High Entropy Alloy Matrix Composites Research Articles

Fabrication of CoCrFeNiMn high entropy alloy matrix composites by thermomechanical consolidation of a mechanically milled powder

CoCrFeNiMn high entropy alloy matrix composites with in-situ carbide and oxide particles were fabricated by thermomechanical consolidation of a mechanically milled powder at 1000 and 1150 °C respectively. The sample consolidated at 1000 °C exhibited a microstructure consisting of Cr-rich M23C6 carbide particles, spinel (Cr, Mn)3O4 oxide particles, ultrafine grains with an average size of 920 nm and a major 〈001〉 + minor 〈111〉 dual fiber texture. When the consolation temperature increased to 1150 °C, Cr-rich M23C6 carbide particles were dissolved and the spinel (Cr, Mn)3O4 oxide particles coarsened. These led to larger grains with an average size of 6.06 μm and allowed formation of only sharp 〈001〉 fiber texture. This microstructural variation with the increase of consolidation temperature led to a decrease of strength and improvement of ductility. Analysis of the strengthening mechanisms reveals that grain boundary strengthening and Orowan strengthening play a major role in strengthening for the high strength sample consolidated at 1000 °C, while these mechanisms contribute significantly less to the strength for the sample consolidated at 1150 °C. It was also found that the sample consolidated at 1150 °C was weakened by the 〈001〉 texture.

Microstructure evolution, mechanical properties and strengthening mechanism of refractory high-entropy alloy matrix composites with addition of TaC

This study focuses on novel refractory MoNbRe0.5W(TaC)x high-entropy alloy matrix composites synthesized by vacuum arc melting. The microstructure evolution, compressive mechanical properties at room temperature and strengthening mechanism of the composites with addition of TaC are analyzed and discussed. The MoNbRe0.5W(TaC)x composites consist of a BCC solid solution as the matrix and an eutectic microstructure (BCC and multi-component carbide (Mo, Nb, W, Ta)C phases) at grain boundaries. The lamellar eutectic structure would be formed from the decomposition of subcarbide (Mo, Nb, W, Ta)2C and the fully solid solubility of Re. The MoNbRe0.5W(TaC)0.5 composite has the maximum failure strain of 10.25%. The MoNbRe0.5W(TaC)0.5 to MoNbRe0.5W(TaC)0.6 composites exhibit excellent comprehensive mechanical properties, with excellent strength and reasonable ductility at room temperature. The reinforcement mechanism of the composites is dominated by precipitation and fine-grained strengthening effect. The good ductility of MoNbRe0.5W(TaC)0.5 composite is contributed to the grain refinement of the BCC matrix phase.

High entropy alloy FeCoNiCu matrix composites reinforced with in-situ TiC particles and graphite whiskers

FeCoNiCu high entropy alloy matrix composites reinforced by in-situ TiC particles and graphite whiskers (5 vol% and 10 vol%, respectively), i.e., (TiCp + Cw)/FeCoNiCu composites, were fabricated from FeCoNiCuTiC powder system using vacuum inductive melting method. The reaction mechanism of the mixed powder (Fe, Ti and C) and the mechanical properties of resulting (TiCp + Cw)/FeCoNiCu composites were studied. It was found that two reactions (Fe+Ti→FeTiandTi+C→TiC) occurred, when the powder system was heated to 1473 K. The apparent activation energy for these two reactions were calculated and found to be 25 kJ/mol and 2709 kJ/mol, respectively. The TiC particles (size, 3–5 μm) and graphite whiskers (diameter, 0.5–3 μm; length, 10–200 μm) were found to distribute uniformly throughout the high entropy alloy matrix. The crystal structure of FeCoNiCu matrix was FCC type. At room temperature, the maximum tensile strength of the composites was determined to be 566 MPa, representing a 57.7% increase over FeCoNiCu high entropy alloy matrix. Moreover, the elongation to failure of the new composites was determined to be 4.5%. The tensile fracture surface consisted of many fine dimples, suggesting a ductile nature in failure.

Microwave Synthesis of AlFeCuCrNi /TiB2 High-Entropy Alloy Matrix Composites

The Al-Fe-Cu-Cr-Ni-Ti-B system was microwaved to generate high entropy alloy matrix composites reinforced by TiB2 particles. The micro structure and reaction process of the composites were observed and investigated by modern analysis methods, including X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS) and differential scanning calorimeter (DSC) analysis. The results show that AlFeCuCrNi /TiB2 composites can be prepared by microwave heating method. The matrix structure was FCC, and the reinforcement TiB2 showed regular geometric morphology in the matrix and evenly distributed in the matrix when the volume fraction of the reinforcement is 10%. When the volume fraction of the reinforcement increased to 15%, TiB2 partially aggregates in the matrix, and the system activation energy was 195.69 kJ/mol.

Deformation twinning structure and interface in a FCC-based Al0.3FeNiCo1.2CrCu high-entropy alloy matrix composites

High entropy alloy composites (HEACs), Al0.3FeNiCo1.2CrCu reinforced by Titanium carbide (TiC) particles were produced by mechanical alloying (MA) and spark plasma sintering (SPS). The results from X-ray diffraction (XRD) and transmission electron microscopy (TEM) shows that a single FCC solid-solution phase with certain nanoscale deformation twins are produced following SPS. Subsequent investigations characterize the mechanical properties and microstructure of nanocrystalline twin HEAs by high resolution electron microscope (HREM) and compression tests. The produced interface was found to be clear and well bonded. The compressive yield strength, fracture strength, plastic strain and hardness are found to be 1730 ± 15 MPa, 2260 ± 15 MPa, 29.50% and 645Hv, respectively. This is attributed to the twin strengthening and the presence of uniformly distributed TiC particles.