Effect of Si on the formation and stability of the icosahedral quasicrystalline phase in Al-Fe-Cr-Ti alloys

The formation and stability of the quasicrystalline icosahedral (i) phase in melt-spun Al93-xFe3Cr2Ti2Six (x = 0-5) ribbons are reported. Samples were characterized by X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. Primitive (P-type) ordered i phase particles were found to be homogeneously distributed in an fcc alpha-Al matrix in the as-melt-spun ribbons. The size of the i phase particles decreased and their thermal stability increased with increasing substitution of Al by Si. The i phase had a decomposition temperature of approximately 480 degrees C in an Al93Fe3Cr2Ti2 ribbon whereas that in an Al92Fe3Cr2Ti2Si1 ribbon was approximately 500 degrees C. The i phase particles are resistant to coarsening prior to decomposition into crystalline phases. The presence of a small quantity of Si ( up to 1.0 at.%) is beneficial to both the thermal stability and the hardness of nanoquasicrystalline Al - Fe - Cr - Ti alloys.