Comparison of surface properties modification by direct and active screen plasma nitriding of an ASTM M2 high-speed steel in a nitrogen rich gas mixture
Comparação da modificação superficial por nitretação direta e por tela ativa de um aço ASTM M2 em mistura rica em nitrogênio
Leonardo Fonseca Oliveira, Alexandre da Silva Rocha, Giovanni Rocha dos Santos
Abstract
The active screen plasma nitriding technique has been studied in recent years as a method to optimize surface properties in steel components, avoiding the negative effects caused in the conventional Direct Current plasma treatments. In this study, ASTM M2 high-speed tool steel samples were plasma nitrided with and without the use of the active screen, in order to compare the surface properties developed by each technique. The treatments were carried out at 500 °C, with the gas mixture of 76 vol.% N2 + 24 vol.% H2 , for 4 and 8 h. The active screen used was built with an expanded sheet of 304 stainless steel. The results were evaluated through optical microscopy, X-ray diffraction, and microhardness measurements. The samples were subjected to dry ball-on-flat tribological tests and the wear tracks were verified by 3D optical interferometry. The active screen use provided the formation of thinner layers, however, avoided the formation of brittle phases, resulting in the lowest wear volumes observed, up to 10 times less than the other analyzed conditions (nitrided and non-nitrided samples).
Keywords
Resumo
A técnica de nitretação com tela ativa vem sendo estudada nos últimos anos como uma maneira de otimizar propriedades superficiais de componentes de aço, evitando os efeitos negativos provocados nos tratamentos a plasma convencionais de corrente contínua. Neste estudo, amostras do aço rápido ASTM M2 foram submetidas a tratamentos de nitretação a plasma com e sem a utilização da tela ativa, a fim de comparar as propriedades superficiais proporcionadas por cada técnica. Os tratamentos foram executados em 500 °C, com a mistura gasosa de 76% N2 + 24% H2 , durante 4 e 8 horas. A tela ativa utilizada foi construída utilizando chapa expandida de aço inoxidável AISI 304. Os resultados foram avaliados através de microscopia ótica, difração de raios-X e medidas de microdureza. As amostras foram submetidas a ensaios tribológicos do tipo esfera-sobre-plano a seco e as trilhas de desgaste foram verificadas por interferometria ótica 3D. A utilização da tela ativa proporcionou a formação de camadas menos profundas, porém, evitou a formação de fases frágeis, resultando nos menores volumes desgastados observados, até 10 vezes menor que as outras condições analisadas (amostras nitretadas e não-nitretada).
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Referências
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Submetido em:
14/08/2020
Aceito em:
10/02/2021
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