Kee-Ahn Lee

High temperature high cycle fatigue behavior of new aluminum alloy strengthened by (Co, Ni)3Al4 particles

High cycle fatigue (HCF) behavior of a new heat-resistant aluminum alloy at elevated temperature was investigated. This alloy consists of an α-Al matrix, a small amount of precipitated Mg2Si, and distributed (Co, Ni)3Al4 strengthening particles. HCF tests were conducted with a stress ratio of (R)=0 and a frequency of (F)=30 Hz at 130 °C. The fatigue limit (maximum stress) of this alloy was 120 MPa at 107 cycles. This is a value superior to that of conventional heat-resistant aluminum alloys such as the A319 alloy. Furthermore, regardless of the stress conditions, the new heat-resistant Al alloy has an outstanding fatigue life at high temperatures. The results of fractography observation showed that second phases, especially (Co, Ni)3Al4 particles, were effective to the resistance of fatigue crack initiation and propagation. On the other hand, Mg2Si particles were more easily fractured by the fatigue crack. This study also clarifies the micromechanism of fatigue deformation behavior at elevated temperature related to its microstructure.

Effect of Heat Treatment Environment on the Properties of Cold Sprayed Cu-15 at.%Ga Coating Material for Sputtering Target

This study attempted to manufacture a Cu-15 at.%Ga coating layer via the cold spray process and investigated the effect of heat treatment environment on the properties of cold sprayed coating material. Three kinds of heat treatment environments, +argon, pure argon, and vacuum were used in this study. Annealing treatments were conducted at /1 hr. With the cold sprayed coating layer, pure -Cu and small amounts of were detected in the XRD, EDS, EPMA analyses. Porosity significantly decreased and hardness also decreased with increasing annealing temperature. The inhomogeneous dendritic microstructure of cold sprayed coating material changed to the homogeneous and dense one (microstructural evolution) with annealing heat treatment. Oxides near the interface of particles could be reduced by heat treatment especially in vacuum and argon environments. Vacuum environment during heat treatment was suggested to be most effective one to improve the densification and purification properties of cold sprayed Cu-15 at.%Ga coating material.

Bonding, Reactivity, and Mechanical Properties of the Kinetic-Sprayed Deposition of Al for a Thermally Activated Reactive Cu Liner

Pure Al coatings were fabricated on Cu substrates via kinetic spraying to produce a thermally activated reactive Cu liner. The coatings need to endure high-strain rate severe plastic deformation and react with oxygen during penetration or after penetration of the liner. In this study, the Al powder underwent large exothermic reactions with a small particle size and fast heating rate, as determined from the differential scanning calorimetric analysis. Process optimization of the Al deposition was facilitated by defining the “critical velocity” of an Al particle in the kinetic spraying process based on numerical modeling and computations using ABAQUS finite element codes. The simulation results revealed that the critical velocity of an Al particle at room temperature (RT) is 780xa0m/s and it decreases as the particle temperature increases. Certain process conditions resulted in improved coating properties as the temperature of the particles was affected by the process gas temperature and pressure. The mechanical properties such as the bond strength of the coatings formed under various process conditions were evaluated and compared. The relationships between the resulting properties, processing conditions, and the structures of the coatings are discussed.

Effect of Heat Treatment Environment on the Densification of Cold Sprayed Ti Coating Layer

This study investigated the effects of annealing environment for the densification and purification properties of pure titanium coating layer manufactured by cold spraying. The annealing was conducted at /1 h and three kinds of environments of vacuum, Ar gas, and mixture gas were controlled. Cold sprayed Ti coating layer (as sprayed) represented 6.7% of porosity and 228 HV of hardness, showing elongated particle shapes (severe plastic deformation) perpendicular to injection direction. Regardless of gas environments, all thermally heat treated coating layers consisted of pure -Ti and minimal oxide. Vacuum environment during heat treatment represented superior densification properties (3.8% porosity, 156.7 HV) to those of Ar gas (5.3%, 144.5 HV) and mixture gas (5.5%, 153.1 HV). From the results of phase analysis (XRD, EPMA, SEM, EDS), it was found that the vacuum environment during heat treatment could be effective for reducing oxide contents (purification) in the Ti coating layer. The characteristic of microstructural evolution with heat treatment was found to be different at three different gas environments. The controlling method for improving densification and purification in the cold sprayed Ti coating material was also discussed.

Effects of Powder Morphology and Powder Preheating on the Properties and Deposition Behavior of Titanium Coating Layer Manufactured by Cold Spraying

Cold spray deposition using Titanium powder was carried out to investigate the effects of powder morphology and powder preheating on the coating properties such as porosity and hardness. The in-flight particle velocity of Ti powder in cold spray process was directly measured using the PIV (particle image velocimetry) equipment. Two types of powders (spherical and irregular ones) were used to manufacture cold sprayed coating layer. The results showed that the irregular morphology particle appeared higher in-flight particle velocity than that of the spherical one under the same process condition. The coating layer using irregular morphology powder represented lower porosity level and higher hardness. Two different preheating conditions (no preheating and preheating at ) were used in the process of cold spraying. The porosity decreased and the hardness increased by conducting preheating at . It was found that the coating properties using different preheating conditions were dependent not on the particle velocity but on the deformation temperature of particle. The deposition mechanism of particles in cold spray process was also discussed based on the experimental results of in flight-particle velocity.

High Temperature Oxidation Behavior of Ni based Porous Metal

【This study investigated the high temperature oxidation behavior of Ni-22.4%Fe-22%Cr-6%Al (wt.%) porous metal. Two types of open porous metals with different pore sizes of 30 PPI and 40 PPI (pore per inch) were used. A 24-hour TGA test was conducted at three different temperatures of

Effect of the pore size on the creep deformation behavior of Ni-Fe-Cr-Al porous metal

900^{circ}C

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

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High Temperature Oxidation Behaviors of Fe-Cr-Al Based Powder Porous Metal and a Strip

1000^{circ}C

Manufacturing and Macroscopic Properties of Cold Sprayed Cu-Ga Coating Material for Sputtering Target

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