Gyuyeol Bae

Dynamic amorphization and recrystallization of metals in kinetic spray process

We reported dynamic amorphization and recrystallization processes of metals upon impact of micron-scaled particles at a high strain rate (109s−1) combining adiabatic heating with rapid cooling (1010Ks−1) in a kinetic spray process. At the interface of the particle/substrate, an amorphous zone with a thickness of about 3nm was observed after individual particle impact. It is consistent with the mechanism of amorphous shear lamella and adiabatic shear instability characteristics in kinetic spray process. At the interface of coating/substrate, a rapid phase transition from unstable amorphous to crystalline helps the formation of ductile joints of coatings.

Effect of powder state on the deposition behaviour and coating development in kinetic spray process

In this work, smooth spherical and irregular granular copper powders were deposited on copper and aluminium substrates through the kinetic spray deposition process in order to find the effect of the feedstock powder state on the deformation process and the deposition behaviour. The effect of the initial state of powder on the coating properties was analysed through scanning electron microscopy, Vickers microhardness tester, electrical resistivity and bond strength characterizations. Simulation for two kinds of powders was performed through ABAQUS explicit 6.7-2 finite element analysis using a dynamic explicit procedure. Powder–substrate interface properties were estimated for two kinds of powders and discussed in order to compare the experimental results. It is found that the coatings produced from irregular granular powder have higher bonding properties.

Deposition Behavior and Microstructural Features of Vacuum Kinetic Sprayed Aluminum Nitride

The vacuum kinetic spray (VKS) method is a relatively advanced technology by which thin and dense ceramic coatings can be fabricated via the high-speed impact of submicron-sized particles at room temperature. However, the actual bonding mechanism associated with the VKS process has not yet been elucidated. In this study, AlN powders were pretreated through ball-milling and heat-treatment processes in order to investigate the effects of microstructural changes on the deposition behavior. It was found that ball-milled and heat-treated powder with polycrystals formed by partially aligned dislocations showed considerably higher deposition rates when compared to only ball-milled powder with tangled dislocations. Therefore, in the VKS process, the deposition behavior is shown to be affected by not only the particle size and defect density, but also the microstructure of the feedstock powder.

Phase separation in kinetic sprayed bulk metallic glasses

During a kinetic spray process, a high strain rate (~109?s?1) induced phase separation of amorphous metals at an impact interface was observed using high resolution transmission electron microscopy. The decrease in viscosity induced by the high strain rate deformation effect acted as the driving force for this process. The phase was further separated by jetting due to differences in the viscosity of the separated phases. The amorphous phase was sustained against nanocrystallization due to a fast quenching rate within the melting jet, even though the composition was separated far from the glass-forming region.

Restoration of face-centered cubic metals subjected to kinetic spraying

Deformation mode and restoration of face-centered cubic (FCC) metal (Al, Ni, and Cu) particles subjected to kinetic spraying (KS) were investigated. The FCC metal particles were accelerated to supersonic velocity by high pressure process gas, and collided with substrates or previously deposited coating layer. The high velocity impact of in-flight particles and their successive deposition leads to severe plastic deformation at ultra-high strain rate and the dissipation of heat energy from the plasticity. Accordingly, highly strained interface undergoes restoration to stabilize strained area during KS. Although Al, Ni, and Cu have equivalent slip systems {111} 〈110〉, the different physical and metallurgical properties of the FCC metals differentiate the deformation mode and lead to variations in static recovery and recrystallization rates. The deformation and restoration behavior of KS FCC metals are discussed, taking into account the physical and metallurgical factors such as stacking fault energy, dislocation mobility, diffusivity, and melting point.

Erratum to: Effect of Plasma Nitriding and Nitrocarburizing on HVOF-Sprayed Stainless Steel Coatings

Gayoung Park, Gyuyeol Bae, and Changhee Lee, Kinetic Spray Coating Laboratory, Division of Materials Science and Engineering, Hanyang University, Seoul 133-791, South Korea; and Kyungil Moon, Heat and Surface Technology Center, Incheon Technology Service Division for SMEs, Korea Institute of Industrial Technology, Incheon 406-840, South Korea. Contact e-mail: chlee@hanyang.ac.kr. JTTEE5 22:1388 Erratum DOI: 10.1007/s11666-013-0042-5 1059-9630/

Effects of Impact Velocity on Crystallization and Activation Energy of Cu-based Bulk Metallic Glasses in Kinetic Spray Coating

19.00 ASM International

Improvement of Coating Properties of Metal/diamond Composite Through Ni Coated Diamond in the Kinetic Spraying Process

In this paper, nanocrystallization of CuNiTiZr bulk metallic glass (BMG) subjecting to a kinetic spraying, dependent on impact velocity, was investigated by numerical and experimental approaches. The crystallization fraction and nucleation activation energy of initial feedstock and as-deposited coating were estimated by DSC and Kissinger method, respectively. The results of numerical modeling and experiment showed that the crystalline fraction and nucleation activation energy in BMG coatings were depended on kinetic energy of incident particle. Upon impact, the conversion of particle kinetic energy leads to not only decreasing free energy barrier but also increasing the driving force for an amorphous to crystalline phase transformation. The nanocrystallization of BMGs is associated with the strain energy delivered by a plastic deformation with a high strain rate.

Finite Element Simulation of Interface Bonding in Kinetic Sprayed Coatings

Generally, deposition mechanism of diamond particle is mainly embedding effect in the kinetic spray process. Accordingly, in spite of high cost, helium gas was employed as process gas to get high diamond fraction in the composite coating. In this study, the deposition behavior of bronze/diamond by kinetic spray process was compared using different process gas (helium and nitrogen). Bare (mean size of , ) and nickel coated diamond (mean size of ) were deposited on Al 6061-T6 substrate with fixed process temperature and pressure. For comparison with experimental results, plastic deformation behavior of nickel layer was simulated by finite element analysis (using ABAQUS/Explicit 6.7-2). The size, broken ratio, and fraction of diamond in the composite coating were analyzed through scanning electron microscopy and image analysis method. The uniform distribution and deposition efficiency of diamond particles in the coating layer could be achieved by tailoring the physical properties of the feedstock.

General aspects of interface bonding in kinetic sprayed coatings

A finite element modeling approach has been described for the simulation and analysis of the micron-scaled solid particle impact behavior in kinetic spraying process, using an explicit code (ABAQUS 6.7-2). High-strain-rate plastic deformation and interface bonding features of the copper, nickel, aluminum, and titanium were investigated via FEM in conjunction with the Johnson-Cook plasticity model. Different aspects of adiabatic shear instabilities of the materials were characterized as a concept of thermal boost-up zone (TBZ), and also discussed based upon energy balance concept with respect to relative recovery energy (RRE) for the purpose of optimizing the bonding process.