New FeMoTaTiZr High-Entropy Alloy for Medical Applications

Abstract

High-entropy alloys are novel metallic materials distinguished by very special mechanical and chemical properties that are superior to classical alloys, attracting high global interest for the study and development thereof for different applications. This work presents the creation and characterisation of an FeMoTaTiZr high-entropy alloy composed of chemical constituents with relatively low biotoxicity for human use, suitable for medical tools such as surgical scissors, blades, or other cutting tools. The alloy microstructure is dendritic in an as-cast state. The chemical composition of the FeMoTaTiZr alloy micro-zone revealed that the dendrites especially contain Mo and Ta, while the inter-dendritic matrix contains a mixture of Ti, Fe, and Zr. The structural characterisation of the alloy, carried out via X-ray diffraction, shows that the main phases formed in the FeMoTaTiZr matrix are fcc (Ti7Zr3)0.2 and hcp Ti2Fe after annealing at 900 ◦C for 2 h, followed by water quenching. After a second heat treatment performed at 900 ◦C for 15 h in an argon atmosphere followed by argon flow quenching, the homogeneity of the alloy was improved, and a new compound like Fe3.2Mo2.1, Mo0.93Zr0.07, and Zr(MoO4)2 appeared. The microhardness increased over 6% after this heat treatment, from 694 to 800 HV0.5, but after the second annealing and quenching, the hardness decreased to 730 HV0.5. Additionally, a Lactate Dehydrogenase (LDH) cytotoxicity assay was performed. Mesenchymal stem cells proliferated on the new FeMoTaTiZr alloy to a confluence of 80–90% within 10 days of analysis in wells where the cells were cultured on and in the presence of the alloy. When using normal human fibroblasts (NHF), both in wells with cells cultured on metal alloys and in those without alloys, an increase in LDH activity was observed. Therefore, it can be considered that certain cytolysis phenomena (cytotoxicity) occurred because of the more intense proliferation of this cell line due to the overcrowding of the culture surface with cells.