In this work, amorphous Zr-based bulk metallic glass deposit was manufactured by cold spray. The bonding mechanism of metallic glass particles was systematically investigated through studying the deformation behavior of individual particles after deposition or rebound. We revealed two collective particle bonding mechanisms that contributed to the formation of metallic glass deposit, i.e., high-velocity impact induced localized metallurgical bonding at the fringe of interface, and high gas-temperature induced partial melting of particles and resultant annular metallurgical bonding band. Moreover, the dynamic evolution mechanism of amorphous phase into nanocrystal structures at severely deformed interfacial regions during cold spray was carefully investigated. For the first time, we observed different amorphous/nanocrystal structures in cold sprayed metallic glass particles, which can represent different evolution stages in nanocrystallization process. Based on the observation, it is inferred that the nanocrystallization process can be divided into following three stages: composition segregation, the formation of ordered 1D and 2D transition structures, and 3D nanocrystals. The current study provides new insights into bonding mechanisms and the mechanistic nanocrystallization origins in cold sprayed metallic glass.

This study investigates the feasibility of producing GaN coatings on stainless steel, aluminum, and indium tin oxide glass substrates by downstream injection low-pressure cold spraying. The formation of GaN layers on all three materials appears to be due to pseudo deformation of super agglomerated GaN particles. The deposition results showed a saturation limit to coating thickness with the number of passes. Based on XRD spectra of the coating and powder, no phase transformations took place during the spraying process.

Bulk metallic glasses (BMGs) are a novel class of metallic materials with disordering atomic structure and excellent mechanical and chemical properties, and are promising for various industry applications. BMGs are usually fabricated by copper-mould casting due to the requirement of fast cooling rate for the obtainment of amorphous structure. However, this casting approach has the limitation for preparation of large size samples (the biggest Fe-based BMG obtained so far is less than 16 mm diameter). In this work, the conventional high velocity oxy-fuel (HVOF) thermal spraying technique was utilized as a novel additive manufacturing route to create large size Fe-based BMGs and BMG composites. It will be reported that a large size of 20x20x20mm BMG (Fe48Mo14Cr15Y2C15B6 (at%) ) and big plate of 100×100×5 mm of Fe-based BMG composites reinforced with 50vol% 316L stainless steel powders was successfully prepared by HVOF thermal spraying. Both BMG and BMG composite showed very dense structure (porosity less than 0.4% ) and good mechanical properties, Especially, BMG composite reinforced with 316 L stainless steel exhibited a yield strength of 1.8 GPa and compressive plastic strain of 2%. More importantly, this Fe-based BMG composite exhibited good toughness of KJ=21 MPa m 1/2 , which is almost 4-times higher than that of as-cast BMG. This present work indicates that HVOF thermal spray can become a versatile technique for preparation of large size of bulk metallic glasses and composites with desired properties.

The practical application of bulk metallic glasses (BMGs) as structural materials is still restricted due to the intrinsic brittleness of BMGs although they have high hardness and strength and even pretty good toughness. As an alternative form of metallic glasses, amorphous coatings based on BMG systems can exactly overcome the drawback of BMGs, but carry forward the superiority in corrosion and wear resistance, thus exhibiting promising applications in surface engineering. However, the monolithic amorphous coatings faces new challenges, such as low adhesion strength and impact toughness. In this presentation, we present some new findings on the design of novel Fe-based amorphous composite coatings by HVOF technique. These include the add stainless steel ductile phase, hard ceramic particles and in-situ carbon phases into the amorphous coating, in addition to form laminar structural coatings. It will be shown that the second phase and their interface structure with amorphous matrix play important role in the resultant mechanical properties of the coatings. The combination of the good mechanical, physical and chemical properties warrants amorphous composite coatings to have extensive applications in industry in near future.

In recent studies, the suspension plasma spray technology (SPS) was shown as a promising method for deposition of photocatalytic TiO 2 coatings on glass substrates. However, only little information about the effects of SPS process parameters on the resulting photocatalytic activity is available. In this study, several suspensions were prepared from different powders and various dispersion mediums successively sprayed. Four titania powders with a proven photocatalytic track record, Evonik P25, Kronoclean 7050, Hombicat UV100 and Sigma Aldrich were used to study the influence of starting powder type. Furthermore, compositions of the dispersing medium were varied in order to investigate their influence on coating structure, adhesion to substrate and photocatalytic activity. Degradation of methylene blue was tested as a marker for the photocatalytic activity. At chosen torch parameters, alcohol and water in a ratio of 1:3 was identified as the best composition. Suspensions sprayed with higher alcohol content suffered from the reduction in anatase phase; higher water content reduced the coating adhesion to the substrate. Regarding the initial powders, films made of Evonik P25 and Sigma Aldrich TiO 2 had higher photocatalytic activity than others. Moreover, the photocatalytic activity of doped TiO 2 coatings illuminated by both an artificial light and sunlight were investigated.

This work investigates the biofunctionality and corrosion resistance of titanium (Ti) and Ti/bioglass composite coatings. Commercially pure Ti (CP-Ti) and 45S5 bioglass powders were deposited on CP-Ti plates by air plasma spraying and the coating samples were placed in Hanks’ balanced salt solution for simulated body fluid (SBF) testing. After four weeks of immersion, the coatings were examined by SEM imaging and EDS and XRD analysis. EDS analysis showed that the Ca content on the Ti/bioglass coatings increased from 4 to 16 wt%, while no increase in Ca was observed on the Ti coatings. Hydroxyapatite formation was found on both coatings, although the relative intensity of HA on the XRD spectrum was higher for the Ti/bioglass composite layers. Weight measurements before and after immersion showed that the CP-Ti samples experienced a mass gain and that the Ti/bioglass samples underwent a mass loss likely due to the dissolution of calcium and phosphate.

In this study, a mathematical model based on 2D heat conduction was developed to determine the temperature distribution within different substrate materials during cold gas dynamic spraying. Heat transfer between the hot gas and substrate was estimated theoretically and experimentally and the results were compared with those obtained from numerical studies. The heat transfer coefficient was found to be dependent on the distance from the stagnation point of the impinging air jet. It was also concluded that at higher air jet temperatures, the Nusselt number of the spreading air film near the stagnation point could be affected by external heat exchange with colder ambient air.

In this work, gas-atomized FeCr powders were deposited on aluminum substrates by HVOF spraying, forming dispersion strengthened coatings with a dense layered structure and low porosity. SEM, TEM, and XRD analyses show that the coatings primarily consist of amorphous matrix (40%) with precipitated nanocrystals and hard boride phases. A number of coating properties, including microhardness, bonding strength, and thermal conductivity, were measured and are correlated with spraying conditions.

The objective of this work is the development of highly amorphous, iron based coatings for thermal barrier applications. Based on the results of previous work, a chemical composition of Fe 72 Si 4 B 20 Nb 4 was selected and modified in order to improve glass forming ability and corrosion resistance. Three metallic glass powder mixtures with different amounts of Cr and Fe were prepared, characterized, and deposited by air plasma and HVOF spraying. Different gas flow rates and standoff distances were used and particle temperatures and velocities were measured during spraying. The deposits were examined, tested, and compared and were found to have good potential for thermal barrier coating applications.

This study investigates the feasibility of forming amorphous iron-based coatings using the cold spray deposition process. Splat tests of cold-sprayed SAM1651 (Fe48Mo14Cr15Y2C15B6 at.%) particles impacting a mild steel substrate were performed using varying gas temperatures and particle diameters. Specimen inspection by scanning electron microscopy revealed splat morphologies that varied from well-adhered particles to substrate craters formed by rebounded particles. Particle flow was analyzed using a finite element model, and impact conditions were predicted using an experimentally validated analytical model, in empirically generating a temperature/velocity window of successful particle deposition as a framework for ongoing work on the formation of cold-sprayed SAM1651 coatings. The results indicate that the unique characteristics of the cold spray process offer a promising means for the formation of metallic glass coatings that successfully retain the amorphous structure, as well as the superior corrosion and wear resistant properties of the feedstock powder.

In this investigation, cold spraying is used to deposit a simple binary amorphous alloy with technical purity. Cu 50 Zr 50 was chosen as the model system due to its glass-forming ability and insensitivity to changes in composition. Critical velocities for coating formation were experimentally determined by systematic variation of spray parameter sets. These values were then used to tune existing bonding models to cold spraying of amorphous Cu 50 Zr 50 powder. It is shown that under suitable conditions, well adhering coatings with the amorphous structure of the powder can be obtained by cold spraying with nitrogen as the process gas.

In this work, tunnel plasma spraying is used to produce Cu 36 Zr 48 Al 8 Ag 8 metallic glass coatings on stainless steel. The results show that cooling gas flow rates play a vital role in oxidation and the formation of intermetallic phases in coating microstructures. Phase formation and microstructural features were evaluated by XRD and SEM-EDX analysis. Coating properties including hardness, sliding wear, and corrosion resistance were measured and the results are compared with the presence of secondary phases. It is shown that an increase in secondary phases improves sliding wear resistance but reduces resistance to corrosion.

Aluminum powder of 99.85 wt.% purity has been sprayed onto three kinds of glass substrates by cold spray. An interface between Aluminum coating and all glass substrates were smooth, and the single aluminum particle adhered without a gap. It is not observed erosion damage of glass substrate by aluminum with lower impact velocity than critical velocity. In Aluminum coating and the neighborhood of interface of Soda-lime glass substrate, sodium included in glass substrate was distributed in high density. There might be the stratum that the element which constituted an aluminum coating and glass substrate scattered, and it was suggested that the solid-phase joining by a chemical reaction were initiated.

As compared to thermal spray techniques, cold spraying allows to retain metastable phases of the feedstock material like amorphous structures, due to lower process gas temperatures. Compared to crystalline metals, metallic glasses are brittle at ambient temperature but viscous at higher temperatures. Therefore, cold spray parameters must be optimized for conditions that allow softening of the amorphous spray material for successfully producing coatings. For this study, a FeCoCrMoBC metallic glass was used that in comparison to others offers advantages with respect to higher hardness, less costly feedstock powder and minimum reactivity with the environment. Necessary impact conditions were investigated to meet the window of deposition. According to calculations and cold spray experiments, neither the glass transition temperature Tg nor the melting temperature Tm can describe required conditions for bonding. Thus, a so called softening temperature between the glass temperature and the melting temperature had to be defined to calculate the critical velocity of metallic glasses. With respect to the bonding mechanism, impact morphologies could prove that a transition to viscous flow gets more prominent for harsher spray conditions. By sufficiently exceeding critical condition for bonding, coatings with rather dense microstructures can be processed at deposition efficiencies of about 70 %. The coatings have a hardness of 1100 HV 0.3, but the results also demonstrate that further work is still needed to explore the full potential for bulk metallic glasses.

In the glass manufacturing, stainless-steel parts are used in characteristic corrosive reduction atmosphere at high temperature. The reactive products, that are induced by volatilization from the stainless steel surface, cause defects of the glass in this usage. Some thermal spraying coating of thermal-resistant alloys is tested in this study for the protection to the volatilization. It is clarified that, the Ni-Cr-Al-Y film, containing plate-like metal oxide dispersions, shows an outstanding effect as followings; 1) The diffusion rate of Fe from a stainless substrate in this coating film is decreased by the dispersions, and Fe is not detected at surface layer of the coating after a long-term exposure test at high temperature. 2) The reaction between Sn and this coating is not active relatively can, and the further inactivation can be possible by pre-existing heat-treatment in oxidant atmosphere. 3) Both effect (decreasing of Fe diffusion rate and inactivation with Sn) are induced by plate-like Al 2 O 3 particles. These particles are generated by oxidation of Al-content in the coating material.

Thermal spray coatings are comprised of millions of heated particles that are driven at high velocity to impact against a substrate; thereby building up to form a consolidated coating. Thus, investigating single solidified droplets contributes to fundamental understanding of coating evolution and their properties. In this study, Scanning Electron Microscopy (SEM) studied the splat morphology of flame sprayed ethylene methacrylic acid (EMAA) with respect to the stand-off distance when deposited onto glass and mild steel substrates. A splat shape transition from a “splash” to a “disc shape” was observed. The morphology of EMAA droplets can be described as a ‘splash splat’ when sprayed onto mild steel at room temperature, whereas a 35 cm stand-off distance produced a disk-shaped splat when the polymer was deposited onto a glass substrate.

The aim of this work is to measure the optical reflective properties of plasma sprayed ceramic coatings on glass substrates. The coatings are made with Al 2 O 3 -TiO 2 powders and are assessed by scanning them with an optical computer mouse. It is shown that mouse movements are smoother on ceramic surfaces than on a standard test pad and tracking performance is more stable, indicating that the reflective properties of ceramic-coated glass are better than those of a typical mouse pad. The ceramic coatings are also shown to have the potential to improve resolution in image recording devices.

This study shows that surface preheating is required to avoid delamination of flame sprayed coating glazes. In the experiments, preheating parameters are determined from heat flux measurements and potential substrate degradation is characterized and controlled by optimizing spray parameters. Coating adhesion is determined by pull-out tests and remains constant even after freeze-thaw cycling. Although gas tightness was not characterized, aging tests show that no water percolates through pore networks in the coatings.

Multilayer ceramic chip capacitors (MLCCs) are produced in large numbers for use in automobiles, cell phones, flat panel displays, and other products. Like many circuit components, they are being required in more compact sizes, larger capacities, and reduced costs year by year. MLCCs are kiln-fired on stacked carriers made from Al 2 O 3 -SiO 2 covered with a Y 2 O 3 -stabilized ZrO 2 topcoat and an Al 2 O 3 basecoat. This paper presents the rationale behind the selection of the coating materials and evaluates processes by which they can be applied. It compares the microstructure and properties of sintered, atmospheric plasma sprayed (APS), and water stabilized plasma sprayed (WSP) yttria-stabilized zirconia and discusses the advantages and disadvantages of each process.

In this study, Cu-based bulk metallic glass coatings were deposited by atmospheric plasma spraying with different hydrogen flow rates. The crystallization and oxidation of the coatings is assessed along with corrosion resistance. As thermal energy in the plasma jet increases, the melting fraction and oxidation of particles in the coating increases as does porosity. All of these factors have an effect on the corrosion resistance of Cu-based bulk metallic glass coatings and their relative impact is discussed.