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The b phase evolution in Ti-6Al-4V additively manufactured by laser metal deposition due to cyclic phase transformations
H.Z. Zhong, M. Qian, W. Hou, X.Y. Zhang, J.F. Gu
Keywords: Hot work die steel; Gas nitriding; Microstructure control; Wear behavior
Abstract: Gas nitriding has become a popular thermo-chemical surface treatment, which is being used to develop thermal/mechanical fatigue and wear characteristics of iron and steels. In this study, the gas nitriding of AISI H13 hot work die steel was carried out in flowing NH3 gas at 550 °C for 5–15 h. By adjusting the nitrogen potential ranging from 0.18 to 2.8, three types of nitrided surface layer consisting of ε-Fe2-3N and γ′-Fe4N phases, γ′-Fe4N single-phase, as well as the α-(Fe, N) phase had been prepared, respectively. The corresponding microstructure, hardness and thickness of the nitrided layer were systematically characterized. A contrastive analysis of influence of nitrided-layer microstructure control on wear behavior of AISI H13 hot work die steel was conducted. The nitrided surface layer consisting of ε-Fe2-3N and γ′-Fe4N phases showed excellent wear resistance under loads of 100 N but poor wear properties at 300 N. The wear mechanism was revealed based on the microstructure characteristics, surface hardness and toughness of each nitrided surface layer.
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