Microstructure and mechanical properties of the hypercooled Ti50Al50 alloy

Hypercooling region of the gamma titanium aluminide alloy Ti50Al50 was achieved by cyclically superheating the alloy melt in a containerless electromagnetic levitation apparatus. The maximum undercooling of the alloy melt amounted to 345 K. XRD, TEM, SEM and optical microscopy techniques were adopted to investigate the microstructure and identify the phase composition. The microstructure of the hypercooled alloy was composed of equaxied gamma phase grains with a mean diameter of 17 nm. The fine microstructure of the gamma phases produced a large strengthening effect, raising the hardness to 545 on the Vickers scale. The aluminum composition distribution in the hypercooled sample was homogenous except for a small difference between first solidified regions and boundaries of cracks. X-ray diffraction results showed that all peaks of the gamma phase shifted slightly in the direction of small angles. This can be explained by the disordering growth pattern caused by the rapid solidification process in the hypercooled melt.