Solidification behavior of IN-100 and effect of alloying elements on it were investigated by means of differential thermal analysis (DTA), microstructural observation, X-ray diffraction, and EPMA analysis.
In alloy IN-100, it was revealed that six phase reactions took place successively during cooling from melt. These reactions and the onset temperatures were as follows, 1) L→γ(1 329°C), 2) L→γ+MC(D) (1319°C), 3) L→γ+MC(ID) (1 310°C), 4) L→γ+γ' (1 259°C), 5)γγ'→(1 210°C), and 6) L→γ+M3B2 (1 200°C), where L is melt, γ is fcc phase. MC(D) and MC(ID) denote MC carbides formed among dendrite arms and interdendritic regions, respectively. γ' is Ll2 type ordered phase and M3B2 denotes boride phase.
The occurrence of two kinds of carbide reactions ((2) and (3)) and M3B2 eutectic reaction ((6)) was identified for the first time in this study. SEM observation on the carbides, which were embossed on the γ matrix by an electrolytic etching, showed that the carbides had three types of morphology. These were blocky, lattice-like and flaky in shape. It was found that the blocky carbides were contained in MC(D), while the lattice-like and flaky carbides were frequently found in MC(ID). The influence of C, Al, Ti, and B on the above phase reactions and solidified structure was also clarified.