Nickel-Titanium Alloys Welding of Thin Sheets Using GTAW: Comparative Study Between Similar and Dissimilar Welding with AISI 304 Stainless Steel

Abstract

The objective of the present work was to evaluate welding of thin sheets (thickness < 1 mm) of similar and dissimilar NiTi alloys with AISI 304 stainless steel using the Gas Tungsten Arc Welding (GTAW) process and to study the mechanical and metallurgical properties of the joints with and without post-welding heat treatment (PWHT). The GTAW process was chosen because it is more economical than the usual welding processes for NiTi alloys, such as the Laser Beam Welding (LBW). The welded joints were characterized by the techniques of SEM, OM, electrical resistance in temperature (ERT), tensile test and Vickers microhardness. It was observed that the dissimilar joints presented a brittle behavior due to the formation of brittle elements along the weld metal by the excessive increase of the hardness in this region with peaks of hardness higher than 900HV. Similar joints presented superior mechanical behavior, with extensive plastic deformation before rupture and fracture surface with ductile appearance. The PWHT in the similar joints promoted a decrease in the rigidity of the material by minimizing the thermal stresses from the welding process, the PWHT did not influence the dissimilar joints mechanical behavior.

Metallurgical and Mechanical Behaviors of 309L-Si and ERNiCrMo-3 Dissimilar Weld on ASTM A182 F22 Steel

“…The failure surface reveals a rapid fracture, probably came from solidification micro-cracks, propagated during the tensile test in 309/INC625 interface. The micrographic exams before the test could not detect these micro discontinuities throughout the interface due to their small dimensions and the internal location, similar to founded by other researchers [31][32][33] . By Figure 12 it is possible to note that the solidification cracks on the buttery were restrict to the 309L-Si weld metal, and were possibly caused by two main factors.…”