In the fast-evolving landscape of additive manufacturing, laser powder bed fusion (LPBF) stands out as a transformative technology reshaping how complex components are produced. Over the past decade, LPBF has moved well beyond prototyping to become a crucial enabler of industrial-scale production, particularly in aerospace, automotive, and biomedical sectors. Recent research conducted by Griffis, Shahed, Meinert, and colleagues has pushed the boundaries even further by delving into the nuances of multi-material LPBF processes. Their groundbreaking study, published in npj Advanced Manufacturing, investigates how build orientation fundamentally influences manufacturing defects, microstructural evolution, and the resulting mechanical performance of parts fabricated from multiple materials simultaneously.
Additive manufacturing techniques have traditionally focused on single-material fabrication, which, while powerful, limits design possibilities and material optimization. The incorporation of multi-material capabilities within LPBF offers unprecedented opportunities to tailor material properties locally within a single part. For instance, regions requiring high strength can be fabricated from titanium alloys, while ductile zones can utilize stainless steel or other compatible metals. However, these multifunctional structures introduce complex thermal and metallurgical interactions that manifest differently depending on how parts are oriented during the build. Understanding this interplay is essential to harness the full potential of multi-material LPBF.
Orientation matters because laser powder bed fusion relies on rapid melting and solidification cycles that create intricate microstructures driven by thermal gradients and solidification rates. When a part is oriented vertically, horizontally, or at any intermediate angle during printing, the thermal history changes drastically, affecting not only phase transformations but also residual stress distribution and porosity formation. Griffis and their team meticulously analyzed these effects by fabricating multi-material specimens in varying build orientations, using state-of-the-art characterization methods such as high-resolution scanning electron microscopy, X-ray computed tomography, and nanoindentation mapping.
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One significant observation from the study was that build orientation directly impacts defect density and morphology. In horizontally oriented samples, the prevalence of lack-of-fusion defects and micro-cracks was notably higher at the interfaces between different materials. This outcome is attributed to altered heat flow patterns and delayed solidification in these geometries, which exacerbate stress concentration and interfacial instability. Conversely, vertically oriented builds exhibited a more homogeneous defect distribution, albeit with an increase in residual tensile stresses that could affect long-term durability.
Beyond defects, the microstructural evolution observed was equally revealing. Multi-material LPBF induces complex diffusion and phase interaction zones, especially when dissimilar alloys abut. The study documented the formation of transition layers where unique microstructures formed, combining cellular dendrites and equiaxed grains. Depending on the build angle, these microstructural features varied in thickness and composition gradients, fundamentally altering local mechanical behavior. In particular, perpendicular build orientations promoted finer grain structures in the transition zones, likely due to higher cooling rates and modified thermal gradients.
The mechanical properties measured through microhardness and tensile testing further illustrated the critical role of build orientation. Samples printed at inclined angles demonstrated optimal combinations of strength and ductility, outperforming purely vertical or horizontal counterparts. This enhanced performance stems from the interplay between reduced defect formation and beneficial microstructural refinement afforded by certain thermal histories. Moreover, fracture analysis indicated that crack propagation paths were sensitive to orientation-induced microstructural anisotropies, influencing failure modes significantly.
From an industrial perspective, these findings are transformative. They suggest that engineers should strategically select build orientations—not only for geometric considerations but to intentionally manipulate microstructures and minimize defects in multi-material AM components. This approach could lead to tailored parts with site-specific properties, greater reliability, and higher fatigue resistance. The implications resonate across sectors aiming to adopt additive manufacturing for load-bearing and high-performance applications where failure is not an option.
Furthermore, the study highlights a critical aspect of multi-material AM: the need for integrated process optimization tools that account for thermal and metallurgical phenomena as functions of build parameters. Current industry practices often rely on heuristics and trial-and-error methods for orientation selection, but Griffis and collaborators advocate for predictive modeling frameworks that can simulate defect formation and microstructural development in complex multi-material geometries. Such models would empower designers to anticipate performance outcomes and optimize build strategies before committing to costly fabrication.
The research also identifies challenges ahead. Achieving perfect metallurgical compatibility between different powders remains elusive, particularly when thermal expansion mismatches introduce residual stresses that exacerbate cracking. The authors suggest that future work should explore tailored alloy systems optimized for co-processing and investigate novel process parameters such as laser power modulation and scan strategies to mitigate interfacial defects. Additionally, real-time monitoring and adaptive control systems could provide feedback to dynamically adjust parameters, enhancing consistency across builds.
Interestingly, environmental factors influencing heat dissipation, such as powder bed temperature and atmosphere composition, were acknowledged as additional variables that intertwine with build orientation effects. The study sets a precedent for comprehensive multi-factorial investigations to untangle these relationships fully. As additive manufacturing strives towards “digital twin” fabrication — where virtual replicas of parts predict real-world behavior — incorporating such detailed empirical data becomes invaluable.
One of the key innovations in this work is the integrated characterization approach, combining volumetric imaging with microscale mechanical testing. This methodology reveals hidden complexities within transition zones that previously went unnoticed. For example, nanoindentation mapping showed substantial heterogeneity in hardness values across material interfaces, which correlated strongly with observed microstructural gradients. Such insight enables precise tuning of post-processing heat treatments or surface modifications to optimize component lifespan.
Beyond technical insights, the study is poised to inspire cross-disciplinary collaboration. Material scientists, mechanical engineers, computational modelers, and manufacturing technologists must converge to translate these findings into practical workflows. Standardizing protocols for multi-material LPBF is essential to unlock predictable, scalable production. Moreover, regulatory bodies will benefit from such research to establish certification norms for safety-critical applications employing multi-material AM parts.
Looking forward, the implications of enhancing multi-material LPBF through orientation control herald a new era in manufacturing agility. Designers could imagine parts with built-in functional gradients, such as wear-resistant exteriors fused seamlessly into lightweight cores, or biomedical implants with gradually varying stiffness to better mimic complex tissue properties. The ability to fabricate such components reliably and reproducibly will accelerate innovation across numerous fields.
In sum, Griffis et al.’s pivotal contribution not only advances fundamental understanding of multi-material LPBF but sets a strategic direction for future technological breakthroughs. By exposing the intricate connections between build orientation, defect formation, microstructure, and mechanical properties, they equip the manufacturing community with a powerful lens to develop next-generation multi-material additive manufacturing solutions. As additive manufacturing continues its rise from niche application to mainstream production methodology, insights like these are instrumental in realizing its full transformative promise.
Subject of Research: Multi-material laser powder bed fusion (LPBF) and the effects of build orientation on defects, microstructure, and mechanical properties.
Article Title: Multi-material laser powder bed fusion: effects of build orientation on defects, material structure and mechanical properties.
Article References:
Griffis, J.C., Shahed, K., Meinert, K. et al. Multi-material laser powder bed fusion: effects of build orientation on defects, material structure and mechanical properties. npj Adv. Manuf. 2, 5 (2025). https://doi.org/10.1038/s44334-025-00020-5
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