This study investigates the influence of volume energy density (VED) on surface quality, density, defects, and microstructure of laser powder bed fusion (L-PBF) GH3536 alloy. Specimens fabricated below 80 J/mm3 exhibit lack-of-fusion pores on surfaces and internally, with pore density decreasing but crack initiation occurring as VED increases. Density consistently exceeds 99.5%, peaking at 99.85% (VED = 167 J/mm3). Excessive VED (208 J/mm3) induces surface warping, reduces cracking, but increases pore size/quantity, causing marginal density reduction. Lack-of-fusion defects nucleate microcracks distributed in layer bands; cracks propagate along high-angle grain boundaries following grain growth directions with significant localized stress. Higher VED increases melt pool overlap rate (70.49% at 208 J/mm3) and aspect ratio (width/depth = 6.9), while reducing cooling rates to 1.2 × 105 K/s.

The dissimilar combination of NiTi shape memory alloy and Ti6Al4V titanium alloy offers superelasticity, biocompatibility and high specific strength, showing broad application prospects in aerospace and medical fields. However, when fabricating NiTi/Ti6Al4V composite components by multi-material laser powder bed fusion (MM-LPBF), brittle cracks or even complete delamination easily occur at the interface. In this paper, without relying on intermediate interlayer materials, we innovatively propose a root-inspired three-dimensional bio-interlocking interface structure. By means of macroscopic three-dimensional geometric interlocking, the crack propagation path and load transfer mode are forced to change. Using the branching angle (45°, 60°) and the structural size multiplier (1.2, 1.5) as variables, the influence of the bio-inspired geometric parameters on the interfacial forming quality, microstructure and mechanical properties was systematically investigated. The results show that the branching angle is the primary factor determining the performance. The 45° low-angle branched specimens exhibit overall brittle delamination along the flat metallurgical reaction interface under shear loading, with an average shear strength of only 17.47 MPa. In contrast, the 60° high-angle branched specimens, owing to their larger normal embedding depth, exhibit a failure mode transitioning to a mixed mode that includes crack deflection, branch shearing and plastic tearing of the Ti6Al4V matrix. Although TEM confirms that a continuous Ti₂Ni brittle phase still exists at the interface, the optimised 60–1.5 structure increases the average shear strength to 128.37 MPa, which is more than six times higher than that of the 45–1.2 group (17.47 MPa). This “geometrical constraint toughening” strategy provides a new paradigm for the interfacial strengthening of dissimilar metals without relying on metallurgical modification.

Hastelloy X (HX) and Y₂O₃/Hastelloy X (YHX) superalloys were fabricated by laser directed energy deposition (LDED). In-situ tensile testing combined with electron backscatter diffraction (EBSD) was employed to systematically investigate the effect of Y₂O₃ addition on the plastic deformation behavior and grain-boundary slip transfer mechanism. The results show that the YHX superalloy develops a significantly larger plastic deformation zone, with more pronounced and more numerous slip bands and shear bands than the undoped HX alloy. A clear transition in fracture mode is also observed. Based on grain-by-grain crystallographic analysis using in-situ EBSD, the active slip systems in both alloys were accurately identified, with particular attention given to slip transfer events at grain boundaries. Using the local crystallographic rotation detected at the tips of slip bands as a criterion for slip transmission, the torsion angle and Luster–Morris parameter m′ were calculated for adjacent grain pairs. It is found that the introduction of Y₂O₃ results in systematically smaller torsion angles and larger m′ values throughout the alloy, indicating lower resistance to slip transmission across grain boundaries. This favorable modification of the crystallographic criteria is the intrinsic mechanism responsible for the improved plastic deformability of the YHX superalloy. The findings provide a theoretical basis for tailoring the mechanical properties of additively manufactured superalloys through oxide dispersion.

This paper investigated the effect of trace P additions on the microstructure and creep behavior of GH3536 alloy produced by laser-directed energy deposition. P microalloying had little influence on the macroscopic morphology, but when the P content reached 0.035wt.%, numerous internal cracks formed due to excessive P segregated to grain boundaries, promoting the precipitation of hard, brittle phosphides and causing grain-boundary embrittlement. As the P content increased, grain-boundary M₂₃C₆ carbides gradually changed from continuous particles to discrete short rods, and the coverage of grain-boundary precipitates first rose and then fell. P microalloying had minimal effect on ductility. When the P content was 0.021wt.%, the steady-state creep rate decreased and the creep life increased by 114%, from 8.4 h to 18 h; however, when the P content was further increased to 0.035wt.%, the creep life dropped sharply. The addition of P altered the creep fracture mode from a mixed mode dominated by intergranular fracture to fully intergranular fracture. An appropriate P level modified the morphology and coverage of grain-boundary precipitates, enhancing their ability to pin dislocations and impede defect propagation during creep, thereby improving creep resistance. In contrast, excessive P caused grain-boundary embrittlement and markedly reduced creep life.