Tungsten Matrix Composite Reinforced with CoCrFeMnNi High-Entropy Alloy: Impact of Processing Routes on Microstructure and Mechanical Properties

Abstract

Tungsten heavy alloy composite was developed by using novel CoCrFeMnNi high-entropy alloy as the binder/reinforcement phase. Elemental tungsten (W) powder and mechanically alloyed CoCrFeMnNi high-entropy alloy were mixed gently in high energy ball mill and consolidated using different sintering process with varying heating rate (in trend of conventional sintering < microwave sintering < spark plasma sintering). Mechanically alloyed CoCrFeMnNi high-entropy alloy have shown a predominant face-centered cubic (fcc) phase with minor Cr-rich σ-phase. Consolidated tungsten heavy high-entropy alloys (WHHEA) composites reveal the presence of Cr–Mn-rich oxide phase in addition to W-grains and high-entropy alloys (HEA) phase. An increase in heating rate restricts the tungsten grain growth with reduces the volume fraction of the Cr–Mn-rich phase. Finally, spark plasma sintering with a higher heating rate and shorter sintering time has revealed higher compressive strength (~2041 MPa) than the other two competitors (microwave sintering: ~1962 MPa and conventional sintering: ~1758 MPa), which may be attributed to finer W-grains and reduced fraction of Cr–Mn rich oxide phase.

Powder metallurgy of Al0.1CoCrFeNi high-entropy alloy

“…MA of the Al 0.1 CoCrFeNi powder to 6 h leads to a marginal increase in the size of the powder particles, which may be attributed to the cold welding incidents that take place during MA [46,62]. The average size of the powder particles is observed to be 25 ± 6.5 μm.…”

“…1 Fig. 2(a)] that some particles exhibit smooth fractured surfaces and others exhibit rough surfaces as a result of repeated welding and fracturing events that take place during MA [46,62]. The smooth surface corresponds to the fracture event, and once they are welded, the surface becomes rough and irregular.…”

“…The increase in the crystallite size (from 37 nm for the 8 h MA powder) and the decrease in the lattice strain (9 × 10 −3 for the 8 h MA powder) after consolidation can be attributed to the supply of thermal energy to the powder during the SPS process, which helps the crystals to grow and the lattices to relax be giving up the internal strain in the material. Retainment of the nanometerscale microstructure after SPS of A-HEA at 1000°C is attributed to efficient heating of the powder [higher heating rate (100°C)] and short holding time [62,63]. The SEM, corresponding electron backscattered diffraction (EBSD) images, and phase maps of the bulk A-HEA sample are given in Fig.…”

“…The SPS process with a higher heating rate enables a higher densification rate with sluggish grain coarsening rate during sintering. Hence, the SPS technique efficiently produces fine-grained bulk samples without affecting intrinsic properties and structures (nano or submicron structure) of the powder [62,63]. By utilizing the advantage of SPS combining with MA, the present study focuses on the processing of A-HEA, where the aim is to improve the strength of the alloy by non-equilibrium powder processing.…”

Microstructure and properties of in‐situ high entropy alloy/tungsten carbide composites by mechanical alloying.

“…Hence, extensive research is being carried out to enhance the properties of fcc‐based HEAs. The strength enhancement can be achieved by changing the processing route, 1,15 thermomechanical treatment, 16 severe plastic deformation, 17 or by composite formation 18–20 . Metal matrix composites (MMC) is one of the flexible strengthening techniques, where hard metallic phases or particles are dispersed in the soft matrix to improve the properties of the material 21–24 .…”