Gradient Distribution of Microstructures and Mechanical Properties in a FeCoCrNiMo High-Entropy Alloy during Spark Plasma Sintering

Abstract

A novel graded material of a high-entropy alloy (HEA) FeCoCrNiMo was fabricated by spark plasma sintering (SPS) processing. After SPS, the HEA specimens consisted of a single face-centred cubic (FCC) phase in the center, but dual FCC and a tetragonal structure σ phase near the surface. Surprisingly, the sintering pressure was sufficient to influence the proportion of phases, and thus the properties of HEA samples. The hardness of the specimens sintered under the pressures of 30, 35, and 40 MPa increased gradually from 210 HV0.2, which is the single FCC phase in the center, to the maximum value near the surface as a result of the gradual increase in the fraction of the transformed σ phase. The σ phase, being a complex hard and brittle intermetallic particle to manipulate the properties of FCC-type HEA systems, which could be influenced by pressure, indicated a major possibility for designing gradient HEA materials.

Microstructures and Wear Resistance of FeCoCrNi-Mo High Entropy Alloy/Diamond Composite Coatings by High Speed Laser Cladding

“…The composition of the light gray phase was closed to the theoretical composition of a FeCoCrNi-Mo HEA matrix with interstitial solid strengthening of C element. The dark grey phase exhibited a relatively high Mo content and less Cr, referred to as the intermetallic σ phase, because the Mo element can promote FCC (Face Center Cubic) σ phase transition of the FeCoCrNi system [21], and has been proved in our previous studies using FeCoCrNi-Mo HEA with the same composition as that in this study [22,23]. The white phase had the highest Mo content and a relatively high C content, which was the Mo-rich carbide phase.…”

“…The white phase had the highest Mo content and a relatively high C content, which was the Mo-rich carbide phase. element can promote FCC (Face Center Cubic) σ phase transition of the FeCoCrNi system [21], and has been proved in our previous studies using FeCoCrNi-Mo HEA with the same composition as that in this study [22,23]. The white phase had the highest Mo content and a relatively high C content, which was the Mo-rich carbide phase.…”

Complex Concentrated Alloys (CCAs)—Current Understanding and Future Opportunities

“…Eight research articles, four reviews, and one perspective have been published in this special issue of Metals. The subjects are multidisciplinary and divided into several topics including: (i) simulation and modeling for predicting structure and properties [1], (ii) unique deformation mechanisms in multi-principal alloys [2][3][4], (iii) microstructure and properties resulting from various processing routes [5][6][7][8][9][10], (iv) corrosion and surface degradation behavior [11,12], and (v) perspectives on ways to design mechanically and functionally advanced concentrated alloys [13]. Beyramali Kivy et al [1] reviewed the computational tools for studying the structure and properties of multi-principal alloys and identified the advantages as well as limitations of simulations in accelerating design and development of new alloys.…”

“…The processing-microstructure-properties relationship in complex concentrated alloys are discussed in one review article and five research papers in this special issue [5][6][7][8][9][10]. Dong et al [5] reviewed the structure, evolution in properties, and deformation behavior of HEAs after high-pressure treatment (HPT).…”

“…Maximum hardness and negligible wear were seen for intermediate aging time. Zhang et al [7] evaluated the distribution in microstructure and mechanical properties of HEAs obtained after spark plasma sintering (SPS). Sha et al [8] and Zhao et al [9] researched the effect of chemical composition on the microstructure and properties of Al x CoCrFe 2.7 MoNi and Al x CoCrFeNiTi 0.5 HEAs, respectively.…”