A newly developed solid-state 3D-printing route of friction-forging tubular additive manufacturing (FFTAM) is applied to produce a low-carbon steel tube with superior mechanical properties. FFTAM technology is based on high-temperature severe plastic deformation and consolidation of metal chips via the friction stir welding/processing (FSW/FSP) mechanism to achieve a fully-dense tubular shape in a layer-upon-layer manner. This achieve metallurgical bonding between the layers using a rotating mandrel to maintain radial friction followed by press-die forging under hydrostatic pressure. After FFTAM deposition, the initial ferrite-pearlite microstructure of the steel chips is transformed to a triple-phase alloy consisting of ferrite, martensite, and austenite grains. The formation of martensitic phases by rapid cooling during layer-upon-layer deposition led to significant material hardening, and this further modified by the thermo-mechanical history upon deposition of subsequent layers. Transmission electron microscopy (TEM) observations revealed the microstructural refinement of the manufactured steel tube at the nano-scale range (<10 nm) to characterize the martensitic shear deformation caused by rapid cooling and severe plastic friction straining during the FFTAM process. The tensile, compression and forming response were evaluated in the additive manufactured steel tube, and attributed to the refined and triple-phases microstructure. A favorable combination of tensile strength (up to ∼675 MPa) and elongation to failure (∼15 %) with a high indentation hardness of ∼400 HV was demonstrated, along with a combination of ductile-brittle fractography features in related fracture surfaces.

摩擦锻造管状增材制造（FFTAM）的新开发的固态3D打印路线被用于生产具有优异机械性能的低碳钢管。FFTAM技术基于高温剧烈的塑性变形和通过摩擦搅拌焊接/加工（FSW / FSP）机制对金属碎片的固结，以层层叠叠的方式获得完全致密的管状形状。这使用旋转的心轴实现层间的冶金结合，以保持径向摩擦，然后在静水压力下进行压模锻造。FFTAM沉积后，钢片的初始铁素体-珠光体显微组织转变为由铁素体，马氏体和奥氏体晶粒组成的三相合金。在逐层沉积过程中通过快速冷却而形成的马氏体相导致显着的材料硬化，并且在随后的层沉积时通过热机械历史进一步改变了马氏体相。透射电子显微镜（TEM）观察表明，所制造的钢管在纳米级范围（<10 nm）上进行了微细化处理，以表征FFTAM过程中由于快速冷却和严重的塑性摩擦应变引起的马氏体剪切变形。在增材制造的钢管中评估了拉伸，压缩和成形响应，并将其归因于精炼和三相显微组织。证明了良好的抗拉强度（至多675 MPa）和断裂伸长率（至15％）的良好组合，压痕硬度高至400 HV，