USO DE ENSAIOS DE MICROESCLEROMETRIA INSTRUMENTADA NO ESTUDO DAS PROPRIEDADES DA AUSTENITA EXPANDIDA
INSTRUMENTED MICROSCRATCH TESTS USAGE FOR STUDY OF EXPANDED AUSTENITE PROPERTIES
Sato, Fernando Luis; Espitia, Luis Armando; Pinedo, Carlos Eduardo; Tschiptschin, André Paulo
http://dx.doi.org/10.4322/2176-1523.0827
Tecnol. Metal. Mater. Min., vol.12, n2, p.115-122, 2015
Resumo
A resistência à corrosão do aço inoxidável austenítico AISI 316 é usualmente acompanhada por propriedades mecânicas limitadas dessa liga. A austenita expandida, ou Fase-S, supersaturada em nitrogênio, endurece superficialmente o material, sem a formação de precipitados e consequente prejuízo da passivação, efeitos comumente observados nos métodos convencionais de endurecimento superficial. Caracterizações mecânicas dessa camada por ensaios de microesclerometria instrumentada fornecem um conjunto de dados empíricos relevantes para a compreensão e modelagem de fenômenos tribológicos atuantes em um dado sistema mecânico. O presente trabalho apresenta os resultados de uma série de ensaios de microesclerometria instrumentada realizados em amostras de aço AISI 316 nitretadas a plasma por 20 h em forno de corrente contínua, utilizando a tecnologia de tela ativa, temperatura de 400°C e atmosfera formada por três partes de nitrogênio para uma parte de hidrogênio (3N2:1H2). Também são discutidos a caracterização das amostras e demais resultados, como o reduzido coeficiente de atrito (< 0,1) e a ausência de falha adesiva da camada.
Palavras-chave
Microesclerometria, Austenita expandida, Fase-S.
Abstract
Corrosion resistance and poor mechanical properties are both characteristics of AISI 316 austenitic stainless steel. Nitrogen supersaturated expanded austenite, or S-phase, promotes surface hardening of the alloy without the formation of undesirable that can reduce passivation properties. Mechanical characterization of this layer using instrumented microscratch tests gives an important set of empirical data useful for comprehension and modeling of tribological phenomena occurring in mechanical system. This work presents results from a series of instrumented microscratch tests performed on Low Temperature Plasma Nitrided (LTPN) AISI 316 stainless steel samples with an expanded austenite layer. The specimens were produced by 20 h active screen plasma nitriding treatment, done in direct current reactor at 400°C in an atmosphere containing three parts of nitrogen for one part of hydrogen (3N2:1H2). The reduced friction coefficient (< 0,1) between the indenter and the expanded austenite layer observed in the initial stage of scratch test and the absence of adhesive failure along the test are also discussed.
Keywords
Microscratch test, Expanded austenite, S-phase.
Referências
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2 Rossi B. Discussion on the use of stainless steel in constructions in view of sustainability. Thin-walled Structures. 2014;83:182-189. http://dx.doi.org/10.1016/j.tws.2014.01.021.
3 Farrar JCM. The alloy tree: a guide to low-alloy steels, stainless steels and nickel-base alloys. Cambridge: Woodhead; 2004.
4 Leyland A, Matthews A. Design criteria for wear-resistant nanostructured and glassy-metal coatings. Surface and Coatings Technology. 2004;177-178:317-324. http://dx.doi.org/10.1016/j.surfcoat.2003.09.011.
5 Pinedo CE. Tecnologia de plasma na geração de camadas duplex em aços inox austeníticos. Metalurgia & Materiais. 2009;65:407-409.
6 Pinedo CE. Nitretação por plasma de aços inoxidáveis. Metalurgia & Materiais. 2004;60:162-164.
7 Dong H. S-phase surface engineering of Fe-Cr, Co-Cr and Ni-Cr alloys. International Materials Reviews. 2010;55(2):65-98. http://dx.doi.org/10.1179/095066009X12572530170589.
8 Center for Tribology Research - CETR. UMT multi-specimen test system: hardware installation & applications manual. Campbell; 2009.
9 Picard S, Memet JB, Sabot R, Grosseau-Poussard JL, Rivière JP, Meilland R. Corrosion behaviour, microhardness and surface characterization of low energy, high current ion implanted austenitic stainless steel. Materials Science and Engineering A. 2001;303(1-2):163-172. http://dx.doi.org/10.1016/S0921-5093(00)01841-4.
10 American Society for Testing and Materials - ASTM. ASTM C1624-05: Standard test method for adhesion strength and mechanical failure modes of ceramic coatings by quantitative single point scratch testing. Pennsylvania; 2010.
11 Holmberg K, Matthews A. Coatings tribology: properties, mechanisms, techniques and applications in surface engineering. 2nd ed. Amsterdam: Elsevier Science; 2009.
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