Microstructure evolution and constitutive model for a Ni-Mo-Cr base alloy in double-stages hot compression with step-strain rates

The flow characteristics of a Ni-Mo-Cr base alloy are researched by the double-stages hot compression with step -strain rates. Electron backscatter diffraction (EBSD) as well as transmission electron microscopy (TEM) are adopted to systematically comprehend the influences of compressed parameters on microstructural changes. To forecast the hot compressed behaviors, a physically-based constitutive model with considering the evolution characteristics of dislocation density, subgrain and the grain structure is developed. Experimental results indicate that the elevated compressed temperature can exacerbate the dislocation consumption, subgrain rotation/ interaction and dynamic recrystallization (DRX) grains coarsening. However, the prominent dislocation accu-mulation, subgrain generation and the refinement of DRX grains come up as the strain rates at the first or second stage of hot compression are ascended. The discontinuous DRX characterized by the bulging/serrated of grain boundaries is the major DRX nucleation mechanism of the researched alloy. The forecasted compressed stress, grain size and DRX fraction well match the tested results, which indicates the constructed physically-based constitutive equations can be employed to model the high-temperature features and microstructural changes of the studied Ni-Mo-Cr base alloy in double-stages hot compression with step-strain rates.

Automated summary

In this study, the flow characteristics and microstructural changes of a Ni-Mo-Cr base alloy were researched through double-stages hot compression with step-strain rates. Electron backscatter diffraction and transmission electron microscopy were used to comprehend the influences of compressed parameters on the alloy. A physically-based constitutive model considering the evolution characteristics of dislocation density, subgrain, and grain structure was developed to forecast the hot compressed behaviors. The experimental results showed that the compressed temperature exacerbated dislocation consumption, subgrain rotation/interaction, and DRX grains coarsening, while the strain rates at the first or second stage of hot compression led to prominent dislocation accumulation, subgrain generation, and DRX grains refinement. The discontinuous DRX characterized by the bulging/serrated of grain boundaries was found to be the major DRX nucleation mechanism. The forecasted compressed stress, grain size, and DRX fraction matched well with the tested results, indicating that the constructed physically-based constitutive equations could effectively model the high-temperature features and microstructural changes of the studied alloy.