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Ti6Al4V alloy–CoCrMo alloy pair is commonly applied for modular head–neck interfaces for artificial hip joint. Unfortunately, the fretting corrosion damage at this interface seriously restricts its lifespan. This work studied the fretting corrosion of Ti6Al4V–CoCrMo pair in calf serum solution. We established this material pair's running condition fretting map (RCFM) regarding load and displacement, and revealed the damage mechanism of this material pair in various fretting regimes, namely partial slip regime (PSR), mixed fretting regime (MFR), and gross slip regime (GSR). The damage mechanism of Ti6Al4V alloy was mainly abrasive wear induced by CoCrMo alloy and tribocorrosion. Adhesive wear (material transfer) also existed in MFR. The damage mechanism of CoCrMo alloy was mainly abrasive wear induced by metal oxides and tribocorrosion in GSR and MFR, while no apparent damage in PSR. Furthermore, a dense composite material layer with high hardness was formed in the middle contacting area in GSR, which reduced the corrosion and wear of Ti alloys and exacerbated damage to Co alloys. Finally, the ion concentration maps for Ti and Co ions were constructed, which displayed the transition in the amount of released Ti and Co ions under different displacements and loads. [ABSTRACT FROM AUTHOR]

The management of bone repair in patients with osteoporosis depends on the clinical situation and the extent of the damage. The repair of bone lesions by inducing new bone formation is important for maintaining bone architecture and density. Herein, we reported the use of Cobalt Chromium Molybdenum (CoCrMo) implants in osteoporotic rabbits and the regenerative outcomes in vivo. The aim was to determine whether the placement of CoCrMo plates would induce qualitative and quantitative differences in the osteoporotic tissue beneath and surrounding the implant. We assessed the effect of the alloy in the bone of animals receiving implants for 4 and 8 weeks and compared the results to those of the osteoporotic non-implanted bone and the healthy controls. After 4 weeks, minimal histological changes were observed, whereas after 8 weeks a marked osteogenesis was evident with both apposition and substitution of new bone. In addition, a greater number of Haversian canals with increased canal area and decreased intracortical pores were observed in the implanted vs non implanted limb for both experimental groups. We show for the first time that the use of CrCoMo plates induces bone formation under osteoporotic conditions. The beneficial effect is localised on the cortical bone in areas in contact with the material. Although this effect may not directly influence the OP disease itself, it has direct implications for new bone formation adjacent to the biomaterial. This potential enhancement could play a crucial role in improving implant fixation in compromised bone, offering increased biocompatibility and stability.

CoCrMo alloys are often used in the manufacture of artificial joints in the medical field, and their special working environment will lead to corrosion and abrasion of the surface materials, thus reducing the service life of the joints. Surface texturing technology can improve the friction performance of joints by reducing the friction area, storing abrasive particles and lubricants, etc. Its application in the field of CoCrMo alloy joint surface strengthening is of great significance. This paper analyses the characteristics of surface fabrication processing technology and the friction reduction mechanism of surface fabrication under fluid lubrication and dry friction conditions, summarizes the influence of various fabrication parameters (fabrication depth, size, density, shape, etc.) on the friction performance of the alloy, introduces other surface technologies of CoCrMo alloy as well as common medical materials, summarizes the existing problems in the research of CoCrMo alloy surface reinforcement technology at this stage and makes a study on the development direction of the surface reinforcement technology of CoCrMo alloy in the field of artificial joints. The development direction of CoCrMo alloy in the field of artificial joints is also prospected. [ABSTRACT FROM AUTHOR]

Due to tribocorrosion, metal ions are released from metallic components in hip implants and cause adverse reactions. The adverse reaction sensitivity to metal ions showed high dependency on individual patient and it has been recognized that adverse reactions even occur in patients with metal-on-polymer articulations. In this study, based on a tribocorrosion model for CoCrMo alloy, a lubricated wear accelerated corrosion model was developed for CoCrMo alloy–UHMWPE tribocorrosion contacts. The model was verified and calibrated using laboratory tribometer experimental results and was used to predict metal ion release from CoCrMo alloy heads in MoP hip joints. The results showed correspondence between model predicted wear accelerated corrosion and literature reported material loss of CoCrMo alloy heads in MoP hip joints tested using hip joint simulators. This model provides a tool to predict the level of metal ions released from MoP hip joints and has the potential to be used by medical doctors to evaluate the risk of adverse reactions for patients planned to receive a MoP hip implant. [ABSTRACT FROM AUTHOR]

Previous investigation has established the formation of tribofilm is influenced by tribochemical reactions between the electrolyte and the articulating surface of cobalt alloy through sliding tests in various simulated fluids. Although it has successfully characterized the film composition via spectroscopy analysis and indicated to have impact on material loss, a comprehensive understanding of the material degradation mechanism in tribocorrosion condition was still lacking. Therefore, this study aims to investigate the role of protein in the tribocorrosive degradation of cobalt-chromium-molybdenum (CoCrMo) alloy in different simulated physiological electrolytes. Using a similar testing protocol, tribocorrosion tests were conducted with reciprocating ceramic ball against CoCrMo samples immersed in saline and culture medium, compared to both electrolytes diluted with 25% fetal bovine serum (FBS). Synergistic and mechanistic approaches were employed to model the tribocorrosive degradation. Results reveal that protein plays a beneficial role in reducing corrosive (electrochemical) surface degradation under tribocorrosion condition, whilst increasing mechanical wear degradation in the process. Despite studies have shown that tribocorrosion behavior in metal alloys is highly influenced by the presence of organic matter, this study provides a more clarity of the roles played by protein in tribocorrosive degradation on CoCrMo surface as its novel finding. [ABSTRACT FROM AUTHOR]

While titanium nitride (TiN) coatings are well known for their biocompatibility and excellent mechanical properties, their wear particle and debris release in orthopedic implants remains a matter of active investigation. This study addresses the efficacy of TiN coatings on CoCrMo and Ti6Al4V alloys to enhance wear resistance and reduce ion release from prosthetic implants. Three different coating variants were utilized: one variant deposited using arc evaporation (Arc) followed by post-treatment, and two variants deposited using high-power impulse magnetron sputtering (HiPIMS) with or without post-treatment. The coatings' performance was assessed through standard wear testing against ultra-high-molecular-weight polyethylene (UHMWPE) in bovine serum lubricant, and in the presence of abrasive PMMA bone cement particles in the lubricant. The results indicated that Arc and HiPIMS with post-treatment significantly reduced wear and eliminated detectable metal ion release, suggesting that these coatings could extend implant longevity and minimize adverse biological responses. Further long-term simulator and in vivo studies are recommended to validate these promising findings. [ABSTRACT FROM AUTHOR]

In this study, TiN thin films were coated on CoCrMo alloys and ceramic samples using vacuum coating technology with high-power impulse magnetron sputtering (HiPIMS), which was followed by coating at 100 and 200 °C to a thickness of 250, 500 or 750 nm to enhance the characteristics of the coated alloys. Through X-ray diffraction measurements, scanning electron microscopy, and microscale hardness testing, the structural, morphological, and mechanical characteristics of the CoCrMo and ceramic samples coated with TiN films were investigated in detail. The experimental results revealed that a smooth surface can be achieved on the film of 250 nm thickness and indicated that the TiN film with the smoother surface, formed by the vacuum coating method, has a higher hardness. It was also found that the TiN film prepared by coating at 200 °C had the smoothest surface and the highest hardness (365.64 HV0.5), leading to enhanced mechanical properties of the CoCrMo alloys. In the ceramic samples, the TiN film prepared by coating at 100 °C had the smoothest surface and the highest hardness (376.81 HV0.5). In addition, the vacuum coating process is helpful for improving the mechanical properties of TiN coating. The TiN materials are used in many sensor applications, and sensor applications can be realized using TiN/CoCrMo materials. In the future, we will study the sensing performance of TiN sensors fabricated on CoCrMo alloys, as well as implants made using the coated alloys. Then, we will further study circuit substrates, heat-resistant sensors, and corrosion- and wear-resistant parts that can be applied with TiN/Al2O3 materials. [ABSTRACT FROM AUTHOR]

In this study, we address the challenge of surface roughness in CoCrMo alloys, typically used in artificial knee joints, which can initiate a cascade of biological responses causing inflammation, osteolysis, joint instability, and increased susceptibility to infection. We propose the application of a chemical mechanical polishing (CMP) technique, using an ecologically responsible slurry composed of 4 wt% SiO2, 0.3 wt% H2O2, 1.0 wt% glycine, and 0.05 wt% benzotriazole. Our innovative approach demonstrated significant improvements, achieving a material removal rate of 30.9 nm/min and reducing the arithmetic mean roughness from 20.76 nm to 0.25 nm, thereby enhancing the nanoscale surface quality of the artificial knee joint alloy. The smoother surface is attributed to a decrease in corrosion potential to 0.18 V and a reduction in corrosion current density from 9.55 µA/cm2 to 4.49 µA/cm2 with the addition of BTA, evidenced by electrochemical tests. Furthermore, the preservation of the phase structure of the CoCrMo alloy, as confirmed by XRD analysis and elemental mapping, ensures the structural integrity of the treated surfaces. These outcomes and our simulation results demonstrate the effectiveness of our CMP method in engineering surface treatments for artificial knee joints to optimize friction behavior and potentially extend their lifespans. [ABSTRACT FROM AUTHOR]

Carbon nanotubes are a promising material for use in innovative biomedical solutions due to their unique chemical, mechanical, electrical, and magnetic properties. This work provides a method for the development of ultrasonically assisted electrophoretic deposition of multi-walled carbon nanotubes on a CoCrMo dental alloy. Functionalization of multi-walled carbon nanotubes was carried out by chemical oxidation in a mixture of nitric and sulfuric acids. The modified and unmodified multi-walled carbon nanotubes were anaphoretically deposited on the CoCrMo alloy in an aqueous solution. Chemical composition was studied by Fourier transform infrared spectroscopy. Surface morphology was examined by scanning electron microscopy. The mechanism and kinetics of the electrochemical corrosion of the obtained coatings in artificial saliva at 37 °C were determined using the open-circuit potential method, electrochemical impedance spectroscopy, and anodic polarization curves. The capacitive behavior and high corrosion resistance of the tested electrodes were revealed. It was found that the kinetics of electrochemical corrosion of the CoCrMo electrode significantly decreased in the presence of the functionalized multi-walled carbon nanotube coating. Electrophoretic deposition was shown to be an effective, low-cost, and fast method of producing nanotubes with controlled thickness, homogeneity, and packing density. [ABSTRACT FROM AUTHOR]

In this paper, we present the mechanisms of premature fracture of modular neck stems in two case studies: (I) when the neck and stem are both made of the same Ti6Al4V alloy, and (II) when the neck and stem are made from two different alloys, CoCrMo and Ti6Al4V alloy. Our study integrates two orthopedic patients who have undergone primary uncemented THA for usual indications in two orthopedic centers (Community Health Centre and University Medical Centre). Both centers are part of the national public health care system. Both surgeries were performed by two skilled orthopedic surgeons with more than 10 years of experience in THA. The survivorship of the modular neck of cast CoCrMo alloy was 24 months. The survivorship of the modular neck from Ti6Al4V alloy was 84 months. Multivariate analyses were performed to assess the differences in the fretting, corrosion, and fatigue of the two prematurely failed modular neck stems: stereo light microscopy (SLM), scanning electron microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS), and electron backscatter diffraction (EBSD). Patient demographic information, including sex, age, body mass index, survivorship of implants, and reason for the revision, was collected from medical records. We found that fretting and fatigue occurred on both neck-stem retrievals due to additional galvanic corrosion, but the CoCrMo/Ti6Al4V alloy system suffered more corrosion due to additional galvanic corrosion and fractured earlier than the Ti6Al4V/Ti6Al4V metal alloy system. Both metallic alloy systems used in this application are known to be highly corrosion-resistant, but the bio-tribo-corrosion processes need to be understood in detail and characterized so that appropriate improvements in design and materials can be made. [ABSTRACT FROM AUTHOR]

While titanium nitride (TiN) coatings are well known for their biocompatibility and excellent mechanical properties, their wear particle and debris release in orthopedic implants remains a matter of active investigation. This study addresses the efficacy of TiN coatings on CoCrMo and Ti6Al4V alloys to enhance wear resistance and reduce ion release from prosthetic implants. Three different coating variants were utilized: one variant deposited using arc evaporation (Arc) followed by post-treatment, and two variants deposited using high-power impulse magnetron sputtering (HiPIMS) with or without post-treatment. The coatings’ performance was assessed through standard wear testing against ultra-high-molecular-weight polyethylene (UHMWPE) in bovine serum lubricant, and in the presence of abrasive PMMA bone cement particles in the lubricant. The results indicated that Arc and HiPIMS with post-treatment significantly reduced wear and eliminated detectable metal ion release, suggesting that these coatings could extend implant longevity and minimize adverse biological responses. Further long-term simulator and in vivo studies are recommended to validate these promising findings.

The hardness of heat (thermally) treated CoCrMo ingots, recycled by electron beam melting and refining (EBMR) of a technogenic CoCrMo material (waste from the dental technology) under different process conditions (temperature and residence time) is examined. The heat treatment consists of two-step heating up to temperatures of 423 K and 1343 K and retention times of 40 and 60 min, respectively. The influence of various loads (0.98 N, 1.96 N, 2.94 N, 4.9 N, and 9.8 N) on the hardness of the CoCrMo alloy, recycled by EBMR, before and after heat treatment is studied. It has been found that regardless of the EBMR process conditions, the obtained samples after heat treatment have similar hardness values (between 494.2 HV and 505.9 HV) and they are significantly lower than the hardness of the specimens before the heat treatment. The highest hardness (600 HV) is measured in the alloy recycled at 1845 K refining temperature for 20 min. This is due to the smaller crystal structure of the resulting alloy and the higher cobalt content. The results obtained show that the heat treatment leads to considerable changes in the microstructure of the CoCrMo ingots recycled by EBMR. With the increase of the e-beam refining temperature, after the heat treatment, the grains' size increases and the grains' shape indicates an incomplete phase transition from γ-fcc to ε-hcp phase. This leads to a slight increase in the hardness of the alloy. [ABSTRACT FROM AUTHOR]

The article researched simulation of the melted metal die forging process of temperature field, velocity field, shrinkage porosity and oxides of femoral stem of CoCrMo alloy and effects of casting temperature, mold temperature and forging speed on the filling and solidification with the help of the software ProCAST. The results indicated molten metal impact ran into the wall of the mold cavity and formed turbulent flow in the neck and head of the femoral stem, which posed risk of gas entrainment. Forging speed has obvious influence on oxides: the higher of forging speed, the lower of oxides contents. The molten alloy ran into the wall of the mold cavity and formed turbulent flow in the neck and head of the femoral stem whose top appeared oxides-rich area. CoCrMo alloy femoral stem whose casting was complete without shrinkage porosity have been gotten by injecting inert gas into the mold cavity before molten alloy pouring and setting the exhaust groove at the front of the femoral stem and exhaust plug at the highest position of the head of femoral stem. [ABSTRACT FROM AUTHOR]

In this work, by employing powders sourced directly from the original ingot for additive manufacturing, we enabled a comparative overview of the performance between CoCrMo manufactured via laser powder bed fusion (LPBF) and those in their original cast condition. Microstructural analysis revealed that the cast (CT) alloy predominantly consisted of coarse grains with distribution of sigma phase, while the LPBF process resulted in a refined grain structure devoid of the sigma phase. The tensile strength tests demonstrated that the LPBF-derived CoCrMo alloy had substantially greater tensile strength, and ductility compared to CT alloy. Corrosion tests indicated superior corrosion resistance in the LPBF alloy, albeit with a lower metal ion release. In vitro assays confirmed that LPBF CoCrMo alloys displayed favorable cytocompatibility. Consequently, it is concluded that the CoCrMo alloy processed through laser powder bed fusion exhibited enhanced mechanical performance and corrosion resistance. These improvements are primarily attributed to the transformation of the original coarse columnar grain structure through the LPBF technique. [ABSTRACT FROM AUTHOR]

CoCrMo sheet triply periodic minimal surface (sheet-TPMS) lattices with two different topologies (Neovius, IWP) were fabricated by laser power bed fusion (LPBF). Compressive behavior and energy absorption characteristic for each topology and direction were investigated. The unique pore channel structures of the fabricated Neovius and IWP lattices were well formed. The microstructural observation revealed that fine cellular substructures existed inside the sheets, and most of their constituent phases were confirmed to be the FCC phase. The results of the compression tests demonstrated that Neovius lattice had higher yield strength and first peak strength than IWP lattice, regardless of the compressive direction. As for the stress–strain curves of the lattices, an abrupt stress drop was found in neither of the two topologies. A comparison of the energy absorption characteristics confirmed that Neovius lattice had higher energy absorption efficiency and ideality than IWP lattice. The deformed structures showed that Neovius lattice displayed a gradual collapse mode, whereas a layer-by-layer compaction mode was indicated in IWP lattice. After the deformation, Neovius showed an evenly distributed and high fraction of the HCP phase caused by strain-induced martensitic transformation. The topology of lattice and strain-induced martensitic transformation effects on the compressive mechanical responses of the LPBF-built TPMS lattices were also discussed.

We determined the in vitro corrosion resistance of the composite chitosan-silver(I) [Ag(I)] ion coating on the cobalt-chromium-molybdenum (CoCrMo) dental alloy in a 0.9% sodium chloride (NaCl) solution at 37°C. We obtained the novel composite chitosan-Ag(I) ion coating by electrophoretic deposition at 20 V for 30 s at room temperature in a 2% (v/v) aqueous solution of acetic acid with 1 g dm-3 chitosan and 10 g dm-3 silver nitrate. We evaluated the chemical composition with energy dispersive spectroscopy and Fourier-transform infrared spectroscopy. We investigated surface topography and electronic properties with a scanning Kelvin probe. We determined the mechanism and kinetics of the electrochemical corrosion of the obtained coatings by electrochemical impedance spectroscopy. The Ag content in the composite chitosan-Ag(I) ion coating was 1.9 ± 1 wt.%. The cataphoretic co-deposition of chitosan and Ag(I) ions in an aqueous solution can be used to modify the CoCrMo alloy surface to obtain new coatings with antibacterial properties. [ABSTRACT FROM AUTHOR]

Corrosion and metal release characteristics of cobalt-based alloys are important factors influential on their biomedical applications. This study fabricated a porous Vitallium (CoCrMo) alloy and then coated with a 58S bioglass coating by applying the sol-gel dipping method with 3, 4 and 5 cycles to examine the corrosion and ion release performance of this alloy. For this purpose, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and immersion tests were conducted in the simulated body fluid (SBF) at 37 °C. Also, the released ion measurements were performed by inductive coupled plasma optical emission spectrometry (ICP-OES). SEM examinations on the porous substrate indicated that this porous scaffold exhibited the porosity of 37% and the content of small porosities was decreased; however, the macrospores on the surface were intact after applying bioglass coatings. Furthermore, increasing the dipping cycles led to enhancing the corrosion potential from − 191 mV (in the uncoated porous sample) to − 98 mV (in the coated porous sample dipped 5 cycles in the bioglass sols). EIS results in SBF demonstrated that the corrosion performance of the coatings was improved by increasing the dipping cycles from 0 to 5. ICP-OES results also proved that the presence of the 58 S bioglass coating on the porous Vitallium decreased the release of cobalt and chromium ions, while it enriched Ca and P, thereby improving the bioactivity of the samples. [ABSTRACT FROM AUTHOR]

The present work focuses on the Tribological properties and corrosion behavior evaluation of sintered CoCrMo alloy. The CoCrMo alloy was elaborated by Powder metallurgy process at various sintering temperatures (1200�C, 1250�C and 1300�C). The structural properties were characterized by X-ray diffraction and scanning electron microscopy. The tribological characteristics were measured using a dry disc-ball tribometer. The corrosion behavior of the samples was studied using different electrochemical tests in a simulated physiological environment (Hank�s solution). The obtained results show that higher sintering temperatures have a positive impact on the tribological behavior as well as the corrosion resistance of CoCrMo alloys. The sintered samples at 1300�C showed a better resistance to friction wear and a lower corrosion rate.

Carbon nanotubes are a promising material for use in innovative biomedical solutions due to their unique chemical, mechanical, electrical, and magnetic properties. This work provides a method for the development of ultrasonically assisted electrophoretic deposition of multi-walled carbon nanotubes on a CoCrMo dental alloy. Functionalization of multi-walled carbon nanotubes was carried out by chemical oxidation in a mixture of nitric and sulfuric acids. The modified and unmodified multi-walled carbon nanotubes were anaphoretically deposited on the CoCrMo alloy in an aqueous solution. Chemical composition was studied by Fourier transform infrared spectroscopy. Surface morphology was examined by scanning electron microscopy. The mechanism and kinetics of the electrochemical corrosion of the obtained coatings in artificial saliva at 37 °C were determined using the open-circuit potential method, electrochemical impedance spectroscopy, and anodic polarization curves. The capacitive behavior and high corrosion resistance of the tested electrodes were revealed. It was found that the kinetics of electrochemical corrosion of the CoCrMo electrode significantly decreased in the presence of the functionalized multi-walled carbon nanotube coating. Electrophoretic deposition was shown to be an effective, low-cost, and fast method of producing nanotubes with controlled thickness, homogeneity, and packing density.

For components built by powder bed fusion with electron beam (PBF-EB), the resulting microstructure arising from non-equilibrium solidification, microsegregation and the formation of interdendritic phases significantly affects the material properties. Notably, the powder characteristics influence the heat absorption and conduction, thereby altering the molten pool behavior and solidification parameters. However, the effect of the powder feedstock on solidification during PBF has not been widely investigated. In this study, a CoCrMo alloy was fabricated using powders prepared by gas-atomization (GA) and plasma rotating electrode process (PREP). Under the given operating conditions, samples built using the two powders were characterized and compared. By performing multi-scale numerical simulations, melting and solidification were visualized and analyzed to elucidate the mechanism through which the powder characteristics influence the non-equilibrium solidification behavior during PBF-EB. The study revealed that after appropriate size control, compared with the GA powder, the PREP powder had a smaller specific surface area and higher sphericity; thus, the generated powder layer exhibited higher heat absorption and dissipation rates. Therefore, a high solidification rate was facilitated, thereby suppressing microsegregation. These findings contribute to PBF knowledge related to feedstock, proving to be an essential reference for selecting and optimizing metallic powders applicable to additive manufacturing.

Additive manufacturing research is continuously growing, and this field requires a full improvement of the capability and reliability of the processes involved. Of particular interest is the study of complex geometries production, such as lattice structures, which may have a potentially huge field of application, especially for biomedical products. In this work, the powder bed fusion technique was utilized to manufacture lattice structures with defined building angles concerning the build platform. A biocompatible Co-Cr-Mo alloy was used. Three different types of elementary cell geometry were selected: Face Centered Cubic, Diagonal, and Diamond. These cells were applied to the radially oriented lattice structures to evaluate the influence of their orientation in relation to the sample and the build platform. Moreover, heat treatment was carried out to study its influence on microstructural properties and mechanical behavior. Microhardness was measured, and compressive tests were performed to detect load response and to analyse the fracture mechanisms of these structures. The results show that the mechanical properties are highly influenced by the cell orientation in relation to the building direction and that the properties can be further tuned via HT. The favorable combination of mechanical properties and biocompatibility suggests that Co-Cr-Mo lattices may represent an optimal solution to produce customized metal implants.

Antecedentes: La osteointegración ha permitido un gran avance en biomateriales y técnicas, y ha contribuido un mayor uso de implantes dentales. Sin embargo, la existencia de un nivel óseo insuficiente es un problema frecuente y crea una base anatómicamente menos favorable para la colocación de implantes. El primer procedimiento quirúrgico debe comprender la reconstrucción de la altura del hueso alveolar. Las aleaciones de CoCrMo se consideran hoy en día como materiales altamente resistentes a la corrosión y biocompatibles en odontología y, por lo tanto, se ha sugerido como un biomaterial adecuado para la regeneración ósea guiada y la ingeniería de tejidos. Objetivo: Determinar el uso de la aleación CoCrMo para dispositivos implantables en cirugía oral y maxilofacial y discutir sobre el potencial de esta aleación para la regeneración y reparación ósea a través de una revisión de alcance. Material y Métodos: La búsqueda se realizó utilizando varias bases de datos, incluidas PubMed, Thomson Reuters y Scopus. Se seleccionó literatura inglesa relacionada con estudios que informan sobre las propiedades de CoCrMo y los procesos de fabricación y los hallazgos relacionados con las técnicas de formación de huesos. Los datos se compararon cualitativamente. Resultados: Se seleccionaron 90 estudios según los criterios de inclusión. y se reportaron diferentes técnicas de fabricación y sus ventajas relacionadas con propiedades mecánicas, químicas y biocompatibles. Conclusión: Las reacciones tisulares mejoradas de los dispositivos de implante CoCrMo pueden adquirirse mediante la aplicación de nuevas técnicas y modificaciones de la superficie. Además, varios procesos han demostrado mejorar la biocompatibilidad in vitro e in vivo de la aleación CoCrMo para promover la unión, proliferación y diferenciación guiada de las células de siembra.

The present work focuses on the Tribological properties and corrosion behavior evaluation of sintered CoCrMo alloy. The CoCrMo alloy was elaborated by Powder metallurgy process at various sintering temperatures (1200°C, 1250°C and 1300°C). The structural properties were characterized by X-ray diffraction and scanning electron microscopy. The tribological characteristics were measured using a dry disc-ball tribometer. The corrosion behavior of the samples was studied using different electrochemical tests in a simulated physiological environment (Hank's solution). The obtained results show that higher sintering temperatures have a positive impact on the tribological behavior as well as the corrosion resistance of CoCrMo alloys. The sintered samples at 1300°C showed a better resistance to friction wear and a lower corrosion rate. [ABSTRACT FROM AUTHOR]

The present work focuses on the Tribological properties and corrosion behavior evaluation of sintered CoCrMo alloy. The CoCrMo alloy was elaborated by Powder metallurgy process at various sintering temperatures (1200°C, 1250°C and 1300°C). The structural properties were characterized by X-ray diffraction and scanning electron microscopy. The tribological characteristics were measured using a dry disc-ball tribometer. The corrosion behavior of the samples was studied using different electrochemical tests in a simulated physiological environment (Hank’s solution). The obtained results show that higher sintering temperatures have a positive impact on the tribological behavior as well as the corrosion resistance of CoCrMo alloys. The sintered samples at 1300°C showed a better resistance to friction wear and a lower corrosion rate.

CrN/CrCN/TaN multilayer films were deposited onto the CoCrMo alloy substrates at different number layers as two, four and 8 layers by close-field unbalanced magnetron sputtering method. Microstructure and the tribo-logical properties of the films were characterized by XRD, SEM, pin-on-disk wear test, scratch test, micro hardness. CrN/CrCN/TaN multilayer coatings exhibited good adhesion properties on the CoCrMo alloy substrate. A very high hardness value of 60 GPa was obtained for 8 multilayered coating. As a result of the pin-on-disc wear tests, it was found that the tribological properties of the CoCrMo alloy were enhanced by coating its surface with this architecture by using close-field unbalanced magnetron system with used parameters.

CoCrMo alloys, which are well-known Co-based biomedical alloys, have many different types of surface integrity problems reported in literature. Residual stresses, white layer formation and work hardening layers are some those, matters which occur as a microstructural alteration during machining. Therefore, such problems should be solved and surface quality of end products should be improved. In this paper, the surface quality of CoCrMo alloy used in tibial component of the knee prosthesis produced by means of turning was investigated. An improvement was suggested and discussed for the improvement in their machinability with the developed turning-grinding method. Finite element analyses were also carried out to calculate temperature and thermal stresses distribution between the tool and the tibial component. The results showed that many parameters such as cutting speed, feed rate, depth of cut, tool geometry, and tool wear affect the surface quality of workpieces of CoCrMo alloy. In the turning-grinding method, the machining time is reduced by about six times compared to machining only method. The EDX analysis performed on the surface after machining showed that metal diffusion occurred from tool to the tibial component.

The demand for CoCrMo alloy as an artificial prosthesis has increased for its reliable properties. However, machining of CoCrMo alloy is challenging due to meet the high requirements on prosthesis' surface quality. In this paper, a new approach of fine ELID grinding on CoCrMo alloy has been proposed using a Kistler three-component dynamometer to monitor the grinding force in real time. This paper also presents the friction and wear performance of CoCrMo alloy. Results show that better efficiency and surface quality can be obtained with low feed speed and small grinding depth. The passivation layer was found on the surface of CoCrMo alloy after ELID grinding, which makes the CoCrMo alloy prosthesis have better biocompatibility. The wear resistance test has proved that CoCrMo alloy has better wear resistance and lower wear quality and is suitable for manufacturing prosthesis. [ABSTRACT FROM AUTHOR]

This research work describes the impact of the surface mechanical attrition treatment (SMAT) on the microstructure of cobalt–chromium–molybdenum (CoCrMo), a biomedical alloy commonly used for orthopedic applications. This surface treatment induces crystalline phases transformations characterized by X‐ray diffraction (XRD) and selected area electron diffraction (SAED). The corresponding structural changes are observed from cross‐section images obtained by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the SMAT process induces the martensitic transformation of the CoCrMo alloy (from γ‐fcc phase to ε‐hcp phase) related to an important grain refinement due to twinning and sliding. [ABSTRACT FROM AUTHOR]

Photofunctionalization of implant materials with ultraviolet (UV) radiation have been subject of study in the last two decades, and previous research on CoCrMo discs have showed good results in terms of bioactivity and the findings of apatite‐like crystals in vitro. In the current study, CoCrMo domes were photofunctionalized with UV radiation of 254 nm on their internal faces during 24 hr; they were implanted in rabbit tibia and remained for 3, 4, and 6 weeks. The potential to induce bone formation beneath the dome‐shaped membranes was evaluated through morphometric, histologic, and density measurements; and the results were compared with those obtained under control untreated domes. Higher density values were observed for irradiated domes at 3 weeks, whereas higher volumes were obtained under photofunctionalized domes for longer periods (4 and 6 weeks). Histologically, woven bone was formed by endochondral ossification in all cases; differences in the architecture and size of the trabeculae and in the number of osteoblasts were noted between irradiated and non‐irradiated samples. The UV radiation of 254 nm generated a larger bone volume fraction compared to that found in the absence of UVC radiation and induced an increase of density in the early stages of healing, leading to a better initial bone quality and improved osseointegration. [ABSTRACT FROM AUTHOR]

Cobalt-chromium-molybdenum alloys are commonly used for biomedical applications such as dental implants and joint implants. Once the material is implanted into the body it is exposed to the corrosiveness of biological fluids and, in some cases, to mechanical loading that can lead to the combined action of wear and corrosion; better known as tribocorrosion. The effect of four different simulated body fluids on the tribocorrosion behaviour of a CoCrMo alloy has been investigated. The degradation of the studied CoCrMo alloys due to tribocorrosion shows a great dependence on the chemical composition of the media. Phosphate-buffered saline (PBS)-based solutions tend to show higher mass loss than the solutions prepared with distilled water. Phosphates present in PBS tend to accumulate on the surface of the alloy and change its tribological performance. In addition, proteins show a lubricating effect reducing the coefficient of friction of the system in the boundary lubrication regime. [ABSTRACT FROM AUTHOR]

Fretting corrosion at the head‐neck taper junction was compared between silicon nitride (Si3N4) and commercially available cobalt chrome (CoCrMo) femoral heads on titanium (Ti‐6Al‐4V) trunnions. An electrochemical setup was used to capture the fretting currents (characterized by oxide abrasion and repassivation) during cyclic loading. Onset load, pull‐off force (disassembly load), short term and long term (1 million cycles) fretting currents were used to compare the fretting corrosion performance between the test group (Si3N4/Ti‐6Al‐4V) and the control group (CoCrMo/Ti‐6Al‐4V). Incremental cyclic fretting corrosion tests showed that the Si3N4/Ti‐6Al‐4V combination had statistically lower (P <.05) average fretting current of 0.189 µA (SD = 0.114 µA) compared to 0.685 µA (SD = 0.630 µA) for CoCrMo/Ti‐6Al‐4V for cyclic load of 3200 N. Similarly, for the one million cycle fretting corrosion tests, the Si3N4/Ti‐6Al‐4V couples had statistically lower (P <.05) average current (0.048 µA, SD = 0.025 µA) vs CoCrMo/Ti‐6Al‐4V couples (0.366 µA, SD = 0.143 µA). The Si3N4 heads also had higher onset loads (P <.05) for fretting (vs CoCrMo, 2200 N vs 1740 N) indicating a difference in surface contact mechanics between the two groups. Scanning electron microscopy with energy dispersive spectroscopy confirmed material transfer from the trunnions to the heads for both groups tested, and from head to trunnion for the CoCrMo heads. Minimal Si3N4 transfer was noted. The electrochemical, mechanical, and microscopic inspection data supported the hypothesis that Si3N4/Ti‐6Al‐4Vcombination had better fretting corrosion performance compared to CoCrMo/Ti‐6Al‐4V. [ABSTRACT FROM AUTHOR]

To alleviate fretting damage of the artificial joint CoCrMo alloy, the substrate was treated by ultrasonic surface rolling process (USRP) and solid solution treatment (SST) respectively. Meanwhile, the fretting wear behavior and failure mechanism of the treated-samples were quantitatively analyzed via experimental study. Compared with the substrate, the wear rates of USRP and SST samples are reduced by about 8.895 and 13.463 µm3/mJ in slip regime. In addition, the wear resistance of USRP samples is improved due to grain refinement, but the expanded grain boundary channels aggravate the oxidative wear degree (8.13% higher than substrate). The intergranular carbides are dispersed in grains and constructed into stacking faults through SST, hence, the fretting wear resistance of the alloy is greatly improved. • Fretting damage of the CoCrMo alloy was alleviated via strengthening treatment. • Quantitative analysis of wear resistance was conducted based on dissipated energy. • Fretting wear behavior and failure mechanism of the treated-materials were revealed. • Reference to improve the service reliability of the typical artificial joint materials. [ABSTRACT FROM AUTHOR]

Although post-heat treatment can improve the fatigue life of selective laser melting (SLM)-fabricated cobalt chromium molybdenum (CoCrMo) alloys, the effect of cooling conditions on the fatigue properties of such alloys remains unclear. In this study, we fabricated SLM CoCrMo alloy specimens and, after heat-treating them, cooled them either via furnace-cooling (FC) or air-cooling (AC). Subsequently, we analyzed their microstructures using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy, electron backscattered diffraction, confocal laser scanning microscopy, and X-ray diffraction. Tensile and Vickers hardness (HV) tests and axial-fatigue tests were also conducted to assess their mechanical and fatigue properties, respectively. The microstructures of all samples showed homogeneous equiaxed grains, with the grains and precipitates of the AC samples (grain size: 84.9 μm) smaller than those of the FC samples (grain size: 109.7 μm). The AC samples exhibited better ductility than the FC samples. However, we observed no significant differences in the 0.2% yield strength and HV tests. The S–N curve derived from the fatigue tests showed that the AC samples had greater fatigue life than the FC samples. Therefore, a high cooling rate during post-heat treatment is effective in reducing grain and precipitate sizes, resulting in improved ductility and fatigue life.

CoCrMo alloy has been oxidized for 3 and 5h at the temperature of 850°C with 100% O2 gas by thermal oxidation. The XRD, SEM, microhardness and ball-on-disc wear test devices were used to find out the structure, mechanical and wear properties of untreated and treated specimens. Outcomes showed wear resistance of oxidized specimens were became better than untreated CoCrMo alloy. Also, wear resistance of oxidized specimens improved with increased processing time (from 3h to 5h) increased. [ABSTRACT FROM AUTHOR]

CoCrMo alloys, which are well-known Co-based biomedical alloys, have many different types of surface integrity problems reported in literature. Residual stresses, white layer formation and work hardening layers are some those, matters which occur as a microstructural alteration during machining. Therefore, such problems should be solved and surface quality of end products should be improved. In this paper, the surface quality of CoCrMo alloy used in tibial component of the knee prosthesis produced by means of turning was investigated. An improvement was suggested and discussed for the improvement in their machinability with the developed turning-grinding method. Finite element analyses were also carried out to calculate temperature and thermal stresses distribution between the tool and the tibial component. The results showed that many parameters such as cutting speed, feed rate, depth of cut, tool geometry, and tool wear affect the surface quality of workpieces of CoCrMo alloy. In the turning-grinding method, the machining time is reduced by about six times compared to machining only method. The EDX analysis performed on the surface after machining showed that metal diffusion occurred from tool to the tibial component. [ABSTRACT FROM AUTHOR]

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Partial knee replacement and hemiarthroplasty are some of the orthopedic procedures resulting in a metal on cartilage interface. As metal implant material, CoCrMo based alloys are commonly used. The aim of the present study is to assess the role of biotribocorrosion on the CoCrMo-cartilage interface with an emphasis on metal release during sliding contact. The biotribocorrosion experiments were performed under controlled electrochemical conditions using a floating cell with a three electrode set up coupled to a microtribometer. Throughout the experiment the coefficient of friction and the open circuit potential were monitored. Analyses of the electrolyte after the experiment show that metal release can occur during sliding contact of CoCrMo alloy against articular cartilage despite the extraordinary low coefficient of friction measured. Metal release is attributed to changes in passive layer caused at the onset of sliding. The released metal was found to be forming compounds with potential cytotoxicity. Since the presence of metal ions in the cartilage matrix can potentially lead to cell apoptosis, the metabolic activity of human osteoarthritic chondrocytes (2D-cultures) was investigated in the presence of phosphate buffered saline containing metal ions using XTT-assay. The experiments indicate that critical concentrations of Co ions lead to a significant decrease in chondrocyte metabolic activity. Therefore, biotribocorrosion is a mechanism that can occur in partial replacements and lead to chondrocyte apoptosis thus playing a role in the observed accelerated degradation of the remaining cartilage tissue after the mentioned orthopedic procedures. Partial replacements provide an alternative to total joint replacements. This procedure is less invasive, allows a faster rehabilitation and provides a better function of the joint. However, the remaining native cartilage experiences accelerated degradation when in contact with metallic implant components. This work investigates the role of tribocorrosion at the metal-cartilage interface during sliding. Tribocorrosion is a degradation process that can alter significantly the wear rates experienced by metallic implants and lead to the release of metal ions and particles. The released metal can form compounds with potential cytotoxicity on cartilage tissue. The knowledge gained in this work will serve to understand the mechanisms behind the failure of partial replacements and develop future biomaterials with an enhanced lifetime. [ABSTRACT FROM AUTHOR]

CoCrMo alloys are used in a wide range of applications because of their acceptable fatigue strength and corrosion resistance. However, CoCrMo-based components exhibit a deleterious effect of wear. For this reason, surface modification through ceramic coatings has become in a useful alternative to improve mechanical resistance. The main aim of the present study was to investigate the tribological behavior of a system of diffusional boride layers formed on the substrate of CoCrMo alloy. For this purpose, different boron diffusion heat treatment parameters were performed: 1223, 1248 and 1273 K by 6, 8 and 10 h, respectively. Surfaces were characterized using scanning electron microscopy (SEM), surface roughness measurement, micro-hardness testing, and X-ray diffraction. The tribological response was studied by means of ball on disc tribometer under dry-sliding conditions tracking their friction coefficient, mass loss, wear rate and surface damage by stereoscopy and SEM. Boride coating at 1223 K by 6 h showed the better wear resistance, increased it 6 times relative to the wear resistance obtained for the CoCr alloy untreated sample. • CoCr borided sample at 1223 K – 6 h increased 6 times the wear resistance in comparison with the CoCr untreated sample. • The wear resistant borided layer was correlated with temperature and time parameters of boronizing process. • The maximum hardness value achieved on the borided surface was 5 times higher than the hardness of the substrate. • The main wear mechanism was severe abrasion for the untreated sample and surface fatigue for the borided samples. [ABSTRACT FROM AUTHOR]

High carbon CoCrMo alloy has been widely used in orthopedic implants. Carbides improve the strength of the material and influence wear resistance. An atomic force microscopy (AFM)-based single asperity tribology method was developed to investigate the wear performance of individual carbides and base metal matrix of high carbon CoCrMo alloy. Sub-nano to nanoscale wear on single carbides was performed and quantified. Nanowear behavior of two types (Cr-rich and Mo-Rich) of carbides was stress-dependent (from 7.8 GPa to 9.8 GPa) and influenced by chemical composition. The lower wear depth of both Cr-rich and Mo-rich carbide compared to the matrix alloy shows higher wear resistance compared to metal matrix. Cr-rich carbides exhibit significantly smaller wear depth (p < 0.05) compared to Mo-rich carbides after nanowear at the same contact stress (9.8 GPa). The entire region of Cr-rich carbide shows high wear resistance without fracture after nanowear at 14.7 GPa. The AFM-based nanowear methods used are able to detect sub-nanometer wear depths on worn regions as small as 0.2 μm and provide abilities to study local nanometer wear processes in complex alloy systems. • Nanoscale wear performance of individual carbides and base metal matrix of high carbon. • CoCrMo alloy was investigated by an AFM-based tribology method. • Carbides show higher wear resistance compared to metal matrix. • Nanowear behavior of Cr-rich and Mo-Rich carbides was stress-dependent and influenced by chemical composition. [ABSTRACT FROM AUTHOR]

The unique structure and solute distribution of CoCrMo alloys produced using Laser Powder Bed Fusion (L-PBF) technique require custom heat-treating processes to achieve the targeted phase distribution and mechanical properties. The rise of multi-material additively manufactured structures also prompts further study at temperatures beyond standard aging and solution treatment conditions. In the present study, the phase transformation behavior, precipitate distribution, and γ-ε phase boundary orientation relationships of as-printed and solution heat-treated CoCrMo samples after aging heat treatment at 940 °C were investigated. The results show a higher ε-phase fraction of 71.2% in directly aged samples compared to 49.2% in solution heat-treated samples. This discrepancy is attributed to band-like isothermal transformation, coherent grain face massive transformation, and recrystallization. Carbide nucleation sites shifted from disintegrated cellular structures in directly aged samples to grain boundaries and twin interfaces in solution-treated samples. The presence of transgranular ε-phase bands and adjacent grains with analogous orientations observed after direct aging were linked to the weak 〈110〉 // BD and 〈111〉 // BD texture after printing. Tensile tests demonstrated an increase in tensile strength from 1162 MPa to 1261 MPa after direct aging, while significant enhancement in ductility from 16.4% to 26.1% was attained after solution heat treatment. While direct aging is more suitable for applications requiring high strength and wear resistance, solution heat treatment is advantageous when a consistent morphology and stress-free isotropic structures are desired. • The occurrence of isothermal and massive ε-phase transformation has been clarified. • Transgranular ε-phase bands influenced cell decomposition and formation of elongated precipitates. • Carbide nucleation sites shifted from cells to twins and grain boundaries after aging. • Pole figures show ε-γ neighboring grains obey the Shoji-Nishiyama orientation relationship at both aging conditions. [ABSTRACT FROM AUTHOR]

Improving the surface quality of biomedical alloys is of great practical significance to the evolution of orthopaedic implant surgery. In the polishing stage, traditional polishing methods are prone to problems, such as substandard surface roughness values and poor surface morphology, which severely affect the service life of materials. The surface quality of the CoCrMo alloy treated with magnetorheological polishing was studied. First, a polishing tool was designed based on magnetic field simulations of different magnetic pole arrangements and flow field simulations of the shear behaviour of the magnetorheological polishing cluster. Second, to improve the surface quality, an equally spaced pseudo-random path was planned, and the polishing effect for this path was verified using simulations and experiments. Moreover, the effect of different process parameters, i.e., the machining gap, polishing tool rotation speed, and abrasive particle size, on the polishing forces and the surface roughness values was studied. Finally, the wettability of the modified surface of the CoCrMo alloy after polishing was tested. The results confirm the ability of magnetorheological polishing to improve the surface quality of CoCrMo alloys, which has a certain guiding significance for the development of advanced biomedical implants. [Display omitted] • A planning method for an equally spaced pseudo-random polishing path is proposed. • The removal of material by the magnetorheological polishing fluid is simulated. • The process parameters for polishing CoCrMo alloy are obtained. • Magnetorheological polishing can improve the surface quality of CoCrMo alloys. [ABSTRACT FROM AUTHOR]

The paper presents the results of research of DLC coating of a - C:H type obtained by using a technique of physical vapor deposition (PVD) on the surface of CoCrMo alloy, commonly used for the elements of the endoprosthesis. The surface has been observed using a scanning electron microscope (SEM). Analysis of the chemical composition and distribution of the different elements were performed using glow discharge optical emission spectrometry analysis (GDOES). It has been shown that the DLC elements are characterized by high hardness and good adhesion to the substrate.

Most of the reported work on the effect of applied potential on tribocorrosion or corrosive wear of metallic alloys in a corrosive environment were conducted at anodic potentials. Limited tests have been conducted at cathodic potentials for comparison purposes or to derive the pure mechanical wear component in tribocorrosion. This work investigated the effect of cathodic potential on the friction and wear behaviour of an important biomedical alloy, CoCrMo, sliding against an Al2O3 slider in 0.9% NaCl solution at 37 °C. High friction was found at cathodic potentials close to the open circuit potential, where mechanical wear played a predominant role in material removal. At potentials more cathodic than the hydrogen charging potential, low friction and low wear were observed. The coefficient of friction (COF) and total material loss decreased with increasing cathodic potential, such that at −1000 mV (saturated calomel electrode, SCE), extremely low COF values, as low as 0.02, and negligible material loss were obtained. Such reductions in friction and wear at increasing cathodic potentials were accompanied with the formation of parallel lines in the sliding track and were gradually diminished with increasing applied contact load. It is believed that hydrogen charging and hydrogen segregated layer formation at the surface are responsible for such a phenomenon. It can also be concluded that it is difficult to derive the pure mechanical wear component in tribocorrosion by simply conducting a test at an arbitrary cathodic potential.