The thermal spray industry identified the need for repeatable and reproducible feedstock powder characterization methods, especially particle size distribution (PSD), for cost effective manufacturing of thermal barrier coatings. The PSD measurement by a laser light scattering method was identified as the technique most widely used in the industry. This technique offers high resolution, rapid measurements and ease of use. A round robin study by nine laboratories using different models of a commercial light scattering instrument has been completed as the first step towards the development of a Standard Reference Material (SRM) for the calibration of light scattering instrument. Other measurement techniques were also employed for additional comparison. The PSD measurements employing light scattering techniques evidenced some method dependence, despite the use of identical sample preparation procedures. The round robin results will serve as reference values for the development of the SRM.

Two copper powders were deposited with CGT3000 cold gas dynamic spray system on aluminium substrates. The X-ray diffraction patterns allow the characterisation of the microstructure such as grain size, strain in the coating and dislocation densities. Both powders and coatings have been fully characterised. Three methods have been used to interpret the X-ray patterns: the Warren-Averbach method, the Hall Williamson method and the modified Hall-Williamson method. A comparison between the state of the powders before and after deposition will give an insight on the metallurgical processes that take place during the formation of the coating. The influence of the grain size distribution will also be discussed. This article is a follow up of the publication done at ITSC2006: “Comparison Between Coatings from two Different Copper Powders: Mechanical Properties, Hardness and Bond Strength”.

This study evaluates a method for producing carbon fiber composite feedstocks suitable for cold gas spraying. Powders consisting of Al-Si particles and carbon nanofibers were attrition milled at 16.5 Hz and 27.5 Hz for up to 12 h at room and cryogenic temperature. Particle shape and size were examined every hour and carbon fiber integration in the Al-Si matrix was assessed. Detailed results are presented and discussed. In all cases, cryomilled powders had smoother surfaces.

Surface quality lifetime and wear resistance of protective coatings can be improved by decreasing carbide grain size from submicron to nanoscale. In this study, experimental WC-CoCr powders were manufactured via novel powder manufacturing approach using water-soluble raw materials. Produced powders were sprayed with the High-Velocity Air-Fuel (HVAF) spray process to control the particle temperature and to avoid in-flight decomposition of the nanocarbides. As a result, dense and wear resistant coatings with nanosized carbides were produced. Reference coatings were sprayed using commercial sub-micron WC-CoCr powder to compare the properties of the experimental coatings to the current state-of-the-art. Phase composition and microstructural characterization of the coatings were carried out with X-ray diffraction and electron microscopy, respectively. Mechanical properties were studied by using microhardness tester, as well as rubber wheel abrasion and cavitation erosion wear tests. The wear surfaces were characterized after the abrasion and cavitation erosion tests to understand the effect of nano-carbides on degradation mechanisms. Coatings with the nanosized carbides in the structure showed excellent mechanical properties in wear testing, and even outperformed reference coatings in cavitation erosion test. Based on the obtained results, these novel nano-carbide coatings are promising alternatives for demanding applications in which better surface quality lifetime is vital.

The use of HVOF to produce surface coatings is much known. However, the spraying of inner parts or using it to reproduce a mold form is not always easy due to the high bonding strength of HVOF coatings. On the other hand, plasma formed parts are being used in the aerospatial industry for many years partly because the ease of the releasing process. Using the experience and the method developed in the CPT some years ago, some new materials have been sprayed to obtain thick axy-symmetrical self-standing forms. The process involves mechanical removal method and for these reason, the mould can be used several times with minimal maintenance. Amongst the releasing methods, the more simple is mechanical but it could turn out to be complex if the adhesion by impingement takes place too strongly. Hence, the impingement of the material is studied in this work. The materials are mechanical blends of WC-Co with Co-based alloys. However, prior to spraying, the most suitable material is chosen for a concrete purpose. The work includes a study of the spraying parameters in the structure and the properties of the coatings. XRD, SEM-EDS, roughness, microhardness, ASTM G 99-90 and ASTM G 65-91 wear test are performed to characterize the samples.

A novel powder modification method based on the simultaneous softening and agglomeration of steel powders via heat treatment in a rotary tube furnace has been investigated as a means to improve the cold sprayability of H13 tool steel powder. By adjusting starting powder size and shape as well as heat treatment conditions (maximum temperature, cooling rate, and atmosphere), cold spray of H13 powder went from virtually no deposition to the production of thick dense deposits with a deposition efficiency of 70%. Powder agglomeration, surface state, microstructure evolution, and softening are identified as key factors determining powder deposition efficiency and resulting deposit microstructure.

In this paper, the production of NiCr-TiC powder by SHS, suitable for HVOF spraying, is discussed together with results on the microstructure and coating properties. Compacts for SHS were prepared by mixing elemental Ti and C with pre-alloyed Ni-20wt.% Cr powder to give an overall composition of 35wt.% NiCr and 65wt.% TiC. These were then ignited and a self-sustaining reaction proceeded to completion. Reacted compacts were crushed, sieved, and classified to give feedstock powders in size ranges of 10-45 µm and 45-75 µm. All powder was characterized prior to spraying based on particle size distribution, x-ray diffraction (XRD), and scanning electron microscopy (SEM/EDS). Thermal spraying was performed using both H2 and C3H6 as fuel gases in a UTP/Miller Thermal HVOF system. The resulting coatings were characterized by SEM and XRD analysis, and the microstructures correlated with powder size and spray conditions. Abrasive wear was determined by a modified 'dry sand rubber wheel' (DSRW) test and wear rates were measured. It has been found that wear rates comparable to those of HVOF sprayed WC-17wt% Co coatings can be achieved.

For the last few years, the HVAF process has been established as a commercially used process and has gained an increasing share in the market of thermal spraying. The main thermal spray materials being used for HVAF spraying have been those based on the tungsten carbide family. Economical aspects and European regulations on chemicals management REACH (Registration, Evaluation and Authorisation of Chemicals) have motivated the demand for thinner WC based coatings, which are still dense and wear resistant. This demand has progressively increased, and the trend shows a further growth in the need for thermal spray feedstock for HVAF sprayed net shape coatings. The challenge for powder producers lies in providing suitable spray powders, with high and consistent quality as well as in considerable volume, to be able to make reliable recommendations to the users of HVAF technology. A deeper understanding of powder requirements for net shape coatings, matching the needs with new powder solutions, and appreciation of the differences in behavior or performance depending on powder type are essential to address the above challenges and constitutes the theme of this paper.

Cold Spray is a solid-state Additive Manufacturing process of 3D near-net-shape parts which requires the implementation of a good spraying strategy and the choice of the right operating parameters. This paper is the result of empirical studies on the determination of the optimal processing conditions (spraying and kinematics) for the Cold Spray Additive Manufacturing (CSAM) of pure aluminum powder using a stable layers building strategy. Vertical 3D deposits (thick walls) with a height and thickness of 13-100 mm and 5-11 mm, respectively, were obtained through a series of tests that consider an effect of some kinematic parameters. The visual analysis of the deposits shows that the nozzle traverse speed as well as middle/edge pass number ratio constitute the two most influential parameters on the final shape of the deposits (flatness and straightness). All these results prove the potential of the Cold Spray Additive Manufacturing (CSAM) process as fast 3D additive method using micron sized powders, and particularly for Al powder.

The paper deals with an analysis of particle behavior in a HVOF-jet as a function of process parameters. The experiments were carried out using a commercial HVOF gun with hydrogen as fuel gas. A commercial 316 L stainless steel powder was used for spray material. The experiments were conducted by using on-line particle diagnostics in order to simultaneously detect particle velocity, temperature and diameter. The results were correlated with caught spray powder and splats. The experiments released that among many parameters the oxygen/fuel gas ratio is the most important parameter. It was found, that fragmentation of partially melted particles in a supersonic jet is not a neglectable phenomenon. It may cause excessive oxidation inflight and therefore is to be avoided in the production of oxygen-poor coatings. Furthermore, it was found that velocity or temperature measurements of particles have to be interpreted very carefully in order to characterize the process. Without taking a possible change of the particle size due to inflight fragmentation into consideration either measurement value will lead to very limited information benefit.

Segregating the convoluted effects of particle size, impact temperature and velocity on deposition behavior and adhesion is of utmost interest to the cold spray field. The current study aims to associate the particle impact behavior and adhesion to its in-flight characteristics by studying and decoupling the influence of particle size, temperature and velocity for single particle impacts and full coatings. Experimental results reveal that in-situ peening processes contribute to the adhesion at low impact temperature while particle velocity controls the adhesion/cohesion at increased particle impact temperatures. The benefits of both bonding mechanisms are discussed in terms of measured adhesion/cohesion, bend-to-break fracture surfaces, pseudoplasticity, deposition efficiency and critical velocity. Computational fluid dynamics (CFD) results provide individual particle trajectory, size, temperature and velocity, of successfully deposited particles, which have led to the observed signs of metallurgical bonding.

WC-Co powders with nano-sized WC were deposited by dynamic powder deposition process. Microstructural characterization and phase analysis of feedstock powders with different compositions and as-deposited coatings with various substrates were carried out by SEM and XRD. The results show that there is no detrimental phase transformation and/or decarburization of WC by dynamic powder deposition. It is also observed that nano-sized WC in the feedstock powder is maintained in the deposited coatings. It is demonstrated that it is possible to fabricate the nano-structured WC-Co coatings with low porosity and very high hardness by dynamic powder deposition.

The Sulzer Metco Triplex II gun marks a new generation of three cathode plasma guns. In opposition to conventional single cathode guns, it features a stationary plasma jet. Liquid precursors, wire- and powder shaped spray materials were processed with a modified Triplex II gun under controlled atmosphere and characteristics of the obtained coatings were investigated. A new shroud system was developed to handle susceptible to oxidation and reactive materials such as Ti and B 4 C. A conception of a wire conveyance system enables the handling of three wires of titanium simultaneously. Furthermore a liquid spray material feed system, for the generation of Al 2 O 3 -coating with low porosity based on nanoparticle suspensions, was developed and built. All coatings, which were manufactured by the different procedures, are characterized comprehensively by means of optical microscopy (OM) including interactive image analysis, scanning electron microscopy (SEM) with attached electron dispersive X-ray analysis (EDX) system, X-ray diffraction (XRD) and microhardness.

In this work, HVOF sprayed hard metal multi-component Cr 3 C 2 -25Ni+10 vol-% solid lubricant coatings were prepared by HVOF spraying. CaF 2 , BN, MnS and WS 2 were used as solid lubricants. Powders were prepared by the spray drying and sintering method. This method produces homogeneous and spherical powders. Powders were sprayed with DJH 2600 HVOF-system. Microstructures, phase structures and compositions of powders and coatings were analysed with optical microscope, scanning electron microscope with EDS-analysator and x-ray diffractometer. The particle size distributions of sintered powders were determined by laser diffractometer. The amount of retained solid lubricant in the sprayed coatings was evaluated by EDS and compared to that in the spray powder. This study showed that spray drying and sintering method is a preferable method for manufacturing multi-component solid lubricant containing thermal spray powders. In sintering processes, solid lubricant phases remained in powders except for the Cr 3 C 2 -25Ni+10vol-%WS 2 -powder. Also, after HVOF spraying, coatings contained solid lubricants.

In this work, the bonding mechanism between Cu particle and substrates of Mg, Cu and stainless Steel (SS) was investigated by the direct observation of bonding interface on detached particle and substrate crater. In the cases of Cu/Cu and Cu/SS, dimple-like fractures were found on the detached Cu particle and substrate crater for the first time. Accompanying with EDS line scan and mapping results, such dimple fractures can be considered as the signs of strong metallurgical bonding. However, the bonding interface in case of Cu/Mg is smooth without signs of metallurgical bonding. Finite element analysis results revealed a ring of high contact pressure zone on the surface of particle and substrate, which is exactly the place where metallurgical bonding was observed. It can suggest that the high contact pressure zone is the dominant factor for the formation of metallurgical bonding on the oxide-free interface. The evolution of maximum contact pressure in different cases shows that the substrate hardness plays an important role during the single particle bonding. The present study provides a profound insight into the bonding mechanism of a single cold sprayed particle, which can give the guidance to the full deposition of cold sprayed coating.

In conventional powder processing, there has been considerable work on classifying feedstock powders based on particle size distribution, morphology, microstructure and composition, since these influence processability and final properties. Cold spray is a new application for powders and conventional characterization may be insufficient to assess powder cold sprayability. In particular, metallic powders have an oxide layer, which breaks during impact with the substrate or with another coating layer during cold spray; this fragmentation facilitates bonding. It has been suggested that the thickness of the oxide layer can influence the mechanism of fragmentation; thicker oxides are easier to remove, revealing clean metal surfaces that can metallurgically bond. Consequently, not all high-purity powders or powders that are stored in ambient conditions have the potential to give good coating properties after cold-spray. This work focuses on surface oxidation of the powders, characterizing the variation of oxide film aspects with size and composition of nominally pure copper powders using X-ray Photoelectron Spectroscopy (XPS). The results indicate the presence of Cu (I) and Cu (II) oxide species on the surface of as-received, naturally aged and heat-treated powders; their thickness is determined using the depth profiling feature.

Thermal spraying (APS and HVOF) of an agglomerated nanostructured powder, based on the composition of a commercial martensitic steel, is introduced. The nanostructure of the produced powder is examined by means of microscopy and X-ray diffraction. The influence of the two different processes on crucial properties such as porosity, microhardness, adhesion, and wear resistance is studied. High wear resistance is noted for both coatings. The HVOF coating, especially, showed better wear performance in comparison with the APS coating and the bulk martensitic steel. The superiority of the HVOF coating over the APS coating regarding the aforementioned properties is attributed to a higher retention of the nanostructure of the starting powder, higher peening and relatively low oxidation.

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 .

Different Ti-6Al-4V feedstock powders (i.e., plasma atomized, gas atomized and hydride de-hydride) and corresponding cold spray depositions were characterized using electron back scatter diffraction and X ray diffraction. In addition, a low temperature heat treatment was applied to the coatings and characterized using the above techniques to understand the microstructural evolution after annealing. XRD did not show BCC phase in the three powders and coatings. The axial ratio for all the powders and coatings were similar to what has been reported for Ti-6Al-4V. Atomized powders and hydride dehydride (HDH) powders were characterized by α' microstructure, and equiaxed α phase microstructure, respectively. Phase maps for HDH powders revealed β phase microstructure distributed around equiaxed α grains. Microstructural evolution during cold spray deposition resulted in the atomized coatings retaining as-received powder microstructure at particle interiors and formation of nanograins near the interface. On the other hand, HDH coatings were characterized by slightly deformed as-received powder microstructure with no evidence for nanograin formation. Higher average grain size of HDH powders resulted in the higher percentage of low angle grain boundaries observed after cold spray deposition. Subsequent heat treatment resulted in recovery, some recrystallization and grain growth for all the coatings. Nonetheless, the extent to which this took place was higher for atomized cold sprayed coatings.

In high-pressure cold spray, the enthalpy of the particle carrier gas has a significant effect on the propellant gas conditions and ultimately on particle impact velocities and temperatures. Through modelling and experimentation, the current work demonstrates that in low-pressure cold spray, the particle carrier gas enthalpy has a minimal effect on the particle velocity and is rather limited to affecting the particle impact temperature. Consequently, particle impact temperature can be controlled independently from impact velocity. This is a valuable tool when dealing with temperature sensitive substrates: low propellant temperatures can be used in combination with high particle temperatures enabling particle deformation while minimizing substrate heat input. Particle preheating was used to inject pure aluminum particles in a commercial low-pressure cold spray to temperatures up to 500°C. This was accomplished without clogging because of the development of a novel particle preheater, which eliminated the particles exposure to hot metal surfaces. Even after substantial spray time, no evidence of wear or clogging was found. The particle preheating resulted in a deposition efficiency increase of 3.6 times when compared to the injection of room temperature particles.