Metastable phase of β-eucryptite and thermal expansion behavior of eucryptite particles reinforced aluminum matrix composite

The aluminum matrix composites with 15%, 35%, 55% and 75% (volume fraction) of β-eucryptite (Euc) particles were prepared by spark plasma sintering (SPS) process. To prevent the interfacial reaction between Euc and Al, ZnO was coated on the surface of Euc particles. The microstructures of Euc/Al composites were studied by optical microscope (OM) and transmission electron microscope (TEM). The phase compositions in the composite were studied by X-ray diffraction method. The thermal physical properties of Euc/Al composites were analyzed by means of thermal dilatometer. A metastable phase of Euc was discovered which may be produced by the high anisotropic residual stress in the composite. The metastable phase of Euc can transfer to normal Euc when the residual stress is relaxed by stress relief annealing process and has great influence on the CTE behavior of the Euc/Al composite.