Microstructural analysis of rapidly solidified particles of Al-Ni alloys

Kurzfassung

Particles of Al-Ni alloys with different compositions (Al – 50 wt% Ni and Al – 36 wt% Ni) were produced using a drop tube-impulse system, known as Impulse Atomization. The microstructure of these rapidly solidified particles was compared with those solidified in a DSC at low cooling rates (5 and 20 ̊C/minutes). Also, the effects of cooling rate on the microstructure and the phase formation of the rapidly solidified droplets were investigated using scanning electron microscope and neutron diffraction. Rietveld analysis was performed to estimate the phase fractions of Al3Ni2, Al3Ni and eutectic Al. The results were compared to those achieved from electromagnetic levitation under terrestrial and microgravity conditions (TEXUS 44). Effect of cooling rate and microgravity condition on the crystal structure of Al3Ni2 was also studied. It was shown that increasing cooling rate as a result of decreasing particle size or using helium as a cooling gas, rather than nitrogen, would result in a refined microstructure. From Rietveld analysis on neutron diffraction data, it was shown that the increasing cooling rate increases the weight fraction Al3Ni in Al – 36 wt% Ni, while it has an opposite effect in Al – 50 wt% Ni. Also, from Rietveld analysis studies, a striking difference between the samples solidified in the drop tube-impulse system and those produced in microgravity was observed. The former always contain eutectic aluminum, while the latter showed no sign of this element. Crystal structure studies on Al3Ni2 showed that increasing cooling rate changes the c/a ratio in Al – 50 wt% Ni and Al – 36 wt% Ni. It was found that in the sample with higher nickel content, increasing cooling rate increased the c/a ratio, while in the sample with lower nickel content, it showed opposite effect. This work is part of NEQUISOL project supported by ESA within contract 15236/02/NL/SH and CSA within contract number 9F007-08-0154 and SSEP Grant 2008. The authors thank Stefan Schneider for assistance in conducting the TEXUS experiments.