ULTRAHIGH-SPEED IMAGING-SYSTEM FOR THE MEASUREMENT OF SOLIDIFICATION VELOCITY VIA DIRECT OBSERVATION OF RAPID SOLIDIFICATION

An ultrahigh speed imaging system has been developed and built. to Ima ge rapid solidification of materials. The system collects data from a 10 by 10 array of parallel tapped photodiodes. Up to 8192, frames of d ata are digitized with 8-bit flash converters at frame rates ranging f rom 500 to 1 000 000 frames per second. The system has been used to im age solidification of a gamma titanium aluminum (gamma-TiAl) alloy, wi th composition Ti-60a/o Al, over a range of undercoolings. The data co llected includes the first images of solidification from multiple soli dification fronts, images of solidification of a disordered phase foll owed by the alloy ordering, and quantitative measurement of solidifica tion velocity as a unction of undercooling in a gamma-TiAl alloy. (C) 1997 American Institute of Physics.