This study evaluates the daytime thermal-regulation performance of a hybrid composite brick integrated with a phase change material (PCM) core containing paraffin, natural zeolite, and a hydrogel ice pack. A one-dimensional finite volume method (1D FVM) model with a 10-node through-thickness grid and an effective heat-capacity formulation was used to represent transient conduction and was validated against outdoor measurements collected at 15-min intervals from 06:00 to 18:00 over six consecutive days. The measured exterior surface reached 45.52 °C at 12:15, whereas the brick core reached 44.58 °C at 13:45, giving a 90-min peak-temperature time lag. The maximum exterior-to-core temperature difference was 7.88 °C and the maximum exterior-to-interior thermal decrement was 4.65 °C. The calculated conduction heat flux reached 32.50 W/m2 during heat absorption and −4.76 W/m2 during heat release. Model validation yielded MAE = 0.577 °C, RMSE = 0.788 °C, and R2 = 0.994. Because the maximum core temperature only approached the lower end of the reported paraffin melting interval (44–60 °C), a linear phase-fraction interpretation indicates only the onset of melting (approximately 3.6% at the core peak), rather than complete PCM melting. The results therefore support the hybrid brick as a thermal-buffering wall concept while defining the scope of the reduced-order model: radiation and free convection are not solved as separate field equations but are embedded in the measured surface-temperature boundary conditions.
Ti2AlNb alloy is a promising lightweight high-temperature structural material for aerospace. In this study, Ti2AlNb alloys were fabricated by electron beam powder bed fusion (EB-PBF) using pre-alloyed Ti-22Al-25Nb (at,%) powders. This work optimizes the substrate preheating temperature and scanning speed of the EB-PBF process to achieve superior strength. The microstructure, tensile properties, and crack propagation mechanism of the as-deposited alloy were systematically studied. The EB-PBFed Ti2AlNb alloy exhibits a typical refined basket-weave microstructure with uniformly fine lamellar O-phases and dispersed remnant B2 laths. The alloy achieves favorable strength-ductility synergy both at room temperature (ultimate tensile strength (UTS) of 1178 ± 10 MPa, yield strength (YS) of 1058 ± 7 MPa and elongation of 3 ± 0.6%) and at 650 °C (UTS of 933 ± 12 MPa, YS of 790 ± 5 MPa and elongation of 4 ± 1%). Fracture analysis indicates that boundaries of coarse primary O-phases are the main sites for crack initiation and propagation due to local stress concentration and dislocation tangling. The optimized process contributes to retarding the precipitation of coarse primary O-phases and restrains crack evolution, enabling simultaneous improvement of strength and ductility. This work provides an effective route to obtain high strength and ductility in EB-PBF-fabricated Ti2AlNb alloy for aerospace high-temperature lightweight components.
