatings.