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Materials 2019, 12(3), 520; https://doi.org/10.3390/ma12030520

The Effect of Plasma Nitriding on the Fatigue Behavior of the Ti-6Al-4V Alloy

1
Center for Materials Science and Technology, Instituto de Pesquisas Energéticas e Nucleares, São Paulo 05508-000, Brazil
2
Department of Materials Engineering and Nanotechnology, Universidade Presbiteriana Mackenzie, São Paulo 01302-907, Brazil
3
Department of Materials and Processes, Instituto Tecnológico de Aeronáutica—ITA/DCTA, São José dos Campos 12228-900, Brazil
*
Author to whom correspondence should be addressed.
Received: 26 December 2018 / Revised: 28 January 2019 / Accepted: 30 January 2019 / Published: 9 February 2019
(This article belongs to the Special Issue Probabilistic Mechanical Fatigue and Fracture of Materials)
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Abstract

The Ti-6Al-4V alloy is widely used in the manufacture of components that must have low density and high corrosion resistance and fatigue strength. The fatigue strength can be improved by surface modification. The aim of this study was to determine the influence of plasma nitriding on the fatigue behavior of a Ti-6Al-4V alloy with a lamellar microstructure (Widmanstätten type). Nitriding was executed at 720 °C for 4 h in an atmosphere with N2, Ar, and H2. Microstructure characterization of the samples was carried out by X-ray diffraction analysis, optical microscopy, and scanning electron microscopy. The average roughness of the specimens was determined, and fatigue tests were executed in a bending–rotating machine with reverse tension cycles (R = −1). X-ray diffraction analysis of the nitrided alloy revealed the following matrix phases: α, β, ε-Ti2N, and δ-TiN. A nitrogen diffusion layer was formed between the substrate and the titanium nitrides. Plasma nitriding resulted in an increase in low-cycle fatigue strength, whereas at high cycles of 200 MPa, both conditions exhibited similar behaviors. The fracture surface of the fatigue-tested specimens clearly revealed the lamellar microstructure. The fracture mechanism in the non-nitrided specimens appears to be due to cracking at the interface of the α and β phases of the lamellar microstructure. View Full-Text
Keywords: Ti-6Al-4V alloy; plasma nitriding; fatigue Ti-6Al-4V alloy; plasma nitriding; fatigue
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de Castro, M.C.B.; Couto, A.A.; Almeida, G.F.C.; Massi, M.; de Lima, N.B.; da Silva Sobrinho, A.; Castagnet, M.; Xavier, G.L.; Oliveira, R.R. The Effect of Plasma Nitriding on the Fatigue Behavior of the Ti-6Al-4V Alloy. Materials 2019, 12, 520.

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