It is challenging to simultaneously achieve nearly full density and high strength in refractory alloys using selective laser melting (SLM). In this study, the achievement of ultrahigh-strength resulting from nearly full density has been reported in beta-type titanium alloy by controlling the melt pool mode in SLM. The melt pool mode was divided into the conduction and keyhole modes, which were determined from the macroscopic morphology of the melt pool in the SLMed Ti-34.2Nb-6.8Zr-4.9Ta-2.3Si (wt%) (TNZTS) alloy single tracks in combination with the keyhole threshold (P·V^−0.5 = 251.3 W (m⋅s⁻¹)^−0.5) calculated theoretically. Compared with condition mode, the keyhole mode has higher porosity and inevitably causes poor mechanical property. Fortunately, by optimizing the SLM process parameters predicted via the keyhole threshold, an ultrahigh-strength and nearly full density (99.7%) TNZTS alloy with conduction mode was obtained by SLM. The alloy exhibited an ultrahigh compressive yield strength of 1286 MPa, which was higher than the majority of the beta-type titanium alloys reported so far. The microstructural analyses indicated that the ultrahigh-strength TNZTS alloy consisted of a thin shell-shaped (Ti, Nb, Zr)₂Si (S2) phase (20–50 nm) around the columnar β-Ti grain boundaries together with an ultrafine dot shaped (Ti, Nb, Zr)₅Si₃ (S1) phase (50–300 nm) in the β-Ti matrix. The ultrahigh strength resulted from high-density dislocations and the effective dislocation blockage by the semi-coherent S1 and coherent S2 phases, thereby leading to the dislocation-strengthening and hardening effect. The strategy utilized in this study provides the fundamental guidelines for generating refractory metallic alloys with high density and excellent performance.

使用选择性激光熔化 (SLM) 在难熔合金中同时实现几乎全密度和高强度具有挑战性。在这项研究中，通过控制 SLM 中的熔池模式，在 β 型钛合金中实现了由接近全密度产生的超高强度。熔池模式分为传导模式和锁孔模式，由 SLMed Ti-34.2Nb-6.8Zr-4.9Ta-2.3Si (wt%) (TNZTS) 合金单轨中熔池的宏观形貌决定结合锁孔阈值 (P · V ^-0.5  = 251.3 W (m⋅s ^-1 ) ^-0.5) 理论计算。与条件模式相比，锁孔模式具有更高的孔隙率，不可避免地导致机械性能较差。幸运的是，通过优化通过锁孔阈值预测的 SLM 工艺参数，SLM 获得了具有传导模式的超高强度和接近全密度 (99.7%) 的 TNZTS 合金。该合金表现出 1286 MPa 的超高压缩屈服强度，高于目前报道的大多数 β 型钛合金。显微组织分析表明，超高强度 TNZTS 合金由围绕柱状 β-Ti 晶界的薄壳状 (Ti, Nb, Zr) ₂ Si (S2) 相（20-50 nm）和超细点组成异形 (Ti, Nb, Zr) ₅ Si ₃β-Ti 基体中的 (S1) 相（50–300 nm）。超高强度源于高密度位错和半相干S1和相干S2相的有效位错阻挡，从而导致位错强化和硬化效应。本研究中使用的策略为生成具有高密度和优异性能的难熔金属合金提供了基本指导。