Criticism of the paper titled ‘Solidification thermal parameters, microstructural evolution and dendritic growth in an AlCuNi alloy’ by Correa et al.

Recently, Correa et al. [1] conducted experiments on the relationship between solidification parameters, including solidification time ts and secondary dendrite arm spacing λ2, for an Al-3wt.%Cu-3wt.%Ni alloy. Their data for the ts λ2 relationship are presented in Figure 1. Note that there are two regions with very different slopes (i.e. the exponent of ts). The fit to the data by Correa et al. is presented in the figure. Note that the slope in the trend of the data, i.e. the exponent of solidification time, is 0.076 below ts = 70 s – a value significantly less than 1/3. At longer solidification times, the exponent of the solidification time is 0.251, a value approaching 1/3, which is consistent with coarsening. The reason for the existence of two distinct regions is unknown. Correa et al. applied the Rappaz-Boettinger [2] and Tiryakioğlu [3] models for the ts λ2 relationship to their dataset and reported that both models overestimated λ2 significantly. We note that Correa et al. used a surface tension value of 1.29 N/ m, rather than the solid–liquid interfacial energy, in their calculations. This is consistent with their previous studies [4]. We contend that the approach taken by Correa et al. is erroneous on account of the following reasons: