Near critical phenomena in amorphous smart materials

The importance of smart materials e.g. shape memory alloys (SMAs) for technological applications has been growing during the last 20 years. Especially modeling SMAs behavior has become of high interest in materials science for the prediction of macroscopic effects like pseudoelasticity. The key for their behavior is a displacive solid - solid phase transformation, called martensitic phase transformation. However, such a critical phenomenon requires investigations for deep relations between physical quantities nearby the region of phase transformation. The present study is focusing on a statistical mechanics approach for the description of relations between heat capacity, pseudoelasticity, volume fraction compressibility, alternatively fraction expansion coefficient, and a compressibility tensor, leading to the compliance tensor in the case of elasticity. Also a heat expansion tensor along the line of magnetic phase transitions and transformations has been formulated for shape memory alloys. The work discusses martensitic variants (which occur due to a subgroup relation between the austenitic and martensitic phase) and their asymmetry, which influences the above mentioned quantities as well and gives ideas and suggestions for model improvements.