In this study, effect of core-shell structure on compaction behavior of harmonic powder is investigated. Harmonic powders are made by electroless plating method on Fe powders. Softer Cu shell encloses harder Fe core, and the average size of Fe core and thickness of Cu shell are 34.3 μm and 3.2 μm, respectively. The powder compaction procedure is processed with pressure of 600 MPa in a cylindrical die. Due to the low strength of Cu shell regions, the harmonic powders show better densification behavior compared with pure Fe powders. Finite element method (FEM) is performed to understand the roll of core-shell structure. Based on stress and strain distributions of FEM results, it is concluded that the early stage of powder compaction of harmonic powders mainly occurs at the shell region. FEM results also well predict porosity of compacted materials.

In this study, Cu-5Ni-10Sn(wt%) spinodal alloy was manufactured by gas atomization spray forming, and the microstructural features and mechanical properties of Cu-5Ni-10Sn alloy have been investigated during homogenization, cold working and age-hardening. The spray formed Cu-5Ni-10Sn alloy consisted of an equiaxed microstructure with a mixture of solid solution -(CuNiSn) grains and lamellar-structure grains. Homogenization at and subsequent rapid quenching formed a uniform solid solution -(CuNiSn) phase. Direct aging at from the homogenized Cu-5Ni-10Sn alloy promoted the precipitation of finely distributed ' or phase throughout the matrix, resulting in a significant increase in microhardness and tensile strength. Cold working prior to aging was effective in strengthening Cu-5Ni-10Sn alloy, which gave rise to a maximum tensile strength of 1165 MPa. Subsequent aging treatment slightly reduced the tensile strength to 1000-1100 MPa due to annealing effects.

In this study, powder metallurgy and severe plastic deformation by high-pressure torsion (HPT) approaches were combined to achieve both full density and grain refinement at the same time. Water-atomized pure iron powders were consolidated to disc-shaped samples at room temperature using HPT of 10 GPa up to 3 turns. The resulting microstructural size decreases with increasing strain and reaches a steady-state with nanocrystalline (down to ~250 nm in average grain size) structure. The water-atomized iron powders were deformed plastically as well as fully densified, as high as 99% of relative density by high pressure, resulting in effective grain size refinements and enhanced microhardness values.

Green strength is an important property of powders since high green strength guarantees easy and safe handling before sintering. The green strength of a powder compact is related to mainly mechanical and surface characters, governed by interlocking of the particles. In this study, the effect of powder surface roughness on the green strength of iron powders was investigated using a transverse rupture test. Three-dimensional laser profiler was employed for quantitative analyses of the surface roughness. Two different surface conditions, i.e. surface roughness, of powders were compared. The powders having rough surfaces show higher green strength than the round surface powders since higher roughness leads increasing interlocked area between the contacting powders.

In the current study, the effects of particle size on compaction behavior of water-atomized pure iron powders are investigated. The iron powders are assorted into three groups depending on the particle size; 20-45 , 75-106 , and 150-180 for the compaction experiments. The powder compaction procedures are processed with pressure of 200, 400, 600, and 800 MPa in a cylindrical die. After the compaction stage, the group having 150-180 of particle size distribution shows the best densification behavior and reaches the highest green density. The reason for these results can be explained by the largest average grain size in the largest particle group, due to the low plastic deformation resistance in large grain sized materials.

Cu-Sn based alloys were manufactured by gas atomization spray casting route in order to achieve a fine scale microstructure and a high tensile strength. The spray cast Cu-10Sn-2Ni-0.2Si alloy had an equiaxed grain microstructure, with no formation of brittle phase. Aging treatment promoted the precipitation of finely distributed particles corresponding to intermetallic phase throughout the -(CuSn) matrix. The cold-rolled Cu-Sn-Ni-Si alloy had a very high tensile strength of 1200 MPa and an elongation of 5%. Subsequent aging treatment at for 1h slightly reduced the tensile strength to 700 MPa and remarkably increased the elongation up to 30%. This result has been explained by coarsening the precipitates due to over aging and reducing the dislocation density due to annealing effects.

In this study, Cu-10Sn and Cu-10Sn-2Ni-0.2Si alloys have been manufactured by spray casting in order to achieve a fine scale microstructure and high tensile strength, and investigated in terms of microstructural evolution, aging characteristics and tensile properties. Spray cast alloys had a much lower microhardness than continuous cast billet because of an improved homogenization and an extended Sn solid solubility. Spray cast Cu-Sn-Ni-Si alloy was characterized by an equiaxed grain microstructure with a small-sized (Ni, Si)-rich precipitates. Cold rolling of Cu-Sn-Ni-Si alloy increased a tensile strength to 1220 MPa, but subsequent ageing treatment reduced a ultimate tensile strength to 780 MPa with an elongation of 18%.

The degree of WC decomposition and hardness of thermally sprayed WC-Co coatings are important factors determining the wear resistance of the coatings. In order to minimize the degree of decomposition and to increase hardness, the effects of processing parameters of high velocity oxyfuel(HVOF) spraying on various characteristics of nanostructured WC-12Co coating have been evaluated by an experimental design method. The HVOF sprayed WC-12Co coatings consisted of various carbide phases including WC, and , with a much reduced carbon content. The degree of WC decomposition and decarburization was affected by changing barrel length and spray distance. The hardness of WC-Co coatings was strongly related to droplet temperature at substrate, and increased with increasing fuel addition and/or decreasing spray distance. The effective control of processing parameters was discussed in detail for manufacturing a high performance WC-Co coating.