Vacuum kinetic spray (VKS) technology was employed to fabricate AlN films. In order to investigate the relationship between the deposition behavior with change of the size and microstructure of feedstock, AlN powders were pre-treated through ball-milling and heat-treatment. It is observed that the particle size decreased and defect density increased after the ball-milling. After the heat-treatment of the ball-milled powder, on the other hand, the particle size was not changed significantly, while the defect density was reduced by recovery. The coatings of ball-milled and heat-treated powder were obviously thicker than that of only ball-milled powder. It is inferred that, during the heat-treatment, although the defects were reduced by recovery, the dislocations were aligned, through which the cracks were able to propagate more easily. By the combined effects of ball-milling and heat-treatment, more fragmentations with new surfaces of the particles were generated during VKS, which would improve the deposition efficiency. Therefore, in VKS process, the deposition behavior is shown to be affected by not only particle size, but also the defect density and microstructure of the feedstock powder.

Pure Al coatings were fabricated on Cu substrates via kinetic spraying for double-layered Cu liner. The coatings need to endure the high strain rate severe plastic deformation during explosion, in this study, the process optimization of Al deposition was initiated with a definition of “critical velocity” of Al particle in kinetic spraying on a basis of numerical modeling and computations using ABAQUS finite element codes. The simulation results revealed that the critical velocity of Al particle at room temperature (RT) was 780 m s -1 , and the critical velocity decreased as particle temperature increased. On the basis of simulation results, mechanical properties such as bond strength of the coatings formed under various process conditions were evaluated and compared. These properties were discussed in terms of the processing-structure-property relationships.

The new kinetic spray coating technique, vacuum kinetic spray (aerosol deposition), utilizes the pressure gap between powder hopper and coating chamber which is vacuumed. In this study, to investigate the deposition mechanisms present in the vacuum kinetic spray coatings, α-Al 2 O 3 and glass were chosen as the powder and substrate materials, respectively, and these were considered as the reference materials to examine the effect of free surfaces after particle fractures. Based on the finite-element modeling (using an AUTODYN-2D 12.1), single particle impacts were simulated, and the results elucidated the material shape, temperature variation and mass change of particle due to its fracture during impact. The plots of total mass change as a function of particle impact velocity demonstrate the deposition-optimized velocity zone (DOVZ) for successful deposition. Compared to as-received powders, from the transmission electron microscope (TEM) images, the defects such as dislocations of the ball-milled powders might increase the tendency of the powder particles to fracture upon impact. The cross-section images of the coating showed that the particle sizes of the coating were drastically decreased compared to those of initial powders. During coating, fractured particles enlarged the thermodynamically unstable free surface area and have a tendency of formation of bonding.

This study compares the deposition behavior of kinetic sprayed bronze-diamond composite coatings produced using different mixtures of helium and nitrogen gas. To determine impact properties of the diamond particles, bare and nickel-coated diamonds are deposited on bronze layers and the effects of plastic deformation are examined using SEM and finite-element analysis. The results indicate that the deposition efficiency of diamond is determined by several factors and depends more on the angle and shape of the diamond particles than on the deformation properties of the bronze matrix.

In the present investigation, thermally enhanced kinetic spraying of titanium onto mild steel substrates is carried out in conjunction with powder preheating to obtain a dense coating using low-cost nitrogen as the process gas. Prior to this, a prototype model was developed for process optimization based on numerically approximated adhesion factors. The simulation results show that adiabatic shear instability accelerated by thermal energy and subsequent particle impact leads to the formation of an enhanced thermal boost-up zone that closely correlates with deposition behavior and coating properties. It is thus shown that the deposition efficiency of titanium can be more than 90% and porosity less than 1% when nitrogen gas is used for cold spraying.

This study assesses the potential of kinetic-spray coatings for dealing with the effects of soldering and erosion on aluminum casting dies. In the experiments, molybdenum-boride cermet and cobalt-based alloy powders are cold sprayed onto SKD61 substrates. Coating microstructure is assessed via SEM and XRD analysis and several mechanical properties are measured. In order to evaluate soldering resistance, the coatings are immersed in a molten aluminum bath. Although cold-sprayed CoCrNiWC exhibited high coating density and low porosity, its soldering resistance was significantly lower than that of MoB-NiCr. The boride cermet coating not only exhibited superior soldering resistance, but also higher hardness, bond strength, and wear resistance. However, its deposition efficiency needs further improvement.

Manufacturing of diamond abrasive wheel has been achieved through kinetic spraying in order to simplify the manufacturing process and improve the mechanical properties. However, size of the initial feedstock diamond particles is reduced by fracturing during the process. Uniform distribution of diamond particles in the coating layer is significantly important for obtaining grinding properties of diamond abrasive wheel. In this study, optimized nickel thin film which is coated around the surface of diamond particle was used to prevent the fracture of diamond particles during spraying and improve the properties. Thickness of the nickel thin film was optimized by ABAQUS 6.7-2 finite element analysis software as 3 µm for 20 µm diamond and bronze particles. Fraction and size distribution of the diamond particles present in the coating were analyzed through Scanning Electron Microscope (SEM) and Image analyzer methods.

In this work, effect of substrate roughness on the deposition behavior of the particles through kinetic spray technology is studied. Finite element analysis program, ABAQUS 6.7-2 was used to estimate the results. Particle impact on the planar and roughened substrates were analyzed and compared. Interface temperature, contact area and contact time were found to be higher for the particle impact on roughened surfaces than that of the planar one for constant spray condition. These factors are significant for bonding mechanism. Experiments were performed on the polished and grit blasted surfaces in order to compare the results. The deposition efficiency and the bond strength values were used to evaluate the effect of surface roughness.

In this study, individual particle impact behaviors of soft particle on hard substrate were observed. The ratio of bonds was compared to the difference between adhesion and rebound energies. To improve the existing model, the equation for effective yield strength was modified and finite element analysis was applied to estimate the temperature and strain gradients. The energy difference was derived from the strain and temperature of the elements and compared to the experimental ratio of bonds.

In this study, three kinds of engineering metals, which are aluminum (1100-H12), commercially pure titanium and mild steel were combined as particle/substrate and classified into four cases, i.e., soft/soft, hard/hard, hard/soft and soft/hard, according to their physical and mechanical properties respectively. Based on finite element modeling, impacting interface elements of four cases were analyzed and impact behaviors were numerically characterized. For soft/soft and hard/hard cases, the maximum temperature at the substrate side, which approached melting point, is higher than that of particle side when the shear instabilities occur. In particular, the different size of thermal boost-up zone was numerically estimated and theoretically discussed for these two cases. Meanwhile, for soft/hard and hard/soft cases, the specific aspect of shear instability, which has very high heat-up rate, was always observed at the relatively soft impact counterpart, and a thin molten layer was expected as well. Thus, the successful bonding of the above mentioned four cases can be predicted as a result of the synergistic effect of localized shear instability with interfacial melting.