Description
In recent years, iron-based shape memory alloys have become increasingly interesting for application in the construction industry. The reversible phase transformation between a high temperature austenitic phase and a low temperature martensitic phase opens up applications in many different areas, e.g. as damping elements in earthquake prone areas or as prestressing elements in concrete structures. Previous investigations on the electrochemical corrosion properties of a Fe-Mn-Al-Ni-Cr shape memory alloy revealed that the corrosion properties of iron-based shape memory alloys are strongly influenced by the prevailing phases. The martensite phase suffers from a severe selective corrosion attack due to the formation of dislocations at the martensite-to-austenite interfaces. In the present study, the corrosion properties of the above-named alloy are further elucidated by investigating the susceptibility to stress corrosion cracking. The simultaneous occurrence of tensile stresses and unfavourable environmental conditions can lead to spontaneous failure of a building structure. For these investigations tensile tests under constant load control in different chloride-containing solutions have been conducted. The pitting corrosion that occurred during immersion in the test solution has a decisive influence on the martensitic phase transformation and the crack evolution. The high density of dislocations at the phase boundaries promotes the formation of transgranular cracks on the fracture surface as well as stress-induced corrosion cracks between single pitting holes on the lateral surface. Further investigations of the fracture surfaces revealed the occurrence of intergranular crack growth. The detrimental mechanisms lead to failure of the specimens well before the targeted test time of 1000 hours.
