Degradation Of Alloys Research Articles

Current Research Studies of Mg–Ca–Zn Biodegradable Alloys Used as Orthopedic Implants—Review

Biodegradable alloys and especially magnesium-based alloys are considered by many researchers as materials to be used in medicine due to their biocompatibility and excellent mechanical properties. Biodegradable magnesium-based materials have applications in the medical field and in particular in obtaining implants for small bones of the feet and hands, ankles, or small joints. Studies have shown that Mg, Zn, and Ca are found in significant amounts in the human body and contribute effectively and efficiently to the healing process of bone tissue. Due to its biodegradability, magnesium alloys, including Mg–Ca–Zn alloys used in the manufacture of implants, do not require a second surgery, thus minimizing the trauma caused to the patient. Other studies have performed Mg–Ca–Zn system alloys with zinc variation between 0 and 8 wt.% and calcium variation up to 5 wt.%, showing high biocompatibility, adequate mechanical properties, and Mg2Ca and Mg6Ca2Zn compounds in microstructure. Biocompatibility is an essential factor in the use of these materials, so that some investigations have shown a cell viability with values between 95% and 99% compared with the control in the case of Mg–0.2Ca–3Zn alloy. In vivo analyses also showed no adverse reactions, with minimal H2 release. The aim of this review includes aspects regarding microstructure analysis and the degradation mechanisms in a specific environment and highlights the biocompatibility between the rate of bone healing and alloy degradation due to rapid corrosion of the alloys.

(Digital Presentation) Assessment of the Cyclic Stability of a Bench-Scale TiFe-Based Hydrogen Storage Tank

Hydrogen storage devices comprising of low-cost and flexible metal hydrides have recently regained vivid interest as basic elements in energy conversion systems. Among many intermetallic compounds, TiFe-based alloys are one of the most promising candidates to hold atomic hydrogen because of their significant storage capacity of about 1.9 wt.% and moderate operating conditions. However, the alloy degradation in repeated hydriding- and dehydriding cycles inevitably affects the performance of the hydrogen storage system. In this work, the intrinsic degradation behavior of a bench-scale TiFe-based alloy tank has been investigated. Thermal cyclic life tests were performed between 5°C and 45°C, and the heat transfer properties of the storage device were tested over repeated cycles by obtaining temperature histories. A thermal imaging device was used for the internal heat transfer mapping and the charging time and pressure-composition isotherms were recorded for the hydriding- and dehydriding reactions. In Figure 1 thermal images of the discharge reaction at Begin of Life (BoL) and End of Life (EoL) of the storage device are shown. The hydrogen storage capacity was observed to decrease by almost 90% after 100 cycles. Heat transfer mapping revealed that the excess portion of degradation occurs in the middle of the storage device and is attributed to the formation of inactive TiFe clusters based on the measurements. Acknowledgment: Financial support by the Austrian Research Promotion Agency (FFG) through the 8th Call of “COMET-Projects” is gratefully acknowledged. Figure 1 . Thermal image of the TiFe storage device at Begin of Life (BoL) a) and End of Life (EoL) b) after discharging for 240s respectively. Figure 1

Shot Peening Induced Corrosion Resistance of Magnesium Alloy WE43

Mechanical surface treatments like shot peening provide a pathway to stabilize degradation of magnesium alloys without compositional change. The resultant subsurface grain refinement, twin dislocations, and nanoprecipitation improves fatigue life but lowers corrosion resistance of magnesium. The lower corrosion resistance is justified by an increase in surface roughness after shot peening. However, a skewed estimate of surface area is expected to justify the inconsistent corrosion behavior of shot peening magnesium compared to other mechanical surface treatments. The objective of this research was to understand the influence of surface topography due to shot peening on the corrosion kinetics of a magnesium alloy WE43. Results showed that the corrosion resistance increased after shot peening WE43 when using an adjusted surface area that better accounts for the topographical features under exposure to corrosion attack.

Influence of Iron and Silicon Impurities on the in-service Degradation of Alloys of the Al-Cu-Mg and Al-Zn-Mg-Cu Systems

Influence of Iron and Silicon Impurities on the in-service Degradation of Alloys of the Al-Cu-Mg and Al-Zn-Mg-Cu Systems

Early biomimetic degradation of Mg-2Ca alloy reveals the impact of β-phases at the interface of this biomaterial on a micro-scale level

Despite several studies on Mg-Ca alloys as bone implants, the understanding of its early degradation in the first hours of immersion is still lacking. To overcome this gap, advanced localized electrochemical techniques were used to study the corrosion onset of Mg-2Ca alloy 2 h upon immersion. The presence of the nobler β-phase induced Mg dissolution from the matrix, an event supporting the positive response of osteoblast stem cells. This, together with apatite precipitation within the corrosion layer highlights the potential of Mg-2Ca for bone implants. The data gathered in this work contribute to tailoring the design of new Mg-Ca alloys.

Stability of oxide-sulfate mixtures and implications for deposit-induced degradation of advanced alloys and coatings

Turbine engines ingest atmospheric aerosols that include multi-cation oxide-sulfate mixtures, which deposit onto surfaces within the engine. These deposits are often implicated in hot corrosion of alloys and bond coats and can accelerate thermomechanical failure of ceramic coatings through reaction and infiltration mechanisms. Understanding the intrinsic stability of oxide-sulfate deposits, including the tendency for sulfate decomposition, is important to identify efficient testing protocols. This work addresses that need by integrating experiments and computational thermodynamics models to systematically analyze the effect of deposit composition and temperature on the sulfate decomposition and melting behavior of five model mixed-anion deposits. Mass loss analysis and energy dispersive x-ray spectroscopy show that sulfate decomposition occurs much faster in the mixtures compared to pure calcium sulfate. The thermodynamic computations show that reaction pathways forming ternary and quaternary silicates accelerate sulfate decomposition faster than those forming binary reaction products. The results also show that multi-cation mixtures can suppress the evaporation of sodium and potassium sulfates, retaining the sulfate-bearing liquid to higher temperatures. The results can be used to differentiate the behavior of sulfate-, sulfate-oxide-, and oxide-based deposits, and to guide the discovery of new high temperature alloys and coating materials.

The golden alloy Cu5Zn5Al1Sn: effect of immersion time and anti-corrosion activity of cysteine in 3.5 wt% NaCl solution

Abstract The effect of cysteine on the corrosion characteristics of Cu5Zn5Al1Sn alloy in 3.5 wt% NaCl solution has been studied by electrochemical and surface characterization techniques in various immersion times. The results of electrochemical impedance spectroscopy (EIS) revealed that the degradation of Cu5Zn5Al1Sn alloy occurred in 3.5 wt% NaCl and was aggravated with increasing immersion time. The results of inhibition efficiency calculated from EIS data showed that cysteine can act as an effective anti-corrosion substance, which was also proved by the less eroded morphology of the alloy surface observed on scanning electron microscopy (SEM). Furthermore, the elemental analysis of alloy surfaces was investigated by Raman, electron dispersion spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS), which confirmed the presence of S and N species. An adequate adsorption isotherm and inhibition mechanism was also suggested based on EIS results.

Advances in degradation behavior of biomedical magnesium alloys: A review

Magnesium alloys have become promising biomedical metal materials because of their biocompatibility, degradability, and good mechanical properties. However, the rapid degradation of magnesium alloys and its associated effects have limited the applications of magnesium alloys. Alloying and preparation processes can reduce the degradation rate by changing the microstructure of magnesium alloys, such as grain size, porosity, formation of intermetallic compounds/second phases, etc. In this paper, the in vitro and in vivo degradation of magnesium alloys were reviewed in terms of degradation mechanism, influencing factors, and corrosion products. Composition design and manufacturing process were mainly discussed for controlling the degradation, and surface treatment and structural design were briefly described as control methods of degradation. This helps achieve the goal of controlled and predictable degradation rate of magnesium alloys.

Effects of heat treatment on the corrosion behavior and mechanical properties of biodegradable Mg alloys

Biodegradable magnesium (Mg) alloys exhibit great potential for use as temporary structures in tissue engineering applications. Such degradable implants require no secondary surgery for their removal. In addition, their comparable mechanical properties with the human bone, together with excellent biocompatibility, make them a suitable candidate for fracture treatments. Nevertheless, some challenges remain. Fast degradation of the Mg-based alloys in physiological environments leads to a loss of the mechanical support that is needed for complete tissue healing and also to the accumulation of hydrogen gas bubbles at the interface of the implant and tissue. Among different methods used to improve the performance of the biodegradable Mg alloys to address these challenges, it appears that heat treatment is the most effective way to modify the microstructure and thus the corrosion behavior and mechanical properties without changing the composition or shape of the alloys. A desirable combination of corrosion and mechanical properties can be obtained through a precise control of the heat treatment parameters. In this report, the effects of different heat treatments (T4 and T6) on the microstructure, corrosion behavior, and mechanical properties of some of the most important heat-treatable biodegradable Mg alloys (Mg-Zn, Mg-Gd, Mg-Y, Mg-Nd, Mg-Al and Mg-Ag) are examined as well as new perspectives to enhance their clinical implementation.

The deteriorated degradation resistance of Mg alloy microtubes for vascular stent under the coupling effect of radial compressive stress and dynamic medium

The degradation of Mg alloys relates to the service performance of Mg alloy biodegradable implants. In order to investigate the degradation behavior of Mg alloys as vascular stent materials in the near service environment, the hot-extruded fine-grained Mg-Zn-Y-Nd alloy microtubes, which are employed to manufacture vascular stents, were tested under radial compressive stress in the dynamic Hanks’ Balanced Salt Solution (HBSS). The results revealed that the high flow rate accelerates the degradation of Mg alloy microtubes and its degradation is sensitive to radial compressive stress. These results contribute to understanding the service performance of Mg alloys as vascular stent materials.

Biofunctionalization of Mg implants with gadolinium coating for bone regeneration

Magnesium (Mg) alloys are biodegradable and biocompatible in nature, hence used as bio-implants. Mg alloys possess favourable mechanical properties same as that of human bone. In this work, we demonstrate a simple strategy of formulating a gadolinium conversion coating (GCC) on a biodegradable AZ31 Mg implant that effectively diminishes the corrosion rate and enhances bone formation. AZ31 Mg alloys were immersed in gadolinium nitrate solution at different durations (5, 15, 30, 45 and 60 min) and labeled as GCC-5, GCC-15, GCC-30, GCC-45 and GCC-60 to fabricated gadolinium conversion coating (GCC) on AZ31 Mg alloys. The rapid degradation of AZ31 Mg alloy was reduced by GCC. The surface morphological analysis with the Scanning Electron Microscope (SEM) showed that the vertically arranged cross-linked nanolamellar plates were grown on the AZ31 Mg alloy surface. Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) results evident that the GCC consists of magnesium oxide and gadolinium oxide were present in the crystalline state. The in-vitro biomineralization of the GCC was analyzed by immersing in simulated body fluid (SBF) solution for 7 days and confirms the formation of nanoglobular hydroxyapatite. The cell culture studies showed an increase in the cell numbers than the bare.

Role of Lysinibacillus sphaericus on aviation kerosene degradation and corrosion of 7B04 aluminum alloy

Microbial activity leads to degradation of kerosene, corrosion of pipeline and deterioration of stored products. This paper describes the use of the Fourier transform infrared spectroscopy (FT-IR), turbidimetry, pH measurements, electrochemical impedance spectroscopy (EIS), polarization curves and surface analysis to study the degradation of kerosene by Lysinibacillus sphaericus and its effect on the corrosion behavior of 7B04 aluminum alloy. A model strain was isolated from the contaminated kerosene and identified as L. sphaericus based on cloning of the 16 S rDNA gene and sequence analysis. FT-IR results showed that aliphatic protons in kerosene were degraded in the presence of L. sphaericus. SEM and EDS analysis showed that L. sphaericus colonized on the surface of aluminum alloy, formed biofilm and produced organic acids in physiological activities. Thus, the drop of pH resulted in the decrease of the cathodic depolarization, indicating the acceleration of corrosion. In addition, electrochemical measurements showed that the corrosion resistance of aluminum alloy was reduced, and the corrosion current density increased after immersion in the L. sphaericus system compared to the value in the sterile system, revealing the L. sphaericus promoted the corrosion of aluminum alloy.

Influence of Al and Fe additions on metal dusting of NiCr alloys

AbstractCorrosion by metal dusting causes problems in various industries that process carbonaceous gases. Recently, the chromium‐ and aluminum‐rich Ni‐based Alloy 699 XA was introduced as a material with high resistance against metal dusting attacks. In this study, the metal dusting degradation of Alloy 699 XA and model alloys was investigated. In the model alloys, the aluminum, chromium, and iron contents were varied to analyze the role of each element systematically. Alloy 602 CA was included as a reference material. It was found that the alloys with the highest chromium and aluminum contents (30 and 2–3 wt%, respectively) showed the highest resistance against metal dusting. Also, the limited addition of iron enhanced the aluminum activity and thereby promoted the formation and maintenance of an aluminum‐rich oxide scale. This effect at low iron levels is contrary to the negative impact of iron at higher levels, which typically leads to an increased metal dusting susceptibility. Exposure tests were performed with two gas mixtures having similar compositions, but different carbon activities. It was found that both gases had a similar aggressiveness regarding metal dusting attacks.

Advances in bioorganic molecules inspired degradation and surface modifications on Mg and its alloys

Mg alloys possess biodegradability, suitable mechanical properties, and biocompatibility, which make them possible to be used as biodegradable implants. However, the uncontrollable degradation of Mg alloys limits their general applications. In addition to the factors from the metallic materials themselves, like alloy compositions, heat treatment process and microstructure, some external factors, relating to the test/service environment, also affect the degradation rate of Mg alloys, such as inorganic salts, bioorganic small molecules, bioorganic macromolecules. The influence of bioorganic molecules on Mg corrosion and its protection has attracted more and more attentions. In this work, the cutting-edge advances in the influence of bioorganic molecules (i.e., protein, glucose, amino acids, vitamins and polypeptide) and their coupling effect on Mg degradation and the formation of protection coatings were reviewed. The research orientations of biomedical Mg alloys in exploring degradation mechanisms in vitro were proposed, and the impact of bioorganic molecules on the protective approaches were also explored.

A comprehensive review on biocompatible Mg-based alloys as temporary orthopaedic implants: Current status, challenges, and future prospects

Mg and its alloys are drawing huge attention since the last two decades as a viable option for temporary implants applications. A commendable progress has already been made in the development of these alloys. The biodegradable nature of Mg, appreciable biocompatibility of elemental Mg, and its close resemblance to natural bone in terms of density and elastic modulus make them highly preferable option amongst other available alternatives in this field. This review article presents an overview covering the recent advancements made in the field of Mg-based biodegradable implants for orthopaedic implant applications. The paper focuses on alloy development and fabrication techniques, the state of the art of important Mg-based alloy systems in terms of their mechanical properties, in-vitro and in-vivo degradation behaviour and cytotoxicity. Further, the paper reviews the current progress achieved in the clinical transition of Mg-based alloys for orthopaedic fixtures. The review also includes the degradation mechanisms of the alloys in physiological environment and highlights the mismatch existing between the rate of bone healing and alloy degradation due to rapid corrosion of the alloys in such environment, which has still restricted their widespread application. Finally, the surface coating techniques available for the alloys as an effective way to reduce the degradation rate are reviewed, followed by a discussion on the future research prospects.

Segregation sequence of phosphorus and its effect on impact toughness of GH984G alloy during thermal exposure

The segregation sequence of phosphorus and the influence on impact toughness of GH984G alloy, for the application of advanced ultra-super critical (A-USC) power plant, were studied during long-term thermal exposure at 700 °C. The results show that the segregation of phosphorus is associated with the phosphorus content and exposure time. Phosphorus atoms become rich around the MC carbides firstly, then segregates to the grain boundaries and twin boundaries in the form of solute P atoms with increasing phosphorus content and prolonging thermal exposure. Phosphorus can also exist around the MC carbides and at grain boundaries in the form of needle-like phosphide when the alloys with high P content are subjected to long-term thermal exposure. The impact toughness degradation of phosphorus-containing alloys is related to the phosphorus redistribution during thermal exposure. The segregation degree of phosphorus at grain boundaries rises with the increase of P content during thermal exposure. Excess phosphorus segregation at grain boundaries decreases the binding force of grain boundaries and results in the grain boundary embrittlement. Also, the needle-like phosphides around the MC carbides and at grain boundaries in high-phosphorus alloy induce the cracks initiation during impact. Hence, the impact toughness decreases with increasing phosphorus content after thermal exposure at 700 °C.

Processing optimization, mechanical properties, corrosion behavior and cytocompatibility of additively manufactured Zn-0.7Li biodegradable metals

Biodegradable Zn-Li alloys exhibit superior mechanical performance and favorable osteogenic capability for load-bearing bone devices. Additive manufacturing (AM) endows freedom for the fabrication of bone implants of personalized structure to satisfy patient-specific needs. In this paper, AM of Zn-Li alloys was attempted for the first-time using laser powder bed fusion (LPBF), and the fabricated samples exhibited good fusion quality and high dimensional accuracy. The processing optimization, mechanical properties, in vitro corrosion behavior and cytocompatibility were investigated by using Zn-0.7Li bulk and porous samples. The ultimate tensile strength and elastic modulus of bulk samples respectively reached 416.5 MPa and 83.3 GPa, and both were the highest among various additively manufactured Zn alloys reported so far. Porous samples achieved compressive strength (18.2 MPa) and elastic modulus (298.0 MPa), which were comparable to those of cancellous bone. Porous samples exhibited a higher corrosion rate and alleviated the problem of slow degradation of Zn-Li alloys. Nevertheless, osteoblastic cells showed a more spreading and healthier morphology when adhering to the porous samples compared to the bulk samples, thus a better cytocompatibility was confirmed. This work shows tremendous potential to precisely design and modulate biodegradable Zn alloys to fulfill clinical needs by using AM technology. Statement of significanceThis paper firstly studied processing optimization during laser powder bed fusion of Zn-Li alloy. Bulk and porous Zn-0.7Li samples in customized design were obtained with high formation quality. The tensile strength of bulk samples reached 416.5 MPa, while the compressive strength and modulus of porous samples reduced to 18.2 MPa and 298.0 MPa, comparable to those of bone. The weight loss of porous samples was roughly 5 times that of bulk samples; osteoblastic cells showed a more spreading and healthier morphology at porous samples, indicating improved biodegradation rate and cytocompatibility. This work shows tremendous potential to precisely design and modulate biodegradable Zn alloy porous scaffolds to fulfill clinical needs by using additive manufacturing technology.

Electrophoretic deposited boron nitride nanosheets-containing chitosan-based coating on Mg alloy for better corrosion resistance, biocompatibility and antibacterial properties

To reduce the degradation of magnesium alloy, improve its antibacterial activity, and fulfil specific requirements for bone implant material applications, a chitosan (CS)/boron nitride nanosheet (BNNS) composite coating was constructed on the surface of Mg–Zn–Y–Nd–Zr alloy via electrodeposition. The results show that BNNS was uniformly embedded and significantly changed the morphology and roughness of the CS coating. Electrochemical and immersion tests suggest that the CS–BNNS composite coating can effectively provide a long-term protection to the substrate. The antibacterial activity results show that BNNS significantly improved the antibacterial activity of the CS coating against E. coli and S. aureus, and verified the sterilisation mechanism of BNNS in contact with bacterial membranes. Meanwhile, cytocompatibility tests showed that the CS–BNNS coating has no adverse effect on the adhesion and proliferation of mouse osteoblasts cells. Thus, the fabricated CS–BNNS composite coating could be a promising application in surface modification for Mg-based bone implants.

Influences of Extrusion and Silver Content on the Degradation of Mg-Ag Alloys In Vitro and In Vivo.

Binary magnesium-silver (Mg-Ag) alloys were designed as antibacterial materials for biomedical implant applications. In the present study, we focused on the effects of extrusion (extrusion ratio (ER): 1, 7.1, and 72.2) and Ag content (Ag = 0, 3, and 6 wt.%) on the degradation of Mg-Ag alloys in vitro and in vivo via microstructure characterization and corrosion/degradation measurements. The results showed that the Ag promoted a galvanic reaction with the Mg matrix to accelerate degradation or formed a protective oxide mesh texture to inhibit degradation, especially in vivo. Ag might also be beneficial for product crystallization, biomineralization, and organic matter deposition. For pure Mg, extrusion produced a more refined grain and decreased the degradation rate. For the Mg-Ag alloys, a low extrusion ratio (7.1) accelerated the degradation caused by the increase in the proportion of the precipitate. This promoted the release of Mg2+ and Ag+, which led to more deposition of organic matter and calcium phosphate, but also more H2 bubbles, which led to disturbance of product deposition in some local positions or even inflammatory reactions. Extrusion at a higher ratio (72.2) dissolved the precipitates. This resulted in moderate degradation rates and less gas production, which promoted osteogenesis without an obvious inflammation reaction.

Corrosion degradation of aluminium alloys using a computational framework

The paper describes the corrosion based degradation of aluminium alloys using an analytical and numerical framework. The corrosion rate was calculated using analytical equations for aluminium sheets subjected to a corrodent. Parametric analysis for the pit morphology, diameter, depth and distribution on the plate was conducted using finite element analysis. A comparison between elliptical and circular pits of the same area was also made for stress magnification using numerical analysis. It was observed that the stress generated at constant load when a specimen corrodes due to pitting is directly proportional to the pit diameter and pit depth. Zigzag pit morphologies due to the combined effect of mechanical degradation and corrosion have the highest stress at the corners of the pattern, while circular pits have the highest stress at the centre of the pit. The zigzag pit morphology has more detrimental effects than circular pits. For multiple distributed pits, the pits closer to the specimen edges exhibit higher stress values than those near the centre of the specimen. The effect of multiple or quantitatively increased number of pits having smaller geometric properties has a more detrimental effect than a single pit with larger geometric attributes.