Abstract
In this study, submicrometer grain-sized metal matrix composites (MMCs) based on nickel were elaborated via a bottom-up strategy combining the polyol process and a non-conventional heat treatment route. First, four sets of nano-sized Ni–P metastable alloy nanopowders with an average particle size centered at 50, 100, 130, and 220 nm were prepared by the polyol process modified by the addition of hypophosphite (strong reducing agent) and heterogeneous nucleation using silver nitrate and platinum salt (nucleating agents). The heat treatment step was realized by reactive spark plasma sintering (R-SPS) at identical heat treatment conditions (600 °C, 53 MPa, and 10 min as holding time). R-SPS transformed the Ni–P metastable alloys into bulk submicrometer grain-sized MMCs with Ni as the matrix and Ni3P as the reinforcement. Mechanical and magnetic properties of the four MMC samples were found to be closely related to the grain size of the Ni matrix, which varied from 247 to 638 nm. Yield stress, maximum stress, and coercive field increased when the grain size decreased, while plastic strain and magnetization saturation decreased. The reinforcement Ni3P phase enhanced the mechanical characteristics of the composite. Crossover behavior was observed at around 350 nm Ni grain size, where a ductile and soft magnetic composite was tuned into a hard mechanical and semi-hard magnetic one.
Highlights
IntroductionSpark plasma sintering (SPS) is characterized by a specific heat treatment in comparison with powder metallurgy methods; a high sintering rate and a local high temperature generated by spark discharges leading to a very low consolidation time
Spark plasma sintering (SPS) has emerged as a promising nonconventional consolidation process.SPS is characterized by a specific heat treatment in comparison with powder metallurgy methods; a high sintering rate and a local high temperature generated by spark discharges leading to a very low consolidation time
In the first part of this work [8], we reported on the influence of two sintering parameters, namely, temperature and holding time, on the mechanical and magnetic properties of metal matrix composites (MMCs) Ni–Ni3 P obtained from nanoparticles of metastable Ni–P alloys with a 100 nm diameter
Summary
SPS is characterized by a specific heat treatment in comparison with powder metallurgy methods; a high sintering rate and a local high temperature generated by spark discharges leading to a very low consolidation time. When the starting material is in the form of a nanopowder, the as-obtained bulk material is nanostructured or submicrometer grain-sized and shows structural and physical properties closely governed by its fine microstructure [1] Besides these advantages, several recent works have shown that SPS can be used as a reactive process to elaborate nanostructured or submicrometer grain-sized materials starting from raw reactants [2,3,4,5]. Patissier et al reported the synthesis of LaFe13-x Six magnetocaloric compounds by the R-SPS process starting from a mixture of ball-milled LaSi, Fe, and Si elements [6]
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