Spatter is an inherent, unpreventable, and undesired phenomenon in laser powder bed fusion (L-PBF) additive manufacturing. Spatter behavior has an intrinsic correlation with the forming quality in L-PBF because it leads to metallurgical defects and the degradation of mechanical properties. This impact becomes more severe in the fabrication of large-sized parts during the multi-laser L-PBF process. Therefore, investigations of spatter generation and countermeasures have become more urgent. Although much research has provided insights into the melt pool, microstructure, and mechanical property, reviews of spatter in L-PBF are still limited. This work reviews the literature on the in situ detection, generation, effects, and countermeasures of spatter in L-PBF. It is expected to pave the way towards a novel generation of highly efficient and intelligent L-PBF systems.

Multi-material laser powder bed fusion (LPBF) additive manufacturing is a promising approach for integrating the functionality and mechanical performance of dissimilar materials into complex parts. This review offers a comprehensive overview of the recent advancements in multi-material LPBF, with a particular focus on compositionally heterogeneous/gradient parts and their fabrication methods and equipment, control of interfacial defects, innovative designs, and potential applications. It commences with the introduction of LPBF-processed compositionally heterogeneous/gradient structures with dissimilar material distributions, including Z-direction compositionally heterogeneous structures, compositionally gradient structures in the Z-direction and XY planes, and three-dimensional (3D) compositionally heterogeneous structures. Subsequently, various LPBF methods and equipment for fabricating compositionally heterogeneous/gradient structures have been presented. Furthermore, the interfacial defects and process control during LPBF for these types of compositionally heterogeneous/gradient structures are discussed. Additionally, innovative designs and potential applications of parts made from compositionally heterogeneous/gradient structures are illustrated. Finally, perspectives on the LPBF fabrication methods for compositionally heterogeneous/gradient structures are highlighted to provide guidance for future research.

This work investigated the influence of process parameters on the densification, microstructure, and mechanical properties of a Ti–6Al–4V alloy printed by selective laser melting (SLM), followed by annealing heat treatment. In particular, the evolution mechanisms of the microstructure and mechanical properties of the printed alloy with respect to the annealing temperature near the β phase transition temperature were investigated. The process parameter optimization of SLM can lead to the densification of the printed Ti–6Al–4V alloy with a relative density of 99.51%, accompanied by an ultimate tensile strength of 1204 MPa and elongation of 7.8%. The results show that the microstructure can be tailored by altering the scanning speed and annealing temperature. The SLM-printed Ti–6Al–4V alloy contains epitaxial growth β columnar grains and internal acicular martensitic α′ grains, and the width of the β columnar grain decreases with an increase in the scanning speed. Comparatively, the printed alloy after annealing in the range of 750–1050 °C obtains the microstructure consisting of α + β dual phases. In particular, network and Widmanstätten structures are formed at the annealing temperatures of 850 °C and 1050 °C, respectively. The maximum elongation of 14% can be achieved at the annealing temperature of 950 °C, which was 79% higher than that of as-printed samples. Meanwhile, an ultimate tensile strength larger than 1000 MPa can be maintained, which still meets the application requirements of the forged Ti–6Al–4V alloy.