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Porous Si 2 N 2 O ceramics strengthened by directional β-Si 3 N 4 are fabricated by direct ink writing technique and seeding method. Slurries prepared with different contents of β-Si 3 N 4 grains exhibited superior printing behavior. The degree of orientation of β-Si 3 N 4 grains increased with the increase of grains content. The mechanical properties of the porous Si 2 N 2 O ceramic are effectively improved by interspersed β-Si 3 N 4 grains and present anisotropy. This novel strategy provides a reference for fabricating high-performance anisotropic complex structure ceramics. [ABSTRACT FROM AUTHOR]

An embedded dense coating was fabricated on the direct ink writing Si 2 N 2 O porous ceramic by impregnating the SiO 2 -sol and in-situ sintering. The influence of different heat-treatment atmosphere and temperature on the microstructure, phase composition, mechanical properties and water resistance was studied systematically. A relatively flat and dense seal layer was obtained in the air atmosphere. The crystallization of SiO 2 was inhibited by nitrogen atmosphere. The resulting embedded coatings effectively improved the mechanical properties and water resistance of Si 2 N 2 O porous ceramic, and the specimens treated in air exhibited better comprehensive performance due to the higher densification. This strategy provides a reference for in-situ surface reinforced components with complex structures. Unlabelled Image • A strategy for fabricating embedded dense coating on complex structure ceramic was provided. • The samples heat-treated in air exhibits better sealing effect than that in nitrogen. • The crystallization of SiO 2 was inhibited by nitrogen atmosphere. • Mechanical properties and water resistance are improved due to the good sealing effect. [ABSTRACT FROM AUTHOR]

Post heat treatment has been considered as an essential process to relieve residual stress, tailor the microstructure and obtain desired mechanical properties of the parts manufactured by selective laser melting (SLM) technology. The present work comparatively investigated the effect of heat treatment on microstructure evolution and mechanical properties of the SLM-fabricated Ti–6Al–4V alloy (Ti64) and 2 vol% TiB/Ti–6Al–4V titanium matrix composite (TMC). Microstructure analysis indicated that the as-built and heat treated TMC samples showed profoundly different microstructures compared to that of Ti64 samples. With heat treatment temperature increasing, the dominant acicular α′ martensite of Ti64 was decomposed into fine (α+β) lamella and microstructure coarsening occurred. A finer (α+β) dual-phase matrix microstructure, compared to that of Ti64, was achieved for TMC samples when heat treatment temperature exceeded 850 °C. The densely dispersed clusters of parallel nanoscale TiB precipitates of the TMC grew into individually separate TiB whiskers with larger nanoscale and sub-microscale size through a stacking up process of (100) planes based on an Ostwald ripening process. Mechanical testing results showed that the hardness and yield strength values of TMC samples before and after heat treatment were all higher than that of the Ti64 samples. A superior comprehensive mechanical performance with relatively high yield strength (1345 MPa) and significantly improved fracture strain from 17.6% to 31.3% was achieved for the TMC sample after heat treatment at 850 °C. [ABSTRACT FROM AUTHOR]