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This paper presents an improved method for achieving controllable preparation of the composition and size of the monotectic alloy core-shell structure microspheres. This advancement is expected to enhance the commercial application of monotectic alloy core-shell structure microspheres. By installing a heating device at the top of the drop tube in the pulsated orifice ejection method setup, we achieved in-situ heat treatment of falling droplets, resulting in the successful preparation of Al 45 (Sn 42 Bi 58) 55 core-shell structure microspheres. Furthermore, we investigated the formation mechanism of the Al@Sn-Bi core-shell structure. Nine sets of Al-Sn-Bi microspheres with varying in-situ heat treatment temperatures were prepared. Analysis via X-ray diffraction and transmission electron microscopy revealed that the microspheres consisted of Al-rich, Sn-rich, and Bi-rich phases, without any intermetallic compounds. Scanning electron microscopy results indicated that as the in-situ heat treatment temperature increased, the structure of the Al-Sn-Bi microspheres transitioned from irregular to regular core-shell configurations. This suggests that higher heat treatment temperatures prolong liquid phase separation time, leading to increased repetition of Marangoni motion within the droplet, Ostwald ripening of the minor phase droplets, and Soret effect of the matrix phase. However, at temperatures exceeding 700 °C, the solidification rate of alloy droplets decreased, causing the Al-rich phase core to deviate from the center and form a crescent structure due to Stokes motion. [Display omitted] • A method is provided for the controllable production of monotectic alloy microspheres which have a core-shell structure. • Core-shell structure Al@Sn-Bi microspheres were prepared by the pulsated orifice ejection plus in-situ heat treatment. • Performing the microstructure evolution process of the core-shell structure Al@Sn-Bi microsphere. • Using TEM to observe the interface between Al and Sn, which composed of amorphous and nanocrystalline. [ABSTRACT FROM AUTHOR]

In this paper, a novel flat-top laser-aided cold metal transfer additive manufacturing (F-LCAM) method is proposed for titanium alloys to restrict internal defects and anisotropy of mechanical properties in large-scale additive-manufactured titanium structures. The proposed method uses a flat-top laser to stabilise the drifting cathode spot and suppress the irregular shape of the weld deposit by promoting thermionic emission on the molten pool surface. Compared to the cold metal transfer additive manufacturing (CMT-AM) process, the auxiliary flat-top laser promotes the wettability of the molten pool and increases the contact angle of deposition from 95° to 142° in an F-LCAM sample. The non-destructive X-ray testing (NDT) results of multi-bead multilayer deposition showed that the defects caused by the pool weld bead morphology were effectively suppressed. Attributed to fluid flow in the melt pool enhanced by the flat-top laser, the dendritic arms were broken, columnar β grains in the F-LCAM sample were finer than in CMT-AM sample, and the aspect ratios of prior-β grains decreased from approximately 6 to 1. The F-LCAM sample exhibited a higher elongation and lower anisotropy than the CMT-AM sample. Defects were observed on the fracture surfaces of the CMT-AM vertical samples, which reduced the elongation of the CMT-AM samples to lower than that of the F-LCAM sample. The ultimate tensile strength, yield strength, and elongation of the multi-bead multilayer deposition met the standards of as-forged Ti6321 titanium alloy, indicating that the Ti6321 titanium alloy structure fabricated by the F-LCAM process has acceptable tensile properties for engineering applications. [Display omitted] • A novel flat-top laser was introduced in cold metal transfer additive manufacturing (CMT-AM) process for titanium alloys. • The flat-top laser could stabilise the drifting arc cathode spot and suppress the irregular shape of the weld deposit. • Due to the flat-top laser, Marangoni flow was significantly enhanced, and the wettability of the molten pool was promoted. • The internal defects were effectively eliminated and coarse columnar grains were refined in the F-LCAM samples. • The tensile properties of F-LCAM samples met the standards of as-forged Ti6321 titanium alloy for engineering applications. [ABSTRACT FROM AUTHOR]

The microstructural characteristics and mechanical properties of forged parts differ significantly from those of additively manufactured parts, which results in different machinability. In this paper, the microstructure effect on the machinability of Inconel 718 parts obtained by different manufacturing processes, laser directed energy deposition (LDED), laser powder bed fusion (LPBF) and forging, is evaluated and critically discussed in terms of milling forces, surface morphology, surface roughness, chip morphology and subsurface microstructure. The results show that due to having the smallest grain size, high dislocation density, and precipitation hardening provided by the reinforcing phases, the milling force is maximized when cutting LPBF Inconel 718 parts. In addition to grain size and dislocation density, the texture also has an effect on the plastic deformation of the subsurface after milling. Furthermore, LDED and forged Inconel 718 parts undergo a continuous dynamic recrystallization process characterized by sub-grain rotation transforming low angle grain boundaries into high angle grain boundaries during milling. This study provides some theoretical guidance for the integration of additive and subtractive processes in the machining of complex structural parts with Inconel 718 alloy. [ABSTRACT FROM AUTHOR]

Spinning is a common processing method for ultra-thin-walled tube. However, it is susceptible to surface ruptures in the deformation zone due to point-by-point contact, which affects the quality of products. In response to this issue, a ring-roller spinning (RRS) process is proposed, where the spinning roller makes tangential inner contact with the tube blank. This expands the triaxial compressive region, reducing ruptures tendency. And the tangential compressive stress is strengthened on the basis on triaxial compression of the conventional spinning (CS) process, which provides shear stress state in deformation zone. This paper conducts a comprehensive investigation into the RRS for thin-walled tubes made of 304 austenitic stainless steel. The study combines theoretical and experimental approaches and employs the finite element method (FEM) to evaluate the stress state within the tangential region. Various characterization methods are applied to examine the microstructural evolution under ultra-low stress triaxiality (ULST). The results confirm that the deformation zone is primarily characterized by tangential pressure under ULST, which significantly influence the metal microstructure, plastic behavior, and cumulative large deformation. This innovative process facilitates the continued deformation of the tubes, even under the saturated conditions of work hardening with the martensitic plasticising behaviour promotes grain refinement to 124 nm, resulting in an increase in the yield strength of the tubes from -1060 MPa to 1550 MPa. Continuous processing of ultra-thin-walled tube with a cumulative thinning rate of 90% was achieved by conducting RRS five-pass spinability experiments. [ABSTRACT FROM AUTHOR]