Thermal Analysis on Nanoquasicrystalline Al-Based Alloys

NICHOLAS ROUNTHWAITE; M GALANO; F AUDEBERT; G SMITH; P SVEV; D JANICKOVIK

Simposio; Ismanam 2008; 2008

Nanoquasicrystalline Al-Cr-Fe based alloys have a microstructure composed by nanoquasicrystalline icosahedral particles embedded in an α-Al matrix. These alloys have shown a reduced drop off in strength with increasing temperature when compared to traditional aluminium alloys. However the icosahedral phase in these alloys is a metastable phase which leads to a limit in the application temperature due to the icosahedral decomposition. In order to increase the stability of the icosahedral phase several multicomponent alloys were developed. The icosahedral phase in these systems is kinetically retained during the rapid solidification. Thus the understanding of the phase transformation processes from the liquid to the solid state is very important in order to find out the best processing condition for obtaining these alloys in large quantity. In the present work Aluminium and melt-spun samples of alloys varying from binary to quinary compositions in the systems: Al-Cr, Al-Fe-Cr, Al-Fe-Cr-Ti, Al-Fe-Cr-V, Al-Fe-Cr-Nb, Al-Fe- Cr-Ta, Al-Fe-Cr-Ti-V, Al-Fe-Cr-Ti-Nb were studied. The structural characterisation was carried out by means of X-Ray Diffraction and Transmission Electron Microscopy. The melting and the solidification processes were analysed using Differential Thermal Analysis (DTA) up to 1400°C. The effects of each additional alloying element were examined and trends sought. DTA curves showed that all the alloys have an eutectic reaction and some alloys showed metastable melting steps near to the eutectic temperature. Particularly, it was observed that some elements, such as Nb, shift the melting steps towards higher temperatures.