This paper provides a summary of conventional thermal spray powder feeders, examines the influence of carrier gas flow, powder tube diameter, powder tube type, and gas flow path on the feed precision and continuity of pressure-type powder feeders, and discusses the cause of pulsation associated with the injection of super fine ceramic powders.

This paper discusses the basic design and operating characteristics of a precision heavy-duty thermal spray turntable. The system incorporates eccentricity and speed control and accommodates working pieces up to 100 mm in diameter and 2000 mm in height weighing as much as 1500 kg. Site tests, as reported in the paper, indicate that the turntable also meets dust and heat tolerance requirements.

Results of macro- and microhardness investigations of newly developed coatings are presented in this paper. The coatings were produced with flame- and arc spraying technique. The coating structure and hardness is significantly influenced by the spraying method and spraying parameters. It will be shown that properties for flame sprayed coatings are more effected by parameter variations than for arc sprayed coatings. A higher hardness, a greater density and a better particle cohesion can be obtained by using the arc spraying method.

Microscopic fracture mechanisms of thermal spray coatings under bending stress are investigated. Samples of thermally sprayed coatings were made using three distances. The sprayed powder was pure molybdenum. Vertical microcracks occur in lamellae and subsequently, these cracks join together and form vertical macrocracks in the samples sprayed with a short spraying distance. On the other hand, horizontal microcracks occur at the lamellae interfaces, and these cracks link together in the samples sprayed with a long spraying distance. These tendencies can be explained in terms of the hardness of the lamella and the bonding strength between each lamella. It is clarified that the bonding strength between each lamella corresponds to the applied strain at the point of rapid increase of the acoustic emission (AE) event. The amplitude and rate of AE beyond the point of rapid increase are high in the coatings which formed macrocracks. It is concluded that the coating which has high resistance to crack formation has a high point of AE increase, low AE amplitude and low AE increasing rate.

Cold spray additive manufacturing (CSAM) is an emerging process that has garnered significant attention from researchers due to its unique advantages. These include higher deposition rates, no need for a protective atmosphere, and the ability to connect or combine dissimilar materials. While CSAM allows for near-net-shape fabrication of workpieces, the accuracy and properties of the final products often fall short of user requirements. Furthermore, there is an urgent need to develop a generalized manufacturing strategy for workpieces with complex geometries. It appears that integrating various processes throughout the entire manufacturing workflow, from design to delivery, could address these challenges. However, few researchers have explored this area. To fill this gap, this study presents an integrated modular CSAM system designed for efficient and flexible workpiece fabrication. The system comprises two main components: software for modeling and simulation, and hardware for precise fabrication, each containing multiple modules. These modules do not operate independently but are coupled through direct or indirect decentralized and event-driven physical links. The system described in this paper offers a generalized strategy for precision manufacturing of workpieces using CSAM, potentially advancing the field and addressing current limitations in accuracy and versatility.

The Fraunhofer Institute for Material and Beam Technology IWS in Dresden has developed “Lightblast,” a laser ablation technology for creating clean, structured surfaces. Lasers offer precision, reproducibility, cost-effectiveness, and environmental friendliness, opening new possibilities in surface treatment. Traditional blasting processes employ compressed air to propel abrasive particles at high speed onto a substrate. This method often results in embedded abrasive particles, surface contamination, and rapid abrasive wear, compromising process consistency. Additionally, the abrasive waste poses environmental and disposal challenges. Lightblast utilizes a continuous wave single-mode laser and a dynamic galvanometer scanner to precisely vaporize the substrate without abrasives. Adjustable parameters control the resulting surface roughness with high reproducibility. Unlike pulsed laser ablation, the continuous wave laser enables higher productivity due to increased power. Furthermore, Lightblast allows for selective surface structuring based on CAD designs without additional masking. Target applications include surface preparation for coating, bonding, and joining processes.

Although increasing the thickness of thermal barrier coating (TBC) enhances its thermal protection capability, it generally decreases its thermal shock durability. This is caused by an increase of thermal stress due to the increase of the temperature differential between the TBC surface and the metal surface. In order to realize the optimum TBC thickness, the thermal shock durability of TBC should be evaluated precisely and quantitatively. This study focused on two advanced techniques to evaluate the durability of TBC that were developed through joint research with the National Institute for Materials Science (NIMS). The first technique utilizes a new acoustic emission (AE) measurement system called continuous wave memory (CWM), which can analyze AE events more precisely than conventional AE systems. The second technique is a noncontact strain measurement method using laser speckles, which can measure the strain on the TBC surface at high temperature. These techniques were combined with a laser thermal cycle test to establish the “𝜖H-N diagram”, which shows the relationships between the hot shock strain 𝜖H in the laser thermal cycle test and the cycle number N to failure for different TBC thicknesses. In these experiments, CWM was used to determine the TBC failure more precisely, while the laser speckle method was used to measure the thermal shock strain 𝜖H. The obtained 𝜖H-N diagram revealed the durability of TBC for various thicknesses and was transformed to an evaluation map to predict the TBC thickness limitation. For real parts, this evaluation map is useful to estimate if a thicker TBC will fail or not by comparing the maximum strain it is predicted to undergo by numerical analysis.

The deformation behavior of particles plays a significant role in achieving adhesion during cold spray. The deformation behavior of the particles is associated with the fracture of the oxide layer and recrystallization, which are the key elements of the quality of cold spray. Studies of particle compression have been made to understand the deformation behavior of a particle. However, the deformation behavior of particle under controlled load and precise and high strain rate is yet to be studied. Here, we show the oxide layer fracture pattern and recrystallization regime under controlled load with a precise and high strain rate. We found that the cracks in the oxide layer initially appeared on the equator of the particle and propagated towards the edge of the top surface. Meanwhile, on the top surface, the circumferential crack was developed. On the other hand, the nanoindentation result showed that the compressed particle under a high strain rate has an unusual load-displacement behavior. Our results demonstrate that the oxide layer fracture behavior corresponds to the adhesion mechanism suggested by previous studies. Our study also revealed that recrystallization takes place within the particle under a high strain rate. We anticipate this finding to give a general insight into the deformation behavior of particles during cold spray. For instance, since the recrystallization behavior at a given strain rate can be predicted through this study, the resultant grain size and shape, which is associated with mechanical properties, can also be predicted. Furthermore, the amount of strain and strain rate to form optimal adhesion can be evaluated.

High-pressure die casting (HPDC) is a well-established manufacturing process used in the automotive sector to make high-precision components. The necessity to reduce fuel consumption increases the use of low-density components in the automotive industry. Corrosion induced by molten metal is one of many failure modes for dies, changing the die's geometry and surface roughness. All combined wear changes the dimensional precision of the manufactured parts but also the surface quality of the components. Many additive deposition methods are applied to decrease wear and recover the surface. Thermally sprayed coatings can improve the surface properties and recover the geometry of the die caused by the aluminum attack. The main objective of this work is to observe the behavior of the H13, Cr3C2-25NiCr, and WC10Co4Cr coatings deposited by HVOF and HVAF, tested against Aluminum corrosion and Die-soldering tests. After dissolution, the chromium carbide reacts with the aluminum, creating a tough intermetallic interface, and raising the extraction tensile stress. After Aluminum corrosion tests, it was observed that the WC 10Co 4Cr HVAF coating presented low adhesion to the aluminum with no observed coating failure due to the formation of intermetallic. Die soldering tests indicated that the WC 10Co 4Cr protects the substrate, resulting in lower extraction tensile stress than H13 base material and other HVOF coatings. It was possible to observe that WC 10Co 4Cr HVAF coating showed results comparable to AlCrN PVD coating.

Metallization of plastics by thermal spraying is studied. The possibility to obtain high adhesion of metal particles to the surface of a wide range of plastic materials is shown. Powders are sprayed with a new generation detonation gun “Dragon” designed at Lavrentyev Institute of Hydrodynamics SB RAS. The apparatus is characterized by a high-precision gas supply system and a dosed localized powder feeding system. Computer control provides a flexible programmed readjustment of the detonation gases energy impact on powder particles which is a key factor in precision control of spraying parameters for low-melting point powder materials. It is found that under certain spraying conditions molten particles of a low-melting point material not only do not provoke erosion of plastic material at their high velocity impact on the substrate but strong-bond fusion, sufficient to further form a thick coating, occurs. Aluminium, zinc and tin powders are sprayed on substrates from fibreglass, polyester, fluoroplastic and some other plastics. Load capacity of the obtained coatings reaches 100 kg/cm 2 . It is shown that on top of a thin layer from a low-melting point powder material high-melting point metals and even ceramics can be deposited.

This study employs a three-dimensional simulation to investigate the cold gas dynamic manufacturing process. During the buildup of the desired object, sharp edges, stagnation points, and corners are likely to form that can influence the trajectories of the particles. This leads to dispersion and lack of particle deposition in these areas, which can eventually reduce the precision and efficiency of the build process. A cylindrical and frustum-shaped object are numerically simulated on a substrate to represent typical additively manufactured parts. Particle trajectories and impact conditions with and without these objects are compared. The results provide useful information for understanding the limitations and challenges associated with cold gas dynamic manufacturing, which can help improve the quality and precision of the process.

Metal and polymer additive manufacturing is advancing on several applications. On the other hand, materials cermet such as WC/Co for functional structure molding by additive manufacturing are under studying. There are few reports for WC cemented carbide additive manufacturing process by forming with polymer binder then sintering. This indirect process has difficulties to make high precision functional parts due to shape control during additional sintering process. Direct forming is desired for high precision parts. However, factors and/or mechanism to achieve direct formed functional structure have been unclear in many aspects. In this study, the process conditions of the direct selective laser melting were investigated to achieve dense and hard WC cemented carbide mold parts. The optimization of laser melting conditions for WC/Co agglomerated and sintered powder was examined. In order to forming a dense and high hardness parts, the optimum conditions between powder preparation and laser energy density which related with laser power, scan speed and spot diameter were appeared by this experiments. Moldings more than 1500HV are achieved at low laser energy density. However, some of pores were observed in moldings. In addition, the dense molding could be obtained by high laser energy density. This means optimum dense functional WC cemented carbide molding is available by optimization of the molding condition. It is applicable for growing industries like automotive, aviation and cutting tool.

Anilox rolls are used as metering rolls in the flexographic printing process, delivering a precise quantity of ink to the plate roll (which contains the image to be printed). Anilox rolls are high precision parts with respect to their dimensional tolerances as well as to the engraved structures. The latter can nowadays be either very coarse in conjunction with a high volume of ink to be transferred or rather fine showing cell diameter of 20 µm, cell walls below 3 µm in thickness and cell depth of only 6 µm and below. Moreover, the market needs for high quality printing will lead more and more to the outer limits of these ranges, which can be matched only by tailoring the coating properties, as well as the interaction of the laser radiation with the sprayed surface. Besides the needs for extreme screen counts in conjunction with requirements of certain volumes of liquid to be transferred, new types of surfaces are needed to meet these requirements and providing a wear resistant coating and concurrent an easy to clean surface. Therefore this paper will give a review of the interaction of the laser with a thermally sprayed surface focussing on the main laser parameters, different coating materials, the application of sealants as well as the type of engravings with respect to the achievable screen counts and transferrable ink volumes.

The trend in thermal spraying is more and more towards a globally uniform level of high-grade spray coatings. It is therefore extremely important that auxiliaries such as spray materials or industrial gases undergo precise examination in order to exactly define their influence. Based on their application, these auxiliary materials can always be supplied at the required purity level. In order to guarantee such high levels, the gas industry invests a great deal in analysis and supply concepts which ensure this purity from the tank or cylinder through to the point of delivery. A further point is of particular significance in today’s business world. With ever-increasing raw material prices, it is absolutely essential that spray processes are optimized to the maximum. This is not only made possible by selecting the right system, but also by choosing the right gas and gas mixture.

Directed light fabrication (DLF) is a rapid fabrication process that fuses gas delivered metal powders within a focal zone of a laser beam to produce fully dense, near-net shape, 3D metal components from a computer generated solid model. Computer controls dictate the metal deposition pathways, and no preforms or molds are required to generate complex sample geometries with accurate and precise tolerances. The DLF technique offers unique advantages over conventional thermomechanical processes or thermal spray processes in that many labor and equipment intensive steps can be avoided to produce components with fully dense microstructures. Moreover, owing to the flexibility in power distributions of lasers, a variety of materials have been processed, ranging from aluminum alloys to tungsten, and including intermetallics such as M05Si3. Since DLF processing offers unique capabilities and advantages for the rapid fabrication of complex metal components, an examination of the microstructural development hhas been performed in order to define and optimize the processed materials. Solidification studies of DLF processing have demonstrated that a continuous liquid/solid interface is maintained while achieving high constant cooling rates that can be varied between 10 to 10 5 Ks-1 and solidification growth rates ranging up to 10-2 ms-1.

Although it is widely used prior to the spraying stage to eliminate the surface contaminants and to improve the splat contact with substrate, a preheating operation should be precisely controlled to keep the metallic substrate away from an excessive oxidation. In most cases, the oxide scale can deteriorate the interface adhesion. A nanosecond pulsed laser treatment is a powerful tool to remove the surface oxide layers. It is also the fundamental principle of the PROTAL process that combines a laser surface preparation and the thermal spraying process. In this paper, a nanosecond pulsed laser was used to remove the thermally induced oxide while keeping the advantage of preheating. It is shown that the particle splashing was suppressed and the deposit adhesion was significantly improved resulting from the laser cleaning effects. The mechanism of oxide removal is also investigated.

In this investigation, the concepts of fracture mechanics are put to use to determine the adhesion strength of WC-Co coatings on metal substrates. The paper explains how test samples are produced and describes the procedures used to obtain fracture mechanics data. Adhesion strength is determined based on local energy release rates (crack closure integral method) and is verified using a finite element model of the test sample. With this approach, the spraying parameters for WC-Co can be more precisely tuned than would be possible with a frontal pull test. Paper text in German.

Advanced spraying technologies as High Pressure-HVOF Spraying or Cold Gas Spraying as well as new concepts for the next generation of plasma sprayed TBC's demanding spray powders with strongly decreased powder grain sizes (< 15µm or even less). Although, with decreasing powder grain size the flowability of the powder is also decreased, causing finally problems in the transport of powder. Within this paper a new powder feeder design will be presented, that makes the precise feeding of ultrafine powders possible, even through feeding lines several meters in length. All known powder feeders for thermal spraying use the pneumatic convey for powder transport through the feeding line. In opposite, the new developed powder feeder is using the dense phase convey of powders. The powder transport can be compared with the transport of a liquid in an hydraulic system. The new powder feeder shows no restrictions in the flowability of a powder. The feeding of normal spray powders (carbides, oxides, metals) as well as submicron powders were successfully tested. Feeding rates from several grams per hour to hundred kilogram and more per hour can be realised, depending on the design of the system. The transport through feeding lines longer than 10 meters also causes no difficulties. The system is self-cleaning and there are no mechanical parts in contact with the powder.

In cold gas spraying, successful bonding occurs when particle impact velocities exceed the critical velocity. The critical velocity formula depends on material properties and temperature upon impact, relying mainly on tabulated data of bulk material. However, rapid solidification of powder particles during gas atomization can result in strengths up to twice that of bulk materials, causing an underestimation of the critical velocity. Thus, a re-adjustment of the semi-empirical calibration constants could supply a more accurate prediction of the requested spray conditions for bonding. Using copper and aluminum as examples, experimentally determined particle strengths for various particle sizes were 43% and 81% higher than those of the corresponding soft bulk materials. Cold gas spraying was performed over a wide range of parameter sets, achieving deposition efficiencies ranging from 2% to 98%. Deposition efficiencies were plotted as functions of particle impact velocities and temperatures, as calculated by a fluid dynamic approach. By using deposition efficiencies of 50%, the critical velocities of the different powders and the corresponding semi-empirical constants were determined. Based on particle strengths, the results reveal slight material-dependent differences in the mechanical pre-factor. This allows for a more precise description of individual influences by particle strengths on critical velocities and thus coating properties. Nevertheless, the general description of the critical velocity based on bulk data with generalized empirical constants still proves to be a good approximation for predicting required parameter sets or interpreting achieved coating properties.

The Ti-6Al-4V alloy is widely used in aerospace applications for its excellent mechanical properties, however, it presents low wear resistance. It is often coated with a cermet using high-velocity oxy-fuel (HVOF) spraying to improve its wear performance. The Cr3C2-NiCr cermet becomes particularly interesting since it is non-carcinogenic, compared to traditional cermet coatings containing tungsten-cobalt compounds. While the improvement in wear resistance of Ti-6Al-4V with this coating has been demonstrated, its impact on the fatigue performance of the alloy remains to be studied. This is precisely the aim of this study, which focuses on the fatigue life of a Cr3C2-25NiCr-coated Ti-6Al-4V alloy. Among the various influencing factors, surface preparation represents a significant source of crack initiation, particularly in the case of sandblasted surfaces. Indeed, the inclusion of fragmented alumina particles can produce stress concentration zones. Thus, laser texturing, which is a method involving the creation of anchoring points through controlled ablation, can be considered today as a less harmful surface preparation technique. The results obtained from cyclic tensile fatigue tests with a stress ratio of 0.1 for these two surface preparation methods are presented in this paper.