• Journal of Powder Materials
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• v.9 no.2
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• pp.96-102
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• 2002

In the present study, equiatomic porous TiNi shape-memory alloys have been successfully prepared by self-propagating high-temperature synthesis (SHS) using elemental titanium and nickel powders. The porous TiNi alloys thus obtained have an open porous structure with about 64 vol.% porosity, and the pore size is about 1.8 mm. The effect of preheating temperature on the microstructure have been investigated. It is found that the pore size increases with increasing preheating temperature. Moreover, the preheating temperature was shown to have a significant effect on the microstructrue of the SHS-synthesized porous TiNi shape memory alloys.

• Journal of Powder Materials
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• v.6 no.2
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• pp.152-162
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• 1999

The present study is concerned with the effect of PM process variables on the microstructure by using atomized superalloy powders. It is suggested that the inhomogeneity of composition is strongly dependent on the process variables. The contents of segregation elements of plasma rotating electrode process (PREP) powders are larger than those of Ar atomization (AA) powders. As HIP treatment temperature in-increases, the secondary phases on the prior particle boundaries (PPB) have continuous,uniform distribution and high density, but the amount of PPB decreases suddenly at 1150$^{\circ}$C. Segregated phases on the PPB are identified to be MC type carbide. Brittle MC type carbides on the PPB provide fracture initiation sites and preferred fracture path, thereby leading to intergranular type brittle fracture.

• Journal of the Korean Society for Heat Treatment
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• v.24 no.4
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• pp.193-198
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• 2011

Effect of CaO addition on age hardening response has been studied by using optical microscopy, scanning electron microscopy and differential thermal analysis in AZ91 and CaO-containing ECO-AZ91 alloys. After solution treatment, the ${\beta}$($Mg_{17}Al_{12}$) phase formed during solidification mostly disappeared in the microstructure in the AZ91 alloy, whereas numerous ${\beta}$ precipitates containing Ca were still observed in the ECO-AZ91 alloy due to its enhanced thermal stability. The ECO-AZ91 alloy showed the delayed peak aging time and higher peak hardness compared with those of the AZ91 alloy. The activation energies for ${\beta}$ precipitation calculated by means of Kissinger method increased from 71.4 to 85.6 kJ/mole by the addition of CaO, which implies that CaO plays a role in reducing ${\beta}$ precipitation rate in the AZ91 alloy.

• Journal of the Korean Ceramic Society
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• v.33 no.1
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• pp.74-82
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• 1996

Fe-Si based powders prepare by melting the metals in the composition of FeSi2,.Fe0.95Mn0.05Si2 and Fe0.95Co0.05Si0.2 were used as the starting materials together with a commercial FeSi2 powder to study the effect of oxidation on their thermoelectric properties. The powders were heated at 650~80$0^{\circ}C$ in dired air before forming and sintering at 1190 and 120$0^{\circ}C$ in Ar+7%H2. The microstructure and phases of the annealed specimens were observed using the optical microscopty SEM, EDS and XRD. The thermoelectric properties of the specimens were also measured. The temperature at which Seebe다 coefficient showed the maximum value increased with the degree of oxidation. Electrical conductivity showed a tendency to decrease in the oxidized samples regardless of their compositions. Seebeck coefficient of the specimen showed almost the same value even after oxidation which may be explained by the formation of the discontinuous second phases from impurities in the oxidized specimens.

• 한국기계연구소 소보
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• s.16
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• pp.29-39
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• 1986

Several heat treatment were applied to on HSLA steel of type StE47 (German standard) to produce five ferrite microstructures of different strength and at least two different grain sizes respectively. Whereas the ferrite microstructure had a strong influence on yield strength the effect of grain size was negligible. The different strength levels could be explained by regarding the arrangement of dislocations and vanadium carbide particles, and their mutual interaction. Specimens tranformed at $600^{\circ}C$ showed the highest strength levels. In this case precipitation has occured after the $\gamma$- $\alpha$ transformation. Very small VC particles are arranged mostly along dislocation lines. Increasing both, grain size and pearlite volume fraction leads to a remarkable shift of transition temperature which was further enhanced by increasing ferrite strength.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.256-259
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• 2009

In order to investigate the effect of strain states attributed to the lubrication during shape rolling, shape rolling for V-sectioned sheets was carried out with and without lubrication. The evolution of strain states during shape rolling was studied by three-dimensional finite element method (FEM). Shape rolling with and without lubrication produces shape-rolled samples in fairly similar outer shapes, since the distribution of normal strain components is nearly independent of the lubrication condition. In contrast, the distribution of shear strain components strongly depends on the lubrication condition.

• Transactions of Materials Processing
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• v.12 no.4
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• pp.284-289
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• 2003

The effects of nitrogen on the deformation behavior of duplex stainless steel have been studied. The variation of strength was correlated with the characteristic microstructures pertaining to nitrogen. Analysis based on Hall-fetch relation confirmed that nitrogen enhances phase-boundary strengthening effect. The evolution of dislocation structure, slip traces and misorientation distribution during deformation were also characterized to elucidate the effect of nitrogen on inelastic deformation mechanism. It has been verified in this study that the higher nitrogen content provides a dual-phase microstructure with smaller strength difference between austenite and ferrite resulting into the earlier transfer of inelastic deformation from austenite to ferrite.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1138-1139
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• 2006

The present study has shown that the effect of boron and phosphorus in Ni-Cr-Si-X alloy to interfacial reactions and bonding strength of diamond-steel substrate, and the influence of various construction parameters on the formation of the topography of the tool. And these factors are required to making a good brazed tool. The microstructures and phase change of the brazed region were analyzed into SEM, EDS. According to the electron probe microanalysis, while brazing, the chromium present in the brazing alloy segregated preferentially to the surface of the diamond to form a chromium rich reaction product, which was readily wetted by the alloy.

• Journal of Surface Science and Engineering
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• v.24 no.4
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• pp.215-221
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• 1991

Microstructure evolution during low temperature vapor deposition exhibits wel-developed columnar structure mainly owing to geometrical shadowing effect of surface roughness. It is concluded that this structure is concided with many theoretical models suggested so far. In case of aluminum nitride film deposition consisted of etching and nitriding step employing ECR plasma, the rougher the surface before etching, the finer and more cone-and-whisker structure can be developed. In turn, this fine structure affects the formation and growth of columnar as well as offers many sites available for mechanical lock-up. Conclusively, the formation of well-defined columnar structures depends on the initial surface roughness.

• Journal of Powder Materials
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• v.5 no.1
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• pp.35-41
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• 1998

The effect of Mn on the densification and the microstructural change in W heavy alley was investigated with adopting the improved Mn-adding method. In order to avoid the pore formation problems associated with Mn powder mixing to the other constituent powders, Mn was added afterwards to the sintered heavy alloy; Mn powder was spread homogeneously on the surface of the sintered heavy alloy compact, and this Mn powder contained specimen was resintered at the same sintering temperature. As expected, the resintered specimen showed the pore free microstructure because Mn was reduced separately from the other constituent elements. It was also founded that W grains grew rapidly at the initial stage of resintering treatment due to the activated reprecipitation of the excess W atoms substituted by Mn atoms, but the growth rate of W grains was slowly lowered with the prolonged sintering time, especially, compared to the Mn free heavy alloy. Such a retardation of grain growth should be attributed to the decreased W solubility in the Mn contented matrix phase. Furthermore, Mn addition resulted in the decrease of contiguity by improving the wetting between matrix phase and W grain.