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Materials 2017, 10(4), 389; doi:10.3390/ma10040389

The Effect of Milling Time on the Microstructural Characteristics and Strengthening Mechanisms of NiMo-SiC Alloys Prepared via Powder Metallurgy

1
Shanghai Institute of Applied Physics, Chinese Academy of Sciences (CAS), Shanghai 201800, China
2
University of Chinese Academy of Sciences, Beijing 100049, China
3
Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234, Australia
4
School of Materials Science and Engineering, University of New South Wales, Sydney, NSW 2052, Australia
*
Authors to whom correspondence should be addressed.
Received: 7 March 2017 / Revised: 31 March 2017 / Accepted: 1 April 2017 / Published: 6 April 2017
(This article belongs to the Section Energy Materials)
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Abstract

A new generation of alloys, which rely on a combination of various strengthening mechanisms, has been developed for application in molten salt nuclear reactors. In the current study, a battery of dispersion and precipitation-strengthened (DPS) NiMo-based alloys containing varying amounts of SiC (0.5–2.5 wt %) were prepared from Ni-Mo-SiC powder mixture via a mechanical alloying (MA) route followed by spark plasma sintering (SPS) and rapid cooling. Neutron Powder Diffraction (NPD), Electron Back Scattering Diffraction (EBSD), and Transmission Electron Microscopy (TEM) were employed in the characterization of the microstructural properties of these in-house prepared NiMo-SiC DPS alloys. The study showed that uniformly-dispersed SiC particles provide dispersion strengthening, the precipitation of nano-scale Ni3Si particles provides precipitation strengthening, and the solid-solution of Mo in the Ni matrix provides solid-solution strengthening. It was further shown that the milling time has significant effects on the microstructural characteristics of these alloys. Increased milling time seems to limit the grain growth of the NiMo matrix by producing well-dispersed Mo2C particles during sintering. The amount of grain boundaries greatly increases the Hall–Petch strengthening, resulting in significantly higher strength in the case of 48-h-milled NiMo-SiC DPS alloys compared with the 8-h-milled alloys. However, it was also shown that the total elongation is considerably reduced in the 48-h-milled NiMo-SiC DPS alloy due to high porosity. The porosity is a result of cold welding of the powder mixture during the extended milling process. View Full-Text
Keywords: powder metallurgy; DPS strengthening; spark plasma sintering; transmission electron microscopy; electron backscatter diffraction; molten salt reactor powder metallurgy; DPS strengthening; spark plasma sintering; transmission electron microscopy; electron backscatter diffraction; molten salt reactor
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Yang, C.; Muránsky, O.; Zhu, H.; Thorogood, G.J.; Avdeev, M.; Huang, H.; Zhou, X. The Effect of Milling Time on the Microstructural Characteristics and Strengthening Mechanisms of NiMo-SiC Alloys Prepared via Powder Metallurgy. Materials 2017, 10, 389.

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