Molecular dynamics simulation of mechanical deformation of austenitic stainless steels (Fe-Ni-Cr alloys) at supercritical water conditions

Abstract

Austenitic stainless steel (Fe-Ni-Cr alloy) has been identified as potential candidate material for fabrication of str-uctural components of supercritical water-cooled reactor (SCWR), because the alloy has proven nuclear, physical, and mechanical properties for the construction of prototype fast breeder reactor. The variation of mechanical pro-perties of stainless steel grades SS 304, 308, 309 and 316 at supercritical water (SCW) conditions of 300 - 500 ºC and 25 MPa, were simulated by molecular dynamics to examine the thermo-mechanical behavior of the alloys tai-lored for in-core structural components and pressure vessel design of SCWR. Large-scale Atomic/Molecular Mas-sively Parallel Simulator (LAMMPS) deformation of the alloys in uniaxial tensile tests were performed at strain rate of 5.0 x 10¹⁰ s^-1, using Velocity Verlet Algorithm, Periodic Boundary Conditions and Isobaric-Isothermal En-sembles. The stress-stain data were imported into MATLAB for graphical representation, from which values of Ultimate Tensile Strength (UTS), Young’s Modulus (YM), Yield Strength (YS) and Breaking Strength (BS) were extracted. Compared with ambient values, the mechanical properties of the alloys decreased with increase in tem-perature by about 30 - 40 %. Stainless steel grades SS 304 and 308 showed comparatively higher UTS and BS at SCW conditions. The values of thermo-mechanical properties of Fe-Ni-Cr alloys would augment the data base for material design of SCWR.

Keywords: Supercritical Water (SCW) Condition, Molecular Dynamics (MD) Simulation, LAMMPS, Velocity Verlet Algorithm, Embedded Atom Model (EAM), Periodic Boundary Condition (PBC), Isobaric-Isothermal Ens-embles, Austenitic Stainless Steel