Search

An interest in biodegradable metallic materials has been increasing in the last two decades. Besides magnesium based materials, iron-manganese alloys have been considered as possible candidates for fabrication of biodegradable stents and orthopedic implants. In this study, we prepared a hot forged FeMn30 (wt.%) alloy and investigated its microstructural, mechanical and corrosion characteristics as well as cytotoxicity towards mouse L 929 fibroblasts. The obtained results were compared with those of iron. The FeMn30 alloy was composed of antiferromagnetic γ-austenite and ε-martensite phases and possessed better mechanical properties than iron and even that of 316L steel. The potentiodynamic measurements in simulated body fluids showed that alloying with manganese lowered the free corrosion potential and enhanced the corrosion rate, compared to iron. On the other hand, the corrosion rate of FeMn30 obtained by a semi-static immersion test was significantly lower than that of iron, most likely due to a higher degree of alkalization in sample surrounding. The presence of manganese in the alloy slightly enhanced toxicity towards the L 929 cells; however, the toxicity did not exceed the allowed limit and FeMn30 alloy fulfilled the requirements of the ISO 10993-5 standard. [ABSTRACT FROM AUTHOR]

Research into biodegradable porous materials has been increasingly focused on iron-based materials because such materials possess suitable properties for orthopedic applications. In this study, we prepared porous iron with porosities of 32-82 vol.% by powder metallurgy using ammonium bicarbonate as a space-holder material. We studied the influence of initial powder size and compacting pressure on sample microstructure, contamination and mechanical characteristics. The experimental results were analyzed as well, using Gibson-Ashby model and this analysis showed a good agreement in theoretical and experimental data. Whereas increasing compression pressure decreased porosity, the use of finer iron powder led to an increase in porosity. Increasing the amount of space-holder material in the initial mixture increased the total porosity, improved compressibility and consequently decreased the number of pores originating from imperfect compaction. A higher compacting pressure and the use of finer powder enhanced both the flexural and compressive properties. Even the most porous samples prepared from the fine iron powder possessed mechanical properties comparable to human cancellous bone. Based on these results, we can claim that the use of fine initial iron powder is necessary to obtain highly porous iron, which appears to be suitable for orthopedic applications. [ABSTRACT FROM AUTHOR]

The demand for porous biodegradable load-bearing implants has been increasing recently. Based on investigations of biodegradable stents, porous iron may be a suitable material for such applications. In this study, we prepared porous iron samples with porosities of 34–51 vol.% by powder metallurgy using ammonium bicarbonate as a space-holder material. We studied sample microstructure (SEM-EDX and XRD), flexural and compressive behaviors (universal loading machine) and hardness HV5 (hardness tester) of the prepared samples. Sample porosity increased with the amount of spacer in the initial mixtures. Only the pore surfaces had insignificant oxidation and no other contamination was observed. Increasing porosity decreased the mechanical properties of the samples; although, the properties were still comparable with human bone and higher than those of porous non-metallic biomaterials and porous magnesium prepared in a similar way. Based on these results, powder metallurgy appears to be a suitable method for the preparation of porous iron for orthopedic applications. [ABSTRACT FROM AUTHOR]

Abstract: There has recently been an increased demand for porous magnesium materials in many applications, especially in the medical field. Powder metallurgy appears to be a promising approach for the preparation of such materials. Many works have dealt with the preparation of porous magnesium; however, the effect of sintering conditions on material properties has rarely been investigated. In this work, we investigated porous magnesium samples that were prepared by powder metallurgy using ammonium bicarbonate spacer particles. The effects of the purity of the argon atmosphere and sintering time on the microstructure (SEM, EDX and XRD) and mechanical behaviour (universal loading machine and Vickers hardness tester) of porous magnesium were studied. The porosities of the prepared samples ranged from 24 to 29 vol.% depending on the sintering conditions. The purity of atmosphere played a significant role when the sintering time exceeded 6h. Under a gettered argon atmosphere, a prolonged sintering time enhanced diffusion connections between magnesium particles and improved the mechanical properties of the samples, whereas under a technical argon atmosphere, oxidation at the particle surfaces caused deterioration in the mechanical properties of the samples. These results suggest that a refined atmosphere is required to improve the mechanical properties of porous magnesium. [Copyright &y& Elsevier]

Abstract: Porous magnesium-based materials are biodegradable and promising for use in orthopaedic applications, but their applications are hampered by their difficult fabrication. This work reports the preparation of porous magnesium materials by a powder metallurgy technique using ammonium bicarbonate as spacer particles. The porosity of the materials depended on the amount of ammonium bicarbonate and was found to have strong negative effects on flexural strength and corrosion behaviour. However, the flexural strength of materials with porosities of up to 28vol.% was higher than the flexural strength of non-metallic biomaterials and comparable with that of natural bone. [Copyright &y& Elsevier]

The Zn-based alloys, alloyed with the elements of the 2nd group of the periodic table, are considered as potential biodegradable materials suitable for the fabrication of small orthopaedic implants or cardiovascular stents. Unfortunately, the as-cast Zn-based alloys do not fulfil the requirements for mechanical properties for such applications. Extrusion is a thermomechanical process which is very powerful for breaking the cast microstructure and enhancing mechanical characteristics of metallic materials. In this study, we focused on the influence of extrusion parameters, such as temperature and extrusion ratio, on microstructural and mechanical characteristics of a ZnMg0.8Ca0.2 (wt.%) alloy. The extrusion led to a significant grain refinement and the formation of a crystallographic texture. Extrusion temperature played a more significant role in the mean grain size compared to the extrusion ratio (ER). At lower extrusion temperatures, the texture was less intensive and the subsequent mechanical anisotropy was weaker. Constants for the prediction of the grain size based on the Zener-Hollomon parameter were obtained. Prediction of mechanical properties using the Hall-Petch relationship appeared to be difficult because of the dependence of the texture on the extrusion temperature. Extrusion at the temperatures of 200 °C (ER = 25:1) and 150 °C (ER = 11:1) led to mechanical performance fulfilling the requirements for implantology. [ABSTRACT FROM AUTHOR]

Zinc-based alloys containing the elements of the second group of the periodic table have been extensively studied as potential candidates for applications as a biodegradable material. In this study, the ZnMg0.8Ca0.2 (wt%) alloy was prepared and treated by annealing and extrusion at various conditions. The evolution of microstructure and mechanical properties during annealing and after extrusion was performed in detail. Both annealing and extrusion caused microstructural changes influencing mechanical properties. Annealing caused a homogenization of the microstructure and transformation of metastable phases. The extrusion caused a rearrangement of the intermetallic phases, a refinement and a texturing of the zinc matrix. Those lead to a significant strengthening and to an increase in the ductility, but also to mechanical anisotropy. In this paper, the influence of the processing on the microstructure and mechanical properties is discussed in detail based on the results obtained by various methods, such as scanning and transmission electron microscopy, electron backscattered diffraction, tensile and compressive mechanical testing and nanoindentation. • Solidification mechanism of a ZnMg0.8Ca0.2 (wt%) alloy was proposed. • Formation of Zn-MgZn 2 eutectics was observed. • Influence of annealing and extrusion was studied. • Anisotropy of the extruded alloy was explained. [ABSTRACT FROM AUTHOR]

In this paper, the effect of laser shock peening (LSP) of mono- and polycrystalline copper was studied. It is shown that the residual stress caused by this process is accumulated at the LSP treated surface of the material, the thickness of which is several hundreds of micrometers. The affected layer contains an enhanced density of dislocations. These dislocations are homogeneously distributed on the cross-section in the single crystal along the single slip plane. The dislocations in the polycrystal are distributed heterogeneously on the sample cross-section. This heterogeneity is discussed from the viewpoint of the orientation dependence of individual grains and varied values of the Schmid factor and confirms the compressive nature of the stress caused by LSP. Depth dependence of the microhardness of the material decreases from the LSP treated surface in direction to the sample center correspondingly. • study of the laser shock peening (LSP) of mono- and polycrystalline copper; • residual stress caused is accumulated at the surface of the material; • dislocations are homogeneously distributed on the cross-section on the single slip plane in single crystal; • dislocations in the polycrystal are distributed heterogeneously due to different Schmid factor of individual grains. [ABSTRACT FROM AUTHOR]

This work aims to optimize the parameters of the SHS process for the preparation of NiTi shape memory alloy to obtain a high-purity, low-porosity material. For this purpose, high heating rate (over 300 °C min−1), temperature of 1100 °C and process duration of 20 min were determined as the optimal parameters. To prevent nickel depletion of the product and to minimize the porosity, the use of coarse titanium particles (200–600 μm) with fresh surface can be recommended. SHS products were composed of NiTi with the admixture of Ti2Ni phase. The formation of this phase cannot be fully avoided in SHS preparation route. [ABSTRACT FROM AUTHOR]

An equiatomic CoCrFeNiNb alloy was prepared by conventional induction melting and by 8 h of mechanical alloying and compaction via spark plasma sintering. The alloy prepared via mechanical alloying showed a uniform ultrafine-grained microstructure composed of an FCC solid solution strengthened by HCP Laves phases. A detailed TEM inspection revealed the presence of nanocrystalline Cr 2 O 3 particles at the triple junctions of the present grains as well as stacking faults and nanotwins found exclusively in the interior of the FCC solid solution grains. The as-cast alloy had a high initial hardness of 648 ± 18 HV 30 and ultimate compressive strength of 1374 MPa. On the other hand, the mechanically alloyed alloy compacted at 1000 °C showed even higher hardness of 798 ± 9 HV 30 as well as an ultra-high strengths that reached 2412 MPa. Based on the TEM quantitative analyses considering the contributions of different structural constituents and lattice defects, the aforementioned strength value was found to be in good agreement with results from microstructure strengthening modelling, which indicated a calculated mean value of 2300 ± 300 MPa. Moreover, the mechanically alloyed alloy also showed exceptional thermal stability even after long-term annealing/testing at 600 °C because it maintained a hardness of 777 ± 5 HV 30, and strength of 2284 MPa. Image 1 • MA + SPS yield ultrafine-grained FCC + HCP (Laves) binary alloy. • The two-phases are characterized by Cr 2 O 3 at the triple grain junctions. • FCC γ-like and HCP Laves were within 200 nm. • Ultimate Compression Strength (UCS) reached 2412 MPa by compaction at 1000 °C. • TEM quantitative analysis confirmed and modelled the experimentally obtained UCS. [ABSTRACT FROM AUTHOR]