Fabrication and Evaluation of a Bioactive Sr–Ca–P Contained Micro-Arc Oxidation Coating on Magnesium Strontium Alloy for Bone Repair Application

Considering the compatibility between degradation and bioactivity of magnesium-based implants for bone repair, micro-arc oxidation is used to modify the magnesium alloy surface in aqueous electrolytes,allowing strontium, calcium, and phosphorus to be incorporated into the coating. The thickness, composition, morphology and phase of this Sr–Ca–P containing coating are characterized by scanning electron microscopy equipped with energy dispersive X-ray spectrometer and X-ray diffraction. The in vitro and in vivo degradation of the coating is evaluated by immersion test, electrochemical test and implantation test. Moreover, the cytocompatibility is tested with osteoblast cell according to ISO 10993. The results show that Sr, Ca and P elements are incorporated into the oxide coating, and a refined structure with tiny discharging micro-pores is observed on the surface of the coating. The Sr–Ca–P coating possesses a better corrosion resistance in vitro and retards the degradation in vivo. Such coating is expected to have significant medical applications on orthopedic implants and bone repair materials.     

Effects of zinc coating on magnesium alloy–steel joints produced by cold metal transfer method

Magnesium alloys are lap-joined to galvanised and bare steel sheets by a cold metal transfer method. The weld appearance, cross-section, tensile strength and fracture behaviour of these joints are characterised by scanning electron microscopy, tensile tests and energy-dispersive spectroscopy. The joints were found to have good weld appearance and satisfactory tensile strength. The spreadability and wettability of the Mg alloy–galvanised steel joint are superior to those of the Mg alloy–bare steel joint, but the tensile strength is lower. In particular, the presence of Zn on the galvanised steel sheet improves wettability but decreases tensile strength. Aluminium has a high affinity for Fe, and the thinner layer of Fe–Al improves the mechanical properties of the Mg alloy–bare steel joint.     

Blood compatibility of zinc–calcium phosphate conversion coating on Mg–1.33Li–0.6Ca alloy

Magnesium alloys as a new class of biomaterials possess biodegradability and biocompatibility in comparison with currently used metal implants. However, their rapid corrosion rates are necessary to be manipulated by appropriate coatings. In this paper, a new attempt was used to develop a zinc-calcium phosphate (Zn-Ca-P) conversion coating on Mg-1.33Li-0.6Ca alloys to increase the biocompatibility and improve the corrosion resistance. In vitro blood biocompatibility of the alloy with and without the Zn-Ca-P coating was investigated to determine its suitability as a degradable medical biomaterial. Blood biocompatibility was assessed from the hemolysis test, the dynamic cruor time test, blood cell count and SEM observation of the platelet adhesion to membrane surface. The results showed that the Zn-Ca-P coating on Mg-1.33Li-0.6Ca alloys had good blood compatibility, which is in accordance with the requirements for medical biomaterials.     

Electroless deposition of Ni–P–B4C composite coating on AZ91D magnesium alloy and investigation on its wear and corrosion resistance

In the present work, the effect of applying ternary Ni–P–B₄C composite coating from an electroless plating bath containing sulfate nickel, sodium hypophosphate and suspended B₄C particles, on the corrosion and wear resistance of an AZ91D, high aluminum cast magnesium alloy, was investigated. Regarding low corrosion resistance of magnesium alloys, chromium oxide plus HF (Hydro Fluoric Acid) pretreatment was applied to prepare the substrate for coating treatment in electroless bath. The pH value and temperature of the electroless bath were 9 and 82 °C, respectively. The coating was characterized for its micro structure, morphology, microhardness, wear and corrosion resistance. SEM (Scanning Electron Microscope) observation showed dense and coarse nodules in the ternary composite coating and the cross section of Ni–P–B₄C coating offered presence of well dispersed B₄C particles in the coating. The hardness of the Ni–P–B₄C composite coatings was around 1200 MPa, more than what can be obtained for Ni–P coatings (about 700 MPa). The wear test which was carried out by using pin on disc method, showed that ternary Ni–P–B₄C composite coating had a good wear resistance and more superior than Ni-P coating. The polarization test results for ternary Ni–P–B₄C composite coating exhibited good corrosion resistance properties in protecting the AZ91D magnesium alloy, but not better than Ni–P coating.     

Interface microstructure and mechanical properties of zinc–aluminum thermal diffusion coating on AZ31 magnesium alloy

The zinc–aluminum (Zn–Al) alloy coating with excellent wear and corrosion resistance was fabricated on the surface of magnesium substrate (AZ31) using thermal diffusion technique. The microstructure, phase constitution and chemical composition were investigated. The experimental observation exhibited that the interfacial microstructures were composed of network eutectic structures and lamellar eutectoid structures at heating temperature of 350 °C for holding time of 30 min under 0.1 MPa in a vacuum of 10⁻³ Pa. X-ray diffraction (XRD) pattern analysis identified that α-Mg, Mg₇Zn₃ and MgZn phases were formed in the diffusion layer. The interdiffusion of Mg and Al atoms were restricted by Mg–Zn intermetallic compounds (IMCs). The value of microhardness at the diffusion layer increased due to the formation of Mg–Zn eutectic phases. This technique is beneficial to improving poor wear and corrosion resistance of magnesium alloy.     

Corrosion behavior of Ti–Al–N/Ti–Al duplex coating on AZ31 magnesium alloy in NaCl aqueous solution

In this study, Ti–Al–N/Ti–Al duplex coating was deposited on AZ31 magnesium alloy by magnetron sputtering with a Ti/Al composite target. Scanning electron microscopy and Auger electron spectroscopy were applied to investigate the morphology and elemental concentration of the obtained coating, respectively. The top layer was Ti–Al–N film with a Ti:Al:O:N ratio of 0.32:0.84:0.08:1, and the bottom layer was Ti–Al film with a Ti:O:Al ratio of 1.94:0.12:1. Each layer of this coating presented a developed columnar structure. The polarization test and immersion test were used to investigate corrosion behavior of the coated sample in 3.5 wt.% NaCl aqueous solution. The results showed that this duplex coating could protect the substrate effectively in NaCl aqueous solution. Nevertheless, several through-thickness micropores in the coating finally induced the failure of the coated AZ31 in the immersion test.     

Corrosion resistance of AZ91D magnesium alloy with electroless plating pretreatment and Ni–TiO2 composite coating

In this paper, a protective multilayer coating, with electroless Ni coating as bottom layer and electrodeposited Ni–TiO₂ composite coating as top layer, was successfully prepared on AZ91D magnesium alloy by a combination of electroless and electrodeposition techniques. Scanning electron microscopy and X-ray diffraction were employed to investigate the surface, cross-section morphologies and phase structure of coatings, respectively. The electrochemical corrosion behaviors of coatings in 3.5 wt.% NaCl solutions were evaluated by electrochemical impedance spectroscopy, open circuit potential and potentiodynamic polarization techniques. The results showed that the corrosion process of Ni–TiO₂ composite coating was mainly composed of three stages in the long-term immersion test in the aggressive media, and could afford better corrosion and mechanical protection for the AZ91D magnesium alloy compared with single electroless Ni coating. The micro-hardness of the Ni–TiO₂ composite coating improved more than 5 times than that of the AZ91D magnesium alloy.     

Effects of zirconium addition on as-cast microstructure and mechanical properties of Mg–3Sn–2Ca magnesium alloy

At present, the mechanical properties of the Mg–3Sn–2Ca magnesium alloy are not satisfying and further enhance needs to be considered via further alloying/microalloying additions. The effects of Zr addition on the as-cast microstructure and mechanical properties of the alloy were investigated by using optical and electron microscopies, differential scanning calorimetry (DSC) analysis, and tensile and creep tests. The results indicate that adding 0.41, 0.76 or 1.18 wt.% Zr can refine the grains of the alloy, and the primary CaMgSn phases in the Zr-containing alloys are changed from coarse needle-like net to relatively fine short block and/or particle-like shapes. As a result, the tensile and/or creep properties of the Zr-containing alloys are improved. Among the Zr-containing alloys, the alloy with the addition of 0.76 wt.% Zr exhibits the relatively optimum mechanical properties.     

Effect of mechanical coating with Ni and Ni–5% Al on the structure and electrochemical properties of the Mg–50% Ni alloy

The Mg–Ni metastable alloys (with amorphous or nanocrystalline structures) are promising candidates for anode application in nickel–metal hydride rechargeable batteries due to its large hydrogen absorbing capacity, low weight, availability, and relative low price. In spite of these interesting features, improvement on the cycle life performance must be achieved to allow its application in commercial products. In the present paper, the effect of mechanical coating of a Mg–50 at.% Ni alloy with Ni and Ni–5 at.% Al on the structure, powder morphology, and electrochemical properties is investigated. The coating additives, Mg–Ni alloy and resulting nanocomposites (i.e., Mg–Ni alloy + additive) were investigated by means of X-ray diffraction and scanning electron microscopy. The Mg–Ni alloy and nanocomposites were submitted to galvanostatic cycles of charge and discharge to evaluate their electrode performances. The mechanical coating with Ni and Ni–5% Al increased the maximum discharge capacity of the Mg–Ni alloy from of 221 to 257 and 273 mA h g⁻¹, respectively. Improvement on the cycle life performance was also achieved by mechanical coating.     

Effect of solidification conditions on microstructure,mechanical and wear properties of Mg–5Al–3Ca–0.12Sr magnesium alloy

In the present study, the microstructure, mechanical and wear properties of AXJ530 alloy under different solidification condition were investigated. AXJ530 alloys were cast in a multi-step permanent mould casting (PMC) with five different cooling rates, and also in high pressure die casting (HPDC). The effect of cooling rate was determined for the room temperature mechanical properties and the dry sliding wear resistance of the AXJ530 alloys. The results showed that grain size of AXJ530 alloy was refined and thinner lamellar eutectic phase formed at higher cooling rate. It was concluded that these changes led to the observed concurrent increases in ultimate tensile strength (σ_uts), yield strength (σ_0.2) and elongation (δ) of the AXJ530 alloy. The relationship between grain size and yield strength/hardness agreed with Hall–Patch behavior. The dry sliding wear rate of the PMC specimens decreased with increasing of cooling rate, but micro-porosity/inclusion in the HPDC specimen decreased its wear resistance properties. Abrasion was determined to be the dominant wear mechanism for the AXJ530 alloys.     

Effects of minor additions of Ce and Y on as cast microstructure of Mg–3Sn–2Ca magnesium alloy

Abstract

The effects of minor additions of Ce and Y on the as cast microstructure of Mg–3Sn–2Ca (wt-%) magnesium alloy are investigated and compared. Results indicate that adding minor Ce or Y to Mg–3Sn–2Ca alloy does not cause formation of any new phases in the alloy. The as cast Mg–3Sn–2Ca alloy with addition of 0·5 wt-%Ce or Y is still composed of α-Mg, CaMgSn and Mg₂Ca phases. However, after adding 0·5 wt-%Ce or Y to Mg–3Sn–2Ca alloy, not only the formation of CaMgSn phase in the alloy is suppressed but also the CaMgSn phases in the alloy are effectively refined. In addition, adding 0·5 wt-%Ce to Mg–3Sn–2Ca alloy exhibits higher refinement efficiency to the CaMgSn phase in the alloy than adding 0·5 wt-%Y. Further investigations need to be considered in order to understand the difference of minor Ce and Y with regard to the refinement of CaMgSn phase in the Mg–3Sn–2Ca alloy.     

Bioactive sol–gel glass added ionomer cement for the regeneration of tooth structure

Dental cements including the glass ionomer cement (GIC) have found widespread use in restoring tooth structures. In this study, a sol-gel derived glass (SG) with a bioactive composition (70SiO(2) . 25CaO . 5P(2)O(5)) was added to the commercial GIC (GC, Fuji I) to improve the bioactivity and tooth regeneration capability. The SG powders prepared with sizes in the range of a few micrometers were mixed with GIC at SG/GC ratios of 10 and 30 wt%. The setting time, diametral tensile strength, and in vitro bioactivity of the GC-SG cements were examined. The setting time of the GC-SG cements increased with increasing amount of SG. However, the addition of SG did not significantly alter the diametral tensile strength of the GC. GC-SG induced the precipitation of an apatite bone-mineral phase on the surface after immersion in a simulated body fluid (SBF), showing in vitro bone bioactivity. However, no mineral induction in SBF was observed in the commercial GIC after the immersion. The in vitro cell assay confirmed that the GC-SG samples produced higher cell viability than the GC sample with cell culturing for up to 7 days.     

Thermal–mechanical modelling of laminates with fire protection coating

This paper presents a modelling approach to analyse the protection provided by passive and intumescent surface coatings on glass fibre reinforced laminate substrates exposed to fire. The modelling involves a multi-stage analytical approach: (i) thermal analysis of heat transfer from the fire through the surface insulation coating, which includes decomposition and expansion in the case of an intumescent material; (ii) thermal–chemical analysis of heat transfer through the fibreglass laminate substrate (beneath the fire protective coating), including decomposition of the polymer matrix; and (iii) thermal–mechanical analysis of softening and failure of the laminate under in-plane tension or compression loading. The modelling approach is validated using experimental temperature and strength data from fire structural tests performed on woven glass–vinyl ester laminates insulated with passive (ceramic fibre mat) or organic intumescent surface coatings.     

Modulation effects of collagen ? on the structure of electrochemically deposited hydroxyapatite coating

In this work, collagen ? was introduced as an additive to the dilute electrolyte used for direct electrochemical deposition of hydroxyapatite (HA) coating, and its modulation effects on the morphology and crystal structure of the HA coating were examined by SEM and XRD, respectively. Collagen I-modified HA coating was found to exhibit a micro-porous structure, formed by the ordered arrangements of ultra-fine HA crystals. The crystal structure of the modified HA coating was demonstrated to be similar to that of the natural bone. Further compositional studies using FTIR spectroscopy supported the integration of the collagen into the HA coating.     

Improved mechanical properties of magnesium–graphene composites with copper–graphene hybrids

New magnesium nanocomposites reinforced with copper–graphene nanoplatelet hybrid particles have been prepared through the semipowder metallurgy method. Compared with the monolithic Mg, the Mg–1Cu–xGNPs nanocomposites exhibited higher tensile and compressive strength. In tension, nanocomposites revealed substantial enhancement in elastic modulus, 0.2% yield strength, ultimate tensile strength and failure strain (up to +89, +117, +58 and +96% respectively) compared to monolithic Mg. In compression, the nanocomposites showed the greatest improvement in 0.2% yield strength, and the ultimate compressive strength and failure strain (%) (up to +34, +59 and +61% respectively), whilst the compressive elastic modulus first increases and then decreases with an increase in the graphene nanoplatelets (GNPs) contents. The enhanced strength of the composites is likely to result from strengthening mechanisms invoked by the addition of Cu–GNPs hybrids.     

Large load friction stir welding of Mg–6Al–0.4Mn–2Ca magnesium alloy

Friction stir welded (FSW) magnesium alloys usually exhibit a lower yield strength and elongation compared with base materials. In this study, large load FSW associated with an extremely low welding speed and rotation rate were applied to a non-combustive Mg–6Al–0.4Mn–2Ca magnesium alloy to modify the microstructure and texture in the weld zone and improve the mechanical properties of the joint. The twin structure in the stir zone provided adequate barriers for dislocation motion for strengthening and created more local sites for nucleating and accommodating dislocations, thereby elevating ductility and strain hardening in the transverse tensile test. The results showed that the yield strength and elongation of the joint were enhanced to 98% and 126% of the base material levels, respectively.     

Studies on the structure and gas sensing properties of nickel–cobalt ferrite thin films prepared by spin coating

The influence of Co²⁺ ions content on structure and sensing properties of Ni_1−xCo_xFe₂O₄ (x = 0.25, 0.5, 0.75) thin films deposited on glass substrates by spin coating is presented. Structural characterization evidenced thin films with cubic spinel structures and morphologies dependent on cobalt content. Repartition of cations in spinel tetrahedral and octahedral sites was determined and was found that the presence of Co²⁺ ions in octahedral sites favor the formation of Fe²⁺ species. The sensitivity to some reducing vapor gases (acetone, liquefied petroleum gas LPG, ethyl alcohol and methyl alcohol) was investigated and was found that thin films with x = 0.75 exhibit high sensitivity to ethyl alcohol and thin films with x = 0.25 have high sensitivity to acetone. This sensitivity largely depends on the temperature and test gas concentration and was related to the Fe²⁺ species formed in octahedral sites.     

Corrosion resistance of Zn–Al layered double hydroxide/poly(lactic acid) composite coating on magnesium alloy AZ31

A Zn–Al layered double hydroxide (ZnAl-LDH) coating consisted of uniform hexagonal nano-plates was firstly synthesized by co-precipitation and hydrothermal treatment on the AZ31 alloy, and then a poly(lactic acid) (PLA) coating was sealed on the top layer of the ZnAl-LDH coating using vacuum freeze-drying. The characteristics of the ZnAl-LDH/PLA composite coatings were investigated by means of XRD, SEM, FTIR and EDS. The corrosion resistance of the coatings was assessed by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results showed that the ZnAl-LDH coating contained a compact inner layer and a porous outer layer, and the PLA coating with a strong adhesion to the porous outer layer can prolong the service life of the ZnAl-LDH coating. The excellent corrosion resistance of this composite coating can be attributable to its barrier function, ion-exchange and self-healing ability.     

Electroless Ni–Mo–P diffusion barriers with Pd-activated self-assembled monolayer on SiO2

Ternary Ni-based amorphous films can serve as a diffusion barrier layer for Cu interconnects in ultralarge-scale integration (ULSI) applications. In this paper, electroless Ni–Mo–P films deposited on SiO₂ layer without sputtered seed layer were prepared by using Pd-activated self-assembled monolayer (SAM). The solutions and operating conditions for pretreatment and deposition were presented, and the formation of Pd-activated SAM was demonstrated by XPS (X-ray photoelectron spectroscopy) analysis and BSE (back-scattered electron) observation. The effects of the concentration of Na₂MoO₄ added in electrolytes, pH value, and bath temperature on the surface morphology and compositions of Ni–Mo–P films were investigated. The microstructures, diffusion barrier property, electrical resistivity, and adhesion were also examined. Based on the experimental results, the Ni–Mo–P alloys produced by using Pd-activated SAM had an amorphous or amorphous-like structure, and possessed good performance as diffusion barrier layer.