• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2004년도 추계학술대회논문집
• /
• pp.199-202
• /
• 2004

In this present study, an attempt was made to determine the deformation mode of the Zr-Ti-Cu-Ni-Be bulk metallic glass by compression test over a wide range of temperatures and strain rates. From the results, empirical deformation map could be constructed including the boundaries of different deformation modes. Considering power dissipation map and instability map developed on the basis of the Dynamic Materials Model (DMM), the processing map for extrusion could also be constructed. In addition, the macroscopic formability of this BMG alloy has also been examined through the extrusion in laboratory scale within undercooled liquid state. From the results of macroscopic extrusion formability, both deformation map and processing map present good criteria to determine optimal forming conditions.

• 소성∙가공
• /
• 제15권4호
• /
• pp.333-339
• /
• 2006

Hot deformation behavior of a carbon steel (A350 LF2) was characterized by compression tests in the temperature range of $800-1250^{\circ}C$ and the strain rate range of $0.001-10s^{-1}$, The microstructural evolution during hot compression was investigated and deformation mechanisms were analyzed by constructing a deformation processing map. Processing maps were generated using the combination of dynamic material model (DMM) and flow instability theories based on the flow stability criteria and Ziegler's instability criterion. In order to evaluate the reliability of the map, the mirostructural characteristics of the hot compressed specimens were correlated with test conditions in the stable and unstable regime. The combined microstructural and processing map of A350 LF2 was applied to predict an optimum condition and unstable regions for hot forming.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2004년도 춘계학술대회 논문집
• /
• pp.80-83
• /
• 2004

High temperature deformation behavior of AZ31 Mg alloy was investigated in this study on the basis of a processing map $(\varepsilon\approx0.6)$. To construct a processing map, compression tests were carried out at wide range of temperatures and strain rates $(T=250\~500^{\circ}C,\;\varepsilon=10^{-4}\~100/s)$. Two regions of high deformation efficiency $(\eta)$ were identified as: (1) a dynamic recrystalization (DRX) domain at $250^{\circ}C$ and 1/s and (2) a superplasticity domain at $450^{\circ}C$ and $10^{-4}/s$. Possible deformation mechanisms operating at high temperature were discussed in relation to the activation energy. A two-stage deformation method was found to be effective in enhancing the superplasticity of AZ31 Mg alloy. From the two-stage deformation method, tensile elongation of $1200\%$ was obtained at the superplastic domain.

• Metals and materials international
• /
• 제24권6호
• /
• pp.1249-1255
• /
• 2018

High temperature compression tests for newly developed Al-Zn-Mg alloy were carried out to investigate its hot deformation behavior and obtain deformation processing maps. In the compression tests, cylindrical specimens were deformed at high temperatures ($300-500^{\circ}C$) and strain rates of 0.001-1/s. Using the true stress-true strain curves obtained from the compression tests, processing maps were constructed by evaluating the power dissipation efficiency map and flow instability map. The processing map can be divided into three areas according to the microstructures of the deformed specimens: instability area with flow localization, instability area with mixed grains, and stable area with homogeneous grains resulting from continuous dynamic recrystallization (CDRX). The results suggest that the optimal processing conditions for the Al-Zn-Mg alloy are $450^{\circ}C$ and a strain rate of 0.001/s, having a stable area with homogeneous grains resulting from CDRX.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2006년도 춘계학술대회 논문집
• /
• pp.168-171
• /
• 2006

Hot deformation behavior of A350 LF2 alloy was characterized by compression tests in the temperature range of 800-$1250^{\circ}C$ and the strain rate range of $0.001-10s^{-1}$. The microstructural evolution during hot compression was investigated and deformation mechanisms were analyzed by constructing processing map. Processing maps were generated using the dynamic material model (DMM). The combination of dynamic material model and Ziegler's instability criterion was applied to predict an optimum condition and unstable regions for hot forming.

• 대한금속재료학회지
• /
• 제46권7호
• /
• pp.449-457
• /
• 2008

Compression deformation behaviors at high temperature as a function of temperature and strain rate were investigated in the 6061 aluminum alloy, which is used for automobile wheel. Compression tests were carried out in the range of temperatures $300{\sim}475^{\circ}C$ and strain rate $10^{-3}{\sim}10^{-1}sec^{-1}$. By analyzing these results, strain rate sensitivity, deformation temperature sensitivity, the efficiency of power dissipation, Ziegler's instability criterion, etc were calculated, which were plastic deformation instability parameters as suggested by Ziegler, Malas, etc. Furthermore, deformation processing map was drawn by introducing dynamic materials model (DMM) and Ziegler's Continuum Criteria. This processing map was evaluated by relating the deformation instability conditions and the real microstructures. As a result, the optimum forging condition for the automobile wheel with the 6061 aluminum alloy was designed at temperature $450^{\circ}C$, strain rate $1.0{\times}10^{-1}sec^{-1}$. It was also confirmed by DEFORM finite element analysis tool with simulation process.

• 소성∙가공
• /
• 제11권6호
• /
• pp.529-537
• /
• 2002

A series of load-relaxation tests and tensile tests were conducted to study the high temperature deformation mechanism of fine duplex gamma TiAl alloy at temperatures ranging from 800 to 105$0^{\circ}C$. Results of load relaxation test showed that deformation behavior at a small imposed strain ($\varepsilon$≒0.05) was dominated by dislocation glide and dislocation climb. To investigate the deformation behavior at a large amount of strain, the processing map was constructed using a dynamic materials model. Two domains were characterized in the processing map obtained at a strain level of 0.6. One domain was found at the region of 98$0^{\circ}C$ and $10^{-3}/sec$ with a peak efficiency of 48%, which was identified as a domain of dynamic recrystallization from the microstructural observation. The order was observed at the region of 125$0^{\circ}C$ and $10^{-4}/sec$ with a peak efficiency of 64%. The strain rate sensitivity measured indicates that the material was deformed by the superplasticity in the region.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2006년도 춘계학술대회 논문집
• /
• pp.429-433
• /
• 2006

High Temperature deformation behavior of newly developed beta-gamma TiAl alloy was investigated in this study. The optimum processing condition was investigated with the aid of Dynamic Materials Model (DMM). Processing maps representing the efficiency of power dissipation for microstructural evolution and instability were constructed utilizing the results of hot compression test at temperatures ranging from $1000^{\circ}C$ to $1200^{\circ}C$ and strain rate ranging from $10^{-4}/s$ to $10^2/s$. The Artificial Neural Network (ANN) simulation was adopted to consider the deformation heating. With the help of processing map and microstructural analysis, the optimum processing condition was presented and the role of $\beta$ phase was also discussed in this study.

• 소성∙가공
• /
• 제16권4호
• /
• pp.309-312
• /
• 2007

Deformation behavior of $Zr_{55}Cu_{30}Al_{10}Ni_5$(at. %) bulk metallic glass(BMG) fabricated by suction casting method has been investigated at elevated temperatures in this study. The BMG was first verified to have an amorphous structure with the analysis of X-ray diffraction(XRD) and differential scanning calorimetry(DSC) data. A series of compression tests has consequently been performed in the region of supercooled liquid temperature to investigate the behavior of high temperature deformation. A transition from Newtonian to non-Newtonian flow appeared to take place depending upon both the strain rate and test temperature. A processing map based on a dynamic materials model has been constructed to estimate a feasible forming condition for this BMG alloy.

• 소성∙가공
• /
• 제16권6호
• /
• pp.473-478
• /
• 2007

In this study, a deformation mechanism map of metallic nanocrystalline materials(NCMs) using the phase mixture model is proposed. It is based on recent modeling that appears to provide a conclusive description of the phenomenology and the mechanisms underlying the mechanical properties of NCMs. The proposed models adopted the concept of a 'phase mixture' in which the grain interior and the grain boundaries are treated as separate phases. The volume fraction of this grain boundary 'phase' may be quite appreciable in a NCM. Based on the theoretical model that provides an adequate description of the grain size dependence of plasticity covering all grain size range from coarse down to the nanoscale, the tensile deformation response of NCMs, especially focusing on the deformation mechanisms was investigated. The deformation mechanism map is newly proposed with axes of strain rate, grain size and temperature.