Abstract
This work reports on the spark plasma sintering (SPS) of self-propagating high-temperature-synthesis (SHS)-derived Ni-W and Ni-W-2wt%hBN (4:1 molar ratio of metals) powders. The synthesis was carried out from a mixture of NiO and WO3 using Mg + C combined reducers through a thermo-kinetic coupling approach. Experiments performed in the thermodynamically optimal area demonstrated the high sensitivity of combustion parameters and product phase composition to the amount of reducers and hBN powder. The powder precursors with and without the addition of hBN were consolidated using SPS at a temperature and pressure of 1300 °C and 50 MPa, respectively, followed by a thorough phase and microstructural characterization of the obtained specimens. SHS-derived powders comprised the nano-sized agglomerates and were characterized by a high sinterability. The specimens of >95% density were subjected to ball-on-plate dry sliding wear tests at a sliding speed of 0.1 ms−1 and a distance of 1000 m utilizing an alumina ball of 10 mm in diameter under a 15 N normal load. The tests were performed at a temperature of 800 °C. A significant improvement in wear behavior was demonstrated for SHS-processed composites in comparison with their counterparts produced via conventional high-energy ball milling technique owing to the phenomena of ‘micro-polishing’, cyclic ‘self-healing’ and fatigue. However, the decisive effect of hBN addition in imparting lubrication during an HT wear test was not confirmed.
Highlights
Mechanical, chemical or electro-chemical wear is a major concern in industries such as mining, material processing, electrical, chemical and surface engineering
The results are discussed in reference to the spark plasma sintering (SPS)-consolidated bulks from high-energy ball-milled (HEBM) Ni-W and Ni-W-Hexagonal boron nitride (hBN) composites
The results reported are an average of at least five to determine the volume of the wear scar
Summary
Mechanical, chemical or electro-chemical wear is a major concern in industries such as mining, material processing, electrical, chemical and surface engineering. The incorporation of refractory metals, such as W, Mo, Ni and Cu in the transition metals, to enhance mechanical, tribological and corrosion properties, in conjunction with the preservation of thermal and electrical properties, is gaining popularity In this respect, nickel-tungsten (Ni-W) alloys have shown fair potential for enhanced surface protection in electronics and mechanical industries; as high-temperature substrates for superconductors, barriers or capping layers in micro-electromechanical circuits; as catalysts for hydrogen evolution processes, etc., in comparison with elemental Ni [1]. SHS was shown to deliver powders of Mo-Cu and W-Cu in the nano-to-submicron size range using a similar pathway [10,11,12] It was earlier reported [13] that the incorporation of W into Ni matrix results in grain refinement at micro and nano levels promoted properties such as hardness and wear; a higher amount of W induced a decrease in oxidation stability of the sintered materials. The results are discussed in reference to the SPS-consolidated bulks from high-energy ball-milled (HEBM) Ni-W and Ni-W-hBN composites
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