CoCrMo Alloy Research Articles

Effect of two strengthening processes on the fretting wear mechanism of CoCrMo alloy

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.

Nanoscale Surface Refinement of CoCrMo Alloy for Artificial Knee Joints via Chemical Mechanical Polishing.

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.

Cobalt and Chromium Ions Impair Macrophage Response to Staphylococcus aureus Infection.

Cobalt-chromium-molybdenum (CoCrMo) alloys are routinely used in arthroplasty. CoCrMo wear particles and ions derived from arthroplasty implants lead to macrophage-driven adverse local tissue reactions, which have been linked to an increased risk of periprosthetic joint infection after revision arthroplasty. While metal-induced cytotoxicity is well characterized in human macrophages, direct effects on their functionality have remained elusive. Synchrotron radiation X-ray microtomography and X-ray fluorescence mapping indicated that peri-implant tissues harvested during aseptic revision of different arthroplasty implants are exposed to Co and Cr in situ. Confocal laser scanning microscopy revealed that macrophage influx is predominant in patient tissue. While in vitro exposure to Cr3+ had only minor effects on monocytes/macrophage phenotype, pathologic concentrations of Co2+ significantly impaired both, monocyte/macrophage phenotype and functionality. High concentrations of Co2+ led to a shift in macrophage subsets and loss of surface markers, including CD14 and CD16. Both Co2+ and Cr3+ impaired macrophage responses to Staphylococcus aureus infection, and particularly, Co2+-exposed macrophages showed decreased phagocytic activity. These findings demonstrate the immunosuppressive effects of locally elevated metal ions on the innate immune response and support further investigations, including studies exploring whether Co2+ and Cr3+ or CoCrMo alloys per se expose the patients to a higher risk of infections post-revision arthroplasty.

Pit initiation on biomedical alloys-A review.

Biomedical alloys, like many engineering alloys, have chemical or physical heterogeneities at the surface, and such heterogeneities can potentially act as sites for pit initiation. Alloys of particular interest are 316/316L (and 316LVM) stainless steel, nitinol, and CoCr alloys. This review focuses on the sites-generally inclusions-that have been associated with pitting in various studies of biomedical alloys in simulated physiological solutions. The effect of these sites is discussed in relation to factors such as type and size. For both 316/316L stainless steel and nitinol, pitting has been found to initiate at two different types of inclusions: sulfide and oxide inclusions in stainless steel, and carbide and oxide inclusions in nitinol. Sulfide inclusions tend to be the predominant sites for pitting on 316/316L stainless steel, while there is some evidence to suggest that carbide inclusions may be more effective than oxide inclusions for pitting on nitinol. CoCrMo alloys differ from the other two alloys in that, although particles can be present in the form of carbides, the carbides typically do not provide sites for pit initiation except possibly for alloys with a high-C content, certain heat treatments, and when anodically polarized to high potentials. CoNiCrMo differs further in that TiN inclusions can be present in the vicinity of pits and might be associated with them, but irrespective of the initiation site, any pits are unlikely to grow because of repassivation.

Surface Nanostructures Enhanced Biocompatibility and Osteoinductivity of Laser-Additively Manufactured CoCrMo Alloys.

Cobalt-chromium-molybdenum (CoCrMo) alloys are widely used in orthopedic implants due to their excellent corrosion and wear resistance and superior mechanical properties. However, their limited capability to promote cell adhesion and new bone tissue formation, poor blood compatibility, and risk of microbial infection can lead to implant failure or reduced implant lifespan. Surface structure modification has been used to improve the cytocompatibility and blood compatibility of implant materials and reduce the risk of infection. In this study, we prepared CoCrMo alloys with surface nanostructures of various aspect ratios (AR) using laser-directed energy deposition (L-DED) and biocorrosion. Our results showed that medium and high AR nanostructures reduced platelet adhesion, while all of the alloys demonstrated good blood compatibility and antibacterial properties. Moreover, the medium and high AR nanostructures promoted cell adhesion and spreading of both preosteoblast MC3T3 cells and human bone marrow mesenchymal stem cells (hMSCs). Furthermore, the nanostructure promoted the osteogenic differentiation of both cell types compared with the flat control surface, with a substantial enhancing effect for the medium and high ARs. Our study proposes a promising approach for developing implant materials with improved clinical outcomes.

Massive Nitrogen Supersaturation to CoCrMo alloys for Surface Microstructure Control

Massive Nitrogen Supersaturation to CoCrMo alloys for Surface Microstructure Control

Electrophoretic Deposition of Multi-Walled Carbon Nanotube Coatings on CoCrMo Alloy for Biomedical Applications.

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.

Phase transformation in additively manufactured Co-Cr-Mo alloy after solution and aging heat treatment

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.

Effect of Artificial Saliva Modification on the Corrosion Resistance and Electronic Properties of Bego Wirobond® C Dental Alloys

Wirobond® C is a commercial dental casting alloy suitable for the fabrication of crowns, bridges, and metal ceramic restorations. This study aims to investigate the effect of ready-to-use Listerine® and Meridol® mouthwashes and sodium fluoride on the resistance of CoCrMo dental alloys to electrochemical corrosion in artificial saliva at 37 °C. SEM, EDS, SKP, and microhardness investigations were carried out to characterize the material under study. The in vitro corrosion resistance of the CoCrMo alloy was conducted using the open-circuit potential method, electrochemical impedance spectroscopy, and anodic polarization curves. The presence of Co 59.8(8) wt.%, Cr 31.5(4) wt.%, and Mo 8.8(6) wt.% was confirmed. The CoCrMo alloy was characterized by a Vickers microhardness value of 445(31) µHV0.3. Based on the EIS data, the capacitive behavior and high corrosion resistance of the CoCrMo alloy were revealed. The kinetics of pitting corrosion in the artificial saliva were lower after being modified with NaF, Listerine®, and Meridol® mouthwashes. The potentiodynamic characteristics revealed the passive behavior of the CoCrMo alloy in all solutions. Based on the SKP measurements of the CoCrMo alloy after corrosion tests, the effect of artificial saliva modification on the electronic properties of Bego Wirobond® C dental alloy was found.

Characterization of CoCrMo alloy fabricated by sintering for biomedical materials

Characterization of CoCrMo alloy fabricated by sintering for biomedical materials

Surface polishing of CoCrMo alloy by magnetorheological polishing

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.

Unraveling the role of sintering temperature on physical, structural and tribological characteristics of ball milled Co28Cr6Mo biomaterial based alloy

This work aim to investigate the effect of sintering temperature (950–1250 °C) on structural, physical, tribological properties of nanobiomaterial Co28Cr6Mo alloy for total hip prosthesis obtained by high Energy ball milled. Several techniques such as density, porosity, microhardness, and Young’s modulus were used to assess the mechanical and physical characteristics. Tribological behavior were conducted using a ball-on-plate type Oscillating tribometer, under different applied loads (2, 10 and 20 N), under a wet condition using hank’s solution to simulate human body fluid. SEM, EDS and XRD analysis results, showed that Co-Cr-Mo alloy samples sintered exhibit the same phases created by the Co element. The alloy sintered at 1250 °C displayed the highest micro-hardness value in terms of mechanical characteristics (386.75 HV0.1. The porosity changes from 17% to 10% and endorse a higher change in Young’s modulus around 61.84 and 92.5 GPa for samples sintered beteewn 950 and 1250 °C, respectively,. A remarkable decrease in the wear rate and volume values is obtained for the sample sintered at 1250 °C (32.1610–3 μm3 (N.m)− 1) compared to other samples sintered at 1150 and 1250 °C. Under wet tribological conditions, the abrasive and adhesive wear mechanisms were identified as the main degradation mechanisms for all sintered samples.

Single asperity nanoscale wear of carbides and matrix of wrought high carbon CoCrMo alloy

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.

Mesoscopic chemical heterogeneities in laser powder bed fused CoCrMo and Ni mixed powders and their effect on the mechanical properties

Microstructural heterogeneity is a feature of common occurrence in alloys additively manufactured using techniques such as laser powder bed fusion (LPBF). Additionally, chemical heterogeneities can arise both at micro- and meso-scales, especially when powder mixtures are used. While such chemical heterogeneities are considered undesirable hitherto, recent studies show that they may be beneficial in tailoring for the desired mechanical property combinations. In this study, we fabricated a graded alloy coupon with the mixed powders of the CoCrMo alloy and elemental Ni and investigated the microstructural and mesoscopic chemical heterogeneities in it. Chemical heterogeneities, which are either rich in Ni or CoCrMo, were observed due to the incomplete mixing of the powders. Banded patterns, with alternating layers that are enriched with different chemical species, were also observed. Distinct stacking fault energies between these chemical heterogeneities result in distinct deformation mechanisms; while planar slip and strain-induced martensitic transformation occur in the CoCrMo-rich heterogeneities, homogenous deformation associated with the wavy slip occurs in the Ni-rich ones. Detailed mechanical property characterizations show that the microscale chemical segregation not only strengthens the matrix but also improves the work hardening ability of the bulk material through kinematic hardening mechanism. These findings substantiate the key design principles for exploiting chemical segregations that form during in situ alloying for simultaneous enhancement of the strength and ductility in AM alloys.

THE EFFECT OF A COMPOSITE CHITOSAN-SILVER(I) ION COATING ON THE CORROSION RESISTANCE OF THE COBALT-CHROMIUM-MOLYBDENUM ALLOY IN SALINE SOLUTION

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 Fouriertransform 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.

Adhesion and Activation of Blood Platelets on Laser-Structured Surfaces of Biomedical Metal Alloys.

The laser surface modification of metallic implants presents a promising alternative to other surface modification techniques. A total of four alloyed metallic biomaterials were used for this study: medical steel (AISI 316L), cobalt-chromium-molybdenum alloy (CoCrMo) and titanium alloys (Ti6Al4V and Ti6Al7Nb). Samples of metallic biomaterials after machining were subjected to polishing or laser modification in two different versions. The results of surface modification were documented using SEM imaging and roughness measurement. After modification, the samples were sterilized with dry hot air, then exposed to citrate blood, washed with PBS buffer, fixed with glutaraldehyde, sputtered with a layer of gold and imaged using SEM to enable the quantification of adhered, activated and aggregated platelets on the surface of biomaterial samples. The average total number, counted in the field of view, of adhered platelets on the surfaces of the four tested biomaterials, regardless of the type of modification, did not differ statistically significantly (66 ± 81, 67 ± 75, 61 ± 70 and 57 ± 61 for AISI 316L, CoCrMo, Ti6Al4V and Ti6Al7Nb, respectively) and the average number of platelet aggregates was statistically significantly higher (p < 0.01) on the surfaces of AISI 316L medical steel (42 ± 53) and of the CoCrMo alloy (42 ± 52) compared to the surfaces of the titanium alloys Ti6Al4V (33 ± 39) and Ti6Al7Nb (32 ± 37). Remaining blood after contact was used to assess spontaneous platelet activation and aggregation in whole blood by flow cytometry. An in-depth analysis conducted on the obtained results as a function of the type of modification indicates small but statistically significant differences in the interaction of platelets with the tested surfaces of metallic biomaterials.

Improving tribocorrosion resistance of a medical grade CoCrMo alloy by the novel HIPIMS nitriding technique

In this work, tribocorrosion performance of the High Power Impulse Magnetron Sputtering (HIPIMS) nitrided (F75) CoCrMo alloys was examined with the help of sliding wear corrosion experiments carried out in Hank's solution. Results indicate that under Open Circuit Potentials (OCP), both nitrided and the untreated specimens exhibited near similar Sliding-Wear-Corrosion coefficient (KSWC) values (6.52 × 10−15 and 3.95 × 10−15 m3N−1m−1 respectively). However, the benefits of HIPIMS nitriding were evident under accelerated corrosion (anodic potentials) and passivating conditions. KSWC values of the nitrided specimens were an order of magnitude lower (6.41× 10−15 m3N−1m−1) than the untreated specimens (3.4 × 10−14 m3N−1m−1), indicating that nitrided surfaces had higher resistance against tribocorrosive mechanisms. This superior performance was attributed to the formation of a nitrided microstructure consisting mainly of expanded austenite (ƔN) without the formation of the detrimental CrN phase, which resulted in high hardness and sustained resistance to corrosion. A rationale for lower synergy between wear and corrosion and its relation to the nitride microstructure has been presented.

Improving the protective properties of an artificial joint friction couple by using TiN and DLC films

Artificial joint replacement represents the most effective approach for addressing joint pathologies. However, friction and wear, the production of debris and the release of metal ions reduce the durability of artificial joints and negatively impact human health.This study focuses on a CoCrMo alloy joint femoral head and an ultra-high molecular-weight polyethylene cup, which are commonly used as standard artificial joint friction couples. Two different types of films have been deposited on the surface of the joint femoral head. Multilayer TiN/(Ti/DLC) × 3 films were deposited on the surface of the alloy ball via pulsed cathode-arc discharge, and a friction experiment was carried out by a hip friction simulation tester. As an alternative film for use in medicine, TiN films were deposited by direct current arc evaporation of the titanium cathode in a nitrogen atmosphere at a partial pressure of 1.2 × 10−1 Pa. Prior to conducting the wear test, the film structure was studied through Raman and XPS spectroscopy. The surface morphology and adhesion of the films to the joint femoral head were studied.A change in the mass of the prosthesis has been seen when comparing the presence and absence of deposited films. Inductively coupled plasma mass spectroscopy has shown the effectiveness of protecting the surface of the prosthesis with the deposited TiN/(Ti/DLC) × 3 film. This method successfully reduces the concentration of Co and Cr released during friction. The findings indicate that the TiN/(Ti/DLC) × 3 film deposited on the joint femoral head reduces the wear of the UHMWPE cup and did not degrade over five million cycles, thus significantly exceeding the operating life of the TiN film. The results show that TiN/(Ti/DLC) × 3 film demonstrates a 55 % reduction in the generation of abrasive debris in the UHMUPE cup. Furthermore, it effectively prevents the release of metal ions from the alloy femoral head.

Multi-Scale Structuring of CoCrMo and AZ91D Magnesium Alloys Using Direct Laser Interference Patterning

In this work, the technique of Direct Laser Interference Patterning (DLIP) was used to fabricate micrometric structures at the surface of Cobalt-Chromium-Molybdenum and AZ91D magnesium alloys. Line-like patterns with spatial periods of 5 μm were textured using an ultra-short pulsed laser (10 ps pulse duration and 1064 nm wavelength) with a two-beam interference setup. The surface topography, morphology, and chemical modifications were analysed using Confocal Microscopy, Scanning Electron Microscopy, and Energy Dispersive Spectroscopy (EDS), respectively. Laser fluence and pulse overlap were varied to evaluate their influence on the final structure. Homogeneous structures were achieved for the CoCrMo alloy for every condition tested, with deeper structures (up to 0.85 μm) being achieved for higher energy levels (higher overlap and/or fluence). For high energy, sub-micrometric secondary structures, so-called LIPSS, could also be observed on the CoCrMo. The EDS analysis showed some oxidation after the laser texturing. Regarding the AZ91D alloy, deeper structures could be achieved (up to 2.5 μm), but more melting and oxidation was observed, forming spherical oxide particles. Nonetheless, these results bring new perspectives on the fabrication of microtextures on the surface of CoCrMo and AZ91D using DLIP.

Effect of annealing on the mechanical properties and cytocompatibility of CoCrMo alloy with tantalum coating

Cobalt–chromium–molybdenum (CoCrMo) alloy is frequently utilized to replace artificial joints and dental components. Tantalum (Ta) coating is used to improve the osteogenic property of CoCrMo alloy. Annealing treatment can increase the Ta coating adhesion and further improve wear resistance and biocompatibility. In this study, two kinds of thicknesses of Ta coatings were applied on CoCrMo alloy substrates via magnetron sputtering technology. The average thicknesses of the Ta coatings were 4.3 and 9.5 μm. The Ta coatings were annealed for 5 h at 800 °C, 900 °C, and 1000 °C, respectively. Results indicated that heat treatment improved the adhesion of the coatings. The Ta coatings were composed of stable body-centered cubic phase (α-Ta) and metastable tetragonal phase (β-Ta). The Ta coating with a thickness of 4.3 μm exhibited excellent wear resistance after being annealed at 800 °C, with little variability in the friction curve and a low average coefficient of friction. The adhesive force of the two coated samples increased initially and subsequently dropped as the annealing temperature increased. At 900 °C, the Ta-coated samples exhibited the highest adhesive force; after being annealed, the rate of cell proliferation increased. At 900 °C, samples with Ta coatings exhibited the highest rate of cell multiplication and the best cell compatibility compared with the other samples. Ta coatings' adhesive force, wear resistance, corrosion resistance, and cytocompatibility were all significantly enhanced at various annealing temperatures. Thus, the results of this work are a useful benchmark for the surface modification of metal implants used in medical procedures, and Ta coatings are a practical orthopedic material for the replacement of joints and bones.