New material for orthopedic implants: Electrochemical study of nickel free P558 stainless steel in minimum essential medium

Nickel, a component of stainless steels (SS) applied in orthopedic implants may cause allergic processes in human tissues. P558 nickel free SS was studied to verify its viability as a substitute for stainless steel containing nickel. Its performance is compared to ISO 5832-9 and F138 most used nowadays grades in implants fabrications, in minimum essential medium, MEM, at 37 °C. Potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and “in vitro” cytotoxicity were used as techniques. From the electrochemical point of view P558 SS is comparable to ISO 5832-9 SS in MEM. It remains passivated until the transpassivation potential, above which generalized corrosion occurs. F138 presents pitting corrosion at 370 mV/SCE. The cytotoxicity results showed that P558, ISO 5832-9 and F138 do not present cytotoxic character. Therefore, these results suggest that P558 SS can be applied in orthopedic implants.     

Compatibility of ferritic and duplex stainless steels as implant materials: in vitro corrosion performance

The pitting corrosion, crevice corrosion and accelerated leaching of iron, chromium and nickel of super-ferritic and duplex stainless steels, and for effective comparison the presently used 316L stainless steel, have been studied in an artificial physiological solution (Hank's solution) by the potentiodynamic anodic polarization method. The results of the above studies have shown the new super-ferritic stainless steel to be immune to pitting and crevice corrosion attack. The pitting and crevice corrosion resistances of duplex stainless steel were found to be superior to those of the commonly used type 316L stainless steel implant materials. The accelerated leaching study conducted for the above alloys showed very little tendency for the leaching of metal ions when compared with 316L stainless steel. Thus the present study indicated that super-ferritic and duplex stainless steels can be adopted as implant materials due to their higher pitting and crevice corrosion resistance.     

Transient liquid phase bonding of a microduplex stainless steel using amorphous interlayers

Abstract

Microduplex stainless steels are two phase alloys which show excellent corrosion resistance and toughness. In order to join these special steels, fusion welding processes are normally used and a second post-weld heat treatment is necessary to regain the original ferrite to austenite ratio. In this study, transient liquid phase diffusion bonding was used to join a 2205 duplex stainless steel with the aid of amorphous interlayers. The research compares a Ni–B–Si ternary system with that of an Fe–B–Si interlayer, and compositional, microstructural and mechanical assessment was used to determine the quality of the bonds produced. These preliminary results show that the nickel based interlayer stabilises the austenitic phase along the bond length, which hinders grain growth across the joint region. In contrast, the iron based interlayer produces diffusion bonds, which show microstructural and compositional homogeneity across the joint region. Furthermore, mechanical and pitting corrosion tests show that transient liquid phase diffusion bonds can achieve properties similar to those of the parent alloy.     

Bioactive Materials for Regenerative Medicine: Zeolite‐Hydroxyapatite Bone Mimetic Coatings

We report the synthesis and characterization of a novel zeolite‐hydroxyapatite composite coating on titanium alloys and stainless steel. The zeolite‐hydroxyapatite coating is superhydrophilic and outperforms the state‐of‐the‐art Ti6Al4V alloys in corrosion resistance tests in aggressive pitting NaCl media, phosphate buffer solution with BSA protein, as well as highly complex DMEM cell culture media. And the composite coating also eliminates the elastic modulus mismatch between coating and bone. In addition, the composite coating has an osteoconductive and osteoinductive effect on hFOBs, indicating that it may enhance osteointegration of implants and speed up post‐surgical recovery, and thus reduce the need for recurring implant replacement surgeries. Replacing titanium with zeolite‐hydroxyapatite coated steel can also significantly reduce implant cost while improving implant lifespan.     

铸造双相不锈钢点腐蚀行为研究

采用化学浸泡腐蚀试验及微观组织和化学成分分析研究了5种铸造双相不锈钢在6%Fe Cl3溶液中的点腐蚀行为,并与316L奥氏体不锈钢进行了对比。结果表明,铸造双相不锈钢的抗点腐蚀性能均优于316L的,腐蚀速率和点腐蚀深度均小于316L奥氏体不锈钢的;双相不锈钢主要耐点蚀能力合金元素在奥氏体和铁素体相内分布不均匀,铬、钼更多地分配于铁素体相内,而镍、氮则更多地分配于奥氏体相内,铁素体相的耐点蚀指数PRE(Cr%+3.3Mo%+16N%)大于奥氏体相;双相不锈钢的耐点腐蚀性能与化学成分有关,随着PRE的增加,双相不锈钢的耐点腐蚀性能提高,铜元素在铁素体内析出的富铜相导致点蚀优先在铁素体内发生和发展。     

Corrosion of bio implants

Chemical stability, mechanical behaviour and biocompatibility in body fluids and tissues are the basic requirements for successful application of implant materials in bone fractures and replacements. Corrosion is one of the major processes affecting the life and service of orthopaedic devices made of metals and alloys used as implants in the body. Among the metals and alloys known, stainless steels (SS), Co-Cr alloys and titanium and its alloys are the most widely used for the making of biodevices for extended life in human body. Incidences of failure of stainless steel implant devices reveal the occurrence of significant localised corroding viz., pitting and crevice corrosion. Titanium forms a stable TiO₂ film which can release titanium particles under wear into the body environment. To reduce corrosion and achieve better biocompatibility, bulk alloying of stainless steels with titanium and nitrogen, surface alloying by ion implantation of stainless steels and titanium and its alloys, and surface modification of stainless steel with bioceramic coatings are considered potential methods for improving the performance of orthopaedic devices. This review discusses these issues in depth and examines emerging directions.     

In vitro corrosion resistance of Lotus-type porous Ni-free stainless steels

The corrosion behavior of three kinds of austenitic high nitrogen Lotus-type porous Ni-free stainless steels was examined in acellular simulated body fluid solutions and compared with type AISI 316L stainless steel. The corrosion resistance was evaluated by electrochemical techniques, the analysis of released metal ions was performed by inductively coupled plasma mass spectrometry (ICP-MS) and the cytotoxicity was investigated in a culture of murine osteoblasts cells. Total immunity to localized corrosion in simulated body fluid (SBF) solutions was exhibited by Lotus-type porous Ni-free stainless steels, while Lotus-type porous AISI 316L showed very low pitting corrosion resistance evidenced by pitting corrosion at a very low breakdown potential. Additionally, Lotus-type porous Ni-free stainless steels showed a quite low metal ion release in SBF solutions. Furthermore, cell culture studies showed that the fabricated materials were non-cytotoxic to mouse osteoblasts cell line. On the basis of these results, it can be concluded that the investigated alloys are biocompatible and corrosion resistant and a promising material for biomedical applications.     

Electrochemistry of AISI 316L stainless steel in calcium phosphate and protein solutions

The influence of calcium phosphate and serum on the corrosion resistance of AISI 316L stainless steel in 0.9% NaCl solution was investigated. Both substances are responsible for an increase in the pitting corrosion resistance. Calcium phosphate accelerates the rate of film formation, enhances the release of iron and nickel, and retards that of chromium from a corroding surface. Proteins induce the incorporation of phosphorus and calcium in corrosion products. These effects appear to replicate the accumulation of the same elements observed on stainless steels corrodedin vivo.     

Deformation capability and protective role of zirconia coatings on stainless steel

ZrO₂ coatings were obtained by the alkoxide route and deposited on to stainless steel using the dip-coating technique. The starting solutions were prepared by mixing zirconium tetrabutoxide, isopropanol, acetylacetone. The water content for the hydrolytic reaction came from atmospheric moisture. These coatings were characterized by scanning electron microscopy, X-ray fluorescence, Fourier transform-infrared spectroscopy, and X-ray diffraction. Their deformation capability was studied by using the stretch deformation test. It is worth noting that these coatings deposited on stainless steel have the capacity to deform extensively without apparent cracks or fracture. Their ability to protect the metallic substrate against corrosion, in a neutral chloride medium, was investigated. For this purpose, the pitting potential of the coated metal was measured by the potentiodynamic polarization technique and the a.c. impedance diagram of the coating was recorded in the potentiostatic mode at the rest potential. The variation in the pitting potentials revealed a temporary increase in the corrosion resistance of coated stainless steel, which disappeared after ageing of the coatings in the chloride solution. During ageing, the coating resistance deduced from the complex diagram via an equivalent circuit, decreases, thus showing a deterioration.     

Corrosion behaviour and biocompatibility of a novel Ni-free intermetallic coating growth on austenitic steel by hot dipping in an Al-12.6%Si alloy

Commercial 316 LVM austenitic stainless steel samples have been coated by immersion in a bath of molten Al–12.6%Si alloy for 120 s. The coating consists of the Al₁₂(Fe,Cr)₃Si₂ intermetallic. In vitro corrosion behaviour has been evaluated in the Ringer’s solution by means of potentiodynamic curves and electrochemical impedance spectroscopy. The results reveal that the coated specimens exhibit lower susceptibility to localised corrosion with respect to the substrate. XPS analysis suggests that the ennoblement of the pitting potential is due to the formation of a chromium oxyhydroxide containing passive layer. The intermetallic coating shows a good biocompatibility, as demonstrated by culturing human mesenchymal stem cells isolated from bone marrow which attached, grew and differentiated to the osteoblastic lineage to a similar extent on coated and bare steels. In summary, this study proposes a method that generates Ni-free coatings of the stainless steel with useful properties for biomedical applications.     

Optimizations of wear resistance and toughness of hydroxyapatite nickel free stainless steel new bio-composites for using in total joint replacement

The aim of this work was to produce novel bio-composites made of hydroxyapatite and nickel free stainless steel (prepared by heat treating bone ash) and studying their mechanical properties including their tribology under various loads, toughness, and compressive and bending strengths. Different amounts of nickel free stainless steel powder (30, 40, 50 and 60 wt.%) was added to this hydroxyapatite powder to get bio-composites. Their hardness, wear resistance and friction coefficient, as a function of the metal (nickel free stainless steel) content were investigated. Hardness and wear resistance were decreased by increasing of the weight percentage of stainless steel, while friction coefficient was increased. Strength and toughness of composites increases considerably by increasing of NFSS content. The toughness enhancement is contributed mainly by crack bridging and plastic deformation of the nickel free stainless steel. The strengthening effect is contributed by both the matrix grain refinement and the toughness enhancement. According to results of all mechanical tests done on composites, composite with 50 wt.% nickel free stainless steel has the most appropriate mechanical properties among other composites for using in orthopaedic applications.     

含Cu抗菌不锈钢的工艺与耐蚀性能

与普通0Cr17铁素体不锈钢和0Cr18Ni9奥氏体不锈钢相比，含铜铁素体和奥氏体抗菌不锈钢均具有良好的冷热加工性能和焊接性能．通过提高浇铸温度，抗菌不锈钢能保持良好的铸造性能．奥氏体抗菌不锈钢的抗应力腐蚀性能比0Cr18Ni9不锈钢有很大的提高，而铁素体抗菌不锈钢比0Cr17有明显的下降．与相应的普通不锈钢相比，两种类型抗菌不锈钢的耐点蚀性能均略有下降．     

Super austenitic stainless steels — a promising replacement for the currently used type 316L stainless steel as the construction material for flue-gas desulphurization plant

Potentiodynamic anodic cyclic polarization experiments on type 316L stainless steel and 6Mo super austenitic stainless steels were carried out in simulated flue-gas desulphurization (FGD) environment in order to assess the localized corrosion resistance. The pitting corrosion resistance was higher in the case of the super austenitic stainless steel containing 6Mo and a higher amount of nitrogen. The pit-protection potential of these alloys was more noble than the corrosion potential, indicating the higher repassivation tendency of actively growing pits in these alloys. The accelerated leaching study conducted for the above alloys showed that the super austenitic stainless steels have a little tendency for leaching of metal ions such as iron, chromium and nickel at different impressed potentials. This may be due to surface segregation of nitrogen as CrN, which would, in turn, enrich a chromium and molybdenum mixed oxide film and thus impedes the release of metal ions. The present study indicates that the 6Mo super austenitics can be adopted as a promising replacement for the currently used type 316L stainless steel as the construction material for FGD plants.     

Synthesis of nanostructured zirconia electrodeposited films on AISI 316L stainless steel and its behaviour in corrosion resistance assessment

This work deals with the study of AISI 316L stainless steel samples coated with nanostructured zirconia thin films, using electrodeposition methods. The chemical composition and compounds formed were determined by X-ray photoelectron spectroscopy (XPS). The morphology of zirconia films was analysed by scanning electron microscopy (SEM) and atomic force microscopy (AFM).Corrosion resistance of the coated steel was tested in a chloride environment. XPS analysis results show zirconium element on the metal surface, bound to oxygen-forming zirconia. The anodic polarization curves obtained in Hank's solution show that zirconia coating can be used as protective coating against pitting corrosion of AISI 316L stainless steels.     

Grain size dependence of mechanical, corrosion and tribological properties of high nitrogen stainless steels

Austenitic stainless steels have been indispensable for the progress of technology during the last 80 years. Due to the cost of nickel and to the prospective of allergic reactions caused by this element, more and more laboratories and industries are trying to develop a new class of austenitic stainless steels with a low nickel content. In order to maintain the austenitic microstructure, nickel reduction is balanced with nitrogen addition. Nitrogen addition to austenitic stainless steels is also very effective for improving yield strength and corrosion resistance without reducing ductility and toughness. In order to further increase the strength, it is possible to combine the effect of nitrogen addition and grain refining. The purpose of this study is to examine the relationship between microstructures and mechanical, corrosion and tribological properties of a high nitrogen stainless steel with an ultrafine grained structure.     

不锈钢表面电化学合成导电聚苯胺膜的研究

在酸性电解液中分别用电化学恒电位法和恒电流法在不锈钢基材上成功制备了导电聚苯胺膜，该膜在空气中呈绿色，稳定、完整致密，为结晶态结构，与基体的结合情况较好。在氯化钠溶液中测定试样的阳极极化曲线后发现，表面覆盖聚苯胺膜后的不锈钢，其点蚀电位比无膜时升高1000mV左右，表明导电聚苯胺膜可显著提高不锈钢的抗点蚀性能，具有良好的点腐蚀防护效果。     

The effect of TiN inclusions and deformation-induced martensite on the corrosion properties of AISI 321 stainless steel

Stainless steel of type 321 is commonly used for the production of exhaust systems because of its temperature resistance and welding properties, which are better than those of AISI 304 or similar steels. AISI 321 is a titanium stabilized austenitic stainless steel, where this element is added to form carbides in order to avoid chromium impoverishment due to chromium carbide formation. Cold shaping can, in the case of austenitic stainless steel, cause the formation of deformation induced martensite, which can improve its mechanical properties, but unfortunately can also spoil its good resistance to corrosion. Titanium nitride inclusions are cathodic with respect to steels, and therefore cause their anodic dissolution. Martensite is, however, more susceptible to the corrosion than austenite in steels. The main aim of this study was to analyze the pitting corrosion and stress corrosion cracking which is initiated on prototype cold-formed outer exhaust sleeves during the testing of different cleaning procedures before chromium plating. Various microscopic methods were used to identify the initiation of corrosion and its propagation.     

A review on nickel-free nitrogen containing austenitic stainless steels for biomedical applications

The field of biomaterials has become a vital area, as these materials can enhance the quality and longevity of human life. Metallic materials are often used as biomaterials to replace structural components of the human body. Stainless steels, cobalt–chromium alloys, commercially pure titanium and its alloys are typical metallic biomaterials that are being used for implant devices. Stainless steels have been widely used as biomaterials because of their very low cost as compared to other metallic materials, good mechanical and corrosion resistant properties and adequate biocompatibility. However, the adverse effects of nickel ions being released into the human body have promoted the development of “nickel-free nitrogen containing austenitic stainless steels” for medical applications. Nitrogen not only replaces nickel for austenitic structure stability but also much improves steel properties. Here we review the harmful effects associated with nickel and emphatically the advantages of nitrogen in stainless steel, as well as the development of nickel-free nitrogen containing stainless steels for medical applications. By combining the benefits of stable austenitic structure, high strength, better corrosion and wear resistance and superior biocompatibility in comparison to the currently used austenitic stainless steel (e.g. 316L), the newly developed nickel-free high nitrogen austenitic stainless steel is a reliable substitute for the conventionally used medical stainless steels.     

Corrosion properties of S-phase layers formed on medical grade austenitic stainless steel

The corrosion properties of S-phase surface layers formed in AISI 316LVM (ASTM F138) and High-N (ASTM F1586) medical grade austenitic stainless steels by plasma surface alloying with nitrogen (at 430°C), carbon (at 500°C) and both carbon and nitrogen (at 430°C) has been investigated. The corrosion behaviour of the S-phase layers in Ringer’s solutions was evaluated using potentiodynamic and immersion corrosion tests. The corrosion damage was evaluated using microscopy, hardness testing, inductive coupled plasma mass spectroscopy and X-ray diffraction. The experimental results have demonstrated that low-temperature nitriding, carburising and carbonitriding can improve the localised corrosion resistance of both industrial and medical grade austenitic stainless steels as long as the threshold sensitisation temperature is not reached. Carburising at 500°C has proved to be the best hardening treatment with the least effect on the corrosion resistance of the parent alloy.     

Microstructural characterization of medical-grade stainless steel powders prepared by mechanical alloying and subsequent annealing

The harmful effect of nickel ions released from conventional stainless steel implants has provided a high level of motivation for the further development of nickel-free stainless steels. In this paper, the microstructure of medical-grade nickel-free stainless steel powders, with the chemical composition of ASTM F2581, is studied during mechanical alloying and subsequent annealing. Rietveld X-ray diffraction and transmission electron microscopy evaluations reflect nanocrystallization, austenitization and amorphization of the powders due to mechanical activation. It is also realized that annealing of the as-milled powder can develop a single austenitic structure with nanometric crystallite sizes, implying a considerable inherent resistance to grain growth. This study demonstrates the merit of mechanical alloying and subsequent annealing in the development of nanostructured medical-grade stainless steels.