科研之友
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摘要
beta-eucryptite (LiAlSiO4) with a negative thermal expansion coefficient can be used as reinforcement in metal matrix composites to reduce the coefficient of thermal expansion (CTE) of the composites. It is necessary to clarify the phase transformation of beta-eucryptite (LiAlSiO4) which influences the CTE of the composite. A copper matrix composite reinforced by beta-LiAlSiO4 was fabricated by spark plasma sintering. The composite was characterized using X-ray diffraction and transmission electronic microscope. A new phase of eucryptite has been found, which is a polymorph phase and has primary cubic structure with the lattice constant of 0.435 nm. The reason for the phase transition from beta-LiAlSiO4 to the new phase was discussed which may result from the large anisotropic stress in the beta-LiAlSiO4 particles of beta-LiAlSiO4/Cu composite. The discovery of the new polymorph of LiAlSiO4 in beta-LiAlSiO4/Cu composite indicates that the phase transformation caused by thermal mismatch stress may be easier than that caused by hydrostatic pressure.
