Anyu Shang

Microlattices hold significant potential for developing lightweight structures for the aeronautics and astronautics industries. Laser Powder Bed Fusion (LPBF) is an attractive method for producing these structures due to its capacity for achieving high-resolution, intricately designed architectures. However, defects, such as cracks, in the as-printed alloys degrade mechanical properties, particularly tensile strength, and thereby limit their applications. This study examines the effects of microlattice architecture and relative density on crack formation in the as-printed 718 superalloy. Complex microlattice design and higher relative density are more prone to large-scale crack formation. The mechanisms behind these phenomena are discussed. This study reveals that microlattice type and relative density are crucial factors in defect formation in LPBF metallic alloys. The transmission electron microscopy observations show roughly round γ″ precipitates with an average size of 10 nm in the as-printed 718 without heat treatment. This work demonstrates the feasibility of the additive manufacturing of complex microlattices using 718 superalloys towards architectured lightweight structures.

Ceramic materials with high strength and chemical inertness are widely used as engineering materials. However, the brittle nature limits their applications as fracture occurs before the onset of plastic yielding. There has been limited success despite extensive efforts to enhance the deformability of ceramics. Here we report a method for enhancing the room temperature plastic deformability of ceramics by artificially introducing abundant defects into the materials via preloading at elevated temperatures. After the preloading treatment, single crystal (SC) TiO ₂ exhibited a substantial increase in deformability, achieving 10% strain at room temperature. SC α-Al ₂ O ₃ also showed plastic deformability, 6 to 7.5% strain, by using the preloading strategy. These preinjected defects enabled the plastic deformation process of the ceramics at room temperature. These findings suggest a great potential for defect engineering in achieving plasticity in ceramics at room temperature.

Twinned Al–Mg alloys have been reported. However, the role of Mg solute in facilitating the formation of growth twins remains unclear. By using a precession-assisted crystal orientation mapping technique (PACOM) coupled with transmission electron microscopy (known as ASTAR), we examined the evolution of twin boundaries in Al, Al–1Mg, and Al–2.2Mg (at. %) films. The twinned grain fraction elevates with increasing film thickness until it reaches a peak when the film thickness is 120–160 nm. The Al–Mg alloys exhibited greater twinned grain fractions than pure Al. To investigate the fluctuation of twinned grain fraction, two types of twin boundaries were classified including intergranular and intragranular twins. The initial increase in twin density is attributed to the impingement of twinned grains during island coalescence and the twinned grains are more likely to survive during the grain growth process. Whereas the decrease in twinned grain fraction in thicker films is related to the removal of intragranular twins, and a lack of formation mechanisms of new twins.