State-of-the-Art Developments in Advanced Hard Ceramic Coatings Using PVD Techniques for High-Temperature Tribological Applications

Hard and wear-resistant coatings created utilizing physical vapor deposition (PVD) techniques are extensively used in extreme tribological applications. The friction and wear behavior of coatings vary significantly with temperature, indicating that advanced coating concepts are essential for prolonged load-bearing applications. Many coating concepts have recently been explored in this area, including multicomponent, multilayer, gradient coatings; high entropy alloy (HEA) nitride; and functionally modified coatings. In this review, we highlighted the most significant findings from ongoing research to comprehend crucial coating properties and design aspects. To obtain enhanced tribological properties, the microstructure, composition, residual stress, hardness, and HT oxidation resistance are tuned through doping or addition of appropriate materials at an optimized level into the primary coatings. Such improvements are achieved by optimizing PVD process parameters such as input power, partial pressure, reactive gas flow rates, substrate bias, and temperature. The incorporation of ideal amounts of Si, Cr, Mo, W, Ag, and Cu into ternary and quaternary coatings, as well as unique multilayer designs, considerably increases the tribological performance of the coatings. Recent discoveries show that not only mechanical hardness and fracture toughness govern wear resistance, but also that oxidation at HT plays a significant role in the lubrication or wear failure of coatings. The tribo-induced metal oxides and/or Magnéli phases concentrated in the tribolayer are the key governing factors of friction and wear behavior at high temperatures. This review includes detailed insights into the advancements in wear resistance as well as various failure mechanisms associated with temperature changes

Multifunctional Coatings on Implant Materials—A Systematic Review of the Current Scenario

The challenges and demands of implant materials are changing as a result of the substantial expansion in the global population. Suitable implants are required for aged people, physical injuries, patients who need revised surgeries, contaminated implants, and accident victims. Hence, the requirement for implants is drastically increasing day by day. Metals, ceramics, and polymers are used as implant materials by biomedical industries for long-term suffering patients. Stainless steel, titanium and its alloys, aluminum alloys, cobalt, zirconium, etc. (metals), hydroxyapatite (ceramic), polyurethane, polyethylene, polyimide, etc. (polymers), are some of the examples that fulfill the implant requirements. There are many other obstructions, such as adhesion, inflammation, and bacterial attack, which minimize the implant’s performance and its activity. However, coatings on ideal implant materials are significant to avoid its failure and to enhance its durability and longevity. Advanced techniques, such as physical and chemical methods, are suitable coating approaches to promote the surface of implants with respect to mechanical, biological, and other multifunctional activities. This review paper focuses on and investigates several strategies for bioactive implants’ coatings, analysis, and emerging applications for biomedical industries

Doping effects on the tribological performance of diamond-like carbon coatings: A review

Diamond-like carbon (DLC) coatings have garnered considerable interest due to their unique features, which include wear resistance with a low friction coefficient, high hardness, biocompatibility, and chemical inertness. Their tribological performance is highly dependent on tribological environment, structure, and mechanical properties of the coating. A major problem that can adversely impact the tribological properties of the DLC coating is insufficient adhesion to the substrate. This issue caused by mismatch of the substrate and coating thermal expansion coefficient (TEC) and high amount of internal stress in DLC coating. The limitations of DLC coatings for tribological performance can be overcome by incorporating different types of metallic and non-metallic elements into the coating structure. Recently, various efforts have been made to address this issue by doping certain elements into the DLC coating, including fluorine, nitrogen, silicon, and metals. This review discusses new advancements in doped DLC coatings designed to improve their tribological behavior in different specific applications such as high relative humidity, elevated temperature, and bio-implant

Recent Advancements in Materials and Coatings for Biomedical Implants

Metallic materials such as stainless steel (SS), titanium (Ti), magnesium (Mg) alloys, and cobalt-chromium (Co-Cr) alloys are widely used as biomaterials for implant applications. Metallic implants sometimes fail in surgeries due to inadequate biocompatibility, faster degradation rate (Mg-based alloys), inflammatory response, infections, inertness (SS, Ti, and Co-Cr alloys), lower corrosion resistance, elastic modulus mismatch, excessive wear, and shielding stress. Therefore, to address this problem, it is necessary to develop a method to improve the biofunctionalization of metallic implant surfaces by changing the materials’ surface and morphology without altering the mechanical properties of metallic implants. Among various methods, surface modification on metallic surfaces by applying coatings is an effective way to improve implant material performance. In this review, we discuss the recent developments in ceramics, polymers, and metallic materials used for implant applications. Their biocompatibility is also discussed. The recent trends in coatings for biomedical implants, applications, and their future directions were also discussed in detail

Efficacy of Graphene-Based Nanocomposite Gels as a Promising Wound Healing Biomaterial

The development of biocompatible nanocomposite hydrogels with effective wound healing/microbicidal properties is needed to bring out their distinguished characteristics in clinical applications. The positive interaction between graphene oxide/reduced graphene oxide (GO/rGO) and hydrogels and aloe vera gel represents a strong strategy for the advancement of therapeutic approaches for wound healing. In this study, the synthesis, characterization, and angiogenic properties of graphene-based nanocomposite gels have been corroborated and substantiated through several in vitro and in vivo assays. In this respect, graphene oxide was synthesized by incorporating a modified Hummer’s method and ascertained by Raman spectroscopy. The obtained GO and rGO were uniformly dispersed into the aloe vera gel and hydrogel, respectively, as wound healing materials. These formulations were characterized via in vitro bio-chemical techniques and were found suitable for the appropriate cell viability, attachment, and proliferation. In addition, in vivo experiments were conducted using male Wistar rats. This revealed that the GO/rGO-based gels stimulated wound contraction and re-epithelialization compared to that of the non-treatment group. From the study, it is suggested that GO/rGO-based aloe vera gel can be recommended as a promising candidate for wound healing applications