Resumo:
Multi-principal element alloys based on refractory metals have been the subject of study with the aim of competing with nickel super alloys due to their high melting temperatures and promising mechanical properties such as high hardness, thermal stability, and elevated temperature yield strength. However, a major drawback of refractory metal-based alloys is their low oxidation resistance at high temperatures. To overcome this problem, it is known that the addition of aluminum helps to improve resistance to oxidation, forming a protective layer of alumina in addition to reducing density. This study analyzed the influence of aluminum on the microstructure, hardness, and oxidation resistance of five new multicomponent refractory alloys produced by arc melting from raw elements, WMoNbTiCrAlx (x = 0, 0.25, 0.5, 0.75, and 1) (mol %). Microstructural analyses were carried out by scanning electron microscopy (SEM) and X-ray diffraction in all alloy conditions (cast and heat treated at 1200 °C for 24 hours), with electron backscattered diffraction (EBSD) analyses in the treated alloys. ThermoCalc software assisted in interpreting experimental results regarding equilibrium phases and their compositions. The cast alloys exhibited a highly segregated BCC phase with a dendritic structure. After heat treatment, the alloys predominantly maintained the BCC phase, with minor precipitation of the Laves phase. Nanoindentation tests revealed that the addition of aluminum increased hardness from 10.5 to 12.2 GPa, while the density of the alloy decreased with increasing aluminum content, from 9.7982 to 8.7745 g/cm³. In thermogravimetric tests (TGA), aluminum demonstrated benefits in improving oxidation resistance. The Al0.25 alloy showed the highest mass gain, approximately 40 mg/cm², while the Al1 alloy showed the lowest mass gain, approximately 9 mg/cm².
