Titanium porous transport layers (PTL) are important components in proton exchange membrane water electrolysis (PEMWE) cells. The performance enhancement and the reduction of manufacturing cost of PTLs are of importance for market expansion of PEMWE. Vacuum plasma spraying (VPS) was used to prepare PTL or modify PTL of sintered titanium powders and the PTLs by VPS showed a high performance. Regarding the cost efficiency, it is of great interest to produce PTLs using more economical spray processes than VPS. In this study, high velocity oxy-fuel spraying (HVOF) was used to produce highly porous titanium coatings for this purpose. The spray process was developed to achieve a high porosity of up to Φ = 30 % using three titanium powders with size distributions of fA = -90 +45 μm, fB = -63 +20 μm and fc = -45 +11 μm. The coating structures were examined on the cross sections of the titanium coatings with scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The porosity was determined using the image analysis system ImageJ. The deposition efficiency of the titanium powder fC = -45 +11 μm was determined. The results show that the coating structure significantly depends on the titanium powders. Highly porous titanium coatings of Φ = 24 - 40 % can be produced with the titanium powders of fB = -63 +20 μm and fc = -45 +11 μm. Titanium oxides are hardly visible on the cross-sections of the titanium coatings. A high deposition efficiency of approximately DP ≈ 70 % was measured for the titanium powder of fc = -45 +11 μm.

The aim of this work is to study the effects of the titanium plasma spray (TPS) coating process on the fatigue resistance of a titanium-6Al-4V substrate. The combination of TPS processes and Ti alloy substrate is widely applied on components intended for cementless total hip replacement (THR). In order to understand the coating process mechanism behind the implants’ fatigue resistance decrease, one air-developed coating (Ti-APS) and one controlled atmosphere developed coating (Ti-CAPS) were considered. The effects of the most representative parameters of the plasma spray process on the fatigue resistance were analysed: the sandblasting process, the plasma and the coating powder. Fatigue resistance studies were performed by means of rotating bending fatigue testing. After fatigue failure specimens underwent morphological analyses both on the primary crack surface and on the cross-sectional area complemented by of the metallographic analyses of the coating. The titanium substrate fatigue resistance decreased after being blasted with direct relationship with the grain size. Ti-CAPS process showed a relatively limited further influence on the fatigue resistance reduction with respect to only sandblasted samples. By contrary a remarkable fatigue limit decreased was seen for Ti-APS coated samples against Ti-CAPS and simply sandblasted samples. The experiment pointed out the critical importance of cracks oxidation as a fatigue failure driving factor.

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.

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.

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.

This paper describes a process that has been developed for producing thick composite coatings with friction and wear properties that were once only achievable in diamond-like carbon (DLC) films. The process is based on cold spraying and the use of surface modified metallic powders. In this investigation, two such powders were prepared by placing either copper or titanium particles on a negatively biased stainless steel tray and then coating them with a DLC film by pulse plasma chemical vapor deposition. The powders are then cold sprayed onto aluminum plates, creating metal-matrix composite coatings. The thickness of the Cu-DLC composite coating is 250 µm and that of the Ti-DLC coating is 435 µm. In each case, the presence of dispersed DLC in the metal matrix was verified by Raman spectroscopy. Sliding wear tests were also conducted, revealing that the Cu-DLC composite has a lower coefficient of friction than copper film, while the Ti-DLC composite has lower specific wear rate than titanium film.

The fracture toughness of pure Al, Cu, Ni, and Ti deposited by cold spraying was investigated to gain a better understanding of the damage process and quantify material performance. Rectangular specimens of self-standing deposits with fatigue pre-cracks were tested in three-point bending. KIC values were obtained from J-R curves and stress-strain curves were plotted. The cold-sprayed deposits exhibited significantly lower fracture toughness than the same wrought materials, and fractographic analysis revealed either ductile or cleavage intergranular fracture as the major failure mode.

The work concerns a study of the properties of cold sprayed Ti coatings. This material is an attractive choice for many applications because it exhibits high strength-to-weight ratios, very good oxidation resistance, corrosion resistance and biocompatibility. Cold spraying is applied to deposit Ti coatings and elements as additive manufacturing process, however it needs higher critical velocity for deposition than other, more ductile metals. Nowadays nitrogen as cheap gas is used as working gas in cold spray process, however application helium as accelerating gas allows to obtain elements with higher strength. It allows to understand the mechanism of cohesion between sprayed particles. In carried out experiment Ti powder with angular shape was applied in the cold spraying process. The coatings were sprayed by means of Impact Innovations 5/8 system with nitrogen and addition of helium onto 7075 Al alloy. The investigations revealed that the cold sprayed Ti coatings with addition of helium as working gas exhibit better mechanical properties, lower porosity and roughness.

Commercial available Ni and Ti powder were blended together and deposited on stainless steel by atmospheric plasma spray(APS). Subsequently the as-sprayed coatings were laser remelted with a Nd -YAG pulsed laser source. Cross-sections of as-sprayed and laser-remelted coatings were characterized by scanning electron microscopy (SEM). Prior to SEM observations, the laser remelted coatings were polished and etched by Kroll etchant. Meanwhile, the energy dispersive spectrometer (EDS) was employed to analyze the chemical distribution of the coating both as-sprayed and laser remelted. The results indicated that APS sprayed NiTi coatings presented a dense microstructure with Ni splats and Ti splats distributing uniformly. Oxygen partial pressure in the argon leads to the burning of Ti splats during the laser remelting process. And Ti oxides located at the bottom of the laser molten pool because of the laser stiffness and molten flow. Moreover, the top part of the molten pool mainly involved in Ni columnar grains.

High quality coatings of titanium can be obtained by cold spraying using high process gas temperatures and pressures. However, the performance of cold sprayed coatings is determined not only by the respective material properties and the impact conditions, but also by the temperature and properties of the substrate—including the already deposited— material. In the present study, cold spray of spherical titanium grade II powders was performed on titanium grade II, copper, and stainless steel substrates, using two sets of parameters and three different substrate temperatures. Single impacts and respective particle adhesion were investigated using wipe tests followed by a modified cavitation test. Higher bond strengths were achieved for substrates that were held at higher temperatures during spraying. Moreover, the electrical conductivity of coating, taken as a measure of particle-particle bonding quality within the coating, improved and the porosity decreased for increased substrate temperatures. The findings are discussed in view of the thermal conditions, as well as the mechanical response of the uppermost layer of the substrate/deposit set.

This study investigates the development of fatigue failure in steel specimens coated by various spraying methods with and without grit blasting. Commercial titanium powder was deposited on structural steel substrates by low-pressure and portable cold spray as well as plasma and warm spray. Coating samples were subjected to strain-controlled cyclic bending, while monitoring resonant frequency as a measure of accumulated damage. A change in frequency of 4 Hz was chosen as the test-stop with the corresponding cycle count serving as the main indicator of fatigue life. Test results are presented in the paper along with explanations of fatigue mechanisms and process-related factors.

In this present work, investigators determine how particle temperature, combustion pressure, and heat treatment affect the porosity, oxide content, and tensile properties of warm-sprayed titanium. Coatings were deposited with nitrogen flow rates ranging from 0.5 to 1.5 m 3 /min and combustion pressures of 1 and 4 MPa. Optimal coating properties were found for specimens formed at a nitrogen flow rate of 0.75 m 3 /min and a combustion pressure of 4 MPa. Post-spray heat treatment was found to improve bonding between deposited particles, significantly increasing the strength and ductility of the titanium coatings.

Aluminum-titanium powder mixtures were deposited on γ-TiAl alloy substrates by cold spraying then heat treated for 5 h at 600, 650, and 700 °C. SEM and XRD examination showed that the treatment caused Al to diffuse into the substrate where it reacted with Ti, resulting in changes in microstructure. The diffusion of Al left pores in the fringes of the TiAl 3 phase, increasing the porosity of the coatings. A surplus of Al remained in the coatings after heat treatment at 600-650 °C, but at 700 °C, all Al was consumed, contributing to the formation of a continuous TiAl 3 layer.

In the present study, spherical Ti-6Al-4V powders were cold sprayed on titanium, aluminum, and magnesium alloy substrates to investigate influences over a wide range of damping conditions and respective deceleration of impacting particles. Single impacts were produced via wipe tests and bonding was evaluated by cavitation testing followed by SEM examination of impact and fracture morphologies. The results show that better bonding is achieved for material combinations with similar properties due to high adiabatic shear instabilities that result in microfusion at the particle-substrate interface. In the case of dissimilar materials, the conditions for bonding can be reached in an intermediate stage, but bonded areas may later separate due to particle movement around the interface.

In this study, the dust explosion properties of aluminum, titanium, zinc, and iron based alloy powders were evaluated by JIS Z 8818: “Test method for minimum explosible concentration of combustible dusts,” IEC 61241-2-3 (1994-09) Section 3: “Method for determining minimum ignition energy in dust-air mixtures,” and JIS Z 8817: “Test method for explosion pressure and rate of pressure rise of combustible dusts.” The test are described and the results are presented and discussed.

A new high-pressure warm spray gun was designed with the aim of increasing particle velocities to 1000 m/s for 30 µm Ti particle at 1000 °C or below. Nozzle geometry and combustion chamber pressure were optimized based on one-dimensional simulations. The flow rate of nitrogen gas injected into a mixing chamber was determined by calculation. The fuel injector was developed experimentally, its geometry optimized to spay small well-diffused droplets of kerosene into a 4 MPa chamber.

This study investigates the effects of gas composition on cold-sprayed titanium coatings deposited under nine different spray conditions. Experiments show that higher levels of gas purity translate to higher particle velocities and measurable improvements in bending strength. The influence of gas temperature, pressure, and chemical composition is considered in the study along with interactions between carrier gases and sprayed particles. In addition to bending strength, the resulting coatings are assessed in terms of porosity and oxygen content.

In this study, finite element analysis and experimental observation are used to evaluate the effect of substrate hardness and spray angle on the deposition of cold-sprayed Ti particles. It is found, in the case of Cu substrates, that both the particle and substrate deform during impact, resulting in a large contact area. Metallurgical bonding is highly likely under such conditions, facilitating formation of thick coatings. In the case of Al substrates, although the contact area is smaller, Ti particles are trapped by the softer substrate material, resulting in mechanical interlocking and a relatively thick coating. In the case of stainless steel substrates, mechanical interlocking does not occur due to the relative hardness of the material, which limits coating thickness. The results of the study also show that decreasing the spray angle reduces interfacial contact area and coating thickness, while increasing porosity.

Thick titanium coatings were prepared by warm spraying (WS) and cold spraying (CS) process to investigate the oxidation and microstructure of the coating layers. Prior to the coating formations, the temperature and velocity of in-flight titanium powder particle were numerically calculated. Significant oxidation occurred in WS process using higher gas temperature conditions with low nitrogen flow rate, which is mixed to the flame jet of an HVOF spray gun in order to control the temperature of the propellant gas. Oxidation, however, decreased strikingly as the nitrogen flow rate increased. In CS process using nitrogen or helium as a propellant gas, little oxidation was observed. Although most of the cross-sections of the coating layers prepared by conventional mechanical polishing looked dense, coating cross sections prepared by an ion-milling method revealed the actual microstructures containing small pores and unbounded interfaces between deposited particles. Even when scanning electron microscopy or x-ray diffraction method did not detect oxides in the coating layers by WS using high nitrogen flow rate or CS using helium, the inert gas fusion method revealed minor increase of oxygen content below 0.3 wt%.

Fundamental properties of Titanium coating prepared by low temperature HVOF process aided by injection of water had been published by our research group. The results showed that low temperature HVOF process provided as a good means for the deposition of comparatively dense Ti coating, however the interconnected pores observed in Ti coating degraded corrosion resistance of Ti coating, therefore it was necessary to manufacture denser Ti coating. Two processes were respectively applied for the densification of Ti coating. One process was to perform post heat treatment for as-sprayed Ti coating with conventional Ti powder as feedstock. The other process was to modify thermal spray powder. Ti powder mixing with spherical glass powder was used to deposit denser Ti coating as a result of shot peening effect of hard glass powder. Finally the corrosion resistance for densified Ti coatings was evaluated by electrochemical characterization.