Effect of micro-alloying chromium on the corrosion resistance of nanocrystalline nickel aluminide intermetallic produced by mechanical alloying process

In this study, Ni₅₀Al_50 − xCr_x nanocrystalline intermetallic compound was synthesized by using the high energy mechanical milling of pure Ni, Al and Cr elemental powders for 16 h. The morphological investigation was done by using the optical and scanning electron microscope. The corrosion behavior of the samples was studied by using the electrochemical impedance spectroscopy in 3.5% NaCl solution. The results showed that when the micro-alloying Cr content is increased, the particles distribution is modified and the size of particles is decreased. Therefore the passive film which is formed on the surface of samples is less porous, so the corrosion resistance is increased.     

In vitro study on equal channel angular pressing AZ31 magnesium alloy with and without back pressure

The equal channel angular pressing (ECAP) technique with and without back pressure (BP) was introduced in this paper to prepare biomedical AZ31 magnesium alloy, with the effect of pass number (from 1 to 4) on the corrosion properties as well as in vitro biocompatibility being investigated. The results indicated that ECAPed or BP-ECAPed AZ31 alloys exhibited similar corrosion rate to that of the as-extruded one, but the corrosion rate slightly increased after 1-2 passes ECAP or BP-ECAP and further decreased after 4-pass procedure. Additionally, severe local corrosion was observed for the 1-3 passes ECAPed or BP-ECAPed AZ31 alloy samples. Compared to the as-extruded AZ31 alloy, the samples after ECAP or BP-ECAP procedure showed much smaller sized corrosion pits on the surface after removing the corrosion product. The surface analysis after 20 days immersion in Hank's solution revealed that the composition of the corrosion product consisted of C, O, Mg, P, Ca whereas only weak signal of Mg(OH)₂ could be detected beside the dominant α(Mg) peak by X-ray diffraction. The cytotoxicity results suggested that the multi-pass ECAPed or BP-ECAPed AZ31 alloy exhibited Grade I-II cytotoxicity according to ISO 10993-5: 1999.     

Corrosion and ion release behavior of ultra-fine grained bulk pure copper fabricated by ECAP in Hanks solution as potential biomaterial for contraception

Ultra-fine grained (UFG) bulk pure copper has been successfully fabricated by equal-channel angular pressing (ECAP), with the grain size about 380 nm after 8 passes. The potentiodynamic polarization results of the ECAP copper specimens tested in Hanks solution revealed that the corrosion current of UFG copper is higher than that of the coarse grained copper. The cupric ion release behaviors of UFG copper immersed in Hanks solution for 30 days only displayed a burst release during the first 3 days (in comparison to the 1-2 months for the conventional Cu) from 115 μg/day to 12.5 μg/day, after which the ion release remained constant and slow. During the immersion experiments, Cu₂O was the only corrosion product found on the surface and it took 10 days or so to form a uniform Cu₂O layer. Uniform corrosive damage on the surface and few localized corrosion is observed. The above results indicate that UFG copper could have high potential as biomedical materials for contraception.     

In vitro investigation of cellular effects of magnesium and magnesium-calcium alloy corrosion products on skeletal muscle regeneration

Biodegradable magnesium(Mg) has garnered attention for its use in orthopaedic implants due to mechanical properties that closely match to those of bone.Studies have been undertaken to understand the corrosion behaviour of these materials and their effects on bone forming cells.However,there is lack of research on how the corrosion of these biomaterials affect surrounding tissues such as skeletal muscle.Mg plays an important role in the structural and functional properties of skeletal muscle.It is therefore important to investigate the response of skeletal muscle cells to both soluble(Mg ions) and insoluble(corrosion granules) corrosion products.Through in vitro studies it is possible to observe the effects of corrosion products on myotube formation by the fusion of single muscle precursor cells known as myoblasts.To achieve this goal,it is important to determine if these corrosion products are toxic to myotubes.Here it was noted that although there was a slight decrement in cellular viability after initial exposure,this soon recovered to control levels.A high Ca/Mg ratio resulted in the formation of large myotubes and a low Ca/Mg ratio negatively affected myotube maturation.Mg~(2+)and Ca~(2+)ions are important in the process of myogenesis,and the concentration of these ions and the ratio of the ions to each other played a significant role in myotube cellular activity.The outcomes of this study could pave the way to a bio-informed and integrated approach to the design and engineering of Mg-based orthopaedic implants.     

In vitro corrosion resistance and antibacterial performance of novel tin dioxide-doped calcium phosphate coating on degradable Mg-1Li-1Ca alloy

A SnO_2-doped calcium phosphate(Ca-P-Sn) coating was constructed on Mg-1 Li-1 Ca alloy by a hydrothermal process. The fabricated functional coatings were investigated using scanning electron microscopy(SEM), X-ray diffraction(XRD) and Fourier transform infrared spectroscopy(FT-IR). A triple-layered structure, which is composed of Ca_3(PO_4)_2,(Ca, Mg)_3(PO_4)_2, SnO_2, and MgHPO_4·3 H_2O, is evident and leads to the formation of Ca_(10)(PO_4)_6(OH)_2 in Hank's solution. Electrochemical measurements, hydrogen evolution tests and plating counts reveal that the corrosion resistance and antibacterial activity were improved through the coating treatment. The embedded SnO_2 nanoparticles enhanced crystallisation of the coating.The formation and degradation mechanisms of the coating were discussed.     

Influence of remelting on microstructure,hardness and corrosion behaviour of AlCoCrFeNiTi high entropy alloy

Abstract

High entropy alloys are a newly developed class of alloys, which tend to form a single solid solution or a mixture of solid solutions with simple crystal structures. These alloys possess excellent mechanical properties, thermal stability and corrosion resistance. In the present paper, an AlCoCrFeNiTi high entropy alloy was obtained by induction melting, and the influence of the remelting process on the mechanical and corrosion resistance characteristics of the alloy was investigated. Thus, optical and scanning electron microscopy revealed less phase segregation and a fine dendritic structure for the remelted alloy, while corrosion tests indicated that present alloy, in remelted state, has better corrosion resistance than as cast alloy and stainless steel. The Vickers microhardness measurements demonstrated an improvement of the alloy microhardness by remelting process due to the decrease in phase segregation and the increase in dendrite refinement level.     

Characteristics and mechanical properties of a (Ti, O, N)/Ti composite coating fabricated on NiTi shape memory alloy via PIIID

In this investigation, (Ti, O, N)/Ti composite coating was fabricated on a NiTi shape memory alloy (SMA) to improve its biocompatibility, bioactivity and wear resistance for its long-term medical applications, using the plasma immersion ion implantation and deposition (PIIID) technique. Scanning electron microscopic (SEM) examination of coating cross-sections showed that the (Ti, O, N)/Ti composite coating was uniform and compact. Energy dispersive X-ray (EDX) analysis not only indicated that the interface between the coating and NiTi SMA substrate was gradual rather than sharp, but it also showed the thickness of the composite coating to be ∼ 1.0 μm. The EDX mapping of cross-sections of (Ti, O, N)/Ti composite coating revealed that Ni was not present on the surface of the coated samples. Nanoindentation tests were performed to evaluate mechanical properties of the composite coating. Pin-on-disc wear test results showed greatly improved wear resistance of (Ti, O, N)/Ti coated NiTi SMA.     

Effect of Mn on damping capacities, mechanical properties, and corrosion behaviour of high damping Mg–3 wt.%Ni based alloy

The effect of Mn on the damping capacities, mechanical properties, and corrosion behaviour of high damping Mg–3 wt.%Ni based alloys has been studied. The damping vs. strain amplitude spectrum of the studied alloys could be divided into three parts. The strain amplitude weakly dependent part appears again when the microplastic strain occurs at high strain amplitude. The mechanical properties of as-cast Mg–3 wt.%Ni alloy could be improved by the addition of Mn, which is due to the refinement of α-Mg dendrites and solid solution strengthening by Mn. In addition, the corrosion resistance of the alloys could also be improved remarkably by the addition of Mn.     

Improve stress corrosion cracking resistance and mechanical properties of Al‐Zn‐Mg‐Cu‐Zr alloy with heterogeneous lamellae structure produced by high pressure torsion

High pressure torsion experiment followed with heat treatment were carried out on as‐cast Al‐Zn‐Mg‐Cu‐Zr alloy at 400 °C under the pressure of 1 GPa. The microstructure, mechanical property and stress corrosion resistance properties for the as‐cast and high pressure torsion processed samples were studied. The results show that high pressure torsion processing can improve the mechanical property by the refinement of grains and grain boundary precipitates, as well as the homogeneous distribution of fine matrix precipitates. On the other side, the grain refinement, broken of coarse grain boundary precipitates and narrowed precipitates free zone caused by the high pressure torsion result in the improvement of stress corrosion cracking resistance. And due to the influence of heterogeneous lamellae structure, the sample after 0.5 high pressure torsion turn shows preferable mechanical property and stress corrosion cracking resistance than the sample after 2 high pressure torsion turns.     

Characteristics and in vitro biological assessment of (Ti, O, N)/Ti composite coating formed on NiTi shape memory alloy

In this investigation, plasma immersion ion implantation and deposition (PIIID) was used to fabricate a (Ti, O, N)/Ti coating on NiTi shape memory alloy (SMA) to improve its long-term biocompatibility and wear resistance. The surface morphology, composition and roughness of uncoated and coated NiTi SMA samples were examined. Energy dispersive X-ray elemental mapping of cross-sections of (Ti, O, N)/Ti coated NiTi SMA revealed that Ni was depleted from the surface of coated samples. No Ni was detected by X-ray photoelectron spectroscopy on the surface of coated samples. Furthermore, three-point bending tests showed that the composite coating could undergo large deformation without cracking or delamination. After 1 day cell culture, SaOS-2 cells on coated samples spread better than those on uncoated NiTi SMA samples. The proliferation of SaOS-2 cells on coated samples was significantly higher at day 3 and day 7 of cell culture.