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Ni-Sn anomalous eutectic is obtained by single track laser cladding with the scanning velocity from 1 mm/s to 10 mm/s using the Ni-32.5 wt.%Sn eutectic powders. The microstructure of the cladding layer and the grain orientations of anomalous eutectic were investigated. It is found that the microstructure is transformed from primary α-Ni dendrites and the interdendritic (α-Ni + Ni 3 Sn) eutectic at the bottom of the cladding layer to α-Ni and β-Ni 3 Sn anomalous eutectic at the top of the cladding layer, whether for single layer or multilayer laser cladding. The EBSD maps and pole figures indicate that the spatially structure of α-Ni phase is discontinuous and the Ni 3 Sn phase is continuous in anomalous eutectic. The transformation from epitaxial growth columnar at bottom of cladding layer to free nucleation equiaxed at the top occurs, i.e., the columnar to equiaxed transition (CET) at the top of cladding layer during laser cladding processing leads to the generation of anomalous eutectic. [ABSTRACT FROM AUTHOR]

Abstract: The microstructure variation of as-deposited Inconel 718 superalloy sample in deposition direction fabricated by laser solid forming (LSF) was investigated. It was found that the as-deposited microstructure was mainly consisted of predominant γ columnar dendrites directionally growing along the deposition direction. Primary dendrite arm space measurement revealed spaces of 11.5, 17.5 and 38.0μm at the bottom, the middle and the top section of the LSF sample respectively. The result was further studied by comparing with the Kurz–Giovanola–Trivedi (KGT) dendrite growth model, which was in a reasonable agreement with the experimental result. The various microstructures and micro-segregation situations at different sections of the LSF sample, which were induced by the thermal accumulation during LSF process, were also carefully discussed. [Copyright &y& Elsevier]

Abstract: The microstructure and residual stress of laser rapid formed (LRFed) nickel-base superalloy Inconel 718 was investigated. The as-deposited microstructure of an LRFed Inconel 718 alloy is composed of columnar dendrites growing epitaxially along the deposition direction, and the columnar dendrites transformed to unevenly distributed equiaxed grains after annealing treatment at high temperature. Residual stress evaluation in microstructure scale by Vickers micro-indentation method indicates that the residual thermal stress is unevenly distributed in the LRFed sample, and it has a significant effect on the recrystallization during solution annealing treatment. The residual stress is introduced by rapid heating and cooling during laser rapid forming. There is an alternative distribution between high residual stress regions and low residual stress regions, within a single deposited layer, resulting in a similar distribution of recrystallized grain size. [ABSTRACT FROM AUTHOR]

To improve the high temperature oxidation resistance of TA2 titanium alloy, a gradient Ni-Ti coating was laser cladded on the surface of the TA2 titanium alloy substrate, and the microstructure and oxidation behavior of the laser cladded coating were investigated experimentally. The gradient coating with a thickness of about 420–490 µm contains two different layers, e.g. a bright layer with coarse equiaxed grain and a dark layer with fine and columnar dendrites, and a transition layer with a thickness of about 10 µm exists between the substrate and the cladded coating. NiTi, NiTi 2 and Ni 3 Ti intermetallic compounds are the main constructive phases of the laser cladded coating. The appearance of these phases enhances the microhardness, and the dense structure of the coating improves its oxidation resistance. The solidification procedure of the gradient coating is analyzed and different kinds of solidification processes occur due to the heat dissipation during the laser cladding process. [ABSTRACT FROM AUTHOR]

Traditionally, the laser melt injection (LMI) technique can only be used for forming ceramic particles reinforced metal matrix composites (MMCs) for enhancing surface properties of lightweight engineering materials. In this research, the LMI method was employed to form metal particles reinforced MMCs on AZ91D instead. This was viable because of the unique properties of the AlCoCrCuFeNi high-entropy alloy (HEA) metal particles used. The large difference in melting point between the HEA and the substrate material (AZ91D), and the limited reaction and the lack of fusion between the HEA and Mg have made it possible that a metal particles reinforced AZ91D composite material was produced. The reason of limited reaction was considered mainly due to the relatively high mixing enthalpy between the HEA constituent elements and Mg. Although there was some melting occurred at the particles surface with some solute segregation found in the vicinity close to the surface, intermetallic compounds were not observed. With regard to the wear resistance of the MMCs, it was found that when the volume fraction of the reinforcement phase, i.e. the HEA particles, reached about 0.4, the wear volume loss of the coating was only one-seventh of that of the substrate material. [ABSTRACT FROM AUTHOR]

• The process characteristics of quasi-continuous-wave laser-based directed energy deposition is studied. • Laser mode-related formation mechanism of powder adhesion is revealed. • Critical factors of the deposition point formation are confirmed. • Surface quality is improved by the process adjustment strategy. Directed energy deposition (DED) is an advanced additive manufacturing technique that has garnered considerable success in various industrial sectors. However, the conventional continuous-wave laser mode employed in DED often results in excessive heat buildup and coarse microstructure, leading to compromised performance. The utilization of quasi-continuous-wave laser-based DED (QCW-DED) has emerged as a promising solution to these challenges. Nevertheless, limited understanding of the process characteristics associated with QCW-DED has impeded further exploration of thermal and microstructural control. Therefore, this study aims to comprehensively evaluate QCW-DED process characteristics, including deposition point morphology and surface quality, through a combination of experimental measurements and simulation analysis. The findings indicate that the height of the deposition point is primarily governed by heat and mass transfer, while the diameter is predominantly influenced by heat transfer. Consequently, optimizing process parameters based solely on laser input energy calculations is inadequate for QCW-DED. Furthermore, the phenomenon of powder adhesion was observed to accumulate more prominently at the periphery of the deposition point rather than in its central region. As a result, suggesting higher laser power and shorter laser exposure time is recommended to enhance the quality of the deposition point and mitigate powder adhesion issues. [ABSTRACT FROM AUTHOR]

Abstract: The effect of overlap rate on the residual stress, recrystallization nucleation location and the distribution of recrystallized grains of LSFed Inconel 718 superalloy were investigated. It is found that the as-deposited microstructures with different overlap rates have the similar characteristics including that columnar grains grow along the deposition direction. The overlap area possesses higher residual stress compared with the inner-pass area, and the position of peak residual stress is closer to previous pass. The increase in the overlap rate will broaden the variation range of the residual stress. During heat treatment, the recrystallization nucleation first occurs in the overlap area with the lower overlap rate, and then expands to both overlap area and inner-pass area paralleling with the increasing of the overlap rate. Although the overlap rate is only one of basic factors in the Laser Solid Forming process, it plays an important role in controlling residual stress distribution, material microstructure and mechanical properties. The higher overlap rate adopted, the finer and the more evenly distributed grains could be obtained through recrystallization for LSFed Inconel 718 superalloy. [Copyright &y& Elsevier]

The coarse columnar grains and special interface in laser solid formed (LSFed) Inconel 718 superalloy workpieces seriously affect their mechanical properties. To improve the microstructure and mechanical properties of LSFed Inconel 718 superalloy, electromagnetic stirring (EMS) was introduced to alter the solidification process of the molten pool during LSF. The results show that EMS could not completely eliminate the epitaxially growing columnar grains, however, the strong convection of liquid metals can effectively influence the solid–liquid interface growing mode. The segregation of alloying elements on the front of solid–liquid interface is inhibited and the degree of constitutional supercooling decreases correspondingly. Comparing the microstructures of samples formed under different process parameters, the size and amount of the γ+Laves eutectic phases formed in interdendritic area decrease along with the increasing magnetic field intensity, resulting in more uniformly distributed alloying elements. The residual stress distribution is proved to be more uniform, which is beneficial to the grain refinement after recrystallilzaiton. Mechanical properties testing results show an improvement of 100 MPa in tensile strength and 22% in elongation was obtained after EMS was used. The high cycle fatigue properties at room temperature was also improved from 4.09 × 10 4 cycles to 8.21 × 10 4 cycles for the as-deposited samples, and from 5.45 × 10 4 cycles to 12.73 × 10 4 cycles for the heat treated samples respectively. [ABSTRACT FROM AUTHOR]

In this paper, laser additive manufacturing (LAM) technology with powder feeding has been employed to fabricate 50%LAMed specimens (i.e. the volume fraction of the laser deposited zone was set to 50%). With aid of the 3D-DIC technique, the tensile deformation behavior of 50%LAMed Ti64ELI titanium alloy was investigated. The 50%LAMed specimen exhibits a significant characteristic of strength mismatch due to the heterogeneous microstructure. The tensile fracture of 50%LAMed specimen occurs in WSZ (wrought substrate zone), but the tensile strength is slightly higher and the plastic elongation is significantly lower than that of the wrought specimen. The 3D-DIC results shows that the 50%LAMed specimen exhibits a characteristic of dramatic plastic strain heterogeneity and the maximal strain is invariably concentrated in WSZ. The ABAQUS simulation indicates that, the LDZ (laser deposited zone) can constrain the plastic deformation of the WSZ and biaxial stresses develop at the interface after yielding. [ABSTRACT FROM AUTHOR]

• A bend-resistant high-resolution imaging optical fiber comprising over five thousand cores was reported and characterized. • The fiber is made of low-cost commercial-available glasses and has high numerical aperture. • No degradation of imaging is demonstrated at a bending radius of less than 2 cm and at an extensive wavelength range. We report design, fabrication, and characterization of bend-resistant high-resolution imaging optical fiber comprising over five thousand cores. The fiber is made of low-cost commercial-available H-ZK9B and H-K3 glasses which gives rise to a maximum numerical aperture up to 0.552 at 750 nm wavelength. The multi-stacking arrays of three-sized cores can effectively suppress the core-to-core crosstalk and raise the bend resistance. No degradation of imaging is demonstrated at a bending radius less than 2 cm and at an extensive wavelength range from the visible to the near-infrared, showing a substantial improvement over commercial state-of-the-art fiber bundles. [ABSTRACT FROM AUTHOR]

Abstract: By using a moving disc heat source model, an analytical model was developed to describe laser solid forming (LSF) process with the feedback of the surface temperature of the molten pool, which can be used to estimate the geometric characterizations (width and height) of the clad layer rapidly. An on-line temperature measurement system was established and some single-pass cladding experiments were conducted while the molten pool temperature was monitored. It was found that the estimated geometric characterizations agreed well with the experimental results. In addition, the power consumed by conduction, convection, radiation, evaporation and absorption during LSF were also estimated by the model. It was shown that the majority of the total absorbed power was conducted to the substrate. The effective model can not only be used to optimize the processing parameters but also potentially applied to the real-time feedback control. [Copyright &y& Elsevier]

Abstract: Laser solid forming (LSF) from blended elemental powders is a powerful tool for the synthesis of novel materials. Accurate composition control is critical for the application of this technique. It is found that the chemical composition of as-deposited sample can be controlled the same as the premixed elemental powders by keeping the identity of the divergence angles of the elemental powder streams. A mathematical model was established to describe the powder delivery process during LSF from blended elemental powders. Based on the consistency condition for divergence angles of different elemental powder streams, the match condition among the elemental powder characteristics (including particle size and density) can be obtained, which ensures the consistency in composition between the laser deposits and the premixed elemental powders. LSF experiments were carried out using a blend of Ti, Al, and V powders and the composition analysis was performed on as-deposited samples. The experimental results demonstrate the validity of the developed mathematical model. [Copyright &y& Elsevier]

• An analysis model of direct energy deposition on inclined substrate is established. • The effect of the inclined angle on the laser energy and powder flow distributions is studied. • The influence of scanning strategy on the surface quality is researched. • Deposition mechanisms of direct energy deposition on inclined substrate are revealed. Directed Energy Deposition (DED) has the potential to be widely used in many industries. Deposition on non-horizontal substrate is a practical process that must be faced, but it is rarely studied. This paper discusses the interaction between laser, powder, and inclined substrate based on an analytical model and the deposition profile measurements. It shows that the inclined angle of substrate has a significant effect on the laser energy density and powder flow mass distributions on the inclined substrate. Also, the influence of gravity and surface tension of liquid melt pool cannot be ignored during the deposition process on the inclined substrate, resulting in the significant difference between the simulated and measured deposited height. With increasing inclined angle of the substrate, the melt pool tends to flow downward due to the effect of gravity and surface tension, forming a concave melt pool in the upward scanning strategy and the horizontal melt pool in the downward scanning strategy, resulting in a greater deposited height in the upward scanning strategy and lower deposited height in the downward scanning strategy relative to the simulated results. Also, more adhered powders were formed on the deposited layer surface in the upward scanning strategy compared to that in the downward scanning strategy due to the lower laser energy distribution on the tail of the upward melt pool. [ABSTRACT FROM AUTHOR]