Metal additive manufacturing (AM) offers exceptional design freedom, but its high thermal gradients often generate non-equilibrium microstructures with chemical and interfacial instabilities. Steels that solidify as δ-ferrite often experience a further solid-state phase transformation to austenite during AM. The detailed nature of this phase transformation during AM is yet to be fully understood. Duplex stainless steel, which is known for its unique combination of high corrosion resistance and mechanical properties, is a suitable alloy to further study this phase transformation.

The current study aims to gain novel insights into solid-state phase transformations and mechanical properties of duplex stainless steels during laser powder-bed fusion (LPBF). As-printed microstructures exhibit significant deviations when compared to conventionally manufactured counterparts in terms of phase balance and morphology, elemental partitioning, and interface character distribution. During LPBF, only a small fraction of austenite forms, mostly at the ferrite-ferrite grain boundaries, via a phase transformation accompanied by diffusion of interstitials. Austenite/ferrite boundaries are shown to terminate on {100}_F//{111}_A planes. This is due to the character of parent ferrite-ferrite boundaries which is dictated by the sharp <100> texture and geometry of austenite grains induced by directional solidification and epitaxial growth of ferrite. Benchmarking mechanical properties against a wrought counterpart demonstrates that AM offers high strength but relatively low ductility and impact toughness. A short heat treatment reverts the microstructure back to its equilibrium state resulting in balanced tensile and toughness properties, comparable to or even better than those of wrought counterparts.

金属增材制造 (AM) 提供了卓越的设计自由度，但其高热梯度通常会产生具有化学和界面不稳定性的非平衡微结构。凝固为 δ-铁素体的钢通常在 AM 过程中经历进一步的固态相变奥氏体。AM 期间这种相变的详细性质尚未完全了解。双相不锈钢以其独特的高耐腐蚀性和机械性能组合而闻名，是进一步研究这种相变的合适合金。

目前的研究旨在对激光粉末床融合 (LPBF) 过程中双相不锈钢的固态相变和力学性能有新的认识。与传统制造的对应物相比，印刷后的微结构在相平衡和形态、元素分配和界面特征分布方面存在显着偏差。在 LPBF 过程中，只有一小部分奥氏体形成，主要是在铁素体-铁素体晶界处，通过伴随填隙扩散的相变。显示奥氏体/铁素体边界终止于 {100} _F //{111} _A飞机。这是由于母体铁素体-铁素体边界的特征，其由铁素体定向凝固和外延生长引起的奥氏体晶粒的尖锐<100>织构和几何形状决定。针对锻造对应物的基准机械性能表明，AM 提供高强度但相对较低的延展性和冲击韧性。短暂的热处理使微观结构恢复到其平衡状态，从而产生平衡的拉伸和韧性性能，与锻造对应物相当甚至更好。