• Smart Structures and Systems
• /
• v.4 no.2
• /
• pp.123-135
• /
• 2008

Damping capacity of SMA damping devices is simulated numerically under distinct geometry and loading conditions. Two-dimensional numerical simulations are performed on the basis of a phenomenological model of dynamics of martensite-austenite phase boundaries. Results of the simulations predict the time delay and the value of the stress transferred to other parts of a construction by a damper device.

• Journal of the Korean Society for Heat Treatment
• /
• v.15 no.2
• /
• pp.65-69
• /
• 2002

$Llo{\rightarrow}Ni_5Al_3$ reordering and related properties in Ni-Al alloys consisting of 64-65at%Ni are characterized by X-ray diffraction, shape memory effect and damping capacity. Formation of $Ni_5Al_3$ takes place by simple ordering of atoms with a continuous increase in c/a ratio. As a result, degradation of shape memory effect and damping capacity is observed after short time annealing at $200-300^{\circ}C$.

• Proceedings of the KSME Conference
• /
• 2004.04a
• /
• pp.706-709
• /
• 2004

A numerical method was developed that imposes constraint condition on the order parameters in martensitic phase transformation. In the method, an amplitude function having values of 1 or 0 was multiplied to transformation rates. The merit of the method is that the imposition of the constraint condition is more straightforward than a method with Lagrangian multiplier and easy to implement in the tangent modulus method. The developed method is applied to three-dimensional finite element analyses of single and poly crystalline shape memory alloys.

• Journal of the Korean Society for Heat Treatment
• /
• v.10 no.2
• /
• pp.93-100
• /
• 1997

Effect of austenite grain size on starting temperature of ${\gamma}{\rightarrow}{\varepsilon}$ martensitic transformation($M_s$) has been studied in an Fe-18%Mn alloy. Particular attention was paid on the variation of stacking fault energy with austenite grain size, which is considered to be a important factor affecting ${\gamma}{\rightarrow}{\varepsilon}$ martensitic transformation. Austenite grain size was increased in a wide range from $13{\mu}m$ to $185{\mu}m$ with increasing solution treatment temperature from $700^{\circ}C$ to $1100^{\circ}C$. Hardness was decreased with increasing austenite grain size while the volume fraction of ${\varepsilon}$ martensite showed a reverse tendency, which indicates that the hardness is more dependent on austenite grain size than ${\varepsilon}$ martensite content. No significant change was found in $M_s$ temperature when the grain size was larger than about $30{\mu}m$. In case that, the austenite grain size was smaller than about $30{\mu}m$, however, $M_s$ temperature was marlkedly decreased with decreasing austenite grain size. A linear relationship between $M_s$ temperature and the stacking fault formation probability, i.e. the reciprocal of the stacking fault energy was obtained, which suggests that the variation of $M_s$ temperature with austenite grain size is closely related to the change in stacking fault energy.

• Journal of the Korean Society for Heat Treatment
• /
• v.8 no.1
• /
• pp.75-83
• /
• 1995

The purpose of this study is to investigate the effect of heat treatments on the martensite transformation and tensile deformation behavior in Ti-Ni-B alloys with various boron concentration. Three types of heat treatment are given to the specimens; i) solution treatment ii) aging iii) thermo-mechanical treatment. In solution treated specimens. R-phase transition which is related to abnormal increase of electrical resistance prior to martensitic transformation has been formed at a boron content of 0.2at % and the $M_s$ temperature has been decreased with the increasing of boron content. However. It has not been affected by aging, while that of thermo-mechanically treated specimens has been remarkably increased in the vicinity of recrystallization temperature. The thermo-mechanically treated specimen has showed a good thermal fatigue characteristics, shape memory effect and superelasticity in comparison with the solution treated specimen.

• Journal of Powder Materials
• /
• v.31 no.1
• /
• pp.8-15
• /
• 2024

The emergence of ferrous-medium entropy alloys (FeMEAs) with excellent tensile properties represents a potential direction for designing alloys based on metastable engineering. In this study, an FeMEA is successfully fabricated using laser powder bed fusion (LPBF), a metal additive manufacturing technology. Tensile tests are conducted on the LPBF-processed FeMEA at room temperature and cryogenic temperatures (77 K). At 77 K, the LPBF-processed FeMEA exhibits high yield strength and excellent ultimate tensile strength through active deformation-induced martensitic transformation. Furthermore, due to the low stability of the face-centered cubic (FCC) phase of the LPBF-processed FeMEA based on nano-scale solute heterogeneity, stress-induced martensitic transformation occurs, accompanied by the appearance of a yield point phenomenon during cryogenic tensile deformation. This study elucidates the origin of the yield point phenomenon and deformation behavior of the FeMEA at 77 K.

• Journal of the Korean Society for Heat Treatment
• /
• v.23 no.5
• /
• pp.233-238
• /
• 2010

The phase transformations and the shape memory effect in In-rich Pb alloys and In rich-Sn alloys have been studied by means of X-ray diffractometry supplemented by metallographic observations. The alloys containing 12~15 at.%Pb transform from the ${\alpha}_2$ (fct) phase to the ${\alpha}_1$ (fct) phase by way of an intermediate phase (m phase) on cooling. The results of X-ray diffraction show that the metastable intermediate phase is observed both on cooling and heating, and has a face-centered orthorhombic (fco) structure. It is concluded that the ${\alpha}_1{\rightleftarrows}{\alpha}_2$ transformation is expressed by the ${\alpha}_1{\rightleftarrows}m{\rightleftarrows}{\alpha}_2$ transformation both on usual cooling and heating with the rate more than $8{\times}10^{-3}$ K/s. The $m{\rightleftarrows}{\alpha}_2$ transformation takes place with a mechanism involving macroscopic shear and are of diffusionless (martensitic) type. The temperature hysteresis in the two transformations is 10~13 K between the heating and cooling transformations. The alloys containing 0~11 at.%Sn are -phase solid solutions with a face centered tetragonal structure (c/a > 1) at room temperature, the axial ratio increasing continuously with tin content. The In-(11~15) at.%Sn alloys are mixtures of ${\alpha}$ and ${\beta}$ phases, the ${\beta}$ phase having a f. c. tetragonal structure (c/a < 1). The alloys containing more than 15 at.%Sn are ${\beta}$-phase solid solutions. The In-(12.9~15.0) at.%Sn alloys show a shape memory effect only when quenched to the temperature of liquid nitrogen, although their effect becomes weak and finally disappears after keeping at room temperature for a long time. The ${\beta}{\rightarrow}{\alpha}^{\prime}$ phase transformation is of the diffusionless (martensitic) type, and takes place between 330 K at 12.9 at.%Sn and 150 K at 14.5 at.%Sn. The hysteresis of transformation temperatures on heating and cooling is considerably large (29~40 K), depending on the composition. Both In-Pb and In-Sn alloys showed distinct the shape memory effects.

• Nuclear Engineering and Technology
• /
• v.54 no.6
• /
• pp.1972-1981
• /
• 2022

A typical ferritic/martensitic (F/M) steel sheet was subjected to pulsed laser surface remelting (LSR) and corrosion test in lead-bismuth eutectic (LBE) at 550 ℃. There present two modification zones with distinct microstructures in the LSRed specimen: (1) remelted zone (RZ) consisting of both bulk δ-ferrite grains and martensitic plates and (2) heat-affected zone (HAZ) below the RZ, mainly composed of martensitic plates and high-density precipitates. Martensitic transformation occurs in both the RZ and the HAZ with the Kurdjumov-Sachs and Nishiyama-Wassermann orientation relationships followed concurrently, resulting in scattered orientations and specific misorientation characteristics. Hardnesses of the RZ and the HAZ are 364 ± 7 HV and 451 ± 15 HV, respectively, considerably higher than that of the matrix (267 ± 3 HV). In oxygen-saturated and oxygen-depleted LBE, thicknesses of oxide layers developed on both the as-received and the LSRed specimens increase with prolonging corrosion time (oxide layers always thinner under the oxygen-depleted condition). The corrosion resistance of the LSRed F/M steel in oxygen-saturated LBE is improved, which can be attributed to the grain-refinement accelerated formation of dense Fe-Cr spinel. In oxygen-depleted LBE, the growth of oxide layers is very low with both types of specimens showing similar corrosion resistance.

• Structural Engineering and Mechanics
• /
• v.22 no.5
• /
• pp.563-574
• /
• 2006

This paper studies mechanical behavior of the superelastic shape memory alloy (SMA) rods in terms of local deformations and time via tensile loading-unloading cycles for both ends fixed end constraints. Besides the unique stress induced martensitic transformation (SIMT), SMA's time dependent behavior when it is in mixed-phase condition upon loading and unloading, also need careful attention with a view of investigating the local deformation of the structural elements made of the same material. With this perspective, the so-called stress-relaxation tests have been performed to demonstrate and investigate the local strains-total strains relationships with time, particularly, during the forward SIMT. Some remarkable phenomena have been observed pertaining to SIMT, which are absent in traditional materials and those unique phenomena have been explained qualitatively. For example, at the stopped loading conditions the two ends (fixed end and moving end of the tensile testing machine) were in fixed positions. So that there was no axial overall deformation of the specimen but some notable increase in the axial local deformation was shown by the extensometer placed at the middle of the SMA specimen. It should be noted that this peculiar behavior termed as 'inertia driven SIMT' occurs only when the loading was stopped at mixed phase condition. Besides this relaxation test for the SMA specimens, the same is performed for the mild steel (MS) specimens under similar test conditions. The MS specimens, however, show no unusual increase of local strains during the stress relaxation tests.

• Journal of the Korean Society for Heat Treatment
• /
• v.11 no.2
• /
• pp.111-120
• /
• 1998

The effects of chemical composition and thermal cycling on the martensitic transformation characteristics in Cu-rich, equiatomic and Zr-rich CuZr binary alloys have been studied by calorimetry. Only martensite could be indentified in equiatomic $Cu_{49.9}Zr_{50.1}$ alloy, while $Cu_{10}Zr_7$ and $CuZr_2$ intermetallic compounds as well as martensite were formed by rapid cooling from the melts in Cu-rich $Cu_{52.2}Zr_{47.5}$ alloy and Zr-rich $Cu_{48.4}Zr_{51.6}$ alloy, respectively. The $M_s$ temperature of $Cu_{49.9}Zr_{50.1}$ was $156^{\circ}C$ but those of $Cu_{52.5}Zr_{47.5}$ and $Cu_{48.4}Zr_{51.6}$ alloys, being $109^{\circ}C$ and $138^{\circ}C$, were lower than that of equiatomic $Cu_{49.9}Zr_{50.1}$ alloy. In all the alloys, the $M_s$ temperature has fallen but the $A_s$ temperature has risen, resulting in widening of the transformation hysteresis with thermal cycling. The anomalous characteristics in the transformation temperature are due to the presence of the intermetallic compounds i.e. $Cu_{10}Zr_7$ and $CuZr_2$ formed by an eutectoid reaction during thermal cycling in the temperature range between $-100^{\circ}C$ < $T_c$ < $400^{\circ}C$.