Lamellar microstructure alignment and fracture toughness in Ti-47Al alloy by electromagnetic confinement and directional solidification

Large-scale Ti-47Al sample without contamination is shaped by electromagnetic confinement and directional solidification. Controlled by a Ti-43Al-3Si seed, numerous columnar grains grow directionally in transition region and the lamellar microstructure within those grains is aligned parallel to the growth direction. Because the solid/liquid interface is convex towards the liquid and its h/r value is 0.25, one of the columnar grains in sample center grows divergently and then a near single (NS) crystal forms with crystal growth. Fracture toughness of the NS crystal with the desired lamellae is detected and the value is measured 34.7 MPa m1/2. The crack propagation path is checked after the fracture toughness testing and a schematic model is used to illustrate the relevant toughness mechanism.