• Proceedings of the Materials Research Society of Korea Conference
• /
• 2012.05a
• /
• pp.106.2-106.2
• /
• 2012

Ti-Ni합금은 CsCl구조의 B2상, monoclinic 구조의 B19'(M)상과 rhombohedral 구조의 R상(R)이 나타난다고 알려져 있고, 이들 상의 변태에 의해 열탄성 마르텐사이트와 응력유기 마르텐사이트에 의한 형상기억효과와 초탄성 효과를 가지고 있다. 또한 Ti-Ni 합금은 우수한 형상기억특성을 가질 뿐만 아니라 생체적합성, 가공성 및 내식성 등이 뛰어나 공업분야 및 생체분야에서 폭 넓게 활용되고 있다. Ti-Ni합금의 형상기억특성은 냉간가공 후 어닐링 처리의 온도와 시간에 따른 matrix 내 Ni의 농도, 석출물의 밀도와 크기, 전위밀도와 전위주위의 응력장에 의해 영향을 받는다고 알려져 있다. 본 연구에서는 Ti-Ni합금의 형상기억 특성 및 변태온도에 미치는 영향을 조사하기 위해 다양한 냉간가공률의 시료를 제작하여 다양한 온도에서 Annealing 처리를 하여 냉간가공률 및 Annealing 온도가 형상기억특성에 미치는 영향을 조사하였다. Ti-50.4 at.% Ni 합금은 진공 아크 용해로에서 용해 하였으며, 용해된 Ingot는 열간단조 및 열간 압출한 후 냉간 인발과 중간온도에서 어닐링을 반복하면서 직경 0.5mm의 선재로 만들었다. 최종적으로 제작한 선재의 냉간가공률은 9.5%, 18.2%, 34.5%, 45% 이었다. 각 시편은 5X10-5torr의 진공으로 석영관에 진공 봉입하여 각각 673K, 723K, 783K에서 1hr 열처리 하였다. 합금의 형상기억특성과 변태온도는 DSC에 의해 조사되었다. DSC 측정 결과, 냉간가공률이 증가함에 따라 마르텐사이트 변태 온도는 감소하였고, 어닐링 온도가 증가함에 따라 마르텐사이트 변태 온도는 증가하였다. 또한 가공률이 증가하여도 R상 변태온도는 큰 변화가 없었고, Annealing온도가 증가함에 따라 R상 변태온도는 감소하였다. 또한, 형상기억특성은 인장시험기를 이용한 정하중 열싸이클 테스트를 이용하여 평가 하였다. 냉간 가공률이 증가함에 따라 안정한 형상기억특성을 나타내었다.

• Korean Journal of Materials Research
• /
• v.30 no.6
• /
• pp.308-314
• /
• 2020

A commercial AA1070 alloy for electrical wire is severely deformed by drawing process in which a rod with an initial diameter of 9mm into is reduced to a wire of 2mm diameter. The drawn AA1070 wire is then annealed at various temperatures from 200 to 450 ℃ for 2h. Changes in microstructure, mechanical properties and electrical properties of the specimens with annealing temperature are investigated in detail. The specimen begins partially to recrystallize at 250 ℃; above 300 ℃ it is covered with equiaxed recrystallized grains over all regions. Fiber textures of {110}<111> and {112}<111> components are mainly developed, and {110}<001> texture is partially developed as well. The tensile strength tends to decrease with annealing temperature due to the occurrence of recovery or/and recrystallization. On the other hand, the elongation of the annealed wire increases with the annealing temperature, and reaches a maximum value of 33.3 % at 300 ℃. Electric conductivity of the specimens increases with annealing temperature, and reaches a maximum value of 62.6 %IACS after annealing at 450 ℃. These results are discussed in comparison with those for the other aluminum alloy.

• Transactions of Materials Processing
• /
• v.14 no.8 s.80
• /
• pp.704-711
• /
• 2005

The influence of process parameters in drawn wire on residual stresses was investigated. Based on a FE-simulation of the wire drawing process, the effects of process parameters such as semi-die angle, reduction, friction coefficient and bearing length on the residual stresses were investigated. The validity of the FE-simulation results was verified by the comparison of the previous simulated results with experimental data. In this study, semi-die angle and die reduction have significant effect on the residual stresses at the surface of drawn wire. Several methods such as, addition of axial tension, application of skin pass, straightening in multi-roll straightener etc, were suggested in the previous studies to reduce the residual stresses. In this study, the results show that the concurrent application of skin pass with low die reduction and low semi-die angle at the final stage of drawing operation reduces dramatically the both axial and hoop residual stresses after drawing

• Transactions of Materials Processing
• /
• v.22 no.8
• /
• pp.470-476
• /
• 2013

The aim of the current study was to predict shape recovery behavior of Ni-Ti shape memory alloy (SMA) wire after loading-unloading and after wire drawing. The superelasticity of SMA was analyzed by a hyper-elastic model for the Mullins effect using ABAQUS. Firstly, tensile tests and loading-unloading tests of the Ni-Ti SMA wire with a diameter 1.0 mm were performed using an MTS servo-hydraulic tester. The parameters for the Mullins effect were computed by ABAQUS based on curve-fitting of the loading-unloading test data. The proposed FE-model predicted the shape recovery of Ni-Ti SMA after wire drawing. Finally, the effectiveness of the model was verified by drawing experiments. The wire drawing experiments using the Ni-Ti SMA were conducted on a drawing machine(1ton, 50mm/s). In order to evaluate the shape recovery of Ni-Ti SMA, the drawn wires are annealed for 30min at $450^{\circ}C$.

• Transactions of Materials Processing
• /
• v.24 no.3
• /
• pp.187-193
• /
• 2015

The objective of the current study is to determine cross-sectional profile of intermediate dies in order to improve the plastic strain homogeneity which directly affects not only the dimensional accuracy but also the mechanical properties of final product by redesigning the intermediate dies using the conventional electric field analysis (EFA) method. Initially, the multi-pass shape wire drawing was designed by using the equivalent potential lines from EFA. The area reduction ratio was calculated from the number of passes in multi-pass shape wire drawing but constrained by the capacity of the drawing machine and the drawing force. In order to compensate for a concentration of strain in a region of the cross section of the wire, the process for multi pass wire drawing from initial round material to an intermediate die was redesigned again using the electric field analysis. Both drawing process designs were simulated by the finite element method in which the strain distribution and standard deviation plastic strain of the cross section of drawn wires were examined.

• Korean Journal of Metals and Materials
• /
• v.50 no.7
• /
• pp.511-516
• /
• 2012

Low temperature ${\delta}$-precipitation phenomenon below 2-step aging ($718^{\circ}C$, $8hr+621^{\circ}C$, 8 hr) temperature of cold drawn Inconel 718 alloy wire was investigated. The investigation was carried out on wires with a cold drawn ratio of 0, 20, 50 and 70% using OM, SEM, XRD, TEM, and DSC. In microstructures of 50 and 70% drawn wire, many precipitates were found along the grain boundaries and the twin boundaries in deformation band. From the results of the XRD and TEM analysis, the precipitates were identified as plate-like ${\delta}$-phase. From the results of the DSC analysis, it was also found that a temperature of ${\delta}$-precipitation decreases with an increase of the cold drawn ratio. We concluded that cold drawing of inconel 718 wire promotes the ${\delta}$-precipitation, and under the condition of a high drawing ratio, the ${\delta}$-phase could be precipitated at a temperature below the aging temperature ($718^{\circ}C$).

• Korean Journal of Materials Research
• /
• v.11 no.4
• /
• pp.312-318
• /
• 2001

The mechanical and electrical properties of Cu-Nb filamentary nanocomposite fabricated by the bundling and drawing process were examined. The strength increased gradually with increasing Nb content while the ductility was insensitive to Nb content. The ratio of yield stresses at 293K and 75K are found to be 치ose to that of Young's moduli in various Cu-Nb nanocomposites, suggesting that athermal obstacles primarily control the strength. The fracture morphologies show ductile fractures irrespective of Nb contents. Secondary cracking along the interfaces between subelemental wires was occasionally observed and the frequency of secondary cracking increased with increasing Nb content. The conductivity and the resistivity ratio decreased with increasing Nb content. The decrease of the conductivity and the resistivity ratio(${\rho}_{293k}$/$\{rho}_{75k}$) can be explained by the increasing contribution of interface scattering.