Effects of post-processing on the thermomechanical fatigue properties of laser modified NiTi

Abstract

The multifunctional capabilities needed for advanced shape memory alloys (SMA) actuators has been shown to be achievable by locally tuning the properties through laser processing. Before the wide-spread use of these SMAs is realized, a detailed understanding on the long-term stability and functional life span of these material must be achieved. The current study systematically investigates the effects of thermomechanical treatment on laser modified NiTi wires, while comparing them to the original base material. Surface analysis was done using a scanning electron microscope (SEM), while microstructure analysis was performed using transmission electron microscopy (TEM). Mechanical properties were assessed using standard tensile tests and a custom built thermomechanical fatigue. Results showed that the coarse-grains, large precipitates and surface defects associated with as laser modified NiTi resulted in reduced mechanical performance. However, subsequent thermomechanical treatment restored the refined microstructure and mechanical performance similar to the base material while providing the added functionality.

Highly Active Biphasic Anatase-Rutile Ni-Pd/TNPs Nanocatalyst for the Reforming and Cracking Reactions of Microplastic Waste Dissolved in Phenol

“…Ni 4 Ti 3 is a NiTi alloy intermediate phase that occurs as lenticular precipitates with the central plane parallel to the crystallographic [111] B2 directions in the B2 matrix. − The Ni 4 Ti 3 precipitate is typically formed during the thermomechanical method of Ni-rich Ni–Ti alloys . Panton stated that “metastable Ni 4 Ti 3 is the preferred phase to strengthen the microstructure, forming coherent lenticular precipitates in the matrix”. The diffraction lines owing to rhombohedral phase structures of NiTiO 3 for two JCPDS card numbers of 01-083-0202 at 2θ angles of 21.26° (101) and 43.09° (202) and JCPDS card number of 01-083-0204 at 2θ angles of 35.25° (110), 41.56° (021), and 53.11 (116) can be observed in the XRD pattern of Ni-Pd/TNPs nanocatalysts.…”

Advances in enhancing structural and functional fatigue resistance of superelastic NiTi shape memory alloy: A Review

“…NiTi components and devices in many applications are often subjected to dynamic stresses or deformations, resulting in fatigue failures. The phase transformation (Alarcon et al, 2015), thermomechanical treatments (Panton et al, 2019), pre-strain (Senthilnathan et al, 2019), asymmetric stress-strain response under tension, compression, and torsion results in remarkable complexity (Desroches et al, 2004) and (b) Typical stress-temperature phase diagram for NiTi. Loading path 1 represents SME, path 2 represents SE, and path 3 represents isobaric thermal cycling (Zeng et al, 2017).…”

“…The laser processing of SMAs enables the alteration of properties by altering the chemistry. Panton et al (2019) compared the effects of laser treatment on NiTi wire with original base NiTi wires. They further investigated the effects of thermomechanical treatment (solutionized at 1000°C for 3600 s), then cold worked with interannealing (600°C for 600 s) and heat treatment (400°C for 3600 s) on laser modified wire.…”

High strength impact welding of NiTi and stainless steel wires

“…The biomedical industry has an increasing demand for reliable welding processes to join NiTi and stainless steel (SS) wires to make devices that increase patient standard of care [3,4]. Traditional welding processes degrade the functional properties of nitinol, which limits the joint performance and fatigue life of a medical device [5][6][7][8][9].…”

“…The high energy density beam can cause the volatilization of elements which changes the local chemical composition [13]. This change in composition can result in a change in the functional properties such as the phase transformation temperature and the onset stress of martensite transformation in the thermally affected zones [6,13,14]. Panton et al [9] studied laser welding of NiTi to MP35N wire and the highest peak load of welds was limited to 66% of the BM failure load.…”