This study investigates the microstructural development of commercial low-alloyed AISI 4340 steel through the synergistic application of Binder Jetting and Quenching and Partitioning (QP) processes. The material in the as-sintered condition exhibited significant variations in microstructure and mechanical properties, primarily influenced by the processing route. Carbon content was influenced by the building technique as decarburization was observed at different intensities mainly during the heating stage of sintering, driven by carbothermic reduction. Vacuum-debinding was found to be optimal, leading to the most homogeneous microstructure, predominantly granular bainite with superior hardness and tensile strength. Different QP treatments were optimized considering the decarburization effect on the optimal as-sintered condition, stabilizing 4–8 % retained austenite in a martensitic matrix, with optimal results observed after isothermal holding at either 220 °C or 240 °C for 30 min. These conditions resulted in high UTS values of 1231 MPa and 1151 MPa, respectively, compared to 750 MPa in the as-sintered state. Despite high tensile properties, A% was limited by the presence of residual porosity. This study highlights the critical importance of controlled debinding and sintering atmospheres as well as decarburization-informed QP treatments in achieving desirable microstructural and mechanical properties in additively manufactured AISI 4340 steel components.

Due to elevated potential associated with the extremely vast compositional space of high-entropy alloys (HEAs), there is a significant drive to explore these alloys in high-performance contexts such as intensive wear and oxidative environments. In this regard, this review article comprehensively explores the utilization of HEAs in cemented carbides, focusing on their role as binders in cermets. The wear resistance and oxidation behavior of HEA-containing cermets depends on the ceramic-binder thermodynamic compatibility, phase transformations during sintering, microstructure, and mechanical properties. Hence, much high quality research has been focused into exploring the combination of several HEAs with tungsten carbide, titanium carbides, nitrides, carbonitrides and diborides along with other ceramic compounds. As there are many HEA-ceramic combinations, this review aims to provide a landscape of the developments in this field, providing detailed information about the chemical compositions, sintering techniques, mechanical properties and wear and oxidation resistance obtained. Finally, the need for further research to fully understand the complex interactions between composition, microstructure, and wear and oxidation resistance is highlighted, aiming to tailor HEA compositions for optimized performance. The findings presented in this review contribute valuable insights into the promising applications of HEAs in cemented carbides.

Refractory high-entropy alloys (RHEAs) are promising candidates for those applications requiring of strong materials at high temperatures with elevated thermal stability and excellent oxidation, irradiation, and corrosion resistance. Particularly, RHEAs synthesized using mechanical alloying (MA) followed by spark plasma sintering (SPS) has proven to be a successful path to produce stronger alloys than those produced by casting techniques. This superior behavior, at both room and high temperature, can be attributed to the microstructural features resultant from this powder metallurgy route, that include the presence of homogeneously distributed non-metallic particles, fine- and ultrafine-grained microstructures, and higher content of interstitial solutes. Nevertheless, the powder metallurgy fabrication relies over a complex balance of several operational variables, and the process is no exempt of certain challenges, such as contamination or the presence of pores in the bulk parts. This review aims to cover all the peculiarities of the MA + SPS route, the resultant microstructures, their mechanical properties, and the strengthening and deformation mechanisms behind their superior performance, as well as a brief description of their oxidation resistance.