Dynamic Behavior Research Of FeCrNi Alloy

This paper studied the dynamic mechanical behavior of FeCrNi alloy under different temperature and strain rate, observed the effect of temperature and strain rate on dislocation movement, investigated the dislocation dynamic mechanism of plastic deformation, established a physically based dislocation constitutive model suitable for describing the mechanism behavior of FeCrNi alloy under 104s-1 strain rate based on the dislocation density evolvement. First, using versatile material test machine (MTS) and spilt Hopkinson pressure bar (SHPB), carried out three kinds of mechanical tests at different temperature under quasi-static load, different strain rate load at room temperature and high strain rate load at high temperature. The results show that the FeCrNi alloy has apparent strain hardening, strain rate hardening and temperature soften effects. The changing of flow stress as temperature changing has comparability at quasi-static and dynamic loading, the strain rate only changes the flow stress and temperature curve's position. Then, observed the dislocation configurations of FeCrNi alloy after different mechanical tests using HITACHI H-700H TEM. Discussed the relationship among dislocation behavior, temperature, strain rate. The results show that: temperature and strain rate have contrary effect on dislocation behavior. Temperature makes the cross-slip probability rise, dislocation configuration evolves from wall to cell, but strain rate makes the cross-slip probability reduce, the configuration evolves from cell, wall to high density stacking fault. Finally, based on the forest dislocation incising mechanism of fcc metal's plastic deformation, analyzed the dislocation movement and accumulation mechanism of FeCrNi alloy as temperature and strain rate changing. Discussed the relationship of strain rate, the varying tendency of flow stress while temperature changing, and the relationship of strain hardening effect, temperature and strain rate in detail. Using single parameter dislocation dynamics describe the constitutive model of FeCrNi alloy, discussed the effects of all kinds of barriers during movement of dislocation, and the effect of evolvement of dislocation on flow stress. Established a physically-based constitutive model based on dislocation density evolvement, and compared it with the calculated results of Johnson-Cook model. The results show that the plastic deformation of FeCrNi alloy can be described by single parameter dislocation dynamics, when the strain rate is below 104s-1, the flow stress is the plus of athermal stress and thermal activated stress. Our physically-based constitutive model suitable for describing the stress-strain relationship of FeCrNi alloy at different temperature of quasi-static and the strain rate below 3000s-1 at 15℃.