• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.26 no.1
• /
• pp.95-104
• /
• 2002

Densification behavior of aluminum alloy(A16061) powder was investigated under cold compaction. Experimental data were obtained under triaxial compression with various loading conditions. A special form of the Cap model was proposed from experimental data of A16061 powder under triaxial compression. The proposed yield function and several yield functions in the literature were implemented into a finite element program (ABAQUS) to compare with experimental data for densifcation behavior of A16061 powder under cold isostatic pressing and die compaction. The agreement between finite element calculations from the proposed yield function and experimental data is very good under cold isostatic pressing and die compaction.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.30 no.10 s.253
• /
• pp.1242-1248
• /
• 2006

Densification behavior of nanocrystalline titania powder was investigated under cold compaction. Experimental data were obtained under triaxial compression with various loading conditions. Lee and Kim proposed the Cap model by developing the parameters involved in the yield function of general Cap model and volumetric strain evolution under cold isostatic pressing. The parameters in the Drucker/Prager Cap model and the proposed model were obtained from experimental data under triaxial compression. Finite element results from the models were compared with experimental data for densification behavior of nanocystalline ceramic powder under cold isostatic pressing and die compaction. The proposed model agreed well with experimental data under cold compaction, but the Drucker/Prager Cap model underestimated at the low density range. Finite element results, also, show the relative density distribution of nanocystalline ceramic powder compacts is severe compared to conventional micron powder compacts with the same averaged relative density.

• Journal of Powder Materials
• /
• v.7 no.3
• /
• pp.137-142
• /
• 2000

In order to analyze the densification behaviour of stainless steel powder compacts during hot isostatic pressing (HIP) at elevated temperatures, a power-law creep constitutive model based on the plastic deformation theory for porous materials was applied to the densification. Various densification mechanisms including interparticle boundary diffusion, grain boundary diffusion and lattice diffusion mechanisms were incorporated in the constitutive model, as well. The power-law creep model in conjunction with various diffusion models was applied to the HIP process of 316L stainless steel powder compacts under 50 and 100 MPa at $1125^{\circ}C$. The results of the calculations were verified using literature data. It could be found that the contribution of the diffusional mechanisms is not significant under the current process conditions.

• Proceedings of the Korean Ceranic Society Conference
• /
• 2003.04a
• /
• pp.111.1-111
• /
• 2003

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.24 no.12
• /
• pp.3061-3071
• /
• 2000

Densification behavior of titanium alloy powder was investigated under hot pressing at various pressures and temperatures. Experimental date were obtained for densification of titanium alloy powder under an instantaneous loading and subsequent creep deformation during hot pressing. The constitutive models of Fleck et al. and the modified Gurson were employed for thermo-phastic deformation under the instantaneous loading and that f Abouaf and co-workers for creep deformation of titanium alloy powder during hot pressing. By implementing these constitutive equations into a finite element program(ABAQUS), finite element results were compared with experimental data during hot pressing. To investigate the effect of friction between the power and die wall, density distributions of power compacts were measured and compared with finite element calculations. Finite element results from the models of Fleck et al. and the modified Gurson agreed reasonably good with experimental data for densification and density distribution of titanium alloy powder under the instantaneous loading during hot pressing. Finite element results from the model of Abouaf and co-workers, however, somewhat overestimate experimental data for creep deformation of power compacts during hot pressing.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.34 no.2
• /
• pp.73-77
• /
• 2024

The spinel-type oxide (Ni_x, Mn_y, Co_3-x-y)O₄ (NMC) is widely utilized as a material for temperature sensors with a negative temperature coefficient (NTC), finding applications across various industries including electric vehicle battery management systems. Typically, NMC is manufactured using solid-state reaction methods employing powders of Ni, Mn, and Co compounds, with the densification process through sintering recognized as a crucial factor determining the electrical properties of the temperature sensor material. In this study, NMC pellets were synthesized via solid-state reaction and their crystallographic and microstructural characteristics were investigated. Also, the activation energy for densification behavior during the sintering process was determined. According to the analysis results, the room temperature resistance of the NMC pellets was measured at 10.03 Kohm, with the sensitivity parameter, B-value, recorded at 3601.8 K, indicating their potential applicability as temperature sensors across various industrial fields. Furthermore, the activation energy for densification was found to be 273.3 ± 0.4 kJ/mol, providing valuable insights into the thermodynamic aspects of the sintering process of the NMC.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.5 no.2
• /
• pp.98-102
• /
• 2004

Ion exchange behavior and property change of soda-lime-silicate glass by advanced ion exchange process were investigated. Refractive index, specific gravity and optical transmittance were changed similarly to $K^+$ ion penetration depth, and amount of ion exchange increased with the increase of the time and temperature. Especially, thermal expansion decreased greatly because of the structural compaction and residual stress by ion exchange process.

• Journal of the Korean Ceramic Society
• /
• v.37 no.11
• /
• pp.1071-1077
• /
• 2000

표면 윤활층을 가진 나노 알루미나를 진공중에서 가압성형함으로써 결함발생없이 높은 충전압력을 가할 수 있었으며, 높은 밀도, 미세기공, 좁은 기공경 분포를 가지는 성형체를 제조할 수 있었다. 윤활제의 화학 및 기계적 특성에 의하여 변하는 모세관 현상을 조정함으로써 충전효율을 증대하고 결함발생을 억제할 수 있다. 나노분말의 소결에서도 성형 미세구조의 균일도가 치밀화 거동에 여전히 지배적인 역할을 하였다.

• Journal of Powder Materials
• /
• v.4 no.4
• /
• pp.298-303
• /
• 1997

The activated sintering behavior of $MoSi_2$ powder compacts with addition of 0.5 and 1.0 wt.%Ni during the sintering under As atmosphere was studied. The shrinkage was measured and the microstructures were observed by SEM (scanning electron microscopy) and BEI (backscattered electron image) along with the phase analysis by EDS during heating up to 155$0^{\circ}C$ and holding for various time at 155$0^{\circ}C$. The most of shrinkage occurred upon heating and 92% of theoretical density was attained after sintering for 1 hr at 155$0^{\circ}C$. However, little shrinkage ensued even for prolonged sintering over 1 hr at 155$0^{\circ}C$. A liquid film formed at about 135$0^{\circ}C$ along necks and grain boundaries. The polyhedral grain structure composed of $(Mo,Ni)_5Si_3$and $Ni_2Si$ across the $MoSi_2$ grain boundary developed at 155$0^{\circ}C$. It was concluded that the activated sintering of $MoSi_2$ powder by Ni led to the diffusion of Si into Ni decreasing the liquidus temperature and the enhanced diffusion of Mo and Si through such a liquid phase and/or interboundary of $(Mo,Ni)_5Si_3$.

• Korean Journal of Materials Research
• /
• v.7 no.4
• /
• pp.267-275
• /
• 1997

본 연구에서는 암석폐재를 대상으로 직경이 60mm인 고화체를 얻을 수 있는 수열 hot press 장치를 개발하였고, 고형화를 위한 최적조건을 찾아내는 내용을 다루었다. 이어 고화체의 기계적 성질을 평가하였고, 고화기구와 미시적 파괴거동을 규명하기위하여 SEM관찰 및 음향방출실험을 실시하였다. 고형화를 위한 최적조건은 NaOH용액이 10wt%, 수열온도가 30$0^{\circ}C$이고, 유지시간이 1시간이었다. 또한 수열반응동안에 다양한 제 2화합물들이 생성되었으며, 이들은 고화체의 기계적 성질에 큰 영향을 미쳤다. 아울러 원석의 경우에는 AE Counts가 초기화중에서부터 나타났으나, 고화체는 초기하중에서 전혀 AE Counts가 검출되지 않았다. 이와같은 사실로부터 수열 hot press법에 의해 얻어진 고화체는 원석과는 다르게 암석 입자간의 결합이 보다 치밀하게 이루어지고 있음을 유추할 수 있다.