A Study of the Dependence of Microsegregation on Critical Solidification Parameters in Rapidly-Quenched Structures.

The aims of the present program were to determine both experimentally and analytically the cooling rates experienced by material during laser melting in the deep penetration and shallow penetration metling modes, to determine the microstructures and degrees of microsegregation associated with these cooling rates, to correlate the structure and segregation with weld cracking behavior, and to eventually determine the mechanism involved in weld cracking. A literature survey was performed and two new mathematical models were developed, a two dimensional model for deep penetration welding and a one dimensional model for shallow penetration surface melting. The results of both model calculations were eventually verified by experimental tests and comparisons of results, with excellent agreement being obtained for the deep penetration model and adequate agreement being obtained for the shallow penetration model. In addition a series of three special Ni-Al-Mo alloys was weld-crack tested to determine effects of microstructure on cracking behavior.