Laser Cladding of Ti-Based Ceramic Coatings on Ti6Al4V Alloy: Effects of CeO2 Nanoparticles Additive on Wear Performance

Research Progress of Laser Cladding on the Surface of Titanium and Its Alloys

Titanium (Ti) and its alloys have been widely employed in aeronautical, petrochemical, and medical fields owing to their fascinating advantages in terms of their mechanical properties, corrosion resistance, biocompatibility, and so on. However, Ti and its alloys face many challenges, if they work in severe or more complex environments. The surface is always the origin of failure for Ti and its alloys in workpieces, which influences performance degradation and service life. To improve the properties and function, surface modification becomes the common process for Ti and its alloys. The present article reviews the technology and development of laser cladding on Ti and its alloys, according to the cladding technology, cladding materials, and coating function. Generally, the laser cladding parameters and auxiliary technology could influence the temperature distribution and elements diffusion in the molten pool, which basically determines the microstructure and properties. The matrix and reinforced phases play an important role in laser cladding coating, which can increase the hardness, strength, wear resistance, oxidation resistance, corrosion resistance, biocompatibility, and so on. However, the excessive addition of reinforced phases or particles can deteriorate the ductility, and thus the balance between functional properties and basic properties should be considered during the design of the chemical composition of laser cladding coatings. In addition, the interface including the phase interface, layer interface, and substrate interface plays an important role in microstructure stability, thermal stability, chemical stability, and mechanical reliability. Therefore, the substrate state, the chemical composition of the laser cladding coating and substrate, the processing parameters, and the interface comprise the critical factors which influence the microstructure and properties of the laser cladding coating prepared. How to systematically optimize the influencing factors and obtain well-balanced performance are long-term research issues.

Friction Properties of Solid Lubricants with Different Multiwalled Carbon Nanotube Contents

Bushes are circular bearings that surround a shaft and help it rotate smoothly. In heavy equipment, bushes are coated with solid lubricants to reduce friction. Although the coating layer of the lubricant has a stable coefficient of friction (CoF), it is important that this should last for a long time. In this study, multiwalled carbon nanotubes (MWCNTs), which have a low CoF, were added to the lubricant to improve its performance. When 2.3 wt% MWCNTs were added to the polymer resin, the dynamic CoF (under a 29 N external load) decreased by 78% in relation to that of the resin without MWCNTs. As the MWCNT content increased, the roughness of the coating decreased, which reduced the CoF. Moreover, MWCNT addition increased the overall tensile strength owing to an increase in the bonding force between the resins. Under a high load of 20 tonnes (t), the MWCNT-based solid lubricant had a CoF of 0.05, lower than commercial MoS₂-based solid lubricants; this was maintained for more than 10,000 cycles in a bush and shaft test. With the MWCNT-based solid lubricant, a lubricating polymer film formed, even on worn bush surfaces. The CoF of the solid lubricant was reduced and the number of cycles with a constant CoF increased when MWCNTs were added owing to the formation of the lubricating polymer film.

Effects of La2O3contents on microstructure and properties of laser-cladded 5wt%CaB6/HA bioceramic coating

In the present work, 5wt%CaB6/HA bioceramic coatings with different La2O3contents (0-0.6wt%) have been fabricated by a laser cladding technique on Ti-6Al-4V. The effects of La2O3 contents on microstructure and properties of the laser-cladded 5wt%CaB6/HA coatings have been carefully investigated. The results show that the microstructure is obviously refined, and the structure is relatively uniform after doping 0.2-0.4 wt% La2O3. As the La2O3 content increases, the corrosion resistance are found to increase firstly and then gradually decrease. The XRD analysis confirms that the amount of HA and TCP in the coating reaches maximum after doping 0.2wt% La2O3. The La2O3-doped coatings show a significantly higher bone-like apatite precipitation after immersion in SBF compared with La2O3-free coating. In vitro experiment also shows that 5wt%CaB6/HA bioceramic coatings with 0.2-0.4wt% La2O3 are more suitable for the attachment and proliferation of MG63 cells, exhibiting superior bioactivity and biocompatibility.

Optimization of Corrosion Wear Resistance of the NiCrBSi Laser-Clad Coatings Fabricated on Ti6Al4V

Ni-based alloy powder (NiCrBSi) was applied to prepare coatings on Ti6Al4V by laser cladding to improve the wear resistance of the latter under corrosion. The scanning speed was found to be an essential parameter that could adjust the microstructure of the coatings. Changes in the microstructures of the coatings with the scanning speed were highlighted, and the relationships between the microstructures and microhardness, fracture toughness, corrosion, and corrosion wear resistance of the coatings were established. Results indicated that the matrix changes from Ti2Ni + TiNi to primary γ(Ni) + eutectics (γ(Ni) + Ni3Ti) with increasing scanning speed. Moreover, reinforcement phases changed from TiB2 + TiC (5 mm∙s−1) to TiB2 + TiC + Cr7C3 (11 mm∙s−1) to TiB2 + TiC + Cr7C3 + CrB (17 mm∙s−1). The average microhardness of the coatings first increased and then decreased, and the corresponding fracture toughness showed the opposite trend. The optimum combination of these properties was observed in the coating prepared at 11 mm∙s−1. This coating demonstrated excellent wear resistance in 3.5 wt.% NaCl solution, as well as a high corrosion potential, a low corrosion current density, and a low current density when the electrode initially entered a comparatively stable corrosion state. Moreover, compared with coatings prepared at other scanning speeds, this coating revealed a higher critical potential for oxidation film destruction. The results of this research collectively show that regulating the microstructures of laser-clad coatings by applying different scanning speeds is a feasible strategy to optimize the wear resistance of the coatings under corrosion.

Lanthanides-Substituted Hydroxyapatite/Aloe vera Composite Coated Titanium Plate for Bone Tissue Regeneration

PURPOSE

To develop the surface-treated metal implant with highly encouraged positive properties, including high anti-corrosiveness, bio-activeness and bio-compatibleness for orthopedic applications.

METHODS

In this work, the surface of commercially pure titanium (Ti) metal was treated with bio-compatible polydopamine (PD) by merely immersing the Ti plate in PD solution. The composite of trivalent lanthanide minerals (La3+, Ce3+ and Gd3+)-substituted hydroxyapatite (MHAP) with Aloe vera (AV) gel was prepared and coated on the PD-Ti plate by electrophoretic deposition (EPD) method. The choice of trivalent lanthanide ions is based on their bio-compatible nature and bone-seeking properties. The formation of the PD layer, composites, and composite coatings on Ti plate and PD-Ti surface was confirmed by FT-IR, XRD, SEM and HR-TEM observations. In-vitro assessments such as osteoblasts like MG-63 cell viability, alkaline phosphatase activity and mineralization ability of the MHAP/AV composite were tested, and the composite-coated plate was implanted into a rat bone defect model for in-vivo bone regeneration studies.

RESULTS

The coating ability of the MHAP/AV composite was highly preferred to PD-treated Ti plate than an untreated Ti plate due to the metal absorption ability of PD. This was confirmed by SEM analysis. The in-vitro and in-vivo studies show the better osteogenic ability of MHAP/AV composite at 14th day and 4th week of an experimental period, respectively.

CONCLUSION

The osteoblast ability of the fabricated device without producing any adverse effect in the rat model recommends that the fabricated device would serve as a better platform on the hard tissue regeneration for load-bearing applications of orthopedics.

Process Parameter Optimization When Preparing Ti(C, N) Ceramic Coatings Using Laser Cladding Based on a Neural Network and Quantum-Behaved Particle Swarm Optimization Algorithm

The formation process of surface coatings fabricated with laser cladding is very complicated and coating quality is closely related to laser cladding process parameters. Generally, the optimization and control of process parameters play key roles when preparing high-quality ceramic coating. In this paper, three reasonable parameters were selected for each process parameter based on the preliminary experiment. The experiment of Ti(C, N) ceramic coating prepared with laser cladding was designed via the Taguchi method. The laser power, spot diameter, overlapping ratio, and scanning velocity were selected as the main process parameters, and their effects on coating micro-hardness were analyzed using the signal-to-noise (S/N) ratio and analysis of variance (ANOVA). Then, based on the back-propagation neural network (BPNN) and quantum-behaved particle swarm optimization (QPSO) algorithm, we created the prediction model of BPNN-QPSO neural network for laser cladding Ti(C, N) ceramic coating. The mapping of process parameters to the micro-hardness of the coating was obtained according to the model and we analyzed the influence of process parameters that interacted with the coating’s micro-hardness. The results showed that the interaction of laser cladding process parameters had a significant effect on the micro-hardness of the coating. The established BPNN-QPSO neural network model was able to map the relationship between laser cladding process parameters and coating micro-hardness. The process parameters optimized by this model had similar results with ANOVA. This research provides guidance for the selection and control of ceramic coating process parameters Ti(C, N) prepared via laser cladding.

Technical Characteristics and Wear-Resistant Mechanism of Nano Coatings: A Review

Nano-coating has been a hot issue in recent years. It has good volume effect and surface effect, and can effectively improve the mechanical properties, corrosion resistance and wear resistance of the coatings. It is important to improve the wear resistance of the material surface. The successful preparation of nano-coatings directly affects the application of nano-coatings. Firstly, the preparation methods of conventional surface coatings such as chemical vapor deposition and physical vapor deposition, as well as the newly developed surface coating preparation methods such as sol-gel method, laser cladding and thermal spraying are reviewed in detail. The preparation principle, advantages and disadvantages and the application of each preparation method in nano-coating are analyzed and summarized. Secondly, the types of nano-coating materials are summarized and analyzed by inorganic/inorganic nanomaterial coatings and organic/inorganic nanomaterial coatings, and their research progress is summarized. Finally, the wear-resistant mechanism of nano-coatings is revealed from three aspects: grain refinement, phase transformation toughening mechanism and nano-effects. The application prospects of nano-coatings and the development potential combined with 3D technology are prospected.

Preparation and Characterization of Low Infrared Emissive Aluminum/Waterborne Acrylic Coatings

An aluminum/waterborne acrylic coating was developed by orthogonal experiments, and the gloss, emissivity, chromatic distortion, hardness, adhesion, impact resistance, and corrosion resistance of the coatings were examined. The results showed that the effect of drying time on the infrared emissivity of coatings was more significant than that of the Al powder concentration and nano-silica slurry. When the drying time was prolonged from 0.5 to 6.0 min, the gloss of the coating decreased slowly and the gloss remained low. The infrared emissivity first decreased and then increased. The infrared emissivity of coatings dried for 2.0 min was better. The L’ value gradually decreased and showed a small change of range. With the increasing of the drying time, the hardness of the coating gradually decreased and was the highest at 0.5–2.0 min. The drying time had no effect on the adhesion level. The impact resistance of the coating was better during the drying period of 1.0–3.0 min. The corrosion resistance of the coating was better at 2.0 min. When the drying time was 2.0 min, the waterborne coating showed the better comprehensive performance. This study provides new prospects in using low infrared emissive coatings for infrared stealth and compatibility with visible light.

Investigation on Wear Behavior of Cryogenically Treated Ti-6Al-4V Titanium Alloy under Dry and Wet Conditions

Titanium alloys are widely used in many fields because of their excellent comprehensive properties. However, its poor friction and wear properties limit its many potential applications. In general, the surface roughness of important parts manufactured by titanium alloy should meet certain requirements. As a low-cost and high-efficiency processing method, barrel finishing has been used for the surface finishing of titanium alloys. The main material removal mechanism of barrel finishing is micro-cutting/grinding, which is similar to the material wear mechanism under some conditions. In addition, titanium alloys are subjected to a low force in common surface finishing processes. Cryogenic treatment is a method that can improve the comprehensive properties of titanium alloys. Therefore, the friction and wear behavior of cryogenically treated Ti-6Al-4V titanium alloy (CT Ti alloy) and non-cryogenically treated Ti-6Al-4V titanium alloy (NT Ti alloy) at a low load and scratch speed was studied comparatively in this paper. The results show that the CT Ti alloy exhibits a lower friction coefficient and wear rate under both dry and wet wear conditions. Under wet conditions, the stabilized friction coefficient is lower than that under dry conditions. The stabilized friction coefficient of CT Ti alloy is 0.18 after reaching a stable wear stage under wet conditions. Under dry wear conditions, the NT Ti alloy mainly showed typical abrasive wear, heavy adhesion wear and oxidation wear characters. The wear mechanisms of CT Ti alloy are mainly abrasive wear, slight adhesion wear and oxidation wear. Under wet wear conditions, the wear mechanism of NT Ti alloy is abrasive wear and slight adhesion wear. After cryogenic treatment, the mechanism for CT Ti alloy is slight abrasive wear.

TiBCN-Ceramic-Reinforced Ti-Based Coating by Laser Cladding: Analysis of Processing Conditions and Coating Properties

In this paper, TiBCN-ceramic-reinforced Ti-based coating was fabricated on a Ti6Al4V substrate surface by laser cladding. The correlations between the main processing parameters and the geometrical characteristics of single clad tracks were predicted by linear regression analysis. On this basis, the microstructure, microhardness, corrosion resistance, and wear resistance of the coating and the substrate were investigated. The results showed that the clad height, clad width, clad depth, and dilution rate depended mainly on the laser power, the powder feeding rate, and the scanning speed. TiBCN-ceramic-reinforced Ti-based coating was mainly composed of directional dendritic TiBCN phases, equiaxed TiN phases, needle-like Al3Ti phases, and Ti phases. The microhardness gradually increased from the bottom to the top of the coating. The highest microhardness of coating was 1025 HV, which was three times higher than that of the Ti6Al4V substrate (350 HV). Furthermore, the coating exhibited excellent corrosion resistance and wear resistance. The corrosion potential (Ecorr) reached −1.258 V, and the corrosion density (Icorr) was 4.035 × 10−5 A/cm2, which was one order lower than that of the Ti6Al4V substrate (1.172 × 10−4 A/cm2). The coating wear mass loss was 4.35 mg, which was about two-third of the wear mass loss of the Ti6Al4V substrate (6.71 mg).

Thermally Charged MHD Bi-Phase Flow Coatings with Non-Newtonian Nanofluid and Hafnium Particles along Slippery Walls

The present study is about the pressure-driven heated bi-phase flow in two slippery walls. The non-Newtonian couple stress fluid is suspended with spherically homogenous metallic particles. The magnetic susceptibility of Hafnium allures is taken into account. The rough surface of the wall is tackled by lubrication effects. The nonlinear coupled partial differential equations along with the associated boundary conditions are first reduced into a set of ordinary differential equations by using appropriate transformations and then numerical results were obtained by engaging the blend of Runge–Kutta and shooting techniques. The sway of physical quantities are examined graphically. An excellent agreement within graphical illustration and numerical results is achieved.