In this study the effect of three different nickel concentration on the microstructure, hardness and corrosion properties of high entropy alloys (HEAs) from AlCrFeCoNi system as an alternative material for medical instruments fabrication was investigated. The analyzed HEAs were AlCrFeCoNix obtained by vacuum arc remelting from high purity raw materials and having nickel atomic ratio x = 1.0, 1.4 and 1.8. The microscopy examination revealed the dendritic morphology for the reference alloy (AlCrFeCoNi) and that the extent of the interdendritic areas increased with the concentration of nickel while Cr was more segregated in the interdendritic areas than in dendrites. Hardness values decreased as the percentage of nickel increased due to the dissolution of the precipitates in a nickel-rich matrix and consequently the formation of continuous solid solutions. The corrosion properties of the synthesized HEAs were evaluated using a potentiodynamic polarization method. The alloys were immersed in Simulated Body Fluid during one week and the corrosion parameters were recorded. The low corrosion rates, low corrosion currents and high polarization resistance attest the good stability of these HEAs in simulated biological environment indicating their possible use for surgical and dental instruments.
The β-Ti alloys have attracted the attention of researchers due to their excellent properties and their remarkable biocompatibility. The present study evaluated the mechanical behavior analysis (hardness, compressive strength, and modulus of elasticity) of the Ti-15Mo-W system. For experimental research, we chose the TiMo15 biocompatible alloy as a starting material. In order to improve the mechanical properties, we added tungsten amounts of 3.88 to 12.20 wt.% and analyzed the results obtained. The successive melting of the samples was done using a vacuum arc furnace in a copper crucible cooled with water. Following micro-structural investigations, we found this alloy possessed a homogeneous structure and showed β-phase predominance. The investigated alloys have good mechanical properties—the mean Vickers micro-hardness values are between 251 to 321 HV, the compressive strength values range from 717 to 921 MPa, and the modulus of elasticity is between 17.86 and 45.35 GPa. These results are compatible to the requirements of a metallic material for medical applications as artificial implant devices.
The AlCrFeCoNi high entropy alloy exhibits unexpected properties that can be obtained after mixing five different elements, which could not be obtained from any one independent element. The difference to conventional alloys is that these alloys may have, at the same time, both hardness and plasticity, can be used in severe impact applications. In order to study the influence of aluminum content on the microhardness and microstructure of the high entropy alloys AlxCrFeCoNi (x: atomic ratio, x= 0.2 to 2.0) nine types of samples were obtained as mini-sized ingots (50x15x9.5 mm and 40 g weight). The mini-ingots were obtained using arc melt casting process in a vacuum arc remelting device (VAR MRF ABJ 900). The influence of the chemical elements on the microstructure, phases morphology and microhardness of AlxCrFeCoNi system was studied. The results have confirmed that mechanical properties could be greatly adjusted by the chemical composition change. The main element that influences the microhardness of the analyzed system is aluminum, due to the formation of Al-Fe compounds with high hardness. Increasing the aluminum content in the alloy to values greater than 1.8 ... 2 at.% contribute to the increase of hardness and also to the embrittlement thereof. Other elements like Cr, Fe, Co and Ni can contribute to mitigate increasing the hardness of the alloy. The type of phases formed in high entropy alloy are dependent to the aluminum concentration. So, depending on of aluminium content, different phases are obtained, like FCC for low Al content, mixture of FCC and BCC for about 2.5 %Al and BCC for high Al content. The crystallite size depends on the chemical composition and increase with the aluminium content.
The paper presents the microstructure and corrosion behavior of an AlTiNiCuAgSn new equiatomic multicomponent alloy. The alloy was obtained using the vacuum arc remelting (VAR) technique in MRF-ABJ900 equipment. The microstructural analysis was performed by optical and scanning electron microscopy (SEM microscope, SEM-EDS) and the phase transformations were highlighted by dilatometric analysis and differential thermal analysis (DTA). The results show that the as-cast alloy microstructure is three-phase, with an average microhardness of 487 HV0.1/15. The obtained alloy could be included in the group of compositionally complex alloys (CCA). The corrosion resistance was studied using the potentiodynamic method in saline solution with 3.5% NaCl. Considering the high corrosion resistance, the obtained alloy can be used for surface coating applications.
Considering the future trends of biomaterials, current studies are focused on the corrosion resistance and the mechanical properties of new materials that need to be considered in the process of strengthening alloys with additive non-toxic elements. Many kinds of titanium alloys with different biocompatible elements (Mo, Si, Zr, etc.,) have been recently developed for their similar properties with human bone. Four new different alloys were obtained and investigated regarding their microstructure, mechanical, chemical, and biological behavior (in vitro and in vivo evaluation), the alloys are as follows: Ti15Mo7Zr15Ta, Ti15Mo7Zr15Ta0.5Si, Ti15Mo7Zr15Ta0.75Si, and Ti15Mo7Zr15Ta1Si. There were changes with the addition of the silicon element such as the hardness and the modulus of elasticity increased. An MTT assay confirmed the in vitro cytocompatibility of the prepared alloys.
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