Numerical and Experimental Investigation of the Influence of Growth Restriction on Grain Size in Binary Cu Alloys

Abstract

Grain refinement by elemental addition has been extensively investigated within the last decades in Al or Mg alloys. In contrast, in the Cu system, the role of solute on grain size is less investigated. In this study, the grain refinement potency of several alloying elements of the Cu system was examined. To predict grain size depending on the growth restriction factor Q, grain size modelling was performed. The results obtained by the grain size model were compared to variations in the grain size of binary Cu alloys with increasing solute content under defined cooling conditions of the TP-1 grain refiner test of the Aluminium Association©. It was found that the experimental results differed significantly from the predicted grain size values for several alloying elements. A decreasing grain size with increasing alloy concentration was observed independently of the growth restriction potency of the alloying elements. Furthermore, excessive grain coarsening was found for several solutes beyond a transition point. It is assumed that contradictory variations in grain size result from a change in the nucleating particle density of the melt. Significant decreases in grain size are supposed to be due to the in-situ formation of potent nucleation sites. Excessive grain coarsening with increasing solute content may occur due to the removal of nucleating particles. The model shows that the difference in the actual number of particles before and beyond the transition point must be in the range of several orders of magnitude.

On the Role of Dilute Solute Additions on Growth Restriction in Binary Copper Alloys

“…Plots of the variation of grain size values with Q conv. were reported for many binary Cu alloys in the former studies [4][5][6], however, only for P, Zr, and Ni in the latter study [8]. Here, we report columnar grain length values from Northcott's work [1] for binary Cu alloys plotted against the undercooling parameter (P), the reciprocal of the conventional growth restriction factor (Q conv. )…”

“…In line with investigations on the effect of solute additions on the grain size in copper, growth restriction factors (Q) have been determined as exemplified by means of the conventional (Eq. 1) [4][5][6][7] or true (Eq. 2) [2,8,9] Q values to quantify the potential restriction to growth imposed by a solute.…”

“…Previous studies have shown a low correlation between Q conv. [4][5][6] and Q true [8] values and grain size in binary Cu alloys. Plots of the variation of grain size values with Q conv.…”

Effects of Superheat and Solute Additions on the Grain Size in Binary Copper Alloys

“…Grain refinement of copper and copper alloys has recently attracted the interest of the scientific community [1][2][3][4][5][6][7]. It is worthwhile briefly highlighting previous studies on grain refinement in copper and copper alloys [8][9][10][11][12][13]: in air, in the late 1930s by Northcott [8,9], and in a protective atmosphere of pure Ar (99.997 pct), in the early 1990s by Bustos and Reif [10][11][12][13].…”