Microstructure and mechanical properties of the hypercooled Ti50Al50 alloy

Hypercooling region of the gamma titanium aluminide alloy Ti,,AI,, it as ac hieved by cyclically superheating the alloy melt in a containerless electro magnetic levitation apparatus. The maximum undercooling of the alloy melt a mounted to 345 K;. XRD, TEM, SEM and optical microscopy techniques were ado pted 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 tine 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 hyp ercooled sample was homogenous except for a small difference between first solidified regions and boundaries of cracks. X-ray diffraction results show ed that all peaks of the gamma phase shifted slightly in the direction of s mall angles, This can be explained by the disordering growth pattern caused by the rapid solidification process in the hypercooled melt. (C) 2001 Else vier Science Ltd. Ah rights reserved.