Titanium (Ti) and its nanoparticles are widely used in 3D printing due to a high corrosion resistance, biocompatibility, and lightweight potential. However, the atomic-scale mechanism of sintering densification and phase transition remains unclear, which limits the performance regulation of additively manufactured Ti components. In this work, molecular dynamics simulations were performed to study the sintering and phase-transition behavior of multi-sized Ti nanoparticles under 3D printing conditions. The melting point of 2 nm Ti nanoparticles decreases to about 1000 K, while that of 12 nm particles approaches the bulk value of 1941 K. Two distinct stages were observed during surface-energy-induced phase transition: initial lattice reconstruction at 800–1100 K, followed by complete melting above 1500 K. Smaller nanoparticles exhibited stronger pre-melting and faster atomic diffusion, which effectively filled interparticle pores and reduced the porosity. Increasing particle contact points shortens atomic diffusion paths, accelerates densification, and alleviates stress concentration. This study reveals the size-dependent sintering mechanism of Ti nanoparticles at the atomic level, providing theoretical guidance for the process optimization, microstructure control, and performance improvement of aerospace and biomedical titanium components fabricated by additive manufacturing.

Aiming at the reduction in penetration depth caused by the deformation and fracture of conventional 90W-Ni-Fe rod penetrators during ultra-high-velocity penetration, a lightweight tungsten-based ceramic alloy was fabricated in this study. Ballistics tests were conducted to verify the penetration performance of the novel lightweight alloy against concrete targets, and the existing theoretical penetration model was modified accordingly. The results indicate that, within the impact velocity range of 1400~1750 m/s, the penetration depth of both rod penetrators presents an initial increasing and subsequent decreasing trend, with an extreme value near 1625 m/s and a dimensionless penetration depth X_p/L close to 4. Compared with the traditional 90W-Ni-Fe alloy, the lightweight tungsten-based ceramic alloy penetrator achieves a mass reduction of 5.7%. In the impact velocity range from 1408.0 m/s to 1743.5 m/s, its penetration depth increases by 6.22%~10.58%, and the improvement becomes more significant with the increase in impact velocity. For the modified theoretical model, the predicted ultimate penetration depth of the lightweight alloy rod penetrator increases by 8.85%, while the average mass loss rate and average erosion rate decrease by 12.09% and 17.65%, respectively. The error between theoretical calculations and experimental data is within 5%.

This study proposes a novel synergistic design strategy to enhance the oxidation resistance of FeNiCuAl-based high-entropy alloys by integrating multi-element alloying (Cr-Co-Mn), trace Y modification, and laser-cladding-induced nanocrystallization. While the Base Alloy exhibited a mass gain of approximately 15 mg/cm² after oxidation at 900 °C for 120 h, the addition of Cr_2.5Co_2.5Mn_2.5 promoted the formation of a multilayered oxide scale (outer MnCr₂O₄/inner Al₂O₃), reducing the parabolic oxidation rate constant to 1.7 × 10⁻⁵ mg²·cm⁻⁴·s⁻¹. The originality of this work lies in the coupling of compositional and microstructural engineering; further addition of 0.5 at.% Y decreased this constant to 1.7 × 10⁻⁶ mg²·cm⁻⁴·s⁻¹—a three-order-of-magnitude reduction relative to the Base Alloy, while increasing the apparent oxidation activation energy to ~350 kJ/mol. After 100 thermal cycles at 1000 °C, the designed alloy showed a mass change of only 0.05 ± 0.02 mg/cm², with its critical load and interfacial fracture energy reaching 78 N and 14.8 J/m², respectively. Furthermore, the alloy retained a hardness of 310 HV, an elastic modulus of 135 GPa, and a tensile strength of 240 MPa at elevated temperature. These results demonstrate that the synergistic integration of chemical and structural optimization provides a new paradigm for designing low-cost, high-performance FeNiCuAl-based protective coatings.