Metallic biomaterials are used in medical devices in humans more than any other family of materials. The corrosion resistance of an implant material affects its functionality and durability and is a prime factor governing biocompatibility. The fundamental paradigm of metallic biomaterials, except biodegradable metals, has been “the more corrosion resistant, the more biocompatible.” The body environment is harsh and raises several challenges with respect to corrosion control. In this invited review paper, the body environment is analysed in detail and the possible effects of the corrosion of different biomaterials on biocompatibility are discussed. Then, the kinetics of corrosion, passivity, its breakdown and regeneration in vivo are conferred. Next, the mostly used metallic biomaterials and their corrosion performance are reviewed. These biomaterials include stainless steels, cobalt-chromium alloys, titanium and its alloys, Nitinol shape memory alloy, dental amalgams, gold, metallic glasses and biodegradable metals. Then, the principles of implant failure, retrieval and failure analysis are highlighted, followed by description of the most common corrosion processes in vivo. Finally, approaches to control the corrosion of metallic biomaterials are highlighted.

Corrosion of Metallic Biomaterials: A Review

Corrosion fatigue of biomedical metallic alloys: Mechanisms and mitigation

High-performance conventional engineering materials (including Al alloys, Mg alloys, Cu alloys, stainless steels, Ni superalloys, etc.) and newly-developed high entropy alloys are all compositionally-complex alloys (CCAs). In these CCA systems, the second-phase particles are generally precipitated in their solid-solution matrix, in which the precipitates are diverse and can result in different strengthening effects. The present work aims at generalizing the precipitation behavior and precipitation strengthening in CCAs comprehensively. First of all, the morphology evolution of second-phase particles and precipitation strengthening mechanisms are introduced. Then, the precipitation behaviors in diverse CCA systems are illustrated, especially the coherent precipitation. The relationship between the particle morphology and strengthening effectiveness is discussed. It is addressed that the challenge in the future is to design the stable coherent microstructure in different solid-solution matrices, which will be the most effective approach for the enhancement of alloy strength.

https://www.mdpi.com/1099-4300/20/11/878/pdf

Coherent Precipitation and Strengthening in Compositionally Complex Alloys: A Review

Microstructure evolution and tensile behavior of the high-entropy alloy Al8Co17Cr17Cu8Fe17Ni33 (at.%) are investigated at room temperature and at 500°C in the as-cast state and under different heat-treatment conditions. Detailed microstructural characterizations are carried out using optical microscopy, scanning electron microscopy, and transmission electron microscopy. The equilibrium phase evolution as a function of temperature was calculated using the Thermo-Calc software (Thermo-Calc Software, Stockholm, Sweden) integrated with TTNi-7 database. The observed majority phase is a face-centered cubic solid solution for all tested specimens. Tensile ductility at room temperature and at elevated temperature is enhanced by heat treatment at 1150°C. An embrittlement phenomenon has been observed after a heat treatment at 700°C resulting in significant degradation in tensile properties.

Microstructure and Tensile Behavior of Al 8 Co 17 Cr 17 Cu 8 Fe 17 Ni 33 (at.%) High-Entropy Alloy

The effect of ɳ-Ni3Ti precipitates and reversed austenite on the passive film stability of nickel-rich Custom 465 steel

The relation between aging temperature, microstructure evolution and hardening of Custom 465® stainless steel

Hydrogen diffusivity measurement and microstructural characterization of Custom 465 stainless steel

The effect of manufacturing processes on the fatigue lifetime of aeronautical bolts

Custom 465 is an advanced precipitation hardened martensitic stainless steel exhibiting a combination of high strength, high fracture toughness and good corrosion resistance. This steel is recommended for use in hydrogen atmospheres, yet only little research has been published on hydrogen behavior in this alloy. Here, the diffusivity, solubility and average detrapping energy for hydrogen were compared in various thermal conditions (solution annealed, H900 and H1000), employing electrochemical permeation and thermal programmed desorption measurements. It is suggested that reversible (low energy) traps in the H900 and H1000 conditions, associated with (semi)coherent η-Ni3Ti precipitates, are responsible for the high hydrogen solubility and low diffusivity. At the peak of coherency of the precipitates in the H900 condition, higher solubility and lower diffusivity and detrapping energy were measured. The value of the diffusion coefficient is found to change during different stages of charging and discharging, depending on the level of occupancy of the reversible traps. © The Author(s) 2018. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0261803jes]

https://iopscience.iop.org/article/10.1149/2.0261803jes/pdf

Hydrogen Diffusivity and Trapping in Custom 465 Stainless Steel

Microstructural changes during plastic deformation and fracture evolution play an important role in the understanding of fracture mechanisms. However, most publications have focused on the initial stages of deformation where the latter is uniform. The current study was focused on the last stages of fracture, the necking, and crack propagation. Tensile specimens were examined by in situ scanning electron microscope equipped with a tensile module and electron backscatter diffraction. It was demonstrated that the fracture evolution consists of scanty diffuse necking followed by pronounced localized necking, in which the deformation band spread through the width of the specimen in two combined mechanisms—shearing and dimpling. The microstructural changes inside the deformation band adjacent to crack edge were compared to those in the uniform deformation zone. In the deformed areas, the grains became elongated and preferentially orientated in the loading direction. The relative frequency of twin boundaries at 60° was reduced in the deformed areas compared to non-deformed areas, while the misorientations at low angles of 3°–15°, which imply on a dislocation pileups subgrained structure, were increased to greater extent at the crack edge. Inside the deformation band, the amount of deformation was increased compared to the uniformly deformed region with grain fragments as a result of the complexity of stresses, although similar deformation mechanisms were identified.

Sigalit Ifergane

Papers

The relation between aging temperature, microstructure evolution and hardening of Custom 465® stainless steel

Hydrogen diffusivity measurement and microstructural characterization of Custom 465 stainless steel

The effect of manufacturing processes on the fatigue lifetime of aeronautical bolts

Hydrogen Diffusivity and Trapping in Custom 465 Stainless Steel

Study of fracture evolution in copper sheets by in situ tensile test and EBSD analysis