Tseng Li-Wei, Chen Wei-Cheng
Department of Mechatronics Engineering, National Changhua University of Education, Changhua 50007, Taiwan.
Micromachines (Basel). 2024 Oct 31;15(11):1338. doi: 10.3390/mi15111338.
Fe-Ni-Co-Al-based systems have attracted a lot of interest due to their large recoverable strain. In this study, the microstructure and thermal cycling behaviors of FeNiCoAlTiNb (at.%) 98.5% cold-rolled alloys after annealing treatment at 1277 °C for 1 h, followed by aging for 48 h at 600 °C, were investigated. From the electron backscatter diffraction results, we see that the texture intensity increased from 9.4 to 16.5 mud and the average grain size increased from 300 to 400 μm as the annealing time increased from 0.5 h to 1 h. The hardness results for different aging heat treatment conditions show the maximum value was reached for samples aged at 600 °C for 48 h (peak aging condition). The orientation distribution functions (ODFs) displayed by Goss, brass, and copper were the main textural features in the FeNiCoAlTiNb cold-rolled alloy. After annealing, strong Goss and brass textures were formed. The transmission electron microscopy (TEM) results show that the precipitate size was ~10 nm. The X-ray diffraction (XRD) results show a strong peak in the (111) and (200) planes of the austenite (γ, FCC) structure for the annealed sample. After aging, a new peak in the (111) plane of the precipitate (γ', L12) structure emerged, and the peak intensity of austenite (γ, FCC) decreased. The magnetization-temperature curves of the aged sample show that both the magnetization and transformation temperature increased with the increasing magnetic fields. The shape memory properties show a fully recoverable strain of up to 2% at 400 MPa stress produced in the three-point bending test. However, the experimental recoverable strain values were lower than the theoretical values, possibly due to the fact that the volume fraction of the low-angle grain boundary (LABs) was small compared to the reported values (60%), and it was insufficient to suppress the beta phases. The beta phases made the grain boundaries brittle and deteriorated the ductility. On the fracture surface of samples after the three-point bending test, the fracture spread along the grain boundary, and the cross-section microstructural results show that the faces of the grain boundary were smooth, indicating that the grain boundary was brittle with an intergranular fracture.
铁镍钴铝基体系因其较大的可恢复应变而备受关注。在本研究中，对经1277℃退火1小时、随后在600℃时效48小时的FeNiCoAlTiNb（原子百分比）98.5%冷轧合金的微观结构和热循环行为进行了研究。从电子背散射衍射结果可知，随着退火时间从0.5小时增加到1小时，织构强度从9.4增加到16.5泥，平均晶粒尺寸从300μm增加到400μm。不同时效热处理条件下的硬度结果表明，在600℃时效48小时的样品（峰值时效条件）达到了最大值。FeNiCoAlTiNb冷轧合金中的主要织构特征由高斯织构、黄铜织构和铜织构的取向分布函数（ODF）表示。退火后，形成了强烈的高斯织构和黄铜织构。透射电子显微镜（TEM）结果表明，析出相尺寸约为10nm。X射线衍射（XRD）结果显示，退火样品的奥氏体（γ，面心立方）结构在（111）和（200）平面有一个强峰。时效后，析出相（γ'，L12）结构的（111）平面出现一个新峰，奥氏体（γ，面心立方）的峰强度降低。时效样品的磁化温度曲线表明，磁化强度和转变温度均随磁场增加而升高。形状记忆性能表明，在三点弯曲试验中，在400MPa应力下可实现高达2%的完全可恢复应变。然而，实验可恢复应变值低于理论值，这可能是由于与报道值（60%）相比，低角度晶界（LABs）的体积分数较小，不足以抑制β相。β相使晶界变脆并降低了延展性。在三点弯曲试验后的样品断口表面，裂纹沿晶界扩展，横截面微观结构结果表明，晶界面光滑，表明晶界脆性且为沿晶断裂。
