Jiqiang Wang

Microdroplet additive manufacturing (MAM) enables high-precision fabrication through the controllable generation and site-specific deposition of microscale liquid entities. This review defines MAM according to the state and fate of the transported liquid: in core MAM, discrete microdroplets or droplet-derived jets serve as spatially addressable material units that directly determine local deposition and contribute to structure formation through solidification, curing, or coalescence. We first examine the governing principles and performance boundaries of atomization, continuous inkjet, and on-demand droplet generation, followed by seven representative actuation mechanisms—piezoelectric, thermal inkjet, pneumatic pulse, electromagnetic, magnetohydrodynamic, electrohydrodynamic, and laser-induced cavitation—and laser-induced forward transfer as a distinct laser-driven transfer strategy. Five direct-forming process families are then positioned within this framework: photopolymer and molten material jetting as core MAM; aerosol jet printing and binder jetting as droplet-mediated or droplet-enabled processes; and direct ink writing as an adjacent continuous-filament process. Representative advances in bioprinting, flexible electronics, and electronic packaging and precision metal fabrication are critically assessed. Key challenges include viscosity–frequency tradeoffs, stable jetting of high-melting-point metals, and multi-material interfacial compatibility. Future priorities are modular and hybrid actuation, closed-loop process control, deposition–consolidation co-design, and industrial scale-up and qualification. By integrating an operational scope definition, unified droplet physics, source-audited quantitative comparisons, and a requirements-driven technology-selection framework, this review provides a systematic basis for technology selection, process optimization, and fundamental research in MAM.

Severe blade tip wear induced by high-speed rubbing against nickel- or cobalt-based abradable seal coatings remains a critical challenge for titanium alloy in compressors. This study introduces silver (Ag) as a modified additive to a CoCrAlY-based coating system to address this issue. The tribological performance and abradability of coatings with 0–20 wt.% Ag were systematically evaluated through reciprocating sliding and high-speed rubbing tests. Results indicate that an optimal Ag content significantly enhances coating abradability, effectively protecting Ti2AlNb blades. However, excessive Ag addition promotes adhesive material transfer to the blade tip at high temperatures and high speeds. Ag functions as a solid lubricant at room temperature but transitions to a viscous phase that aggravates adhesive wear at elevated temperatures. Crucially, Ag addition alters the dominant high-speed wear mechanism from high-temperature adhesion to deformation-induced abrasion. This shift is attributed to the high thermal diffusivity of Ag, which dissipates frictional heat and suppresses blade tip softening. This work demonstrates that moderate Ag modification substantially improves the tribological compatibility of abradable seal coatings, offering a new strategy for protecting high-temperature titanium alloy components.