New Nano-Quasicrystalline Al-Based Alloys

F. AUDEBERT; N. VIVES; P. BOZZANO

Foz do Iguazu

Simposio; International Symposium on Metastable, Mehanically Alloyed and Nanocrystalline Materials; 2003

Nano-quasicrystalline Al-based alloys have been studied intensively on the last years in order to develop new light alloys for technological applications at elevated temperature. These alloys are composed basically of icosahedral particles with size less of 100 nm embedded in a fcc-Al matrix. Particularly, the Al93Fe3Cr2Ti2 (at%) have high strength up to 350 ºC compared to the commercial or to the nano-crystalline Al-based alloys. It is an important objective to obtain icosahedral phases with higher decomposition temperature which would allow to retain the high strength up to higher temperature. In a previous work [1] rapid solidified Al93Fe3Cr2ETM2 (with ETM: Early Transition Metals from group ?V?) were studied. The alloys with icosahedral particles containing Nb or Ta showed better stability. The aim of the present work is to explore the effect of ETM from groups ?IV? and ?VI? on the icosahedral forming and the stability of the microstructure. Melt spun alloys were obtained and the structure were characterized by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM). All samples showed a microstructure composed by spherical icosahedral particles embedded in a fcc-Al matrix, albeit some of they presented additional small precipitates of intermetallic compounds. New quaternary icosahedral phases containing Hf or W were observed. The thermal stability of the microstructure and its transformation process were analysed by differential scanning calorimetry and heat treated samples were characterized by XRD and TEM. The exothermic peak transformation was observed to be displaced at higher temperature as increase the melting point of the ETM component. The microhardness of the as spun alloys and of the heat treated samples was also measured. The microstructure, stability and microhardness values are discussed and related to the chemical composition of the alloys. [1] M. Galano, F. Audebert, B. Cantor and I.C. Stone; Mat. Sci. Eng. A (to be published).