On the strain rate sensitivity of size-dependent plasticity in BCC iron at elevated temperatures: Discrete dislocation dynamics investigation

Abstract

Multiscale discrete dislocation plasticity (MDDP) simulations are carried out to investigate the mechanical response and microstructure evolution of BCC iron micropillars under combined high temperature and strain rate deformation. The simulations are conducted at sizes ranging between 0.25 μm and 2 μm under an applied deformation rate ranging between 103s−1 and 107s−1 and subjected to different temperatures. MDDP based constitutive equation interrelating the size effect exponent to strain rate and temperature is also proposed indicating that the exponent is relatively sensitive to temperature and at a lesser degree to strain rate. Detailed investigation of the microstructure shows that self-multiplication of dislocations is responsible for the strengthening mechanism in BCC iron micropillars. At low temperatures and small sizes, screw dislocations have a weak effect on plasticity for a certain period of time but subsequently control the self-multiplication process. At larger sizes, the motion of screw dislocations is responsible for plasticity at low temperatures. Due to the large volume size, screw dislocations are entangled inside the sample leading to a self-multiplication of dislocations via cross slip and other dislocation–dislocation interactions. At higher temperatures and for all sample sizes, mixed dislocations control plasticity via the multiplication of a complex network of dislocations. MDDP generated results are in good agreement with previous experimental studies on BCC metals. © 2020 Elsevier Ltd