Nickel-based superalloys possess many desirable properties, including high strength, desirable oxidation resistance, and superior thermal stability, and are widely utilized as the preferred materials for crucial hot-end components in the aerospace field. As an important structural material in the aerospace industry, the GH3536 nickel-based superalloy is used to manufacture aero-engine combustion chambers and other high-temperature components of aircraft engines with high operating temperatures and complex structures. Early research on GH3536 mainly focused on deformation behavior, heat treatment, and welding. However, with increasing demand for high-performance, lightweight, and heavy-duty aerospace equipment, higher requirements are placed on traditional complex component manufacturing. Laser powder bed fusion (L-PBF), also known as selective laser melting (SLM), has been introduced to fabricate GH3536 complex-structure components. However, bulkhead, siding, and casing structures tend to be large, and conventional L-PBF technology is not capable of building large parts owing to the limited building dimensions and efficiency. Multi-L-PBF (ML-PBF) technology combines the advantages of high precision and high efficiency and is more suitable for building large-size and complex-structured GH3536 components owing to the composition of multiple single-laser beam modules. However, studies on the influence of defects, microstructures, and mechanical properties of GH3536 parts with different laser beams involved in the ML-PBF process are limited. In this study, using quadruple-laser ML-PBF equipment, the effects of different laser beams on the micro/macro properties of L-PBF-processing GH3536 parts are investigated. In addition, the differences in the defect characteristics, microstructure, residual stress, and tensile properties of the single-, dual-, and quadruple-laser-processing samples are examined. This study is expected to provide a better understanding of multi-laser interactions on the samples, and a scientific basis for the application of nickel-based materials in the aerospace fields.

Using the large-size, four-laser ML-PBF equipment and the gas-atomized GH3536 nickel-based superalloy powder particles with the particle size of 21.2-58.9 μm, GH3536 samples were prepared using single-, dual-, and quadruple-laser beams with the optimized process parameters. First, the relative densities of the samples were measured using the Archimedes method and micrograph analysis. The optical microscopy and scanning electron microscopy equipped with an electron back-scattered diffraction (EBSD) detector were employed to examine the microstructures of the cubic specimens. The residual stress of the samples was measured using an X-Ray diffraction (XRD) testing machine. In addition, a high-temperature endurance testing machine was used to test the room-temperature tensile properties of the alloys.

Re-melting during the ML-PBF process melts the unmelted powder particles on the upper surface and penetrates the powder layer better, which helps to improve the surface quality (Fig. 3). With the increase of laser beams involved in the ML-PBF process, the relative density gradually decreases from 99.82% to 92.35% and 98.97%, respectively, which is mainly due to the pores and microcracks produced during the re-melting process (Fig. 4). In the ML-PBF process, grains in the re-melting regions grow on the solidified materials, which hinders the growth of columnar crystals. With an increase in the number of laser beams, a large number of columnar crystals gradually transform into cellular crystals (Fig. 5). The texture index of the samples along the horizontal direction increases from 3.040 (single-laser) to 3.403 (dual-laser) and 3.465 (quadruple-laser), whereas the volume fraction of high-angle grain boundaries (HAGBs) gradually decreases from 65.9% to 50.1% and 46.3%, respectively (Figs. 6 and 7). This is primarily attributed to the recrystallization of grains during the ML-PBF process, which leads to the transformation of HAGBs to low angle grain boundaries (LAGBs), causing a more significant preferred growth of grains and obvious anisotropy of materials. Values of the residual stress of single-, dual-, and quadruple-laser processing samples are 192.3, 106.5, and 44.1 MPa, respectively. The tensile strengths of the samples are 858.1 (single-laser), 851.4, and 830.5 MPa, respectively, while the elongation at break is 30.3%, 25.9%, and 25.4%. The main reason for this may be that ML-PBF can induce pore and microcrack defects, which are stress concentration components that accelerate crack propagation under tensile stress, resulting in premature fracture failure, and thus reducing the elongation of the samples.

GH3536 nickel-based superalloy is prepared via ML-PBF, and the defects, microstructures, and mechanical properties in single-, dual-, and quadruple-laser-processing regions are investigated. The results indicate that the surface quality improves with an increase in laser beams introduced during the ML-PBF process, while the relative density decreases from 99.82% (single-laser) to 92.35% (dual-laser) and 98.97% (quadruple-laser). Simultaneously, after re-melting in the overlap regions during the ML-PBF inducing recrystallization, the preferred growth orientation along (001) is more apparent, the texture index increases from 3.040 to 3.403 and 3.465, and the volume fraction of LAGBs decreases from 65.9% to 50.1% and 46.3%. Under the multiple laser repeat scanning process, the residual stress in the overlap regions also reduces, where residual stress values of the single-, dual-, and quadruple-laser processing regions are 192.3, 106.5, and 44.1 MPa, respectively. All the samples display an equivalent tensile strength of more than 800 MPa, while the pores and microcracks deteriorate the ductility of the overlap regions. The elongation at break decreases from 30.3% (single-laser) to 25.9% (dual-laser) and 25.4% (quadruple-laser). This work is expected to provide an efficient reference and theoretical guidance for large-size nickel-based superalloy components fabricated via ML-PBF.