The effect of solidification rate on grain structure evolution during directional solidification （I J：5） ot a Ni-oasea superalloy was explored. It was found that a high solidification rate led to sharper 〈001〉 texture and smaller grain size in the DS samples. One of the most important findings in this work was that such result was not in accordance with the general concept, and the sharper 〈001〉 texture was accompanied by the larger grain size. To explain the contradiction, the modeling samples with five grains were produced and the effect of solidification rate on the evolution of grain texture was illustrated based on the modeling samples.
The influence of active elements C and Hf on the interface reactions and wettability between a Ni3Albased superalloy and the ceramic mould material was studied by using a sessile drop experiment, The microstructure of the alloy interface was investigated by scanning electron microscopy analysis and the phase identification was performed by X-ray diffraction analysis, The results show that interface reactions occur as C and Hf contents reach a critical value, The critical values for C and Hf to cause interface reactions are 0,12 wt% and 1,17 wt%, respectively, The reaction products contain HfO2 and 9Al2OH,Cr2O3, Adsorptions of Hf and interface reactions improve the wettability obviously,
The mechanism of grain structure evolution during directional solidification is a fundamental subject in material science. Within the published research there exist conflicting views on the mechanism of grain overgrowth. To study the effect of solidification rate on grain structure evolution, bi-crystals samples were produced in a nickel-base superalloy at different solidification rates. It was found that at the convergent grain boundaries those grains better aligned with respect to the heat flux more readily overgrew neighbouring grains with misaligned orientations and the effect became more pronounced as solidification rate was increased. However, at diverging grain boundaries the rate of overgrowth was invariant to the solidification rate. These experimental results were compared with models in the literature. Thus, a better insight into competitive grain growth in directional solidification processes was obtained.
