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Crossover aluminium alloys have recently been introduced as a new class of coarse-grained age-hardenable alloys. Here, we study the evolution of precipitation of the T-phase — M g 32 (Z n , A l) 49 -phase — in a 5xxx/7xxx crossover alloy with coarse- and ultrafined microstructures. Both alloys were examined using differential scanning calorimetry, X-ray diffraction and in situ transmission electron microscopy. The ultrafine-grained alloy revealed significant different and accelerated precipitation behaviour due to grain boundaries acting as fast diffusion paths. Additionally, the ultrafine-grained alloy revealed high resistance to grain growth upon heating, an effect primarily attributed to inter-granular precipitation synergistically with trans-granular precipitation of T-phase. The effect of coarse and ultrafine grains on the T-phase precipitation behaviour in novel aluminium crossover alloys was investigated. Thermal stability of ultrafine grains was achieved through controlled T-phase precipitation. [ABSTRACT FROM AUTHOR]

Mg-based biodegradable materials are considered promising candidates in the paediatric field due to their favourable mechanical and biological properties and their biodegrading potential that makes a second surgery for implant removal unnecessary. In many cases the surgical fixation technique requires a crossing of the growth plate by the implant in order to achieve an adequate fragment replacement or fracture stabilisation. This study investigates the kinetics of slowly and rapidly degrading Mg alloys in a transphyseal rat model, and also reports on their dynamics in the context of the physis and consecutive bone growth. Twenty-six male Sprague–Dawley rats received either a rapidly degrading (ZX50; n  = 13) or a slowly degrading (WZ21; n  = 13) Mg alloy, implanted transphyseal into the distal femur. The contralateral leg was drilled in the same manner and served as a direct sham specimen. Degradation behaviour, gas formation, and leg length were measured by continuous in vivo micro CT for up to 52 weeks, and additional high-resolution µCT (HRS) scans and histomorphological analyses of the growth plate were performed. The growth plate was locally destroyed and bone growth was significantly diminished by the fast degradation of ZX50 implants and the accompanying release of large amounts of hydrogen gas. In contrast, WZ21 implants showed homogenous and moderate degradation performance, and the effect on bone growth did not differ significantly from a single drill-hole defect. Statement of Significance This study is the first that reports on the effects of degrading magnesium implants on the growth plate in a living animal model. The results show that high evolution of hydrogen gas due to rapid Mg degradation can damage the growth plate substantially. Slow degradation, however, such as seen for WZ21 alloys, does not affect the growth plate more than drilling alone, thus meeting one important prerequisite for deployment in paediatric osteosynthesis. [ABSTRACT FROM AUTHOR]

Magnesium (Mg) alloys have attracted great attention as potential materials for biodegradable implants. It is essential that an implant material possesses adequate resistance to cracking/fracture under the simultaneous actions of corrosion and mechanical stresses, i.e., stress corrosion cracking (SCC) and/or corrosion fatigue (CF). This study investigates the deformation behaviour of a newly developed high-strength low-alloy Mg alloy, MgZn1Ca0.3 (ZX10), processed at two different extrusion temperatures of 325 and 400 °C (named E325 and E400, respectively), under slow strain tensile and cyclic tension-compression loadings in air and modified simulated body fluid (m-SBF). Extrusion resulted in a bimodal grain size distribution with recrystallised grain sizes of 1.2 μm ± 0.8 μm and 7 ± 5 μm for E325 and E400, respectively. E325 possessed superior tensile and fatigue properties to E400 when tested in air. This is mainly attributed to a grain-boundary strengthening mechanism. However, both E325 and E400 were found to be susceptible to SCC at a strain rate of 3.1×10 −7 s −1 in m-SBF. Moreover, both E325 and E400 showed similar fatigue strength when tested in m-SBF. This is explained on the basis of crack initiation from localised corrosion following tests in m-SBF. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) offers significant benefits towards optimized lightweight structures for aircraft and space applications. High-strength aluminium alloys are of special interest to reach a maximum mass reduction. The paper presents the development of appropriate selective laser melting (SLM) processing windows for a scandium modified aluminium alloy (Scalmalloy ® ), reaching densities >99%. The mechanical properties of as-processed material are analyzed, pointing out a comparably low anisotropy with regard to the build orientation. A fine-grained microstructure is observed next to regions of coarser, elongated grains. The paper discusses the observed microstructure, and concludes with suggestions for innovative material design for AM. [ABSTRACT FROM AUTHOR]

In this paper atom probe tomography is used to explore early stage clustering in aluminum alloys. Two novel concepts for a modification of clustering are discussed. Control of early stage clustering is welcome from an application point of view since clustering deteriorates strength evolution during the industrial heat treatment of the important class of Al-Mg-Si precipitation-hardenable alloys. Nanoscale early stage clusters are very diffcult to observe and atom probe tomography is the best technique to visualize and chemically measure Si or Mg-containing clusters in aluminum alloys. Restrictions remain in achieving the ultimate quantification of such small solute aggregates by atom probe tomography, such as detection efficiency, local magnification effects, surface migration of solute atoms, and unresolved issues with the reconstruction procedure. Here we investigate one of these restricting effects, namely the migration of solute atoms during atom probe tomography measurements. In particular Si is found to be preferentially localized or absent at certain crystallographic poles in aluminum, which derogates the experimental results gained from atom probe tomography studies of clustering in Si-containing aluminum alloys. This artifact is investigated for different specimen temperatures, detection rates and pulse fractions during atom probe tomography measurements. Optimal strategies to analyze small-scale solute clusters in Si-containing aluminum alloys are presented. [ABSTRACT FROM AUTHOR]

Abstract: This study investigates the degradation performance of three Fe-based materials in a growing rat skeleton over a period of 1year. Pins of pure Fe and two Fe-based alloys (Fe–10Mn–1Pd and Fe–21Mn–0.7C–1Pd, in wt.%) were implanted transcortically into the femur of 38 Sprague–Dawley rats and inspected after 4, 12, 24 and 52weeks. The assessment was performed by ex vivo microfocus computed tomography, weight-loss determination, surface analysis of the explanted pins and histological examination. The materials investigated showed signs of degradation; however, the degradation proceeded rather slowly and no significant differences between the materials were detected. We discuss these unexpected findings on the basis of fundamental considerations regarding iron corrosion. Dense layers of degradation products were formed on the implants’ surfaces, and act as barriers against oxygen transport. For the degradation of iron, however, the presence of oxygen is an indispensable prerequisite. Its availability is generally a critical factor in bony tissue and rather limited there, i.e. in the vicinity of our implants. Because of the relatively slow degradation of both pure Fe and the Fe-based alloys, their suitability for bulk temporary implants such as those in osteosynthesis applications appears questionable. [Copyright &y& Elsevier]

Abstract: This study investigates the bone and tissue response to degrading magnesium pin implants in the growing rat skeleton by continuous in vivo microfocus computed tomography (μCT) monitoring over the entire pin degradation period, with special focus on bone remodeling after implant dissolution. The influence of gas release on tissue performance upon degradation of the magnesium implant is also addressed. Two different magnesium alloys – one fast degrading (ZX50) and one slowly degrading (WZ21) – were used for evaluating the bone response in 32 male Sprague–Dawley rats. After femoral pin implantation μCTs were performed every 4weeks over the 24weeks of the study period. ZX50 pins exhibited early degradation and released large hydrogen gas volumes. While considerable callus formation occurred, the bone function was not permanently harmed and the bone recovered unexpectedly quickly after complete pin degradation. WZ21 pins kept their integrity for more than 4weeks and showed good osteoconductive properties by enhancing bone accumulation at the pin surface. Despite excessive gas formation, the magnesium pins did not harm bone regeneration. At smaller degradation rates, gas evolution remained unproblematic and the magnesium implants showed good biocompatibility. Online μCT monitoring is shown to be suitable for evaluating materials degradation and bone response in vivo, providing continuous information on the implant and tissue performance in the same living animal. [Copyright &y& Elsevier]

Abstract: A design strategy deployed in developing new biodegradable Mg–Y–Zn alloys is summarized and the key factors influencing their suitability for medical applications are described. The Mg–Y–Zn alloys reveal microstructural features and mechanical characteristics expected to be appropriate for vascular intervention applications. The focus of this article lies in the evaluation of the degradation performance and biological response of the alloys with respect to their potential as implant materials (stents). The degradation characteristics analyzed by immersion testing and electrochemical impedance spectroscopy in simulated physiological media reveal slow and homogeneous degradation. In vitro cell tests using human umbilical vein endothelial cells indicate good cytocompatibility on the basis of the alloys’ eluates (extracts). Animal studies carried out with pigs on Mg–2Y–1Zn (in wt.%) reveal an auspicious in vivo performance. Evaluation of preparations derived from implants in various types of tissues indicates homogeneous degradation and only limited gas formation during in vivo testing. The characteristics of the tissue reactions indicate good biocompatibility. The new Mg–Y–Zn alloys show an interesting combination of preferred microstructural, mechanical, electrochemical and biological properties, which make them very promising for degradable implant applications. [Copyright &y& Elsevier]

Abstract: The aim of this article is to describe a design strategy for the development of new biodegradable Fe-based alloys offering a performance considered appropriate for temporary implant applications, in terms of both an enhanced degradation rate compared to pure iron, and suitable strength and ductility. The design strategy is based on electrochemical, microstructural and toxicological considerations. The influence of alloying elements on the electrochemical modification of the Fe matrix and the controlled formation of noble intermetallic phases is deployed. Such intermetallic phases are responsible for both an increased degradation rate and enhanced strength. Manganese and palladium have been shown to be suitable alloying additions for this design strategy: Mn lowers the standard electrode potential, while Pd forms noble (Fe,Mn)Pd intermetallics that act as cathodic sites. We discuss the efficiency and the potential of the design approach, and evaluate the resulting characteristics of the new alloys using metal-physical experiments including electrochemical measurements, phase identification analysis and electron microscopy studies. The newly developed Fe–Mn–Pd alloys reveal a degradation resistance that is one order of magnitude lower than observed for pure iron. Additionally, the mechanical performance is shown to be adjustable not only by the choice of alloying elements but also by heat treatment procedures; high strength values >1400MPa at ductility levels >10% can be achieved. Thus, the new alloys offer an attractive combination of electrochemical and mechanical characteristics considered suitable for biodegradable medical applications. [Copyright &y& Elsevier]

Corrosion susceptibility and the type of corrosion in AIMgSi alloys depend strongly on microstructure. However, it is still unclear what microstructural features trigger corrosion initiation. The direct correlation of second-phase particles with the corrosion propagation path has also never been thoroughly explored. In this work, the role of second-phase particles in corrosion initiation and propagation were studied in alloy AA6016 by using a microelectrochemically controlled microtomography technique. Three topics are discussed in detail, the role of Fe-containing intermetallics, the effect of MgSi particles, and an evidenced type of directed corrosion (exfoliation-like attack): (i) lntergranular corrosion initiates preferentially in Fe-containing intermetallics located at grain boundaries. However, its propagation path is not promoted by these intermetallics. (ii) MgSi particles do not act as transition Sites to in-depth corrosion propagation, even if they dissolve. (iii) A type of corrosion called exfoliation-like attack is observed. It is characterized by straight attack into the bulk material. The propagation is found to be independent of grain boundaries and second-phase particles. [ABSTRACT FROM AUTHOR]