In-Situ Laser Directed Energy Deposition of Biomedical Ti-Nb and Ti-Zr-Nb Alloys from Elemental Powders

In order to achieve the required properties of titanium implants, more resources and research are needed to turn into reality the dream of developing the perfect implant material. The objective of this study was to evaluate the viability of the Laser Directed Energy Deposition to produce biomedical Ti-Nb and Ti-Zr-Nb alloys from elemental powders (Ti, Nb and Zr). The Laser Directed Energy Deposition is an additive manufacturing process used to build a component by delivering energy and material simultaneously. The material is supplied in the form of particles or wire and a laser beam is employed to melt material that is selectively deposited on a specified surface, where it solidifies. Samples with different compositions are characterized to analyze their morphology, microstructure, constituent phases, mechanical properties, corrosion resistance and cytocompatibility. Laser-deposited Ti-Nb and Ti-Zr-Nb alloys show no relevant defects, such as pores or cracks. Titanium alloys with lower elastic modulus and a significantly higher hardness than Ti grade 2 were generated, therefore a better wear resistance could be expected from them. Moreover, their corrosion resistance is excellent due to the formation of a stable passive protective oxide film on the surface of the material; in addition, they also possess outstanding cytocompatibility.

Electrochemical behaviour of some commercial stainless steel alloys in simulated body fluid electrolytes

Purpose The commercial stainless steels have been used extensively in the biomedicine application and their electrochemical behaviour in the simulated body fluid (SBF) are not uncovered obviously. In this research, the corrosion resistance of the commercial stainless steel of Fe–17Cr–xNi alloys (x = 4, 8, 10 and 14) has been studied. This study aims to evaluate the rate of corrosion and corrosion resistance of some Fe–Cr–Ni alloys in SBF at 37°C. Design/methodology/approach In this research, the corrosion resistance of the commercial stainless steel of Fe–17Cr–xNi alloys has been studied using open circuit potential, electrochemical impedance spectroscopy and potentiodynamic polarization in the SBF at 37°C and pH 7.4 for a week. Also, the surface morphology of the four alloys was investigated using scanning electron microscopy, elemental composition was obtained via energy dispersive spectroscopy and the crystal lattice structure of Fe–17Cr–xNi alloys was obtained using X-ray diffraction technique. The chemical structure of the protective oxide film has been examined by X-ray photoelectron spectroscopy (XPS) and metals ions released into the solution have been detected after different immersion time using atomic absorption spectroscopy. Findings The results revealed that the increase of the Ni content leads to the formation of the stable protective film on the alloys such as the Fe–17Cr–10Ni and Fe–17Cr–14Ni alloys which possess solid solution properties. The Fe–17Cr–14Ni alloy displayed highest resistance of corrosion, notable resistance for localized corrosion and the low corrosion rate in SBF because of the formation of a homogenously protective oxide film on the surface. The XPS analysis showed that the elemental Fe, Cr and Ni react with the electrolyte medium and the passive film is mainly composed of Cr2O3 with some amounts of Fe(II) hydroxide at pH 7.4. Originality/value This work includes important investigation to use commercial stainless steel alloys for biomedical application.

Research of Heat Resistance and Thermophysical Properties of the Diffusion Zone Formed by Annealing by Contact Melting Mode of the Layered Metal-Intermetallic Composite of the Cu-Al System

The results of studying the effect of isothermal annealing on structural, phase transformations, and thermal diffusivity in the diffusion zone of a Cu-Al layered metal-intermetallic composite (LMIC), obtained using technology including explosion welding, pressure treatment and heat treatment, are presented. It was found that, at 530 °C (the highest temperature, excluding the formation of a liquid phase in this system) with a holding time of up to 1000 h, there are no structural phase transformations in the Al (Cu)/CuAl2 metal-intermetallic composition, and a slight increase in its mass is associated with the formation of a thin dense protective oxide film on the surface. The thermal diffusivity of Cu-Al LMIC, obtained after removal of copper residues from the surface of the diffusion zone, is 50–60 W/m×K, which is significantly lower than that of copper (410 W/m×K) and aluminum (220 W/m×K).

Effects of Al, Zn, and rare earth elements on flammability of magnesium alloys subjected to sonic burner–generated flame by Federal Aviation Administration standards

Mg alloys are promising structural materials in aerospace industry due to high strength to weight ratio. However, most Mg alloys are limited in aircraft cabins due to their susceptibility to ignition and burning. To improve fire resistance, adding alloying elements is a strategy. Thus, the goal of this study is to explore the effects of alloying elements Al, Zn, and rare earths on Mg-alloy flammability by experiment, using the system and procedures in compliance with the Federal Aviation Administration (FAA) standards for Mg-alloy flammability test. Six commercial Mg alloys with different alloying elements (AZ91E, ZK61A, ZE63A, EZ33A, WE43B, and EV31A) were tested. Results indicate that Mg alloys with Al or Zn elements were of short ignition time and high weight loss. With rare earths, Mg-alloy flammability was suppressed obviously. It appears that this suppression effect with rare earth addition was attributed to the formation of protective oxide film on the surface of molten alloy. Further, a heat transfer model was established to analyze the temperature evolution of the test specimen subjected to the sonic burner–generated flame by FAA standards, and ignition temperatures of all testing Mg alloys were predicted based on the experimental ignition time. The predicted results confirm that with rare earths addition, ignition was delayed after melting by the protective oxide film formed on the surface of the molten alloy.

STUDY OF THE STRUCTURE AND PHASE COMPOSITION OF THE OXIDE FILM ON THE SURFACE OF A LAYERED COATING OF THE Al-Ni SYSTEM

This work is aimed to the study of the structure and phase composition of the oxide film formed on the surface of the layered coating of the Al-Ni system during high-temperature heating. It was experimentally established that at the initial stages of heat treatment, as a result of the interaction of the Al-Ni system layered coating with atmospheric oxygen, separate sections of Al2O3 oxide are formed on its surface, which are agglomerates of plate crystals of α-modification of nanometer thickness, which increase and grow together with increasing exposure time continuous protective oxide film. An increase in the heating temperature leads to an intensification of oxidation processes and the formation of a complex oxide film of AlO and spinel NiAlO.

The Role of H2O2 and K2S2O8 as Oxidizing Agents for Accelerated Corrosion Testing

In this work, the application of hydrogen peroxide (H2O2) and potassium persulfate (K2S2O8) in accelerated corrosion testing was considered. H2O2 is already used as an accelerant in the standard immersion test ASTM G110, and K2S2O8 is an oxidizing agent that shows promise for corrosion testing applications. A Koutecky-Levich approach was used to investigate the cathodic kinetics of both oxidizing agents as well as dissolved oxygen (O2). Cathodic kinetics for O2, H2O2, and S2O82− were faster when measured on a platinum electrode than when measured on an AA2060-T3 electrode. This difference was attributed to the additional limit to cathodic kinetics posed by the protective oxide film on aluminum. H2O2 was a more potent accelerant than K2S2O8 at a concentration of 0.1 M due to the faster cathodic kinetics of H2O2 on aluminum. However, K2S2O8 was more convenient to use in a laboratory setting due to its stability during storage. The severity of tests using K2S2O8 was increased by lowering the solution pH to 2.28. At the low solution pH, cathodic kinetics and extent of attack increased.

Low Cycle Fatigue Behavior of Superalloy GH4169 in High Temperature Gas Environment

Turbine components (blades, guides and casing) of gas turbine engine usually suffer from fatigue load in company with a HTG environment in service. The corrosive substances in HTG can deposit on the surface of turbine components and induce accelerated damage known as hot corrosion. In this study, an experimental system is designed and built up to conduct LCF tests of superalloy in HTG environment. The influence of HTG on the LCF behavior of the nickel-base superalloy GH4169 at 650°C is studied. According to the test results, the average fatigue life of the specimens in HTG environment (22270 cycles) is about 31.5% less than that in air (32496 cycles). The protective oxide film on the surface of the specimen can be destroyed by the electrochemical reaction between HTG and oxide film. Compared with the specimen tested in air, there are more fatigue sources in the specimen tested in HTG environment, and the transgranular–intergranular transition occurs in the crack growth area.

Surface Characterization and Corrosion Behavior of 90/10 Copper-Nickel Alloy in Marine Environment

Surface characterization and corrosion behavior of 90/10 copper-nickel alloy in seawater from Xiamen bay at 30 °C for 56 days were investigated in this study. The results indicated that the corrosion product layer was mainly a mixture of CuO, Cu2O, and Cu(OH)2, with a transition to CuCl, CuCl2, and Cu2(OH)3Cl during the corrosion process. However, as corrosion proceeds, the resistance of the product film was reduced due to its heterogeneous and fairly porous structures, which led to local corrosion of the alloy. The corrosion potentials (Ecorr) increase while corrosion current densities (Icorr) decrease with time because of the formation of protective oxide film.