Microstructural evolution of mechanically alloyed and spark plasma sintered Ni–W alloy matrix composites

• Published in: Journal of alloys and compounds 2013-09, Vol.571, p.159-167
• Main Authors: Genç, Aziz, Kaya, Pınar, Ayas, Erhan, Öveçoğlu, M. Lütfi, Turan, Servet
• Format: Article
• Language: English
• Subjects: Alloy powders; Annealing; Binary systems; Carbides; Cold working, work hardening; annealing, quenching, tempering, recovery, and recrystallization; textures; Condensed matter: structure, mechanical and thermal properties; Covering; Cross-disciplinary physics: materials science; rheology; Dies; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Graphite; Materials science; Materials synthesis; materials processing; Mechanical alloying; Mechanical and acoustical properties of condensed matter; Microstructure; Nickel base alloys; Ni–W alloys; Physics; Solubility, segregation, and mixing; phase separation; Spark plasma sintering; Transmission electron microscopy; Treatment of materials and its effects on microstructure and properties
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2013.03.238

[Display omitted] •Microstructural characterizations of MA’d and SPS’ed Ni(W) alloys via (S)TEM.•Identification of WC and WO2 phases in the microstructure of the SPS’ed Ni(W) alloys.•Evolution of properties via modifications on the fabrication route.•Enhancement of the hardness via increasing W solubility. Microstructural evolution of Ni(W) solid solution alloys fabricated via mechanical alloying (MA) of Ni – 30wt.% W powders and spark plasma sintering (SPS) at 1000°C for 3min were presented in this study. Due to contaminations during MA, fabricated alloys are termed as Ni(W) solid solution alloy matrix composites. Effects of modifications on the processing conditions such as covering the graphite dies with hexagonal boron nitride spray and/or annealing of the as-MA’d powders on the microstructure of the SPS’ed Ni(W) alloy matrix composites were investigated via analytical transmission electron microscopy (TEM) studies. X-ray diffraction (XRD) and/or TEM investigations revealed that all the samples comprise Ni(W), WC and WO2 phases. A slightly reduced amount of 13.24wt.% WC by covering the graphite dies, significantly reduced to 3.90wt.% with the annealing of the MA’d powders. It is found that covering the graphite dies has led significant grain growth, whereas annealing of the powders had no significant effect on the grain size of SPS’ed samples. A 96.7% relative density value was increased to 97.3% with the covering of graphite dies, which further increased to 99.4% for the sample fabricated via SPS of the annealed powders with covered graphite dies. Although the amount of WC is decreased, a microhardness value of 4.28GPa for the sample fabricated via SPS of as-MA’d powders, slightly increased to 4.35GPa for the samples sintered by spray covered graphite dies, which further increased to 4.52GPa with the applied annealing, revealing the enhancement of the microhardness values by increased W solubility in Ni lattices.