Tribocorrosion studies of metallic biomaterials: The effect of plasma nitriding and DLC surface modifications

Functional medium entropy alloys for joint replacement: An atomistic perspective of material deformation and a correlation to wear, corrosion, and biocompatibility

The present study adopts a multi-facet approach to design bio inspired concentrated alloys for potential application as articulating surfaces in joint replacements. A series of equiatomic, Nb rich and Ti rich TiMoNbZr based medium entropy alloys (MEAs) were processed via arc melting and their mechanical, in-vitro corrosion, wear, and in vitro and in vivo biocompatibility were investigated. Equiatomic MEA had primarily bcc with minor hcp phases where the single bcc was achieved with the addition of Nb. The single bcc Nb rich alloy resulted in 13 % elongation, much higher than equiatomic or Ti rich alloy. All the MEAs showed comparatively higher yield strength due to the climb of edge dislocations which is the main rate limiting mechanism at 300 K, as evident molecular dynamics (MD) simulation. The locally fluctuating energy landscape promotes kinks on edge dislocation, and at local minima nanoscale segments gets pinned. Upon yielding the entangled kink leaves a trail of vacancies/interstitials and escapes via climb motion to render high yield strength. The higher corrosion and pitting resistance of Nb enriched alloys can be attributed to the stable ZrO2, Nb2O5, TiO2, and MoO3 oxides, high polarization resistance (106-105 Ωcm-2), and low defect densities (1016-1018). In vitro cell-materials interaction using MC3T3-E1 showed bioinert but cytocompatible nature of the MEAs. The wear rate of the MEAs was in the range of 7-9 × 10-5 mm3N-1m-1. The wear debris did not show any tissue necrosis when implanted in rabbit femur rather new bone regeneration can be seen around the particles. STATEMENT OF SIGNIFICANCE: In the present work, a noble Nb enriched MEAs with superior mechanical, in vitro wear, corrosion and cytocompatibility properties was designed for articulating surfaces in joint replacement.

Synthesis and characterization of TiNbZrMo medium-entropy bio-composites: Microstructure, mechanical properties, and in vitro degradation

This study reports the synthesis and characterization of hydroxyapatite (HA)-based bio-composites reinforced with varying amounts (by weight, 1-15 wt.%) of bio-medium entropy alloy (BioMEA) for load-bearing implant applications. BioMEA powders consisting of Ti, Nb, Zr, and Mo were mechanically alloyed for 100 h and subsequently added to HA using powder metallurgy techniques. To show the effect of BioMEA, the microstructure, density, and mechanical tests have been conducted and the synthesized BioMEA was characterized by scanning electron microscope (SEM), x-ray diffractometer (XRD), and Fourier-transform infrared spectroscopy (FTIR) analysis. In addition, in vitro degradation behavior and bioactivity analyses of bio-composites have been conducted. XRD analysis revealed the formation of BioMEA after 20 h of mechanical alloying. The highest density value of 2.47 g/cm3 was found in 15 wt.% BioMEA-reinforced bio-composite. The addition of BioMEA reinforcement led to a significant increase in hardness and tensile strength values, with the highest values observed at 15 wt.% reinforcement. Compression tests demonstrated a significant increase in compressive strength and deformation capability of the bio-composites with the highest values observed at 15 wt.% BioMEA addition. The highest toughness of 7.68 kJ/m2 was measured in 10 wt.% MEA-reinforced bio-composites. The produced bio-composite materials have an elastic modulus between 3.5-5.5 GPa, which may provide a solution to the stress shielding problems caused by the high elastic modulus of metallic implant materials. The most severe degradation occurred in 15 wt.% MEA-reinforced bio-composites, and the effect of degradation caused a decrease in Ca and an increase in Ti-Ni-Zr-Mo in all bio-composites. These findings suggest that HA/BioMEA bio-composites have the potential to be developed as advanced biomaterials with moderate mechanical and biological properties for load-bearing implant applications.

Tribocorrosion and Surface Protection Technology of Titanium Alloys: A Review

Titanium alloy has the advantages of high specific strength, good corrosion resistance, and biocompatibility and is widely used in marine equipment, biomedicine, aerospace, and other fields. However, the application of titanium alloy in special working conditions shows some shortcomings, such as low hardness and poor wear resistance, which seriously affect the long life and safe and reliable service of the structural parts. Tribocorrosion has been one of the research hotspots in the field of tribology in recent years, and it is one of the essential factors affecting the application of passivated metal in corrosive environments. In this work, the characteristics of the marine and human environments and their critical tribological problems are analyzed, and the research connotation of tribocorrosion of titanium alloy is expounded. The research status of surface protection technology for titanium alloy in marine and biological environments is reviewed, and the development direction and trends in surface engineering of titanium alloy are prospected.

Triboelectrochemical friction control of W- and Ag-doped DLC coatings in water–glycol with ionic liquids as lubricant additives

This study proves that friction can be electrochemically controlled in metal-doped DLCs using ILs as friction modifying additives in water-based lubricants. The type of friction control depends on the type of dopant (carbide or non-carbide forming) and its oxidation state.

Dual-purpose surface functionalization of Ti-6Al-7Nb involving oxygen plasma treatment and Si-DLC or chitosan-based coatings

The work presents a detailed study on the diamond-like structures doped with Si atoms and biopolymers-based coatings (chitosan, alginate) enriched with Ag nanoparticles (Ag NPs) deposited on the Ti-6Al-7Nb substrate. Multilayers were obtained by Plasma Enhanced Radio Frequency Chemical Vapour Deposition (PE RF CVD) technique and subsequent deposition of biopolymers by immersion method. The impact of Si atoms and Ag NPs on chemical structure, microstructure, topography, cytotoxicity as well as the hardness and Young modulus of the resulting layers was precisely investigated. The most advantageous conditions of plasma functionalization in RF reactor were the mixture of O₂-Ar-NH₃ in volume ratio of 10/1/9 in the first stage of functionalization (pre-activation). In the case of Si-DLC coatings (up to ca. 19 at.%) the lower silane flow (4 cm³/min) resulted in significant decrease of surface roughness (up to ca. R_a = 0.71 nm) of modified surfaces and increase of hardness reaching ca. 900 nm depth into surface (up to ca. 16 GPa). The most attractive among biopolymer-based coating on Ti-6Al-7Nb in terms of biological activity was chitosan with Ag NPs (diameter of ca. 25 nm) with additional alginate layer. AFM analysis revealed a uniform distribution of Ag NPs in the chitosan matrix. This contributed to advantageous physicochemical and biological properties assuring proper cell adhesion and proliferation. Noteworthy, the resulting surface functionalization of Ti-6Al-7Nb alloy did not cause significant cytotoxicity in vitro, giving a strong hope for perspective applications in implantology.

Selected Physicochemical Properties of Diamond Like Carbon (DLC) Coating on Ti-13Nb-13Zr Alloy Used for Blood Contacting Implants

Despite high interest in the issues of hemocompatibility of titanium implants, particularly those made of the Ti-13Nb-13Zr alloy, the applied methods of surface modification still do not always guarantee the physicochemical properties required for their safe operation. The factors that reduce the efficiency of the application of titanium alloys in the treatment of conditions of the cardiovascular system include blood coagulation and fibrous proliferation within the vessel’s internal walls. They result from their surfaces’ physicochemical properties not being fully adapted to the specifics of the circulatory system. Until now, the generation and development mechanics of these adverse processes are not fully known. Thus, the fundamental problem in this work is to determine the correlation between the physicochemical properties of the diamond like carbon (DLC) coating (shaped by the technological conditions of the process) applied onto the Ti-13Nb-13Zr alloy designed for contact with blood and its hemocompatibility. In the paper, microscopic metallographic, surface roughness, wettability, free surface energy, hardness, coating adhesion to the substrate, impendence, and potentiodynamic studies in artificial plasma were carried out. The surface layer with the DLC coating ensures the required surface roughness and hydrophobic character and sufficient pitting corrosion resistance in artificial plasma. On the other hand, the proposed CrN interlayer results in better adhesion of the coating to the Ti-13Nb-13Zr alloy. This type of coating is an alternative to the modification of titanium alloy surfaces using various elements to improve the blood environment’s hemocompatibility.

Low-Temperature Plasma Nitriding for Austenitic Stainless Steel Layers with Various Nickel Contents Fabricated via Direct Laser Metal Deposition

In this study, low-temperature plasma nitriding is applied to austenitic stainless steels at temperatures below 450 °C. This enhances the wear resistance of the steels with maintaining corrosion resistance, by producing expanded austenite (known as the S-phase), which dissolves excessive nitrogen. Austenitic stainless steels contain nickel, which has the potential to play an important role in the formation and properties of the S-phase. In this experiment, austenitic stainless steel layers with different nickel contents were processed using direct laser metal deposition, and subsequently treated using low-temperature plasma nitriding. As a result, the stainless steel layers with high nickel contents formed the S-phase, similar to the AISI 316L stainless steel. The thickness and Vickers hardness of the S-phase layers varied with respect to the nickel contents. Due to lesser chromium atoms binding to nitrogen, the chromium content relatively decreased. Moreover, there was no evident change in the wear and corrosion resistances due to the nickel contents.

A Comparative Study of Friction and Wear Processes of Model Metallic Biomaterials Including Registration of Friction-Induced Temperature Response of a Tribological Pair

Nowadays, metallic alloys are extensively used in wear-related biomedical applications. However, it was shown that one of the factors which may contribute to the premature implant failure is the temperature effect caused by the sliding action between the bearing surfaces. Nevertheless, there are not many papers where the wear-related temperature phenomena of biomedical alloys are discussed. Thus, in our paper, we present findings from the tribological tests of the model metallic biomaterials-316L steel, CoCrMo alloy and Ti gr. 2. In our study, the temperature alterations induced by the wear action of the examined materials were analyzed. According to the findings, the temperature response of the biomedical alloys is tribological pair dependent. While the mass loss of the tribological pair 316L-316L steel was the slightest, at the same time the temperature increase was the greatest. Based on the presented findings, further analyses in friction-induced temperature response of biomedical alloys is recommended.

Effect of Temperature on Anti-Corrosive Properties of Diamond-Like Carbon Coating on S355 Steel

Influence of temperature on the anti-corrosive properties of a diamond-like carbon (DLC) coating, produced using plasma-enhanced chemical vapor deposition (PECVD) on the S355 steel substrate (S355/DLC), was investigated. Corrosion test of the materials were carried out using the electrochemical method. The corrosive environment was an alkaline solution of sodium chloride. The heat treatment of the materials was carried out in air atmosphere, at 400 and 800 °C. It was demonstrated that the DLC coating effectively protected the S355 steel surface from coming into contact with an aggressive corrosive environment. It was found, based on a corrosion test after a heat treatment at 400 °C, that the anti-corrosive properties of the DLC coating did not undergo significant changes. Due to the changes in the surface structure of S355/DLC, the microhardness (HV) of the DLC layer increased. However, after a heat treatment at 800 °C, the carbon coating on the S355 steel surface was destroyed and, thus, lost its protective effect on the substrate.

Plasma nitriding under low temperature improves the endothelial cell biocompatibility of 316L stainless steel

OBJECTIVES

To evaluate the effects of the surface modification of 316L stainless steel (SS) by low-temperature plasma nitriding on endothelial cells for stent applications.

RESULTS

X-ray diffraction (XRD) confirmed the incorporation of nitrogen into the treated steel. The surface treatment significantly increased SS roughness and hydrophilic characteristics. After 4 h the cells adhered to the nitride surfaces and formed clusters. During the 24 h incubation period, cell viability on the nitrided surface was higher compared to the polished surface. Nitriding reduced late apoptosis of rabbit aorta endothelial cell (RAEC) on the SS surface.

CONCLUSION

Low temperature plasma nitriding improved the biocompatible of stainless steel for use in stents.

Wear and Corrosion Properties of Cold-Sprayed AISI 316L Coatings Treated by Combined Plasma Carburizing and Nitriding at Low Temperature

Cold-sprayed AISI 316L stainless steel coatings are treated to form an austenite phase with excessive dissolved nitrogen (known as the S-phase) by plasma nitriding at temperatures below 450 °C. The S-phase is a hard and wear-resistant layer with high corrosion resistance. However, the S-phase layer formed after only nitriding is thin and the hardness abruptly decreases at a certain depth; it lacks mechanical reliability. We examined two types of combined low-temperature plasma treatment to enhance the mechanical reliability of the S-phase layer: (i) sequential and (ii) simultaneous. In the sequential plasma treatment, the carburizing step was followed by nitriding. In the simultaneous treatment, the nitriding and carburizing steps were conducted at the same time. Both combined plasma treatments succeeded in thickening the S-phase layers and changed the hardness depth profiles to decrease smoothly. In addition, anodic polarization measurements indicated that sequential treatment involving carburizing followed by nitriding for 2 h each resulted in high corrosion resistance.

Nano- and micro-tribological behaviours of plasma nitrided Ti6Al4V alloys

Plasma nitriding of the Ti-6Al-4V alloy (TA) sample was carried out in a plasma reactor with a hot wall vacuum chamber. For ease of comparison these plasma nitrided samples were termed as TAPN. The TA and TAPN samples were characterized by XRD, Optical microscopy, FESEM, TEM, EDX, AFM, nanoindentation, micro scratch, nanotribology, sliding wear resistance evaluation and in vitro cytotoxicity evaluation techniques. The experimental results confirmed that the nanohardness, Young's modulus, micro scratch wear resistance, nanowear resistance, sliding wear resistance of the TAPN samples were much better than those of the TA samples. Further, when the data are normalized with respect to those of the TA alloy, the TAPN sample showed cell viability about 11% higher than that of the TA alloy used in the present work. This happened due to the formation of a surface hardened embedded nitrided metallic alloy layer zone (ENMALZ) having a finer microstructure characterized by presence of hard ceramic Ti₂N, TiN etc. phases in the TAPN samples, which could find enhanced application as a bioimplant material.

Characterization of the Micro-Abrasive Wear in Coatings of TaC-HfC/Au for Biomedical Implants

The object of this work was the deposition of a Ta-Hf-C thin film with a gold interlayer on stainless steel, via the physical vapor deposition (PVD) technique, in order to evaluate the properties of different systems subjected to micro-abrasive wear phenomena generated by alumina particles in Ringer's solution. The surface characterization was performed using a scanning electron microscope (SEM) and atomic force microscope (AFM). The crystallographic phases exhibited for each coating were obtained by X-ray diffraction (XRD). As a consequence of modifying the composition of Ta-Hf there was evidence of an improvement in the micro-abrasive wear resistance and, for each system, the wear constants that confirm the enhancement of the surface were calculated. Likewise, these surfaces can be bioactive, generating an alternative to improve the biological fixation of the implants, therefore, the coatings of TaC-HfC/Au contribute in the development of the new generation of orthopedic implants.