Development and characterization of multi-principal elemental alloys for improved hardness and corrosion resistance

Multi-principal Element Alloys (MPEA) have several advantages, and it has a wide range of applications. In this study, we have designed and fabricated three novel MPEAs for aggressive higher concentration oxidizing nitric acid application in nuclear-reprocessing and chemical plants, precisely called medium entropy alloys (MEA), with alloying elements Ti, Ta, Nb, and Zr. Sample1(S1) consists of an equal atom percentage of Ti, Ta, and Nb (Ti0.33Ta0.33Nb0.33 at%); sample2 (S2) contains (Ti0.84Ta0.1Nb0.06 at%), whereas the chemical composition of sample3 (S3) is (Ti0.33Ta0.33Zr0.33 at%), sample S1 and S3 contain equal atom percentage of constitute elements. X-ray diffraction (XRD) and microscopy studies revealed that S1 and S2 contain the β phase exclusively. In contrast, S3 comprises a mixture of α and β phases. The Vickers hardness values for S1 and S2 are 202 and 206 HV, respectively. In contrast, the hardness value of specimen S3 was around 260 HV. The potentiodynamic polarization study reveals that S1 and S2 show similar corrosion behavior, whereas unexpected corrosion behavior has been observed for S3 in an 11.5 M nitric acid medium. A boiling corrosion test in the same solution exposes no weight loss for S1 and S2, whereas S3 shows a high corrosion rate of 156 mpy (3.96 mm/yr). The corrosion-tested specimens were characterized by using Laser Raman Spectroscopy (LRS), X-ray photoelectron spectroscopy (XPS), and Glow Discharge Optical Emission Spectroscopy (GDOES) in correlation with hardness and corrosion resistance are discussed.