Abstract The generation of a high velocity carrier gas flow for cold metal particle applications is addressed, with specific focus on titanium cold spraying. The high hardness of this material makes cold spraying titanium difficult to achieve by industry standard nozzles. The redesign of a commercial conical convergent-divergent cold spray nozzle is achieved by the application of aerospace design codes, based on the Method of Characteristics, towards producing a more isentropic expansion by contouring the nozzle walls. Steady three-dimensional RANS SST k-ω simulations of nitrogen are coupled two-way to particle parcel tracking in the Lagrangian frame of reference. The new contoured nozzle is found to produce higher particle velocities with greater radial spread, when operated at the same conditions/cost of operation as the commercial nozzle. These numerical results have shown the potential for extending cold spray to high density and low ductility particles by relatively minor rig modifications, through an effective synergy between gas dynamics and material science.

Abstract Pulsed plasma transferred arc surfacing is presently used in many industrial applications to make protective layers against corrosion, temperature exposition, and excessive wear. Increasing wear resistance is especially important in areas of industry where titanium alloys are used, such as aviation and cosmonautics, because the wear resistance of titanium alloys is often weak. One way to increase the wear resistance is to deposit or form a cermet with a titanium matrix (TMC) on the surface of the part. The present study deals with the fabrication and characterization of TMC based on B4C. TMC with B4C was formed by cofeeding Ti6Al4V and B4C powder into a melting pool. It has been found that the deposited, relatively thick layers have homogeneously dispersed B4C grains in the matrix. The deposits are metallurgically connected to the substrate - Ti6Al4V. The TMCs were investigated in terms of microstructure and chemical composition. Wear resistance was determined using the linear pin test.

Abstract Additive manufacturing processes have been used to produce or repair components in different industry sectors like aerospace, automotive, and biomedical. In these processes, a part can be built by either melted particles as in selective laser melting (SLM) or solid-state particles as in the cold spray process. The cold spray has gained significant attention due to its potential for high deposition rate and nearly zero oxidation. However, the main concern associated with using the cold spray is the level of porosity in as-fabricated samples, altering their mechanical properties. These pores are primarily found in the regions where adiabatic shear instability does not occur. It is worth noting that the deformation of the impacted solid particle plays a vital role in reaching the shear instability. Therefore, for investigating the adiabatic shear instability region, an elastic-plastic simulation approach has been used. For this purpose, it is assumed that an elevated temperature solid Ti6Al4V particle impacts on a stainless-steel substrate surface at high velocity. The results show that increasing particle temperature will significantly enhance particle deformation because of thermal softening. Additionally, they illustrate that a material jet responsible for producing a bonding between particle and substrate by ejecting the broken oxide layer will be formed when the particle has a temperature above 1073 K and substrate remains at room temperature. In the end, it should be noted that increasing particle temperature up to 723 K will not have a significant effect on substrate deformation and final substrate temperature.

Abstract This paper uses three types of gases (standard Air, nitrogen, and Ar) as atomization gas, and the arc spraying is carried out in air atmosphere. It examines the microstructure change according to the type of atomization gas and the influence of gas elements on crystalline structure of the titanium coatings by X-ray diffraction and quantitative analysis of nitrogen and oxygen contents in the coatings. The paper aims to research the influence of atomization gas on nitriding and oxidizing process of the titanium. Furthermore, with regard to Ar atomized coating, it investigates the change of crystalline structure with increase of spraying distance in order to research the effect of inert gas, Ar. An influence on the nitrogen content is determined. It turns out that TiN0.3 is formed due to the effect of alpha-titanium as a nitrogen-stabilizing element. Paper includes a German-language abstract.

Abstract With cold gas spraying, the particles of the spray powder are accelerated to speeds of over 500 m/s in a preheated gas jet. Due to the relatively low temperatures, the spray material does not melt in the gas jet, and the thermal load on the substrate is also low. This paper provides an overview of the state of the art of the system as well as layers and their properties. It shows a few examples of the applicability of the cold gas spray process. Various metals such as aluminum, copper, zinc, steel, nickel alloys, titanium, and niobium as well as powder mixtures and polymer powders have been sprayed onto a wide variety of substrate materials. The layers are examined metallographically and characterized. Possible applications are discussed on the basis of these results. Paper includes a German-language abstract.

Abstract Oxygen-free titanium coatings are at present produced using vacuum plasma spray systems. The cold spray process can produce titanium coatings in atmospheric air at reduced cost. Variations of the deposition efficiency as well as the coating characteristics with various process parameters were studied. Results show that the deposition efficiency drops drastically below a critical temperature. The parameters which affect the jet velocity; viz., the type of gas and the nozzle geometry have maximum effect on the process deposition efficiency. Sprayed coatings were porous and exhibited a low modulus and high hardness. Post processing of the coating by machining produced dense, strong and hard coatings. Key words: Cold-Spray, Titanium, Oxidation.

Abstract This paper compares two methods for determining the composition of Ti/TiN coatings deposited by reactive plasma spraying. The coatings were obtained by spraying titanium powder in a low-pressure N2/Ar atmosphere. The resulting film has a variable nitrogen content in the form of titanium nitrides, depending on gas partial pressure, total pressure, sample-source distance, and other parameters. The composition of the film was determined using X-ray diffraction and X-ray photoelectron spectroscopy. The two techniques provide similar results and either can be used for the compositional characterization of these coatings.

Abstract Two types of rutile and anatase powders are used for the deposition of TiO2 coatings. The effects of plasma spraying conditions on the structure of TiO2 coatings are investigated in order to clarify controlling factors of the phase formation and to aim at the development of effective photo-catalyst TiO2. It is found that the amount of anatase TiO2 in the coating is influenced by spray parameters. The decrease of the heat input to spray droplet and an increase in the cooling speed during droplet deposition will increase the amount of the anatase TiO2 in the coating. As a photo-catalyst, the coating deposited under limited plasma power and by HVOF spraying using anatase powder is effective for the decomposition of acetaldehyde gas.

Abstract Titanium carbide cermet spray powder was produced by the SHS process (Self-propagating High-temperature Synthesis) using elemental Ti, C, Mo and prealloyed CrNiMo powders as starting materials. The powder was characterised (particle size distribution, phase structure, morphology) and the internal structure of each cermet particle was found out to be dense consisting of fine distribution of carbides embedded in a metallic matrix. The particle size range suitable for thermal spraying was obtained by sieving and air classifying. The coatings were prepared by HVOF spraying (DJH2600 and DJH2700). The dry abrasion wear resistance was evaluated by the rubber wheel abrasion wear test and electrochemical corrosion behaviour by open circuit potential measurements. According to the XRD analysis the amount of retained carbides in the coatings is high and the carbide phase has a spherical shape also in the coatings. The microstructure of coatings obtained is dense and the coatings possess good properties in wear and corrosion tests. WC-Co-Cr and Cr3C2-NiCr powders were used for comparison.

Abstract 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.

Abstract Stoichiometric cordierite (2MgO-2Al2O3-5SiO2) with additions of titania have been investigated for use as coatings on low thermal expansion refractory concretes. These concretes have coefficients of thermal expansion on the order of 2 ppm/°C. Titania additions of up to 8 mole percent were investigated and the effect of titania in the crystallization of cordierite was examined. Cordierite coatings were air plasma sprayed and both glass and crystalline coatings were produced. The crystalline structure of the coating was found to be dependent upon the preheat temperature of the substrate. Preheats greater than 700 °C produced a mixture of a quartz solid solution and indialite whereas glass coatings were produced at preheats less than 700 °C. Coefficients of thermal expansion for the cordierite materials were dependent upon titania addition and generally increased with addition of titania. In the glass state, the thermal expansion was modestly increased (4.6 to 4.9 ppm/°C) with titania additions, but the quartz and indialite forms of the cordierite increased from 1.2 to 4.7 ppm/°C as the titania addition increased from 0 to 8 mole percent.

Abstract This paper presents a novel process that uses RF plasma spraying and premixed elemental powders to produce intermetallic matrix composites in situ without having to add reinforcement fibers or particles. Splats were collected on a stainless steel substrate and were analyzed to determine if nitrides had formed in metal droplets during flight and how it affected splat morphology. The typical splat morphology of impinged Ti droplets is disk-type with an outer peripheral fringe. Aluminum splats, on the other hand, are classified into two categories: a disk-type with an irregular outer periphery and a semi-massive-type. Other composites produced and examined include TiAl, AlN, and Ti2AlN.

Abstract A new plasma atomization process was developed for the production of spherical metal powders. This process, unique in its ability to produce large quantities of fine powders (< 75 µm), is especially interesting for value added products such as refractory or reactive metals/alloys powders. The excellent feeding characteristics of spherical powders make them ideal for applications such as injection molding and vacuum plasma spray (VPS) deposition. Powders are known to have a significant influence on the final characteristics of VPS deposited coatings. A variety of factors will control the coating quality, including: powder chemistry, morphology, microstructure, and feeding behaviour. This article includes a review of titanium coatings, and new results obtained using plasma atomized spherical powders.

Abstract Reactive Plasma Spraying (RPS) is one of several new plasma spray processes. Although several papers have been published on this technology, they are limited in scope to metal powders, such as Ti, Cr, and Si, and coatings composed of metal and non-oxide ceramics. When oxide powders are used among starting materials to fabricate metal or nonceramic coatings, it is important to understand and account for the reduction of oxides during spraying and the chemical reaction among the powder, plasma, and atmospheric gas. The work presented in this paper focuses on the reduction of plasma-sprayed TiO2 and how it is influenced by the amount and type of plasma and chamber gas used, the addition of carbon powder, and process parameters such as chamber pressure.

Abstract The poblems of metal-titanium carbide coatings processing by air, low pressure and underwater plasma as well as high velocity oxygen fuel spraying are under consideration. Among the different methods of metal-TiC powders production, like mixing of carbides with scale structure metals, agglomeration with binders, a matter of special interest is the high temperature synthesis of TiC in presence of metallic alloy. The characteristic features of these materials include the carbide phases forming, their bonding with the alloy and reactions during spraying, grain size and their distribution, alloy behavior during synthesis and spraying. Finally, the abrasive wear and erosion resistance of Al-Si/TiC, Fe-Cr/TiC and Ni-Cr/TiC coatings is analyzed.