The alloy Terfenol-D, $Tb_xDy_{1-x}Fe_y$ (0.27≤χ≤0.30, y≤2), is known to have giant magnetostriction and comparatively low magnetocrystalline anisotropy energy. Therefore, a high strain response, approaching 1600 ppm, can be obtained at a low field (<100 kA/m). It is well known that the $RFe_2$ phase (Laves structure, R denotes the solid solution of rare earth constituents) has a magnetic easy axis of <1 1 1> and hence $\lambda_{111}$ is the largest of all the anisotropic magnetostrains.
However, its usage was restricted due to eddy current loss at high frequency. In addition, it has a shortcoming such as intrinsic brittleness accompanied by maximizing the fraction of the brittle $RFe_2$. The magnetostrictive composite materials have been developed as an alternative way to overcome both eddy current loss and intrinsic brittleness.
Recently, polymer infiltrated grain aligned composite (PlGAC) materials have been developed, which have several advantages, such as maintaining the favorable grain alignment and improving intrinsic brittleness efficiently through composite process. These infiltration composite materials do not need to apply magnetic field in manufacturing process, neither to make powders of $RFe_2$.
The optimum composition of PIGAC Terfenol-D has been examined in this research. Composition of $Tb_xDy_{1-x}Fe_y$ have been varied in the range of x=0.27, 0.3, 0.33;y=1.03, 1.3, 1.6 and Si contamination of 0, 0.25, 0.5 at%. To find out the optimum composition, maximum magnetostriction $(\lambda_{max})$, magnetostriction coefficient $(d_{33})$ and remanence have been analyzed in orthogonal table. The optimum composition of PIGAC Terfenol-D was $Tb_{0.3}Dy_{0.7}Fe_{1.6}$. The effect of Si was also a major factor to determine the magnetostrictive properties
The effects of Si contamination on the magnetostrictive properties of monolithic Terfenol-D have been investigated. The origin of Si contamination is quartz mold during the manufacturing processes. In this study, Tefenol-D rod sealed in quartz ampoule and reacted in 1370, 1400 and 1450℃. The reaction time varied from 1 to 7hour. The composition of Terfenol-D was $Tb_{0.3}Dy_{0.7}Fe_{1.9}$
The reaction layer was analyzed by wavelength diffraction spectroscopy (WDS). Multiple layer of rare earth oxide - rare earth silicide - rare earth oxide layer formed between Terfenol-D melt and the quartz mold. Combining the result of Si contamination in Terfenol-D, it was verified that the Si diffusion is the reaction control step during the formation of reaction layer. The activation energy of Si diffusion was calculated by Arrhenius plot and the value is $E_a=1.592eV$
$Tb_xDy_{1-x}Fe_y$ (0.27≤x≤0.30, y≤2) 조성의 합금인 Terfenol-D는 낮은 자기이방성을 가지며 1600ppm에 근접하는 변형을 보이는 거대자왜재료이다. Laves 구조인 $RFe_2$ 합금은 <111>의 자화용이축으로 자왜변형이 일어난다. 그러나 교류 자장하에서의 와전류로 인한 손실 때문에 고주파 영역에서의 사용은 제한되어 왔다. 또한 $RFe_2$ 의 특성상 구조적으로 취약한 특성을 보여, 이들 특성을 개선하기 위하여 고분자 복합재료의 개발이 이루어져 왔다. 최근에 개발된 polymer infiltrated grain aligned composite (PIGAC) 공정은 Terfenol-D의 결정방향성을 유지하며 구조적인 취성을 극복하고, $RFe_2$ 상간의 절연으로 와전류 손실을 줄이기 위하여 개발되었다. 본 연구에서는 최적의 PIGAC 조성을 찾고, 그 조성 변화에 따른 공정상의 불순물 유입 효과를 보기 위한 실험을 실시하였다. 최적의 조성을 찾기 위하여 최대자기변형 $\lambda_{max}$, 자기변형상수 $d_{33}$ 그리고 보자력 등을 직교표에서 분석하였다. 그 결과로 PIGAC공정의 최적 조성은 $Tb_{0.3}Dy_{0.7}Fe_{1.6} 로 밝혀졌다. 공정중 Quartz tube와의 반응에 따른 Si 불순물의 영향을 보기 위하여 자왜특성 측정과 wavelength diffraction spectroscopy (WDS) 분석을 실시하였다. 반응층의 WDS 분석 결과 희토류 산화물-희토류 규화물-희토류 산화물의 복합적인 반응층이 관찰되었으며, 반응 메커니즘의 열역학적 고찰에 따라 반응은 Si 확산에 의해 주도되었으며 그 확산 과정의 활성화 에너지는 1.592eV로 계산되었다.