Warm spraying-a novel coating process based on high-velocity impact of solid particles

Advanced surface engineering of titanium materials for biomedical applications: From static modification to dynamic responsive regulation

Titanium (Ti) and its alloys have been widely used as orthopedic implants, because of their favorable mechanical properties, corrosion resistance and biocompatibility. Despite their significant success in various clinical applications, the probability of failure, degradation and revision is undesirably high, especially for the patients with low bone density, insufficient quantity of bone or osteoporosis, which renders the studies on surface modification of Ti still active to further improve clinical results. It is discerned that surface physicochemical properties directly influence and even control the dynamic interaction that subsequently determines the success or rejection of orthopedic implants. Therefore, it is crucial to endow bulk materials with specific surface properties of high bioactivity that can be performed by surface modification to realize the osseointegration. This article first reviews surface characteristics of Ti materials and various conventional surface modification techniques involving mechanical, physical and chemical treatments based on the formation mechanism of the modified coatings. Such conventional methods are able to improve bioactivity of Ti implants, but the surfaces with static state cannot respond to the dynamic biological cascades from the living cells and tissues. Hence, beyond traditional static design, dynamic responsive avenues are then emerging. The dynamic stimuli sources for surface functionalization can originate from environmental triggers or physiological triggers. In short, this review surveys recent developments in the surface engineering of Ti materials, with a specific emphasis on advances in static to dynamic functionality, which provides perspectives for improving bioactivity and biocompatibility of Ti implants.

Techno-Economic Analysis and Life Cycle Assessment of High-Velocity Oxy-Fuel Technology Compared to Chromium Electrodeposition

Due to the toxicity associated with chromium electrodeposition, alternatives to that process are highly sought after. One of those potential alternatives is High Velocity Oxy-Fuel (HVOF). In this work, a HVOF installation is compared with chromium electrodeposition from environmental and economic points of view by using Life Cycle Assessment (LCA) and Techno-Economic Analysis (TEA) for the evaluation. Costs and environmental impacts per piece coated are then evaluated. On an economic side, the lower labor requirements of HVOF allow one to noticeably reduce the costs (20.9% reduction) per functional unit (F.U.). Furthermore, on an environmental side, HVOF has a lower impact for the toxicity compared to electrodeposition, even if the results are a bit more mixed in other impact categories.

Surface modification of hybrid composite multilayers spin cold spraying for biomedical duplex stainless steel

The performance of biomaterials in biological systems is of critical significance for advancing biomedical implants. Duplex Stainless Steel alloys are the major biomaterials due to their significant characteristics. Many functional coatings are deposited on DSS alloy surfaces utilizing numerous surface coating techniques to improve their bioactivity and protect them from corrosion degradations. Coatings of titanium dioxide (TiO₂), Hydroxyapatite (HA), and zinc oxide (ZnO) have received considerable attention in the field of surface bioactive modification of DSS alloy implants. The coating techniques play a key role in increasing the required biological characteristics of DSS alloys, such as biocompatibility, mechanical properties, and corrosion resistance. In this regard, HA-ZnO, HA-TiO_2, and TiO₂-ZnO from each coating group are divided into single, double, and triple layers. These coatings were prepared by cold spray and deposited on the surface of the DSS alloy, followed by a heat treatment at 250 °C. The surface morphology of coated surfaces was analyzed utilizing field emission scanning electron microscopy (FESEM), atomic force microscopic (AFM), microhardness test, corrosion test in Ringer solution, and antibacterial test. The coatings showed nano-scale surface morphology with advanced crystallization and homogeneous structures; in the corrosion characteristics utilizing potentiodynamic polarization, triple layers of HA-ZnO coatings displayed advanced nanostructures with higher hardness values (514.75HV). The antibacterial test showed the triple layers of HA-TiO₂ and two layers of TiO₂-ZnO sensitivity to positive bacteria.

Influence of Cr Ion Bombardment on the Growth of Cu Coatings Deposited by Magnetron Sputtering on ABS Substrates

Cu coatings were deposited on acrylonitrile-butadiene-styrene copolymer (ABS) substrates by DC magnetron sputtering with Cu target. Cr ions generated by arc evaporation were used to bombard the ABS substrates before the Cu coating process. The influences of the Cr ion bombardment on the surface topography and chemical bonds of the ABS substrates and the adhesion of the Cu coatings on the ABS substrate were studied using scanning electron microscopy, Fourier transform infrared spectroscopy, and micro-Scratch Tester as a function of bias voltage and treatment duration. The results show that the Cr ion bombardment causes Cr particles to embed in the surface. The Cr particles can interlock with the Cu coatings and ABS substrate and significantly improve the coating adhesion. In addition, the Cr particles can act as the nucleation sites of the Cu coatings and facilitate the growth of columnar crystals. Increasing the duration of Cr ion bombardment increases the number of Cr particles and, thus, enhances the adhesion. However, the continuous bombardment results in the degeneration of the ABS surface, causing the formation of the coarse columnar structure of the Cu coatings. Increasing the bias voltage can increase the energy of the Cr particles without causing degeneration of the ABS. The Cu coating deposited on the ABS substrate treated by Cr ion with high-bias voltage and short duration shows a dense and smooth growth structure. In contrast, the bombardment of the Cr ions carried out at high-bias voltage induces the formation of an interfacial layer (amorphous carbon-rich phase) in the ABS surface, which decreases the coating adhesion. It is believed that Cu coatings with strong adhesion and dense structures could be acquired on ABS substrates by optimizing the bias voltage and duration of the Cr ion bombardment pre-treatment.

Microstructure and Tribological Properties of Lubricating-Reinforcing Laser Cladding Composite Coating with the Ti2SC-Ti2Ni Mosaic Structure Phase

Lubricating-reinforcing composite coatings were successfully prepared on Ti6Al4V using laser-clad Ti6Al4V/Ni60/Ni-MoS2 mixed powders with different Ni-MoS2 contents (25, 35, and 45 wt.%), and their microstructure and tribological properties were studied. The reinforcing phase TiC, Ti2Ni, and the lubricating phase Ti2SC were in situ precipitated while Ti2SC and Ti2Ni formed a mosaic coherent structure within the above three coatings. In the 25 and 45 wt.% Ni-MoS2 coatings, the microstructure distribution uniformity of the coatings was not effectively improved by the Ti2SC-Ti2Ni mosaic structure phase due to the lower or higher content of Ti2SC. In the 35 wt.% Ni-MoS2 coating, the forming quality of the coating was the best due to an appropriate amount of the uniformly distributed Ti2SC-Ti2Ni mosaic structure phase. Furthermore, the microhardness of the coatings gradually decreased as the amount of Ni-MoS2 increased. In the 35 wt.% Ni-MoS2 coating, due to the uniformly and diffusely distributed Ti2SC-Ti2Ni mosaic structure phase, the stable lubricating-reinforcing mosaic structure transfer composite films were formed during the progress of the friction and wear tests, which led to the optimal worn surface evenness and quality, the anti-friction and the wear resistance properties compared with the Ti6Al4V, 25 and 45 wt.% Ni-MoS2 coating.

A Comparative Study of Aluminium and Titanium Warm Sprayed Coatings on AZ91E Magnesium Alloy

Aluminium (Al) and titanium (Ti) coatings were applied on AZ91E magnesium alloy using a low-pressure warm spray (WS) method. The deposition was completed using three different nitrogen flow rates (NFR) for both coatings. NFR effects on coating microstructure and other physical properties were systematically studied. Microstructural characterization was performed using scanning electron microscopy (SEM), and the porosity was estimated using two methods-image analysis and X-ray microtomography. The coating adhesion strength, wear resistance, and hardness were examined. The protective properties of the coatings were verified via a salt spray test. Decreasing NFR during coating deposition produced more dense and compact coatings. However, these conditions increased the oxidation of the powder. Al coatings showed lower hardness and wear resistance than Ti coatings, although they are more suitable for corrosion protection due to their low porosity and high compactness.

On the Importance of Secondary Component Properties for Cold Spray Metallization of Carbon Fiber Reinforced Polymers

In previous studies at McGill University, tin was successfully cold sprayed onto carbon fiber reinforced polymers (CFRPs). A "crack-filling" mechanism was described as the deposition mechanism that allowed deposition of tin onto the CFRP. Improving the coating conductivity for lightning strike protection (LSP) purposes was explored by adding other metal powders (aluminum, copper, zinc) to tin and cold spraying on the CFRP. At the same time, it was noticed that the addition of this secondary component (SC) provided an increase in deposition efficiency (DE); tamping was initially hypothesized to explain this improvement, thus prompting a study solely on the effect of SC hardness. However, it is recognized that other powder characteristics may also be influencing the DE. Thus, in this study, SCs with a wider variety of particle sizes, morphologies, densities and hardness values were mixed with tin and sprayed on CFRPs. The effect of SC properties on tin deposition is discussed and, while SC particle size, morphology and density individually do not notably influence the DE, the impact energy of the SC does. This opens a discussion on optimal parameters for deposition of metals on CFRP, based on results and observations from the literature.

Investigation of Electrocatalysts Produced by a Novel Thermal Spray Deposition Method

Common methods to produce supported catalysts include impregnation, precipitation, and thermal spray techniques. Supported electrocatalysts produced by a novel method for thermal spray deposition were investigated with respect to their structural properties, elemental composition, and electrochemical performance. This was done using electron microscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry. Various shapes and sizes of catalyst particles were found. The materials exhibit different activity towards oxidation and reduction of Fe. The results show that this preparation method enables the selection of particle coverage as well as size and shape of the catalyst material. Due to the great variability of support and catalyst materials accessible with this technique, this approach is a useful extension to other preparation methods for electrocatalysts.

Pitted Corrosion Detection of Thermal Sprayed Metallic Coatings Using Fiber Bragg Grating Sensors

Metallic coatings using thermal spraying techniques are widely applied to structural steels to protect infrastructure against corrosion and improve durability of the associated structures for longer service life. The thermal sprayed metallic coatings consisting of various metals, although have higher corrosion resistance, will still corrode in a long run and may also subject to corrosion induced damages such as cracks. Corrosion and the induced damages on the metallic coatings will reduce the effectiveness of the coatings for protection of the structures. Timely repair on these damaged metallic coatings will significantly improve the reliability of protected structures again deterioration. In this paper, an inline detection system for corrosion and crack detection was developed using fiber Bragg (FBG) grating sensors. Experimental results from laboratory accelerated corrosion tests showed that the developed sensing system can quantitatively detect corrosion rate of the coating, corrosion propagations, and cracks initialized in the metallic coating in real time. The developed system can be used for real-time corrosion detection of coated metal structures in field.