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 lower wear and poor impact resistance of the amorphous coatings has been a great problem in the past few years for their use in industrial applications. Several research methods have been reported recently to overcome this issue. The present paper addresses the main work done recently on iron based amorphous composite coatings by the addition of 0-20% Alumina particles. These particles were homogeneously distributed in the amorphous matrix of the coatings which improved wear and impact resistance as compared to the monolithic coatings without any decrease in corrosion resistance. The hard alumina particles enhanced wear resistance to several times not only in air but also in salt water solution with a decrease in friction coefficient. The combined effect of wear and corrosion were also observed to become better by the alumina addition. Furthermore, the impact resistance was also improved three times by the addition of alumina particles. The hard second phase particles present in the amorphous coating matrix disperses the residual stresses generated during the impact loading. The brittle alumina particles absorb the impact energy by breaking itself which stop the initiation of cracks and also play a vital role in the crack arresting and blocking of the crack propagation.

NiCrBSi is a material generally used in wear-resistant coatings. In order to improve the tribological properties of atmospheric plasma-sprayed NiCrBSi coatings, Molybdenum (Mo) was incorporated into the NiCrBSi coatings to reduce the friction coefficient and wear rate under dry and oil-lubricated conditions. In this paper, Mo-NiCrBSi composite coatings with Mo content of 5, 10, 20 and 30 wt.% were deposited on stainless steel substrates respectively by atmospheric plasma spray. X-ray diffraction, optical microscopy and scanning electron microscopy equipped with energy dispersive spectroscopy were utilized to investigate the phase structure and surface morphology of the composite coatings. Reciprocating friction tests were conducted to measure the friction coefficients and 3D optical microscopy was used to depict the wear track profiles. The results showed that the 30 wt.% Mo-NiCrBSi coating exhibits the best tribological performance. In addition, MoO 2 and MoS 2 films were formed in the friction process under dry condition and oil-lubricated condition respectively.

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.

Conductive thin film residues often referred to as puddles could be challenging fails to detect. A large extant film with no distinct boundaries would make the task more challenging for a comparison between good and bad region. Advanced node 20nm and 14nm technologies mandate use of several conductive thin films in the front end of line processes, and hence a potential for high defects during initial product development stage. Use of other electrical characterization techniques in combination with scanning electron microscopy inspection will be a very powerful tool to detect the root cause affirmatively. Cross-sectional images are necessary to understand the root cause of the fails for corrective actions. This work uses three cases of power supply shorts as a platform to demonstrate the idea, demonstrating a few situations where traditional techniques might reach its limits while the authors depend on additional characterization tools to confidently detect and confirm fails.

In this study, the in-situ corrosion behavior of an Fe-based amorphous coating is investigated in a simulated deep sea environment (80 atm). FeMoCrYCB powder produced by gas atomization was deposited on 316L stainless steel substrates by HVOF spraying. The amorphous iron coatings exhibited greater pitting resistance than stainless steel under high hydrostatic pressures, evidenced by higher pitting potential, longer pitting incubation time, and reduced pitting growth. Passive films that formed on the amorphous coatings were also analyzed and found to be thicker, more uniform, and harder than those that developed on 316L stainless steel, indicating that the former are more difficult to break down and more resistant to Cl- ion penetration.

Amorphous coatings, despite their high strength and hardness and outstanding corrosion and wear properties, have been limited in application due to poor bonding strength and low impact resistance. This paper reviews the progress that has been made in that regard through the addition of ductile metals, ceramic particles, and polymer phases and through laminar structure design consisting of alternating amorphous and NiCrAl layers. Test results show that the composite amorphous coatings realized by the various methods exhibit significantly improved bonding strength and impact resistance along with their other superior properties.

This study assesses the influence of alumina particle additions on the impact and wear behavior of iron based amorphous coatings. Test results show that the presence of Al 2 O 3 particles improved the impact and wear resistance of the coatings by a factor of three. Deformation and fracture mechanisms under impact loading were also investigated. It was revealed via SEM analysis and finite element simulations that hard second phase particles in the amorphous coating matrix disperse residual stresses generated during impact loading and that brittle particles absorb impact energy by fracturing, which plays a vital role in crack prevention and arresting. Abstract only; no full-text paper available.

In this study, hydroxyapatite (HA) coatings were deposited on stainless steel by suspension plasma spraying. Coating samples and suspensions were examined by means of electron microscopy, XRD analysis, and FTIR and Raman spectroscopy. The results show that the coatings are porous and nanostructured with no impurity phases when low H 2 flow rates are used. They also contain a significant amount of OH - and CO 3 2- , which facilitates the formation of well-crystallized HA and improves bioactivity and compatibility in implant applications.

This study investigates the feasibility of using solution precursor plasma sprayed (SPPS) zinc oxide to fabricate NO 2 gas sensors. In the experiments, thin ZnO layers were deposited on Al 2 O 3 substrates that had been printed with interdigitated gold electrodes. FE-SEM images show that the as-sprayed films are highly porous and nanostructured as desired. Diffuse reflectance measurements reveal that significant absorption occurs in the visible light range. In gas sensing tests, the SPPS ZnO films were responsive to concentrations of NO 2 gas down to 0.4 ppm. The performance is attributed to the porous nanostructure and the presence of oxygen vacancies, or mid-bandgap defects, as confirmed by XPS analysis.

ZnO nanostructured coatings have been prepared on Al 2 O 3 substrates fitted with Au electrodes on one side and a Pt heater on the other, forming a solid-state gas sensor. The coatings were deposited by solution precursor plasma spraying (SPPS) using aqueous zinc acetate as the precursor solution. FE-SEM images show that the coatings are nanostructured with grain sizes of 50-100 nm. Surface morphology and grain size were found to be influenced by the flow rate of H 2 in the plasma forming gas. The gas sensing function was characterized by measuring the electrical resistance of the coating in the presence of NO 2 gas, showing good sensitivity down to the sub-ppm range.

A previous study indicated that dense thick Cu-4Cr-2Nb coatings could be formed by cold spraying, and the post-spray heat treatment could significantly influence the microstructure and microhardness of the as-sprayed Cu- 4Cr-2Nb coatings. In this study, the tensile strength and fracture performance of the Cu-4Cr-2Nb coatings after annealing were investigated. The vacuum heat treatment was conducted under 10-2 Pa at 850°C for 4 h. Results showed that the heat treatment had a great contribution to the healing-up of the incompleteness of the interfaces between the deposited particles. In addition, the coating microhardness decreased from 156.8±4.6 Hv0.2 for the as-sprayed coatings to 101.7±4.5 Hv 0.2 for the annealed ones. The mean tensile strength of the annealed coatings was approximately 298.8±31.5 MPa compared to that of 45±10.5 MPa for the as-sprayed ones, which results from the partially metallurgically bonded zones between the deposited particles inducing by the heat treatment process.

This work studied the possibility of using a sensor based on plasma-sprayed zinc oxide (ZnO) sensitive layer for NO 2 detection. The atmospheric plasma spray process was employed to deposit ZnO gas sensing layer and the obtained coating structure was characterized by scanning electron microscopy and X-ray diffraction analysis. The influences of gas concentration, working temperature, water vapor in testing air on NO 2 sensing performance of the ZnO sensors were studied. ZnO sensors showed a good sensitivity and selectivity to NO 2 at an optimal working temperature.

In this investigation, flame spraying is used to deposit polyether ether ketone (PEEK) layers on stainless steel substrates and CO 2 and Nd:YAG laser remelting treatments are performed to densify the deposited material. Microstructural analysis of the as-sprayed and remelted coatings shows that both lasers are suitable for densifying PEEK polymer layers on stainless steel and that the resulting crystalline structure depends on laser processing parameters. Hardness measurements and tribological and scratch tests are also carried out and the results are correlated with microstructure.

The previous studies indicate that the fabrication of metal matrix composites (MMCs) by cold spraying is effective and promising. When light materials, such as SiC and Al 2 O 3 , were used as reforcements, it is difficult to obtain a high volume fraction of hard phase in the composite just through the simple powder mixture. Therefore, in this study, a Ni-coated Al 2 O 3 powder, which was produced through hydrothermal hydrogen reduction method, was employed aiming at increasing the volume fraction of ceramic particles in the deposited composite coating. It was found that a dense Ni-Al 2 O 3 composite coating could be deposited with the Ni-coated Al 2 O 3 powder under the present spray conditions. X-ray diffraction analysis indicated that the composite coating had the same phase structures as the feedstock. The volume fraction of Al 2 O 3 in the composite was about 29±6%, which is less than that in the feedstock (nominal: 40-45%) due to the rebound of some Al 2 O 3 particulates upon kinetic impacting. The microhardness of the composite coating was about 173±33Hv 0.2 .

A certain level of porosity is always presented in thermal spray ceramic coatings. LPPS or some specific APS processes can allow to reduce it but it is difficult to obtain coatings with a low thickness (less than 100 m) which are fully gas-tight because of cracks or interconnected pores. This gas-tight property is for example very suitable for the ceramic electrolyte of solid oxide fuel cells (SOFC). Some ZrO 2 -Y 2 O 3 coatings were obtained by the VLPPS process, a LPPS system operating at a pressure of about 100 Pa. The specific structure of these coatings is a mixture of condensed vapors and splats. The results are very satisfying because ZrO 2 -Y 2 O 3 coatings with a thickness of about 70 micrometers are tight under a hydrogen pressure of 2x105 Pa. This paper presents some ZrO 2 -Y 2 O 3 coatings obtained by different processes (APS, LPPS and VLPPS) and their properties.

Gas permeation behaviour through atmospheric plasma-sprayed 8 mol% yttria stabilized zirconia (YSZ) electrolyte coating was studied experimentally. YSZ coatings were fabricated using different powder feedstock. The temperature and velocity of in-flight particles during spraying were measured with a diagnostic system. The results showed that particle temperature and velocity were significantly influenced by the size of powders. The gas permeability of these coatings was estimated by a specific instrument with pure O 2 , N 2 and H 2 . It was found that the gas permeability was reduced by decreasing the size of powder. Gas permeation behaviour through plasma-sprayed YSZ coating was studied. Transition flow was compatible to gas permeation behaviour for all three plasma-sprayed YSZ coatings. The relationship between gas permeation behaviour and coating microstructure is discussed in this article.

Lanthanum silicate coatings were deposited onto stainless steel substrates by atmospheric plasma spraying (APS) using mechanically mixed (type A) and calcined feedstock (type B) powders. The phase composition, microstructure, density and porosity of coatings prepared from the two types of powder were compared.

In this paper, the effect of velocity on the characteristics of atmospheric plasma sprayed yttria stabilized zirconia was investigated through adjusting auxiliary helium flow. The temperature and velocity of in-flight particles were measured with DPV2000 analyzer. The results showed that helium flow significantly influenced particle velocity and less distinctly influenced particle temperature. The microstructure of the coatings was characterized by scanning electron microscopy and X-ray diffraction analyzer. The ionic conductivity of the deposits through thickness direction was measured by a potentiostat/galvanostat based on three-electrode assembly approach in a temperature range of 500-1000 °C. The specific gas permeability was estimated. The results showed that the gas permeability was improved by increasing the in-flight particle velocity. However, the in-flight particle velocity has little effect on the ionic conductivity of specimens.

The emergence of lanthanum silicate as an electrolyte is required to accelerate the development of synthesis techniques for intermediate temperature solid oxide fuel cells (ITSOFCs). Apatite-type oxide powders of La 10 (SiO 4 ) 6 O 3 have been elaborated through atmospheric plasma spraying (APS) using micro-scale mixtures of La 2 O 3 and SiO 2 powders. Granulometer and scanning electron microscopy analyses have indicated the result of high temperature reaction and rapid solidification in the evolution of multi-scale microstructure.