Creep and stress relaxation of a FeMnSi-based shape memory alloy at low temperatures

Abstract

The creep and stress relaxation behavior of a Fe-17Mn-5Si-10Cr-4Ni-1(V,C) (wt-%) shape memory alloy at low homologous temperatures (-45°C<T<50°C) was systematically studied in stress and strain controlled tensile tests. At constant stresses at-45°C, the alloy exhibits pronounced creep up to 0.6% at 600 MPa after only 30 minutes holding time. If the strain is kept constant, a pronounced stress relaxation of up to 10% of the initial stress was observed. The final creep strains, the creep rates at a constant stress as well as the stress relaxation at a constant strain increase with decreasing temperature. In addition, the change of the recovery stress as a function of time in a restrained sample after 4% elongation and heating to different constant temperatures was monitored. It was observed that the increase of the final recovery stress is more pronounced when the holding temperature is increased. This behavior was explained with the time and temperature dependent formation of stress induced εmartensite from the parent γ-austenite phase during mechanical loading according to the model of Kajiwara et al. as well as with the increased number of stacking faults at lower temperatures, which serve as nucleation sites for the ε-martensite formation.

Recovery stress formation in FeMnSi based shape memory alloys: Impact of precipitates, texture and grain size

“…The amount of stress-induced martensite also depends on the alloy composition, the pre-straining temperature and the final strain [10]. In addition due to the isothermal behavior of the fcc to hcp transformation also time has an impact on the amount of formed martensite [40]. In this recent study about creep phenomena in Fe17Mn5Si10Cr4Ni1(V,C) the amount of stress-induced hcp martensite was about 12% for a final strain of 2.5% achieved at 0°C.…”

Thermally activated iron-based shape memory alloy for strengthening metallic girders

“…This reduction is deemed to be the result of a phase transformation from γaustenite to ε-martensite (i.e., a forward transformation in the Fe-SMA due to mechanical loading) [40]. Further discussions regarding this phenomenon can be found in [19,34,35].…”

“…Studies on the recovery stress behavior [31], durability of the recovery stress subjected to different temperature histories [19,32,33], fatigue [34], relaxation, creep behavior (an approximate prestressing loss of 14% over 50 years) [35,36], and corrosion [37] showed the appropriateness of Fe-SMAs to be used as prestressing elements in civil structures. The first application of the Fe-SMAs commenced at Swiss Federal Laboratories for Materials Science and Technology (Empa), Switzerland.…”

Shape Memory and Mechanical Properties of Cold Rolled and Annealed Fe-17Mn-5Si-5Cr-4Ni-1Ti-0.3C Alloy

“…By restraining the shape recovery, a so-called recovery stress can be generated in the material, resulting in pre-stressing or clamping forces [ 2 ]. Such behavior can be used in pipe joints, rail couplings, or pre-stressing reinforcement of civil structures [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ]. The recovery stress ranging from 130 to 580 MPa has been reported with various heating temperatures between 130 and 580 °C on different Fe-SMAs [ 11 ].…”