Spattering is an unavoidable phenomenon in the selective laser melting (SLM) process, which can cause various printing defects and harmful powder recycling. Since the size of powder spattering is too small at the micron level, it is difficult to investigate the entire dynamic spattering process experimentally. The comprehensive understanding of the intricate dynamics of powder spattering during the SLM process remains incomplete. Therefore, we develop a new multiphase flow model to study the transient dynamic behaviors of the gas phase and powder spattering, which agrees well with the experimental observation result. It is the first time that the whole transient dynamic process of powder motion from starting to move induced by the vapor jet to falling to the substrate wall and stopping completely was observed. Powder spattering motion dynamics induced by metal vapor jet and argon gas flow, as a function of time, laser parameters, and location, are presented. The moving speed, total amount, and dropping distribution on the substrate of powder spattering that varies with laser parameters are quantified.

This paper investigates the oxidation that occurs during the flight movement of a powder particle and during the spatter solidification in the thermal spray process. The effects of oxidation on droplet flattening, on the mechanical and thermal interactions between spatter and substrate, on spatter morphology, on porosity, and on adhesion are studied. The influence of wetting and oxygen dissolution is analyzed. The experimental results show that during High Velocity Oxy-Fuel spraying of the chromium carbide-nickel-chromium powder, the relative mass of chromium oxide in the coating is about 4.95%. The theoretical results agree well with the experimental observations. Paper includes a German-language abstract.

In this paper, the processes as well as the first results regarding the economic efficiency and plasma fuel properties of nanostructured zirconium oxide powder particles are explained. The paper evaluates values for porosity, hardness, roughness, and crystallite size. In addition, both the morphology of the powder particles and the spatter are analyzed by SEM, and cross sections of the coatings are observed using optical microscopy. These results are compared to coatings made from a commercially available yttria stabilized zirconia powder. Paper includes a German-language abstract.

This paper presents an investigation of the influence of the spray angle on thermally sprayed coatings. Spray beads were manufactured with different spray angles between 90° and 20° by means of atmospheric plasma spraying (APS) on heat-treated mild steel (1.0503). WC-12Co and Cr 3 C 2 -10(Ni20Cr) powders were employed as feedstock materials. The spray beads were characterized by a Gaussian fit. This opens the opportunity to analyse the influence of the spray angle on coating properties. Furthermore, metallographic studies of the surface roughness, the porosity, the hardness and the morphology were carried out and the deposition efficiency as well as the tensile strength were measured. The thermally sprayed coatings show a clear dependence on the spray angle. A decrease in spray angle changes the thickness, the width and the form of the spray beads. The coatings become rougher and their quality decreases. In addition, the spray process becomes inefficient as the deposition efficiency declines. Especially, below 30° for Cr 3 C 2 -10(Ni20Cr) and below 50° for WC-12Co a significant change in microstructure was observed.

Thermal spray coatings produced from hard materials show good potential for extending the service life of sheet metal forming tools. However, post-process methods currently used to improve coating surface quality are slow and expensive, especially on complex surfaces. A novel approach, demonstrated in this study, is the optimization of thermally sprayed coatings by roller burnishing. This process shows a high potential to not only reduce surface roughness and porosity, but also increase hardness even on free-formed surfaces. In the experiments, atmospheric plasma-sprayed CrC-NiCr coatings were produced and the burnishing process was performed on a CNC milling machine. Both the spraying and surface finishing processes are described and the results are presented and discussed.

In this work, a 2D axisymmetric model of gas atomization at unsteady state that accounts for break-up and solidification is used to simulate laser melting of gas atomized powder. With an optimal nozzle width of 0.6-1 mm and a nozzle angle of 30-32°, the yield of fine 15-45 μm stainless steel powder, suitable for selective laser melting, is shown to increase from 20% to 35%. The effect of laser power on the melting channel width, microstructure, and mechanical properties of the sample is also investigated.

Alumina and yttria coatings, manufactured by suspension plasma spraying, were investigated to understand the “material effect” in the coating building. Some particle image velocimetry measurements were carried out to evaluate the particle velocities into the plasma. Some particle collections were performed to get information on their molten state. Splats were observed by scanning electron microscopy (SEM) and their dimensions were measured with an interferometric profilometer. Coating cross sections were finally observed by SEM and porosity rates were evaluated by image analysis and ultra-small angle X-scattering. This study revealed no real difference between the two materials concerning particle velocity. However, splat analyses highlighted a better flattening ratio for yttria particles, due to a lower difficulty to melt of this material. This property seems to enhance particle vaporization whose condensates are found on coating surface. These observations explain the difference of pore size distributions observed for both coatings.

Since many years, aluminum alloys are established as lightweight construction materials. To reach a partial wear protection for aluminum components in conjunction with seal faces, inlays, made of wear resistant materials, are commonly used. Problems concerning this approach are the necessary space and the endurance strength of the inlay - part joint. New process equipment offers the potential to control the energy input into the substrate and so the formation of brittle intermetallic phases in the aluminum-steel interface as well as the thermal stresses. The usage of new nano crystalline solidifying wear resistant iron-based feedstock materials with advantageous physical and mechanical properties enables further applications beside the wear protection of surfaces, for example as metallic heat insulation layer with a low heat conductivity, close to the values of ceramics.

Deep-drawing is a widely used sheet metal forming process in the aircraft and automotive industry. The manufacturing of modern parts with complicated shapes and curvatures requires forming tools with highest shape accuracy even at complex surface geometries. However, the application of novel, high-strength sheet metals combined with a continuous increase in productivity impose high tribological demands on forming tools and finally lead to increasing wear. In order to minimize the high costs for the repair and maintenance of such tools it is crucial to enhance their service life by an appropriate surface modification, which is able to preserve the high shape accuracy. Conventional coatings obtained by thermal spraying of coarse grained feedstock materials are not suitable to achieve this aim. In this collaborative study, the feeding and HVOF spraying of WC-Co submicron powders (- 8 + 1 µm) have been investigated to manufacture superfine structured, wear resistant near-net-shape coatings with improved macroscopic properties and smooth surfaces. Special equipment for the powder feeding and a novel HVOF flame spraying system designed by Thermico (optimized for the processing of fine-scaled powder fractions) have been employed. Correlations related to the process dynamics at varying HVOF gas compositions, the thermokinetic particle behavior in-flight and corresponding coating properties have been analyzed.

Copper splats are deposited on the flat stainless steel surface at the ambient and preheated conditions. The splashing occurs as the splats are deposited at an ambient atmosphere. The characteristics of the splashing occurring at different splat regions during spreading of the droplet are examined. The splashing can be classified into two types according to the splashing mechanisms. At the surrounding region of the splat larger than flattening ratio about 1.5 to 2, the radial splashing takes place by jetting-away of splat materials, which leads to the formation of a splat with a reduced diameter. At the central area of the reduced splat, the upward splashing occurs through the blowing up of the top surface layer which results from the high pressure of gas bubbles. At the preheated condition which can remove surface adsorbates, no evident splashing occurs under the normal spray conditions. Two types of splashing can be explained by the gases evolved through evaporation of the adsorbates resulting from the heating of the high temperature droplet. The spreading of the droplet involved in the wave urging flow is presented.

Stainless steel coatings were produced by supersonic air-gas plasma spraying method. Mixture of air and natural gas was used as a plasma forming gas. Powders of 304L and 316L stainless steels were used for plasma spraying. Thickness of coatings was up to 3 mm. Coating structure was studied. Dependence of oxygen content in coatings upon particle sizes and spraying conditions was established. Investigation of electrochemical properties of coatings was carried out by potentiostatic method. Corrosion potential and corrosion rate in sea water, hydrochloric and sulphuric acid solutions were determined.

In this study, high-emissivity NiCr oxide coatings, one with TiO 2 and one with TiB 2 compounds, were deposited on stainless steel substrates by spray granulation and atmospheric plasma spraying. The main phases in both coatings are NiTiO 3 , spinel (NiCr 2 O 4 ), and residual Cr 2 O 3 . The emissivity of the layer with TiO 2 was found to be higher in the 2.5-8 μm range than that of the layer with TiB 2 , which is attributed to higher surface roughness and larger particle size. These results indicate that the NiCr oxide coatings with TiO 2 compounds are more suitable for high-temperature IR applications.

Plasma spraying ZrB 2 ceramic coating is considered as potential candidate method of Thermal Protective System. While the application of plasma sprayed ZrB 2 coating is restricted due to its oxidation. Therefore, it is important to study the oxidation behavior of the ZrB 2 material. In this research, oxidation behavior of the ZrB 2 ceramic, which achieve different density by using SPS and pressureless sintering, is studied to explain the oxidation behavior of plasma spraying ZrB 2 ceramic coating. The oxidation behavior of ZrB 2 ceramics is investigated using SEM, XRD and EDS. The ZrB 2 –based ceramic coating is gravely oxidized at 600°C, but the block ZrB 2 –based ceramics also possess excellent oxidation resistance above 1000°C. The density of ZrB 2 ceramics significantly increase when changing the sintering method from pressureless sintering to SPS. The high density has beneficial effect to improve the oxidation resistance of ZrB 2 ceramic, for there are few open pores channel in high density ceramics. The oxygen cannot diffuse to the inner through pores, as a result, the high density ceramics can only be oxidized from outside to inside progressively, unlike low density ceramics, whose surface and inner is oxidized simultaneously.

This paper proposes a mathematical model for spatter formation at abnormal spray angles in thermal spraying. It is found that the splashes become elliptical when the spray angles are abnormal, and that the ellipse stretches the more the angle deviates from the perpendicular. The model was used to compare test results of the splash elongation at anomalous angles of impact. Paper includes a German-language abstract.

Since many years, aluminum alloys are established as lightweight construction materials. To reach a partial wear protection for aluminum components in conjunction with seal faces, inlays, made of wear resistant materials, are commonly used. Problems concerning this approach are the necessary space and the endurance strength of the inlay - part joint. In the following paper an alternative for the replacement of the inlays by cladding with an innovative and easy to handle short arc technology will be discussed. This technology offers the potential to control the energy input into the substrate and so the formation of brittle intermetallic phases in the aluminum-steel interface as well as the thermal stresses. The usage of new nano crystalline solidifying wear resistant iron-based feedstock materials with advantageous physical and mechanical properties enables further applications beside the wear protection of surfaces, for example as metallic heat insulation layer with a low heat conductivity, close to the values of ceramics.

This study assesses the potential of scandia-stabilized zirconia (ScSZ) produced by very low-pressure plasma spraying (VLPPS) for metal-supported solid oxide fuel cell (MS-SOFC) applications. To investigate the microstructure of ScSZ, coating samples were deposited at spraying distances of 150, 250, 350 mm. The fragile nature of coating cross-sections suggests that the typical lamellar structure of zirconia is replaced by a transgranular structure. Nonetheless, apparent porosity, ionic conductivity, open circuit voltage, and ohmic resistance measurements indicate that VLPPS is a viable method for producing MS-SOFCs.

This paper discusses some of the practical uses of laser cladding and laser fusing in part manufacturing and component repair. It provides an overview of both processes and the types of surfaces they can produce. It presents application examples for each process and interprets corrosion and wear properties of the respective coatings. It also discusses the benefits of repair friendly surfaces.

As it has been demonstrated that the use of the observation equipment applied on the spray process helps to gain a better coating in terms of properties, non-intrusive observation equipment (Control Vision Inc's SprayCam) is used in the current work for the observations of the jet and particles during the spray process. The application of such in-situ observation techniques concerns the field of cold spraying and brings new insights into the formation process of cold sprayed coatings. The build-up of coatings operated with different parameters (copper powder, nozzle, etc.) are recorded with an extreme short unit of time and then analyzed with the help of digital techniques such as image processing. The basic theories on cold spraying were previously verified by simulation and then compared to experimental results considering the distribution of flying particles involving in the build-up of the coating. The accumulation of data collected by in situ processing techniques during the spray allows understanding the complete steps of the coating formation consequently could bring the entire cold spraying mechanism to a higher level of research.

In the present study, surface engineering related to simultaneously thermally sprayed and laser melted corrosion resistant coatings has been carried out. A 6 kW high power diode laser or a Nd:YAG laser and a flame spray gun were used to construct the laser assisted thermal spraying system. The main aims of the study were to find out the optimal processing parameters and materials to create dense corrosion resistant coatings on steels. The corrosion resistance of the manufactured coatings was measured and the microstructure characterized using optical and scanning electron microscopy.

This paper examines an aluminum oxide coating plasma-sprayed onto a substrate made of high-quality stainless steel by means of light microscopy, X-ray diffractometry, and scanning and transmission electron microscopy (TEM). The aim is to determine the phases that form preferentially at the transition. It is observed that high amount of corundum phase was found in a plasma sprayed white alumina coating. XRD phase analysis of the coating indicated that all three major alumina phases were present: alpha-, gamma-, and delta-aluminum oxide. Further development in the field of TEM sample preparation is required in order to obtain larger electron-permeable surfaces, since it is not clear whether the alpha-aluminum oxide found at the transition is in the form of a spatter or a grain introduced by sandblasting. Paper includes a German-language abstract.