A low-cost, low-density and corrosion resistant compositionally complex alloy: AlFeMnSi

A new class of compositionally complex alloy, consisting of equiatomic concentrations of Al, Fe, Mn and Si is reported. The alloy was characterized using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Corrosion behavior of the AlFeMnSi alloy, as evaluated using potentiodynamic polarization tests and electrochemical impedance spectroscopy in 0.6 M NaCl solution, was comparable with that of stainless steel (SS) 304L. X-ray photoelectron spectroscopy was used to study the AlFeMnSi surface film. The AlFeMnSi alloy also exhibited a lower cost, lower density, and a higher hardness as compared with SS 304L, rendering it a promising alloy for bespoke applications.

Effect of Calcium Content on the Microstructure and Degradation of Mg-Ca Binary Alloys Potentially Used as Orthopedic Biomaterials

The effect of calcium addition in modifying the microstructural aspects and corrosion behavior was investigated on two different biodegradable magnesium alloys type Mg-xCa binary alloys (x = 0.8, 1.8 wt. (%)). Systematic microstructure investigations was made using optical microscopy and scanning electron microscopy coupled with energy dispersive X-ray. Following these experimental investigations, in the microstructure of the investigated Mg-Ca alloys a notable refinement was observed occurred with increasing the calcium content. The evaluation of corrosion resistance was performed both using electrochemical measurements and hydrogen release in simulated body fluid (SBF), as proposed by Kokubo and his colleagues, maintaining the temperature at 37°C. The results showed a lower corrosion resistance when the calcium content was increased, due to the increased Mg2Ca intermetallic phase in grain boundaries. Consequently, our preliminary results showed that MgCa0.8 alloy having a minimal amount of Mg2Ca appear to be a promising alloy to be used as a biomaterial for orthopedic implants.

Performance of Oxidation and Creep Resistant Alloys for Primary Surface Recuperators for the Mercury 50 Gas Turbine

Recuperation is a means for increasing the efficiency of a simple-cycle gas turbine, allowing for heat transfer between the exhaust and compressor discharge gas streams to occur in a highly efficient, relatively compact package. The primary surface recuperator operates at high temperatures and gas pressures and is constructed from thin metal sections, presenting challenges for high temperature materials selection. This paper discusses a joint Solar Turbines-ATI Allegheny Ludlum project which was undertaken to address the issue of elevated temperature attack in the presence of high levels of water vapor and its relevance to alloys intended for use in primary surface recuperators. An overview of the alloy selection process will be presented, followed by a detailed study of the two most promising alloy candidates. Breakaway oxidation was mitigated by using alloys with higher nickel and chromium content, and oxide scale evaporation was controlled with selected minor element additions.