Mechanical properties of wood-derived silicon carbide aluminum-alloy composites as a function of temperature

Abstract

The mechanical behavior [i.e., stiffness, strength, and toughness (K IC )] of SiC Al-Si-Mg metal-ceramic composites (50:50 by volume) was studied at temperatures ranging from 25 to 500°C. The SiC phase was derived from wood precursors, which resulted in an interconnected anisotropic ceramic that constrained the pressure melt-infiltrated aluminum alloy. The composites were made using SiC derived from two woods (sapele and beech) and were studied in three orthogonal orientations. The mechanical properties and corresponding deformation micromechanisms were different in the longitudinal (LO) and transverse directions, but the influence of the precursor wood was small. The LO behavior was controlled by the rigid SiC preform and the load transfer from the metal to the ceramic. Moduli in this orientation were lower than the Halpin-Tsai predictions due to the nonlinear and nonparallel nature of the Al-filled pores. The LO K IC agreed with the Ashby model for the K IC contribution of ductile inclusions in a brittle ceramic.

X-ray micro-computed tomography of beech wood and biomorphic C, SiC and Al/SiC composites

“…Fibers and pits were still visible in SEM, but the pit structure and some detail of the fibers cells was lost in the mCT as some pore diameters approached that of the voxel dimensions. Using the 3D data (volumes the same as for the wood), the porosity volume fraction contributed by the vessels was measured at 0.38 (Table 1), which corresponds well with previously conducted mercury porosimetry results [24]. In the porosimetry, 43% of the total sample volume was accounted for by pores with diameters greater than 15 mm, corresponding to %10 voxels, which was the minimum diameter used in the mCT-based calculation.…”

“…SiC reaction front advances through the carbon scaffold. Open pores in the carbon with diameters less than approximately 1 mm were eliminated by the volume expansion [24]. The fraction of porosity contributed by the vessels was measured as 0.43, which is within experimental error of published mercury porosimetry results (0.50).…”

“…The 1% value was determined using a threshold selected to reproduce the observed porous microstructure in slices outside of the volume under analysis; this visual inspection approach is not the most robust method of proceeding (see [42] for a discussion of more involved analyses) but sufficed for the present purpose. Picking a threshold that reproduced the mean residual porosity (%4%), measured by Archimedes' method [24], resulted in segmented slices with pores that were far too large.…”

“…The use of porous biomorphic SiC as a template to make a MCC is a more recent endeavor, and initial research has focused on the processing and mechanical properties of Al/SiC composites [24][25][26]. The composites are made by forcing aluminum into the void space of the porous SiC via gas-pressure infiltration or squeeze casting.…”

Biomorphic ceramics from wood-derived precursors

“…Further, they measured their mechanical properties [86] as well as load partitioning among the phases using in-situ diffraction experiments [87] and performed detailed investigations on their microstructure by means of x-ray computed micro tomography [52]. Copper-SiC composites have also been fabricated by electroplating targeting thermal applications by Pappacena et al [88,89].…”