Abstract
In this work, an in-situ CoCrFeNi-M6Cp high entropy-alloy (HEA) based hardmetal with a composition of Co25Cr21Fe18Ni23Mo7Nb3WC2 was fabricated by the powder metallurgy (PM) method. Microstructures and mechanical properties of this HEA were characterized and analyzed. The results exhibit that this HEA possesses a two-phase microstructure consisting of the face-centered cubic (FCC) matrix phase and the carbide M6C phase. This HEA has an average grain size of 2.2 μm, and the mean size and volume fraction of carbide particles are 1.2 μm and 20%. The tensile tests show that the alloy has a yield strength of 573 MPa, ultimate tensile strength of 895 MPa and elongation of 5.5% at room temperature. The contributions from different strengthening mechanisms in this HEA were calculated. The grain boundary strengthening is the dominant strengthening mechanism, and the carbide particles are significant for the further enhancement of yield strength by the dislocation strengthening and Orowan strengthening. In addition, with increasing temperatures from 600 °C to 900 °C, the HEA shows a reduced yield strength (YS) from 473 MPa to 142 MPa, a decreased ultimate tensile strength (UTS) from 741 MPa to 165 MPa and an enhanced elongation from 10.5% to 31%.
Highlights
High entropy alloys (HEAs) have attracted significant research interests worldwide and shown potential application prospects in different fields due to their unique structure and properties [1,2,3].high entropy-alloy (HEA) are composed of at least four elements mixed in equiatomic or nearly equiatomic ratios and have a single-phase microstructure, possessing remarkable mechanical properties, high wear resistance, exceptional fatigue resistance, excellent corrosion resistance and high resistance to anneal softening [4,5,6,7]
By checking the scanning electron microscopy (SEM) microstructure under back-scattered electron mode shown in Figure 1b, the face-centered cubic (FCC) matrix phase exhibited a grey contrast while the carbide phase showed brightness
The results presented in this study revealed that a two-phase structure composed of an FCC phase
Summary
High entropy alloys (HEAs) have attracted significant research interests worldwide and shown potential application prospects in different fields due to their unique structure and properties [1,2,3]. The CoCrFeNi HEAs possess a single FCC phase resulting in a high elongation of 60% and a relatively low ultimate tensile strength (UTS) of 453 MPa [5]. Such superior ductility of the CoCrFeNi-based HEAs makes them become a hotspot for researchers to develop particle-reinforced HEAs in order to satisfy the structural applications [6,18,19]. The ultrafine grain, rolled and multiple phases make the FCC-based HEAs possess higher room temperature mechanical properties (e.g., UTS is 995 MPa in Reference [30] and 1170 MPa in Reference [16]) but insufficient performances at elevated temperature, which the UTS is less than 600 MPa at 600 ◦ C and basically less than 300 MPa at 800 ◦ C. The tensile tests were carried out at different temperatures and the microstructures were characterized by a combination of X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and transmission electron microscopy (TEM) methods to thoroughly understand the HEA hardmetal
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