ZrO 2 -Y 2 O 3 (YSZ) thermal barrier coatings (TBCs) were manufactured via conventional Air Plasma Spray (APS), Suspension Plasma Spray (SPS) and an additional technology hereby termed Finely-dispersed-particle Air Plasma Spray (FAPS). The FAPS processing employs the exact same classification of finely dispersed particles as used in SPS; however, whereas SPS uses a liquid medium, in the case of FAPS the particles are fed conventionally via a carrier gas into the plasma spray torch by using a newly developed powder feeder for fine (suspension-like) particles (NRC patented technology). These finely dispersed YSZ particles consist of irregularly shaped (fluffy-like) agglomerates made from individual nano-sized particles. The conventional APS YSZ TBC was sprayed via a Metco 3MB torch, whereas, both SPS and FAPS YSZ TBCs were sprayed using the Mettech Axial III torch (using the same set of spray parameters). Both SPS and FAPS YSZ TBCs exhibited porous and vertically-cracked microstructures. The conventional APS YSZ TBC microstructure exhibited the traditional lamellar morphology. Elastic modulus, hardness and thermal conductivity values were evaluated for all YSZ TBCs. Microstructures and phase analysis were investigated via SEM and XRD.

A new arc spray system has been designed which produces coatings with very high density and low oxide content. Advantages of the new process are illustrated by a comparison of coating properties sprayed by a conventional arc process and the new system for various metals.

In the cold spray process, cross-sectional shape of the nozzle has a significant effect on spray pattern of coatings. The circular exit nozzle is parabolic in shape. So, spray pattern with the rectangular nozzle is wider than that with the circular spray nozzle. The goal of this investigation is to establish a design for the cold spray gun nozzle to gain more uniform spray profile of coatings. We have investigated the influence of expansion ratio, nozzle total length and the ratio of nozzle length of divergent section and parallel section of rectangular nozzle on behaviors of gas and particle by the computational fluid dynamics (CFD) in high pressure cold spraying. We have studied copper particles so far. In this study, we will examine aluminum particles. First, we investigate the influence of the size and shape of the rectangular section nozzle on the velocity, temperature, and particle distribution of aluminum particles by CFD. After that, the rectangular section nozzles were fabricated and coating formation experiments were conducted, spray patterns and coating cross-sectional structures were observed, and coating adhesion was also evaluated. The nozzle material was polybenzimidazole resin, which is difficult for aluminum particles to attach to nozzle walls.

Nozzle geometry has a profound effect on HVOF spraying, influencing combustion gas dynamics as well as particle behavior. Nozzle dimensions are also important in cold gas-dynamic spraying (CGDS), particularly the length of the nozzle which affects gas flow temperature and speed. In this study, numerical simulations and experiments were conducted to determine how the length of the entrance convergent section of gun nozzles affects HVOF spraying. Process changes that occur inside the nozzle (as predicted by simulation) were correlated with coating properties. An Al2O3-TiO2 powder was used for the experimental studies. Changes in nozzle length had a significant impact on deposition efficiency, microstructure, hardness, and particle velocity. These relationships (as measured and calculated) were then applied to the nozzle design for the CGDS method.

The rapid emergence of cold spray technology provides numerous applications that require spraying fine (<10 microns) powders, providing more uniform deposition, improved measurement of deposition efficiency and quick turn around time. The performance of high-pressure commercial powder feeders, currently available, lacks one or more of these desired performance characteristics. Further, researchers are interested in spraying many powders of different materials or particle size distributions where the powder feeder can be quickly and easily cleaned without replacing expensive consumables. The Ktech laboratory powder feeder has been designed to operate under a wide variety of carrier gas pressures (0 – 500 psig). This laboratory feeder delivers a continuous flow of powder, has a variable canister volume and is quick and easy to clean. This unique design facilitates short run research applications or higher volume extended run time dispensing. The feeder is designed to operate in either a locally or remotely through a PC based Ethernet connection. The laboratory powder feeder represents an excellent tool for high-pressure cold spray or low-pressure thermal spray processes requiring the delivery of fine powders.

In thermal spray, it is well established that tailoring the powder characteristics is of major importance to achieve reproducible coatings on a microstructural and chemical point of view. Among the techniques developed to produce thermal spray powders, spray drying has proved to be the most versatile process. The spray drying method consists in spraying a slurry containing finely dispersed particles of the materials to be agglomerated. However, in order to prepare specific thermal spray powders, two steps have to be mastered: the slurry stability and the spray drying operating conditions. The present study was focused on the relationships that exist between the slurry rheology, the powder morphology and the coating properties. This work was performed on a model material namely Al 2 O 3 . In a first part, the effects of the surfactant percentage and pH on the stability of the suspensions were determined. The evolution of the viscosity of the slurries versus the amount of binder was measured. In a second part, these slurries were used to prepare spray-dried powders. The effects of some process parameters such as atomizing air pressure and slurry feed rate on the granule characteristics (morphology, density, particle size distribution, and powder flow ability) were investigated. Finally, some coatings were deposited using the APS technique on steel substrates from the non-sintered spray-dried powder previously realized. The coating morphology and the crystallographic structure were evaluated as a function of the spraying conditions.

The present work has the purpose of comparing different thermal spraying techniques, namely axial plasma spray, standard air plasma spray and high velocity oxygen flame (HVOF), for depositing metal matrix composites, in this case chromium carbide nickel-chromium based. The quality of the coatings deposited by these three techniques has been assessed in terms of structural characteristics (porosity, oxide concentration, unmelted particles presence, etc.) and of mechanical characteristics (hardness, adhesion, etc.) as well as surface morphology. A specific efficiency test has been carried out to compare the three examined technologies. The results of the present study indicate that, against a slightly decrease in the quality of the film in terms of structural and mechanical properties, axial plasma sprayed coatings can be sprayed with a higher efficiency in comparison to the traditional technologies.

In the aerospace field as well as in the stationary gas turbine field, thermal sprayed coatings are used to improve the surface properties of Nickel-super-alloys materials. Coatings are commonly used as bond coat and antioxidation materials (mainly MCrAlY alloys) and as thermal barrier coatings (mainly Yttria partially stabilized Zirconia) In the present study, our purpose was to assess the properties of thermally sprayed bond coat CoNiCrAlY comparing the performance of three different techniques: Vacuum Plasma Spray (VPS), High Velocity Oxygen Flame (HVOF) and Axial Plasma Spray (AxPS). The quality of the deposited films has been assessed and compared from the point of view of structural (porosity, oxide concentration, unmelted particles presence) and mechanical characteristics (hardness, adhesion). Furthermore, a study of the surface composition and morphology has been carried out. Specific efficiency trial has been carried out to compare the efficiency of the three examined technologies. We observed that the highest quality films are obtained by VPS, but that also HVOF and AxPS sprayed films have interesting properties which can make their use interesting for some applications in view of the lower cost of HVOF and AxPS.

On-line monitoring of two thermal spray processes by means of an imaging diagnostic technique capable of measuring several spray particle properties, such as individual and average particle temperatures, velocities and number of particles with spatial distributions, was studied by using the Spray-Watch thermal spray monitor. Aim of the work was to demonstrate the capabilities of this novel monitor in quick optimisation of certain spray gun parameters to obtain desired particle characteristics in-flight, and hence desired coating structure and properties with high deposition efficiency. Examples are given in plasma spraying of Al 2 O 3 and HVOF spraying of NiCoCrAlY.

Development of new, low-cost methods for spraying near net shapes of Titanium and Titanium alloys is critical for many industries and applications. Direct fabrication technologies would have an impact on many industries because of the potential to quickly manufacture complex parts or additive features with minimal waste. However, currently used high temperature spray technologies (Lasform, thermal spray methods) involve melting and solidification. Each new layer starts out molten, then solidifies, and must eventually cool to room temperature. This report presents results of feasibility tests for development of a new method of direct fabrication of Ti alloy parts at near-net shapes (nns) using the Cold Spray process (CSP). Several Ti-6Al-4V powders including gas atomized, plasma atomized, and hydride dehydride were tested in these experiments. Feedstock powders were characterized for particle size distribution, morphology, chemical composition, hardness, and deposition efficiency. Coatings in thicknesses of 2 mm were sprayed for evaluation of microstructure, hardness, and porosity. Thick rectangular prisms (10 mm) were sprayed for machining tensile specimens. The material properties of as sprayed and post treated coatings by heat-treating and hot isostatic pressing (HIPing) on material properties was studied. Analysis showed that after HIPing the density of sprayed Ti-6Al-4V coupons is near 100% and material properties met or exceed those of wrought material.

Thermal spray coatings play an important role in the field of surface protection. Threats and opportunities in the thermal spray industry include TS process developments, impact of health and safety, standardization, pre/post treatments, non destructive evaluation of coating characteristics and environment. In this paper, the European thermal spray industry size is estimated. Examples of customer requirements from typical Original Equipment Manufacturers to industry end users are also discussed. The paper provides some views on the ability of a particular spray shop to compete and grow given the market conditions. In addition, it discusses internal benchmarks used by Terolab Services. Paper includes a German-language abstract.

Inside diameter (ID) spraying with a two-wire gun for thermal spraying has become an established practice. While the simplicity of the two-wire arc process is tempting, there is a marked difference between the coating microstructures obtained with standard two-wire arc and two-wire arc ID systems. In conventional two-wire arc spraying, the arc is partially surrounded by the nozzle, which leads to the fused tips being enveloped by the atomizing gas flow. In comparison, the right-angled arc is unprotected if the airflow hits the arc at 90 degree. In this paper, the particle formation process is investigated using diagnostic tools such as Laser Strobe Vision (Control Vision) and DPV2000. Although the data collected may not fully encompass the breadth of the phenomena associated with two-wire arc spraying, a comparison was made between the 0 degree and 90 degree spray processes. Paper includes a German-language abstract.

Meanwhile thermal spray shops may apply a comprehensive works of application and qualification standards, e.g. in the case of building up a spray shop, qualifying thermal spraying personnel, defining requirements for spraying constructions or parts and testing thermally sprayed coatings. High and reproducible quality of products and services are required by the customer. Concerning national and international competition, also pressure on prices by keeping high and reproducible quality of the sprayed coatings will be in store for spray companies. In the following, actual quality management and personnel qualifying standards are described, which are now available. Experiences of a certifying institution and a spray company made by installing a QM- System and certifying audit may serve to orientation for those who will aim at QM certification. Paper text in German.

Novel synthesis of thermal spray grade silicon carbide (SiC) feedstock powder is necessary to allow deposition of this material using atmospheric plasma spraying (APS) method. SiC particles with average size of 1.0 µm are treated using co-precipitation techniques to deliver yttrium aluminum garnet (YAG) binder from its solution precursor as a nano-film onto SiC particles surface. The YAG nano-film will protect SiC core from direct interaction with plasma jet thus hindering their decomposition as well as providing matrix phase within the SiC particles vicinities. The modified SiC particles are sintered and crushed and then sieved to separate 25-45 µm and 45-90 µm size powders, which are then plasma sprayed to deposit SiC coatings of about 300 µm in thickness. Both the feedstock and the coatings were analyzed and compared with regards to their phase composition and microstructures.

Coating technology is progressing at a steady rate with continuous significant improvements in the coatings performance. In the aerospace field, as well as in the stationary gas turbine field, coatings deposited by different processes (thermal spray, CVD, EBPVD) play an important role in order to increase the performances of the engines. In particular, in order to improve the resistance to oxidation and corrosion at high temperature, aluminium is deposited by several techniques (pack aluminising, above the pack and CVD) in alternative or addition to thermal spray coatings (mainly MCrAlY alloys where M stands for Co, Ni or CoNi). These MCrAlY coatings are generally deposited by Low Pressure Plasma Spray (LPPS) or Vacuum Plasma Spray (VPS), but also by High Velocity Oxygen Fuel (HVOF) and Air Plasma Spray (APS). This paper addresses the study of aluminium coatings deposited by CVD on CoNiCrAlY bond coats deposited by different processes: VPS with F4 gun, LPPS with EPI gun and HVOF. The aim is to verify if and how the different CoNiCrAlY coatings obtained by these three processes with different content of oxides and porosity could affect the deposition rate and quality of the Al coatings. The obtained samples have been characterized from the metallographic point of view in order to determine porosity, thickness and structure of both CoNiCrAlY and Al coatings. Al coating thickness has been taken as parameter in order to define the Al coating deposition rate on the three different CoNiCrAlY coatings. Further tests for the determination of aluminium content and chemical composition of the coatings are in progress.

Arc spraying is an economical method for applying metallic layers due to its high spray rates and uniform melting of spray particles. The main disadvantage is the difficulty in achieving sufficient particle velocity to ensure good layer adhesion. This study investigates the influence of nozzle geometry, arc power, and gas pressure on the size and velocity of particles in an arc spray jet. The experiments were conducted using particle image velocimetry (PIV) to measure the spatial and velocity distribution of particles in flight. For X45Cr13 steel, particle velocities were found to be between 85 and 95 m/s at a gas volume flow of around 1 m 3 /min. Velocities of up to 150 m/s were ultimately achieved, but at the expense of higher atomizer gas consumption. Paper text in German.

Thermal spraying for joining and filling of aluminum substrates under atmospheric conditions represents an enrichment in soldering technology. In a respective process, rod-, wire- or cored wire type, zinc-aluminum-based spray materials are applied for joining components or area filling of substrate and fused simultaneously. The advantages, in contrast to soldering, result from the direct application of the spray material, in particular also in constraint positions, and an uncomplex processing, which enables a conditioned inline capability and the use as a comparatively simple procedure for construction-site services or repairs. The aluminum substrate surface and spray material passivation, which would prevent a successful fusing, can be effectively suppressed by the use of a flux in the cored wires as well as straight on the substrates or a brushing activation.

This paper describes the influence of post-spray heat treatment parameters on mechanical properties of Ni-TiC composite coatings. Thin Ni-TiC composite coatings were produced by low pressure cold gas dynamic process (also referred as cold spray or kinetic spray process) on an Inconel alloy substrate. In the coating process, mechanically mixed micron-sized Ni-TiC powders (~50 µm) were injected into a de-Laval nozzle propelled by a supersonic gas stream to high velocity (>300 m/s) to impinge upon a substrate. The coatings are formed subsequently as the metallic particles are severely deformed plastically and bonded to both the substrate and to one another. However the tensile adhesion strength levels were determined to be in the range of 10-14 MPa. A subsequent post-spray heat treatment in vacuum was found to enhance the bond strength of the coated particles with the substrate due to good metallurgical bonding caused by diffusion mechanism.

Thermal spray of Zn, Zn/Al, or Al is extensively used to make anticorrosion coatings on steel structures. Twin arc spray and wire flame spray are the two most practised processes to achieve such coatings. This paper presents measurements of particle emissions generated by these two processes. Sampling and analysis of aerosols generated by both processes have been carried out inside the exhaust ductwork using various instruments: an ELPI impactor, a CNC (Condensation Nucleus Counter), a TEOM microbalance and sampling filters allowing sampling for SEM observations. Electric arc spraying produced much more fumes of ultra fine particles than flame spraying. Aluminum spraying also produces large fume quantities compared to the Zn spraying under the same conditions. The aerosol comprised submicron particles and 95% of the numerical particle size distribution was less than 100 nm. The nanometric nature of the fume particles was confirmed by observations on the SEM. The strong dilution caused by compressed air has the effect of strongly limiting particle coagulation and, in turn, the size of the agglomerated particles. Electric arc spray has taken market share versus wire flame spray for Zn, ZnAl, or Al spraying, but this study shows that it generates much more particle emissions.

This paper will outline the results of a study underway at Utah State University aimed at developing technology to alter the direction and profile of thermal spray flows using the Coanda effect. Coanda-assisted Spray Manipulation (CSM) makes use of an enhanced Coanda effect on axisymmetric geometries through the interaction of a high volume primary jet flowing through the center of a collar and a secondary high-momentum jet parallel to the first and adjacent to the convex collar. The control jet attaches to the convex wall and vectors according to Coanda effect principles, entraining and vectoring the primary jet, resulting in controllable r - θ directional spraying. The basic turning effect was investigated in a fundamental experimental study. The results of the fundamental study were applied to the design of an add-on CSM attached to a Metco 2P powder flame spray gun.