Kinetic Spray Process Research Articles

진공 저온 분사 공정을 통해 형성된 Fe계 비정질 재료의 적층거동 및 미세구조 변화 관찰

Fe-based amorphous coatings were fabricated on a soda-lime glass substrate by the vacuum kinetic spray method. The effect of the gas flow rate, which determines particle velocity, on the deposition behavior of the particle and microstructure of the resultant films was investigated. The as-fabricated microstructure of the film was studied by field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HR-TEM). Although the activation energy for transformation from the amorphous phase to crystalline phase was lowered by severe plastic deformation and particle fracturing under a high strain rate, the crystalline phases could not be found in the coating layer. Incompletely fractured and small fragments 100~300 nm in size, which are smaller than initial feedstock material, were found on the coating surface and inside of the coating. Also, some pores and voids occurred between particle-particle interfaces. In the case of brittle Fe-based amorphous alloy, particles fail in fragmentation fracture mode through initiation and propagation of the numerous small cracks rather than shear fracture mode under compressive stress. It could be deduced that amorphous alloy underwent particle fracturing in a vacuum kinetic spray process. Also, it is considered that surface energy caused by the formation of new surfaces and friction energy contributed to the bonding of fragments.

Deposition Behavior and Microstructure of Fe-based Amorphous Alloy Fabricated by Vacuum Kinetic Spraying Process

Deposition Behavior and Microstructure of Fe-based Amorphous Alloy Fabricated by Vacuum Kinetic Spraying Process

Amorphization of ZrO2 + CeO2 Powders Through Mechanical Milling for the Use of Kinetic Spray

The coating formation in a kinetic spray process mainly depends on the impact of inflight particles at a high velocity. The plastic deformation at the impact interface would disrupt the native oxide scale on the particle and the substrate to generate the intimate contact of the atomic structures. Accordingly, it poses a challenge in producing ceramic coating during kinetic spray because of the lack of plasticity of ceramic powders at room temperature. In this study, we proposed to prepare ZrO2 ceramic coatings using partially amorphized powder with nanometer size in the kinetic spray process. To prepare the powder for the use of the kinetic spray, the amorphization and grain refinement of ZrO2 powder in mechanical ball milling were studied. The results showed that the amorphization and grain refinement were improved because of the formation of solid solution when the CeO2 agent was added. Subsequently, a nearly spherical powder was achieved via spray drying using the milled powders. The plasticity of the milled powders was tested in the kinetic spray process using Nitrogen as process gas. A dense ZrO2-CeO2 coating with a thickness of 50 μm was formed, whereas spraying milled ZrO2 powder can only lead to an inhomogeneous dispersion of the destructible particles on the surface of the substrate.

Manufacturing and Compressive Deformation Behavior of High-Strength Aluminum Coating Material Fabricated by Kinetic Spray Process

The compressive deformation behavior in the thickness direction of a kinetic-sprayed pure-aluminum layer whose thickness is ~15 mm was investigated. The yield strength of coating material was 200 MPa, and a unique strain softening phenomenon occurred even at room temperature. Due to the initial severely deformed structure of the kinetic-sprayed coating material based on the results of microstructure analysis, the production of high-strength metal bulk materials using kinetic spray processes was deemed possible.

Microstructure Evolution of Titanium Nitride Film during Vacuum Kinetic Spraying

Single crystal titanium nitride powder was used to fabricate titanium nitride films using a vacuum kinetic spray (VKS) process. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (FETEM) were used to investigate the microstructure of the as‐fabricated films under different process conditions. Plastic deformation features (i.e., amorphization, rotated grain, slip bands, and distorted lattices in the transition structure) revealed an elastic‐to‐inelastic transition of titanium nitride particles at high strain rate and high pressure induced by hypervelocity impact, which was considered vital for grain refinement and film growth during the process.

Formation of coating and tribological behavior of kinetic sprayed Fe-based bulk metallic glass

Fe-based bulk metallic glass (BMG) was sprayed through the kinetic spraying process using different conditions. By using helium as the process gas and a preheating system for the powder, it was possible to form a dense coating. This study focused on the deposition characteristics and tribological behavior of Fe-based BMG coating in comparison to the bearing materials (bearing steel and steel-backed sintered bearing) for industrial applications. Observations of the worn surface of the coating revealed that the plastic deformation with grooves and some debris were prominent with no visible cracking or fracture. Fe-based BMG coating showed a good wear resistance with a low friction coefficient.

The Effects of Successive Impacts and Cold Welds on the Deposition Onset of Cold Spray Coatings

In this study, the impact and deposition behavior of nickel particles onto relatively soft 6061-T6 aluminum alloy and copper substrates in a kinetic spray process was investigated by comparing individual particle impact with full coating deposition. The results indicated that the deposition onset of nickel coatings on the two substrates follows different deposition mechanisms depending on corresponding deformability of the impact couples (substrate and particle). Nickel particles were hardly attached onto the relatively soft 6061-T6 substrate in case of individual impact, but the deposition onset of full coating took place depending on embedding, tamping of successive impact and metallurgical “cold welds” of viscous metal at impact interface when the impinging particles’ velocity was relatively low. In case of Ni-Cu impact, the bonding formed at the peripheral impact interface dominated the deposition onset of nickel coating due to the comparable deformability of the impact couples (Ni and Cu).

Strain-enhanced nanocrystallization of a CuNiTiZr bulk metallic glass coating by a kinetic spraying process

Nanocrystallization of CuNiTiZr bulk metallic glass (BMG) subjected to kinetic spraying with variable impact velocities was investigated through numerical and experimental approaches. The fraction of crystallization and activation energy of the initial feedstock and as-deposited coatings were estimated through differential scanning calorimetry and the Kissinger method, respectively. The numerical and experimental results showed that the fraction of crystallinity and activation energy for nucleation in BMG coatings is strongly related to the kinetic energy of the impacting particles. Upon high-velocity impact, the kinetic energy of the particle led to a decrease in the free energy barrier and an increase in the driving force for the amorphous-to-crystalline phase transformation. Microstructure observation revealed that the nanocrystallization of the BMG in the kinetic spray process was associated with the strain energy delivered by plastic deformation using a high strain rate.

An Investigation on Powder Injection in the High-Pressure Cold Spray Process

High-pressure cold spray process is a relatively new coating process that uses high-velocity powder particles to form coatings. One of the requirements for this process is to inject the particles to be sprayed into a prenozzle chamber where both the particles and the powder feed gas are entrained into the primary gas stream. In this study, we investigated the effects of powder injection on coating formation through both experimental studies and computational simulations. Several issues related to powder injection will be examined, including the size of powder injector, the differential pressure, powder gas flow, and injector clogging. It is shown that an improved powder injector design not only enables the use of reduced amount of powder carrier gas flow but also maintains steady, clogging-free spraying conditions. Combining with properly selected injection conditions, it can also lead to enhanced coating deposition by kinetic spray process.

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.

저온 분사 공정에서 니켈이 코팅된 다이아몬드 적용을 통한 금속/다이아몬드 복합재료의 코팅성 향상

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.

유한요소 시뮬레이션을 통한 저온 분사 코팅의 계면 접합에 대한 연구

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.

탄소 나노튜브 알루미늄 복합재료 저온 분사 코팅의 적층 거동 및 특성

Carbon nanotube (CNT) aluminum composite coatings were built up through kinetic spraying process. Deposition behavior of CNT aluminum composite on an aluminum 1050 alloy substrate was analyzed based on deposition mechanism of kinetic spraying. The microstructure of CNT aluminum composite coating were observed and analyzed. Also, the electrical resistivity, bond strength and micro-hardness of the CNT aluminum composite coatings were measured and compared to kinetic sprayed aluminum coatings. The CNT aluminum composite coatings have a dense structure with low porosity. Compared to kinetic sprayed aluminum coating, the CNT aluminum composite coatings present lower electrical resistivity and higher micro-hardness due to high electrical conductivity and dispersion hardening effects of CNTs.

Deposition characteristics of copper particles on roughened substrates through kinetic spraying

In this paper, a systematic study of copper particle deposition behavior on polished and roughened surfaces (aluminum and copper) in kinetic spray process has been performed. The particle deformation behavior was simulated through finite element analysis (FEA) software ABAQUS explicit 6.7–2. The particle–substrate contact time, contact temperature and contact area upon impact have been estimated for smooth and three different roughened substrate cases. Copper powders were deposited on smooth and grit-blasted copper and aluminium substrates and characterized through scanning electron microscopy and Romulus bond strength analyzer. The results indicate that the deformation and the resultant bonding were higher for the roughened substrates than that of smooth. The characteristic factors for bonding are reported and discussed. Thus the substrate roughness appears to be beneficial for the initial deposition efficiency of the kinetic spray process.

The Fabrication of Carbon Nanotubes Reinforced Copper Coating by a Kinetic Spray Process

In this paper, multiwalled carbon nanotubes (MWCNTs) reinforced copper coating was deposited on copper sheet through kinetic spraying process. Effect of heat treatment on microstructure, conductivity, and hardness of the coating was investigated. The incompact MWCNTs reinforced copper coating exhibits a comparable hardness, but higher electrical resistivity than pure copper coating. After heat treatment at 600 degrees C for 2 h, the hardness of copper coatings significantly decreased due to the substantial grain growth. MWCNTs reinforced copper coating showed stable hardness and electrical conductivity against heat treatment owing to the inhibition of CNTs to grain growth and the intimate contact between CNTs and copper matrix.

General aspects of interface bonding in kinetic sprayed coatings

In this study, different engineering materials are classified into four impact cases according to their physical and mechanical properties, i.e., soft/soft, hard/hard, soft/hard, and hard/soft (particle/substrate). Based on finite-element modeling, impact behaviors of the four cases were numerically analyzed. For soft/soft and hard/hard cases, the size variation of the thermal boost-up zone (TBZ), accompanied with the different aspects of adiabatic shear instability, was numerically estimated and is theoretically discussed. Meanwhile, for soft/hard and hard/soft cases, the specific aspect of shear instability, which has a very high heat-up rate, is always observed on the relatively soft impact counterpart where a thin molten layer is expected as well. Based on these phenomenological characteristics, bonding aspects are characterized, and a database for numerically estimated critical velocities of different particle/substrate combinations was developed for kinetic spraying process.

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.

Oxidation dependency of critical velocity for aluminum feedstock deposition in kinetic spraying process

In kinetic spraying process, critical velocity is an important criterion which determines the deposition of feedstock onto the substrate. It has been proven experimentally and numerically that the critical velocity is determined by physical and mechanical properties and the state of materials such as initial temperature and size. In this study, the oxidation effect on critical velocity was investigated using experimental methods. As oxygen content of feedstock increased, critical velocity significantly decreased. In order to find out reasons for difference in critical velocity with oxygen content, individual impact behavior was analyzed and interface microstructure was observed. Due to high brittleness and hardness of oxide, oxide layer on particle influences the particle deformation behavior during impact. And oxide accumulated at interface obstructs the adhesion between activated particle and substrate surface during impact.

저온분사 공정에서 알루미늄 분말의 산화가 임계 적층 속도에 미치는 영향

In kinetic spraying process, the critical velocity is an important criterion which determines the deposition of a feedstock particle onto the substrate. In other studies, it was experimentally and numerically proven that the critical velocity is determined by the physical and mechanical properties and the state of materials such as initial temperature, size and the extent of oxidation. Compared to un-oxidized feedstock, oxidized feedstock required a greater kinetic energy of in-flight particle to break away oxide film during impact. The oxide film formed on the surface of particle and substrate is of a relatively higher brittleness and hardness than those of general metals. Because of its physical characteristics, the oxide significantly affected the deposition behavior and critical velocity. In this study, in order to investigate the effects of oxidation on the deposition behavior and critical velocity of feedstock, oxygen contents of Al feedstock were artificially controlled, individual particle impact tests were carried out and the velocities of in-flight Al feedstock was measured for a wide range of process gas conditions. As a result, as the oxygen contents of Al feedstock increased, the critical velocity increased.

저온분사공정을 통한 NiTiZrSiSn 벌크 비정질 코팅의 비정질 분율에 따른 스크래치 반응

A bulk amorphous NiTiZrSiSn powder produced using an inert gas atomization was sprayed by kinetic spraying process that is basically a solid-state deposition process onto a mild steel substrate. They were successfully overlaid onto the mild steel substrate. In order to evaluate the tribological behavior of the kinetic sprayed NiTiZrSiSn BMG (Bulk Metallic Glass) coatings, a partially crystallized coating and a fully crystallized coating were prepared by the isothermal heat treatments. Tribological behaviors were investigated in view of friction coefficient, hardness and amorphous phase fraction of coating layer. Surface morphologies and depth in the wear tracks were observed and measured by scanning electron microscope and alpha-step. From the examination of the scratch wear track microstructure, transition from the ductile like deformation (micro cutting) to the brittle deformation (micro fracturing) in the scratch groove was observed with the increase of the crystallinity.