Martensite stabilization during superelastic cycling of laser welded NiTi plates

Effect of laser welding parameters on the austenite and martensite phase fractions of NiTi

“…(i) in the heat affected zone, Ni 4 Ti 3 precipitation increases the transformation temperatures allowing for martensite to be stable at room temperature [15,16], …”

Welding and Joining of NiTi Shape Memory Alloys: A Review

“…The superelastic recovery was found to be correlated with heat input introduced during welding: higher heat input led to higher extension of the thermal affected regions and, as a consequence, the superelastic recovery decreased. Aside from the evidence of thermal stabilization of martensite in the HAZ and FZ of the welds, mechanical stabilization of the stress-induced martensite during superelastic cycling was also observed under synchrotron radiation [171]. Thermal stabilization of martensite occurred due to a local variation of the chemical composition of both HAZ and FZ due to welding, which raised the transformation temperatures of those regions.…”

“…So, a component was introduced in the mathematical formulation that considered the plastic strain of the thermal affected regions. Such higher irrecoverable strain, after the stress-induced transformation, may be due to martensite stabilization which can be of thermal (due to the local chemical composition changes induced by the welding procedure [171]) or mechanical origin (when, during superelastic cycling, the accumulation of defects allows for an increase of the volume fraction of non-transforming austenite [209]). …”

Production of Al/NiTi composites by friction stir welding assisted by electrical current

“…However, at the regions where the electrical current was inserted and, even after it was removed, a peak of NiTi martensite was observed ( Figure 9 b and c). Previously, it was observed that fully austenitic NiTi can show some martensite in the heat affected zone of laser welded NiTi joints [21,22]. The reason for the observation at room temperature of martensite after welding, was attributed to Ni 4 Ti 3 precipitation, which can occur in a temperature range between 350 and 500 ᵒC according to the TTT diagrams available for these alloys [23,24].…”