Resumo:
High-entropy alloys have emerged as a promising alternative for producing materials with exceptional properties. Among these alloys, refractory alloys, comprising refractory elements, stand out for their significant innovation in the development of materials for high-temperature applications. These applications require thermal stability, wear resistance, and oxidation resistance in extreme environments. Composed of five or more principal elements in equiatomic or near-equiatomic proportions, these alloys exhibit high configurational entropy, facilitating the formation of stable solid solutions, in contrast to conventional alloys. Traditionally, these alloys are produced via fusion, a method plagued by economic, environmental, and production drawbacks, as well as heterogeneous structures and elemental segregation. To overcome these challenges, this study proposes the use of powder metallurgy, which fosters the formation of homogeneous alloys with enhanced solubility in the solid state. This approach offers advantages such as minimal waste, rapid production, sustainability, and innovation compared to conventional methods. This investigation examines the influence of varying atomic proportions of Al and Cr on phase formation and oxidation resistance in the refractory alloy AlCrNiNbMoW produced via powder metallurgy. The variation was implemented at 25% increments from the equiatomic proportion to the total replacement of Al by Cr. The results revealed that all alloys achieved densification of up to 95% relative to the theoretical value and exhibited similar microstructures, comprising solid solutions with body-centered cubic (BCC) crystalline structure and Laves phases. Oxidation tests revealed the formation of aluminum, niobium, chromium, and tungsten oxides. The alloy Al4,2Cr29,2Ni16,7Nb16,7Mo16,7W16,7 demonstrated the smallest mass gain (0.037 g/cm²). It was observed that reducing the Al content favors an increase in the fractions of Ni, Mo, and W, and stabilizes Nb in the matrix. The increase in the Cr content had little influence on the oxidation resistance. This study highlights the potential of high-entropy effects in developing novel refractory alloys via powder metallurgy, featuring homogeneous microstructures and optimized properties for high-temperature applications.
