A Modified Description with Variable Parameters of Flow Behaviors for Ni-38Cr-3.8Al Alloy

Abstract

Nickel-based alloys containing high amount of Cr are desirable materials for the production of critical components that operate under high temperature and severe corrosion conditions. The description of flow behaviors for these alloys is key to designing the hot formation process for achieving the excellent mechanical properties of components. This work aims to study the flow behaviors of Ni-38Cr-3.8Al alloy during thermal deformation. A series of isothermal compression experiments were carried out at temperatures of 1148 K, 1223 K, 1298 K, 1373 K, 1448 K and 1523 K, and strain rates of 0.01 s-1, 0.1 s-1, 1 s-1 and 10 s-1. Results show that the obtained true stress-strain curves exhibit the softening characteristics of dynamic recrystallization (DRX) and dynamic recovery (DRV). The flow stress decreases with temperature increasing and strain rate decreasing. To further quantitatively describe the flow behaviors, an improved segmented Arrhenius constitutive equation was developed according to the softening characteristics under different temperatures. In these equations, the variable coefficients, including activation energy Q and material constants (structure factor A, stress exponent n, stress parameters α), were fitted as the polynomial functions of true strain. Furthermore, a typical Arrhenius constitutive equation was also solved. The comparisons between experimental stress and predicted results obtained from the typical and improved constitutive equations were conducted, and the correlation coefficient (R) and average absolute relative error (AARE) were calculated as 0.932, 15.83%, and 0.9963, 5.61%, respectively. It suggests that the improved constitutive equation can adeptly describe the flow behaviors of Ni-38Cr-3.8Al alloy.

Keywords

• Nickel-based superalloy
• Flow behaviors
• Activation energy
• Constitutive equation