Masahiro Fukumoto

Cold Spray Coating Deposition Mechanism on the Thermoplastic and Thermosetting Polymer Substrates

Cold spraying is a successful and promising coating technique for many engineering applications due to its high-rate and high-dense coating development abilities. Nevertheless, their practical use in polymer substrate is still in the fledgling phase. There are very few articles about the cold spray coating on polymers; however, the interaction of metallic particle with the polymer substrate is poorly understood, and thus a thick coating has not successfully been developed on the polymer substrate. In order to rationalize as full as possible the entire behavior of the high velocity particle with the polymer substrate, we used thermoplastic and thermosetting polymer materials as substrates. The particle behaviors with the substrate were observed under various gas pressure and temperature, and with various particles feed rate. The result showed that the particle behaviors were unique with respect to the substrate. Also it was clearly understood that the metal particles not experienced any plastic deformation due to the soft nature of the polymer substrates. The particles attached to the thermoplastic substrate either through adhesive bonding and/or mechanical inter locking, whereas only pure localized fracture observed on the thermosetting substrate and thus no particles attached firmly on the substrate.

Influence of Substrate Temperature on Adhesion Strength of Cold-Sprayed Coatings

Cold spraying is a promising process for fabricating functional coatings. Because of solid state particle deposition, the electrical and chemical properties of cold-sprayed coatings are almost similar to the bulk materials. The most important factor in depositing a particle through cold spraying is known as the critical velocity. When the particle velocity is beyond the critical velocity, the plastic deformation of both the sprayed metallic particle and the metallic substrate causes the removal of surface oxide layers and newly-formed surfaces are exposed. The newly-formed surface yields the metallic bond, and then cold spray deposition can occur. Therefore, the substrate conditions must also be considered in order to understand the cold spray process. In this study, the influence of substrate temperature on the adhesion strength of coatings was investigated by substrate pre-heating. The adhesion strength was examined by a shear adhesion test. This showed that substrate pre-heating enhances the adhesion strength with a specific combination of coating and substrate materials. Thermal stress and substrate surface oxidation have been suggested ss the causes of these.

The Effect of CFRP Surface Treatment on the Splat Morphology and Coating Adhesion Strength

Metallization of Carbon Fiber-Reinforced Polymer (CFRP) composites aggrandized their application to aircraft, automobile, and wind power industries. Recently, the metallization of CFRP surface using thermal spray technique, especially the cold spray, a solid state deposition technique, is a topic of research. However, a direct cold spray deposition on the CFRP substrate often imposes severe erosion on the surface owing to the high-impact energy of the sprayed particles. This urges the requirement of an interlayer on the CFRP surface. In the present study, the effect of surface treatment on the interlayer adhesion strength is evaluated. The CFRP samples were initially treated mechanically, chemically, and thermally and then an interlayer was developed by atmospheric plasma spray system. The quality of the coating is highly dependent on the splat taxonomy; therefore the present work also devoted to study the splat formation behavior using the splat-collection experiments, where the molten Cu particles impinged on the treated CFRP substrates. These results were correlated with the coating adhesion strength. The coating adhesion strength was measured by pull-out test. The results showed that the surface treatment, particularly the chemical treatment, was fairly successful in improving the adhesion strength.

Microstructures and Thermal Properties of Cold-Sprayed Cu-Cr Composite Coatings

Copper-based composites for thermal conductive components were prepared via the cold spray process, and the deposition efficiency and adhesion morphology of feedstock powders on Cu substrate were evaluated. Cu-based composites were fabricated using Cu-Cr mixed powders with their mixture ratio of 20, 35, 50, and 65xa0mass% Cr onto oxygen-free copper substrate with N2 carrier gas. Cu-Cr composite coatings were investigated for their Cr content ratio, microstructures, and thermal conductivity. The Cr content ratio in the coating was approximately 50-60% of feedstock mixture ratio due to the low formability of the hard particles. Transmission electron microscopy characterizations revealed that an oxygen-rich layer exists at the Cr particle/Cu substrate interface, which contributes to the deposition of the Cr particles. After the heat treatment at 1093xa0K, the coatings showed denser cross-sectional structures than those before the heat treatment, and the thermal conductivity was improved as a result of the recrystallization of Cu matrix.

The Synthesis of Titanium Dioxide (TiO2) Powder for Cold Spray Process

Titanium dioxide (TiO2) has attracted numerous attentions due to its high photocatalytic property. TiO2 as photocatalyst is best to be coated over large area substrate (walls, windows, etc.). In this case, cold spray process is the most suitable technique, not only because its simplicity and efficiency for large area deposition, but also because it is a low temperature process that would retain the high photocatalytic anatase phase of TiO2 in the coating. However, cold spraying of hard ceramic materials, such as TiO2, is widely known to be difficult. In this study, we are reporting a novel synthesis method of TiO2 powder for cold spray via the hydrolysis of titanyl sulphate (TiOSO4) with addition of ammonium sulphate ((NH4)2SO4). It is a relatively simple synthesis method that can obtain pure anatase structure even without high temperature treatment, although post treatments, such as hydrothermal and calcination further increase the crystallinity and change the morphology of synthesised TiO2. It is believed that the synergetic effect of post treatments and adsorption of NH4+ and SO42− ions on the surface of TiO2 causes the alteration in morphology of TiO2 powder. Finally, the cold spray spot test shows that the TiO2 powders can be cold sprayed. This is a remarkable finding as the difficulty of cold spraying TiO2 is widely known.

Microstructure and Mechanical Properties of Warm-Sprayed Titanium Coating on Carbon Fiber-Reinforced Plastic

Polymer materials are increasingly dominating various engineering fields. Recently, polymer-based composite materials’ surface performances—in particular, surface in relative motion—have been improved markedly by thermal spray coating. Despite this recent progress, the deposition of high-strength materials—producing a coating thickness of the order of more than 500xa0μm—remains highly challenging. In the present work, a highly dense and thick titanium coating was successfully deposited onto the carbon fiber-reinforced plastic (CFRP) substrate using a newly developed high-pressure warm spray (WS) system. The coating properties, such as hardness (300xa0±xa020xa0HV) and adhesion strength (8.1xa0±xa00.5xa0MPa), were evaluated and correlated with the microstructures of the coating. In addition, a wipe-test and in situ particle velocity and temperature measurement were performed to validate the particle deposition behavior as a function of the nitrogen flow rate in the WS system. It was found that the microstructures, deposition efficiency, and mechanical properties of the coatings were highly sensitive to nitrogen flow rates. The coating porosity increased with increasing nitrogen flow rates; however, the highest density was observed for nitrogen flow rate of 1000 standard liters per minute (SLM) samples due to the high fraction of semi-molten particles in the spray stream.

Effect of weld line shape on material flow during friction stir welding of aluminum and steel

The effect of weld line shape on material flow during the friction stir welding of aluminum and steel was investigated. The material flow velocity was evaluated with simulated experiments using plasticine as the simulant material. The validity of the simulated experiments was verified by the marker material experiments on aluminum. The circumferential velocity of material around the probe increased with the depth from the weld surface. The effect is significant in cases where the advancing side is located on the outside of curve and those with higher curvature. Thus, there is an influence of weld line shape on material flow.

Weldability in friction stir welding between dissimilar metals with circular weld line

In recent years, hybrid structure, which is composed of aluminum alloy as a representative of light weight material and steel as that of high strength material, has been paid attention remarkably, especially in the transportation industry from the viewpoint of energy saving. To realize the hybrid structure, friction stir welding, FSW, has been recognized to be an effective way for the welding between dissimilar metal materials. Based on our previous knowledge on the weldability between dissimilar metals in butt welding with straight weld line, we are now focusing on the weldability in FSW between dissimilar metals with circular weld line to open a new application field. The objective of this research is to get a fundamental knowledge on the welding in dissimilar metals with circular weld line and verify the effect of Al alloy material and tool design on the friction sir welding in dissimilar metals combination. n nTypical results obtained are summarized as follows: n1) nMacroscopic defects often observed at bottom region of the tool in case of ADC12 sample, indicating that only insufficient stirring was given on that region probably due to its higher thermo-mechanical property. n n2) nThe tensile strength of the specimen fabricated with scroll shoulder tool was 266xa0MPa, while that given with flat shoulder tool was 161xa0MPa. That is, the tensile strength of the welded joint was improved by a factor of 1.65 by introducing the scroll shoulder tool with normal thread probe. n n3) nIt is feasible that high performance defect free ADC12/S45C welded structure with circular weld line can be fabricated by the tool having the combination of scroll shoulder and normal thread probe.