Numerical Analysis of Nucleation and Growth of Stray Grain Formation during Laser Welding Nickel-Based Single-Crystal Superalloy Part III: Kinetic and Thermodynamic Obviation of Solidification Cracking

Abstract

To pertinently balance growth kinetics, solidification thermodynamics and dendrite expitaxy of multicomponent nickel-based single-crystal supralloy during laser processing, effect of thermometallurgy determinant factors, including laser power, welding speed and welding configuration, on solidification behavior, such as nonequilibrium solidification temperature range, and dendrite growth, such as dendrite trunk spacing, are progressively advanced to forestall solidification cracking phenomena. Symmetric developments of dendrite trunk spacing and solidification temperature range alongside solid/liquid interface are crystallographically driven by useful (001)/[100] welding configuration to auspiciously bring about crack-insusceptible and well-oriented dendrite growth. Dissimilarly, unsymmetrical developments of dendrite trunk spacing and solidification temperature range alongside solid/liquid interface are crystallographically driven by (001)/[110] welding configuration to insidiously favor crack-unresistant and disoriented dendrite growth. Higher heat input thermodynamically and kinetically boosts wide solidification temperature range, appalling stray grain growth with excess of solute ahead of dendrite tip and large size of crack-unresistant region to thermometallurgically disintegrate epitaxial growth for untoward solidification cracking, and therefore should be strictly withstood. Although geometry of symmetrical weld pool both sides is the same in infelicitous (001)/[110] welding configuration, [100] region of dendrite growth is more liable to ruinous stray grain growth and extensive solidification temperature range than [010] region of dendrite growth to complicate dendrite growth and exacerbate weld integrity. The determinant mechanism of crystallography-aided amelioration of solidification cracking resistance as result of kinetics-and thermodynamics-driven dendrite growth is propitiously proposed. Furthermore, the credible and understandable theoretical predictions are in conformity with the experiment results.