Effect of micro-structural changes on mechanical properties of La ₆₆Al₁₄(Cu, Ni)₂₀ amorphous and crystalline alloys

The micro-structures and phase selections of La₆₆Al ₁₄(Cu, Ni)₂₀ alloy were studied by Bridgman solidifications with withdraw velocity V between 0.008 and 4.8 mm/s. Composites of α-La dendrites in amorphous matrix or in micro- and nano-sized eutectic matrix were formed with different cooling rates. The volume percent of the dendrite phase reaches a maximum at the cooling rate of about 15 K/s, while the dendritic secondary arm spacing λ₂ decreases from 4.3 to 0.6 μm with the increase in the cooling rate, and obeys the equation of λ₂V^0.57 = 19 μm^1.57s^-0.57. The compression strength, as well as the elastic strain limit of the dendrite/amorphous composite are 600 MPa and 2.3%, respectively. Improved ductility was observed for the amorphous matrix composites with high volume percent of dendrite phase which are obtained by slow cooling rate.