Migration of solidification grain boundaries and prediction

Abstract

Solidification processing is essential to the manufacture of various metal products, including additive manufacturing. Solidification grain boundaries (SGBs) result from the solidification of the last liquid film between two abutting grains of different orientations. They can migrate, but unlike normal GB migration, SGB migration (SGBM) decouples SGBs from solidification microsegregation, further affecting material properties. Here, we first show the salient features of SGBM in magnesium-tin alloys solidified with cooling rates of 8−1690 °C/s. A theoretical model is then developed for SGBM in dilute binary alloys, focusing on the effect of solute type and content, and applied to 10 alloy systems with remarkable agreement. SGMB does not depend on cooling rate or time but relates to grain size. It tends to occur athermally. The findings of this study extend perspectives on solidification grain structure formation and control for improved performance (e.g. hot or liquation cracking during reheating, intergranular corrosion or fracture).

Ultrasonic vibration assisted gas tungsten arc welding of Inconel 690 alloy: Ultrasonic effect to refine grains and improve mechanical properties

“…Their found that the formation of DDC is associated with the straight MGB morphology. There is no DDC in the tortuous MGB and creep-like morphology DDC at the tripe point of the MGB [15] , [16] . So, controlling the weld composition, grain size and morphology are efficient ways to improve the microstructure and mechanical properties of Inconel 690 alloy.…”

Evaluation of residual stresses in CO2 laser beam welding of SS316L weldments using FEA

“…Figures 7(A)-(C) shows the weld bead geometry of the laser beam weldment at top middle and centre of the weld bead with full penetration, and figure 7(D) shows the bead width with a length of 2.9 mm of the weldment, in mid span with a width of 1.02 mm and depth shows with full penetration. The solidification grain barrier (SGB) [22] may be seen in the middle of the fusion zone. The greater laser power density and travel speed are both thought to be caused by the SGB in the middle of the fusion zone.…”