Characterization the microstructure of pulsed Nd:YAG welding method in low frequencies; correlation with tensile and fracture behavior in laser-welded nitinol joints

Abstract

The precise controllability of heat input in pulsed Nd:YAG welding method provided by two additional parameters, frequency and pulse duration, has made this method very promising for welding of alloys sensitive to heat input. The poor weldability of Ti-rich nitinol as a result of the formation of Ti2Ni IMC has deprived us of the unique properties of this alloy. In this study, to intensify solidification rate during welding of Ti-rich nitinol, pulsed Nd:YAG laser beam in low frequency was employed in addition to the employment of a copper substrate. Specific microstructure produced in this condition was characterized and the effects of this microstructure on tensile and fracture behavior of samples welded by two different procedures, full penetration and double-sided method with halved penetration depth for each side were investigated. The investigations revealed although the combination of low frequencies, the use of a high thermal conductor substrate and double-sided method eliminated intergranular fracture and increased tensile strength, the particular microstructure, built in the pulsed welding method in low frequencies, results to the formation of the longitudinal cracks during the first stages of tensile test at weld centerline. This degrades tensile strength of welded samples compared to base metal. The results showed samples welded in double-sided method performed much better than samples welded in full penetration mode.

Comparative study on weld characterisation and corrosion performance of laser-welded NiTinol

“…This experiment aimed to explore the effect of heat input on corrosion performance and surface properties during laser welding of NiTinol alloy. The overall control of the laser welding is related to controlling laser heat input, which controls the melting, solidification rate, cooling cycle, phase transformation, alloying and recrystallisation process during the processing [29]. Even the control of heat input is vital for controlling the surface properties by the generation of different surface textures and by controlling the surface layer material composition.…”

Investigations on the actuation behaviour of friction stir–welded nickel titanium shape memory alloy using continuous fibre laser

“…Most of the literature on welding of NiTi alloy focuses on the parametric investigations of the welding process and its influence on metallurgical and mechanical properties. [12][13][14][15] However, it is extremely important to evaluate the thermomechanical actuation behaviour to ensure suitability of the welded structure for real-time applications. Despite this fact, the actuation behaviour of the welded NiTi alloy was not explored much in literature.…”