Precipitation of dispersive nanoparticles has recently been found to yield superfunctional properties, such as the large and sensitive magnetostriction in body-centered-cubic (bcc) Fe-Ga alloys with face-centered-tetragonal (fct) nanoprecipitates, and applying this strategy to grain-aligned alloys may allow one to obtain better performance. However, the internal stress generated during directional solidification may alter the precipitation behaviors by accelerating atomic clustering, therefore, a careful analysis of the morphology of precipitates and solute partitioning is needed. Herein, we investigated the dynamic precipitation behavior in a directionally solidified Fe₇₃Ga₂₇ alloy with [001] orientation. Through comparisons with random polycrystalline sample subjected to the same aging treatment, we find that the [001]-oriented sample produces sparser fct nanoprecipitates and extra interfacial omega nanoprecipitates. The internal stress accelerates Ga partitioning between the fct nanoprecipitates and the matrix, hence reducing their nucleation sites. The internal stress also alters the mutual elastic interactions between matrix and precipitates, where the Bain strains of fct nanoprecipitates are mostly accommodated by forming Ga-enriched omega nanoprecipitates and {112}<111> stacking faults at the phase front, unlike that for random polycrystalline sample, where the Bain strains are accommodated by local tetragonal distortion of the matrix. As a result, the magnetostriction enhancement ratio is 40% for the grain-aligned sample, weaker than ~165 % for the random polycrystalline sample. Our results not only shed lights on the precipitation difference between stress-containing and stress-free aging conditions but also help to guide the microstructure design of superfunctional alloys in which the type, number density and size of nanoprecipitates should be carefully controlled.

最近发现，分散纳米颗粒的沉淀会产生超功能特性，例如，体心立方（bcc）Fe-Ga合金具有面心四角（fct）纳米沉淀的大而灵敏的磁致伸缩，并将这种策略应用于晶粒排列的合金可以使合金获得更好的性能。但是，定向凝固过程中产生的内应力可能会通过加速原子团聚而改变析出行为，因此，需要仔细分析析出物的形态和溶质分配。在这里，我们研究了定向凝固的Fe ₇₃ Ga _27中的动态沉淀行为。[001]取向的合金。通过与经过相同时效处理的随机多晶样品进行比较，我们发现[001]取向样品会产生稀疏的fct纳米沉淀和额外的界面ω纳米沉淀。内应力加速了fct纳米沉淀和基体之间的Ga分配，从而减少了它们的成核位置。内应力还改变了基体和沉淀物之间的相互弹性相互作用，其中，通过在相前形成富集Ga的ω纳米沉淀物和{112} <111>堆积断层，来适应fct纳米沉淀物的贝恩应变，这与无规多晶不同。样品，其中贝恩应变通过基质的局部四边形变形来适应。结果是，晶粒取向样品的磁致伸缩增强率为40％，比无规多晶样品的〜165％弱。我们的结果不仅揭示了含应力和无应力时效条件之间的沉淀差异，而且还有助于指导应仔细控制纳米沉淀物的类型，数量密度和尺寸的超功能合金的微观结构设计。