Abstract
For Inconel 625, where the γ” and δ phases precipitate, the influence of prior hot rolling on the process is not well covered. The influence of segregation bands and prior hot rolling on the precipitation of secondary phases during aging at 750 °C for different times was investigated. Prior hot-rolling was conducted on a hot rolling mill at 1050 °C and 1150 °C with three different deformation levels. The hot rolled samples were aged at 750 °C for 1, 5, 25 and 125 h. The γ″ precipitated in both the deformed and recrystallized grains in the segregation bands containing a high concentration of niobium and molybdenum and a lower concentration of nickel, chromium and iron. The opposite was observed between the segregation bands where no γ″ precipitate was found. There was a smooth transition in the density and the size of the γ″ particles in the deformed grains at the border of the segregation bands, while a more complex transition occurred in the recrystallized grains. This occurred in the area where the average niobium concentration decreased from 4.5 to 2.7 wt. %, which influenced the mechanical properties.
Highlights
The precipitation and growth of different phases in superalloys is influenced by both the chemical composition and the deformation [1,2,3,4]
The deformed grains have a higher orientation changes which influences the deformation levels is shown in orientation image microscopy (OIM) maps with inverse pole figure electron and the signal theGOS
The advantage of the presented method is the simultaneous observation of the γ” precipitation during aging at 750 ◦ C in deformed grains with a high to low Nb concentration, as well as recrystallized grains with a high to low Nb concentration
Summary
The precipitation and growth of different phases in superalloys is influenced by both the chemical composition and the deformation [1,2,3,4]. The influence of prior deformation on the precipitation of secondary phases is not a well-researched problem. Precipitation can impact on the mechanical properties, corrosion resistance and microstructural stability of a component during service. Intermetallic phases like Ni2 (Cr,Mo) with a Pt2 Mo structure, γ” (Ni3 Nb) with a DO22 structure and δ (Ni3 Nb) with a D0a structure, as well as secondary carbides like M23 C6 and M6 C, precipitate at different temperatures [6,7,8,9,10,11]. The critical nucleus size is an important factor in the precipitation process.
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