Abstract
Melt-grown alumina-based composites are receiving increasing attention due to their potential for aerospace applications; however, the rapid preparation of high-performance components remains a challenge. Herein, a novel route for 3D printing dense (< 99.4%) high-performance melt-grown alumina-mullite/glass composites using directed laser deposition (DLD) is proposed. Key issues on the composites, including phase composition, microstructure formation/evolution, densification, and mechanical properties, are systematically investigated. The toughening and strengthening mechanisms are analyzed using classical fracture mechanics, Griffith strength theory, and solid/glass interface infiltration theory. It is demonstrated that the composites are composed of corundum, mullite, and glass, or corundum and glass. With the increase of alumina content in the initial powder, corundum grains gradually evolve from near-equiaxed dendrite to columnar dendrite and cellular structures due to the weakening of constitutional undercooling and small nucleation undercooling. The microhardness and fracture toughness are the highest at 92.5 mol% alumina, with 18.39±0.38 GPa and 3.07±0.13 MPa·m1/2, respectively. The maximum strength is 310.1±36.5 MPa at 95 mol% alumina. Strength enhancement is attributed to the improved densification due to the trace silica doping and the relief of residual stresses. The method unravels the potential of preparing dense high-performance melt-grown alumina-based composites by the DLD technology.
Highlights
Further development of hot-end components for advanced aero-engines and high-efficiency gas turbines and thermal protection systems for aircraft isJ Adv Ceram 2022, 11(1): 75–93 are eutectic, such as Al2O3/YAG (Y3Al5O12) [5], Al2O3/ GAP (GdAlO3) [6], Al2O3/Er3Al5O12/ZrO2 [7]
When the alumina content was low (70 mol%, AS70), the content of the corundum phase precipitated from the melt was low (~24.2 vol%)
With the alumina content increased up to 80 mol% (AS80), the corundum dendrites transformed into long columnar dendrite structures with directional alignment along the deposition direction (Fig. 4(c))
Summary
Further development of hot-end components for advanced aero-engines and high-efficiency gas turbines and thermal protection systems for aircraft (e.g., re-entry space vehicles, rocket, and strategic bombers) isJ Adv Ceram 2022, 11(1): 75–93 are eutectic, such as Al2O3/YAG (Y3Al5O12) [5], Al2O3/ GAP (GdAlO3) [6], Al2O3/Er3Al5O12/ZrO2 [7]. The inherent oxidation resistance further ensures the stable operation of hot-end components and thermal protection systems under a high-temperature and high-pressure oxidation environment. These are the current limitations of traditional superalloys and SiC-based composites [8,9] in the above applications. As one of the melt-grown alumina-based composites, in addition to the excellent performance mentioned above, alumina–mullite composites (AMC) exhibit outstanding thermal shock resistance performance on account of appropriate porosity, suitable interfacial bonding, and low thermal expansion coefficient of mullite. The demand for lightweight, heat-resistant, and high-performance composites has promoted the development of melt-grown alumina-based composites, especially melt-grown AMC
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
