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On the Influence of Thermomechanical Treatments on Shape Memory Alloys

By D. Treppmann and E. Hornbogen


Thermomechanical treatments (TMT) are used to modify the microstructure of austenite or martensite by introducing lattice defects and / or particles of a second phase. The temperature range extends between T ≥ Md (pure ausforming) and T ≤ Mf (pure marforming). In the intermediate range (Mf<T<Md) a more complex behaviour is found. TMT are discussed in a systematic manner using NiTi-based and Cu-based alloys as examples. Transformation behaviour and mechanical properties of TM-treated alloys are compared with undeformed ones. The following effects can be observed for thermal transformation cycles : (a1) lowering or raising of transformation temperatures, (a2) widening or decreasing of hysteresis, (a3) induction of multiple step transformation mechanisms, (a4) reduction of martensitic retransformability (e.g. plastic deformation of martensite = marforming). The mechanical properties are also highly affected : (b1) increase in pseudo yield stress, (b2) increase or decrease in shape memory strain, (b3) increase in conventional strength, (b4) increase in elongation at fracture (by hot rolling of austenite = ausforming). It is shown how tailor-made microstructures are obtained, which in turn provide the best bulk properties for specified applications of SMA in engineering

Publisher: EDP Sciences
Year: 1997
DOI identifier: 10.1051/jp4:1997533
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