Sharif Digital Repository

AISI 4340 steel bars were austenitized at 900°C for 1 hour followed by heating at 740°C (ferrite and austenite region) for 100 min and quenching into a salt bath at 300°C for different times followed by quenching into water to obtain triple phase microstructures with 34 Vol.% ferrite and various martensite (or bainite) contents. Presence of three phases in adjacent of each other confirmed by metallographic analysis and TEM technique. Volume fraction of different phases was measured by image analyser. The results of optical microscopy showed that by increasing VM, morphology of martensite varies from uniform distribution of small spherical network particles to large blocky islands with... 

Shape memory materials are a kind of smart materials which recently have been used in a wide range of fields in particular medicine and aerospace. These materials can be divided to shape memory polymers and shape memory alloys. The basis of shape memory alloys’ properties is a thermoelastic martensitic transformation taking place between a high symmetric phase, called Austenite, and a low symmetric phase, called Martensite. In this project, by means of finite element methods, continuum thermomechanics and selection of appropriate internal variables (such as amount and orientation of volumetric fraction of each phase) and control variables (like strain, stress, temperature and entropy), their...