The average dynamic and thermal behaviour of electric arc sprayed Fe–0.8wt.%C droplets has been investigated using a laser based time of flight velocimeter system (Laser2Focus—L2F) and a two-colour ...pyrometry system (In-flight Particle Pyrometer—IPP) respectively. Radial and axial variations of the spray velocity and temperature have been investigated, together with their dependence on atomising gas type, arc voltage, atomising gas pressure, and wire feed rate. Under all conditions, the average spray temperature was significantly above the steel liquidus temperature indicating most droplets were fully molten. Once projected away from the region of atomisation, the droplet spray typically cooled at ∼1 °C mm
−1 and ∼10
5 °C s
−1 and typical axial velocities were 100 m s
−1. Because of asymmetry in the arc itself and the resulting differences in the melting behaviour of the wires, the spray exhibited asymmetric radial variations of both velocity and temperature about the spray cone axis. The presence of oxygen in the atomising gas had a significant effect in increasing spray temperature via exothermic oxidation of the steel droplets. Processing maps have been constructed in which the variation of average spray velocity and temperature with arc voltage, gas pressure and wire feed rate have been fitted to a series of simple polynomial expressions. These maps have been explained in terms of the heat and momentum transfer processes occurring during atomisation and subsequent droplet flight.
Impact of high velocity cold spray particles DYKHUIZEN, R. C; SMITH, M. F; GILMORE, D. L ...
Journal of thermal spray technology,
12/1999, Letnik:
8, Številka:
4
Journal Article
Recenzirano
This article presents experimental data and a computational model of the cold spray solid particle impact process. Copper particles impacting onto a polished stainless steel substrate were examined ...in this study. The high velocity impact causes significant plastic deformation of both the particle and the substrate, but no melting was observed. The plastic deformation exposes clean surfaces that, under the high impact pressures, result in significant bond strengths between the particle and substrate. Experimental measurements of the splat and crater sizes compare well with the numerical calculations. It was shown that the crater depth is significant and increases with impact velocity. However, the splat diameter is much less sensitive to the impact velocity. It was also shown that the geometric lengths of the splat and crater scale linearly with the diameter of the impacting particle. The results presented will allow a better understanding of the bonding process during cold spray.
A schematic representation referred to as “process maps” examines the role of process variables on the properties of plasma-sprayed coatings. Process maps have been developed for air plasma spraying ...of molybdenum. Experimental work was done to investigate the importance of such spray parameters as gun current, primary gas flow, auxiliary gas flow, and powder carrier gas flow. In-flight particle temperatures and velocities were measured and diameters estimated in various areas of the spray plume. Empirical models were developed relating the input parameters to the in-flight particle characteristics. Molybdenum splats and coatings were produced at three distinct process conditions identified from the first-order process map experiments. In addition, substrate surface temperature during deposition was treated as a variable. Within the tested range, modulus, hardness and thermal conductivity increases with particle velocity, while oxygen content and porosity decreases. Increasing substrate deposition temperature resulted in dramatic improvement in coating thermal conductivity and modulus, while simultaneously increasing coating oxide content. Indentation reveals improved fracture resistance for the coatings prepared at higher substrate temperature. Residual stress was significantly affected by substrate temperature, although not to a great extent by particle conditions within the investigated parameter range. Coatings prepared at high substrate temperature with high-energy particles suffered considerably less damage in a wear test. The mechanisms behind these changes are discussed within the context relational maps, which have been proposed.
Copper powder was sprayed by the cold gas-dynamic method. In-flight particle velocities were measured with a laser two-focus system as a function of process parameters such as gas temperature, gas ...pressure, and powder feed rate. Mean particle velocities were uniform in a relatively large volume within the plume and agreed with theoretical predictions. The presence of a substrate was found to have no significant effect on in-flight particle velocities prior to impact. Cold-spray deposition efficiencies were measured on aluminum substrates as a function of particle velocity and incident angle of the plume. Deposition efficiencies of up to 95% were achieved. The critical velocity for deposition was determined to be about 640 m/s for the system studied.
Cold spray, a new member of the thermal spray process family, can be used to prepare dense, thick metal coatings. It has tremendous potential as a spray-forming process. However, it is well known ...that significant cold work occurs during the cold spray deposition process. This cold work results in hard coatings but relatively brittle bulk deposits. This work investigates the mechanical properties of cold-sprayed aluminum and the effect of annealing on those properties. Cold spray coatings approximately 1 cm thick were prepared using three different feedstock powders: Valimet H-10; Valimet H-20; and Brodmann Flomaster. ASTM E8 tensile specimens were machined from these coatings and tested using standard tensile testing procedures. Each material was tested in two conditions: as-sprayed; and after a 300 DGC, 22 h air anneal. The as-sprayed material showed high ultimate strength and low ductility, with < 1% elongation. The annealed samples showed a reduction in ultimate strength but a dramatic increase in ductility, with up to 10% elongation. The annealed samples exhibited mechanical properties that were similar to those of wrought 1100 H14 aluminum. Microstructural examination and fractography clearly showed a change in fracture mechanism between the as-sprayed and annealed materials. These results indicate good potential for cold spray as a bulkforming process.
Oxidation in wire HVOF-sprayed steel NEISER, R. A; SMITH, M. F; DYKHUIZEN, R. C
Journal of thermal spray technology,
12/1998, Letnik:
7, Številka:
4
Journal Article
Recenzirano
It is widely held that most oxidation in thermally sprayed coatings occurs on the surface of the droplet after it has flattened. Evidence in this paper suggests that, for the conditions studied here, ...oxidation of the top surface of flattened droplets is not the dominant oxidation mechanism. In this study, a mild steel wire (AISI 1025) was sprayed using a high-velocity oxy-fuel (HVOF) torch onto copper and aluminum substrates. Ion milling and Auger spectroscopy were used to examine the distribution of oxides within individual splats. Conventional metallographic analysis was also used to study oxide distributions within coatings that were sprayed under the same conditions. An analytical model for oxidation of the exposed surface of a splat is presented. Based on literature data, the model assumes that diffusion of iron through a solid FeO layer is the rate limiting factor in forming the oxide on the top surface of a splat. An FeO layer only a few nanometers thick is predicted to form on the splat surface as it cools. However, experimental evidence shows that the oxide layers are typically box thicker than the predicted value. These thick oxide layers are not always observed on the top surface of a splat. Indeed, in some instances the oxide layer is on the bottom, and the metal is on the top. The observed oxide distributions are more consistently explained if most ofthe oxide forms before the droplets impact the substrate.
Electromagnetic calorimeter (ECAL) is being developed to complement dilepton spectrometer HADES. ECAL will enable the HADES FAIR experiment to measure data on neutral meson production in heavy ion ...collisions at the energy range of 2-10 AGeV on the beam of future accelerator SIS100 FAIR. We will report results of the last beam test with quasi-monoenergetic photons carried out in MAMI facility at Johannes Gutenberg Universitat Mainz.
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