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... (QCW) fibre laser, operating in continuous mode. To create the joint, wire sections of 50 mm length were fixed parallel to each other (overlap of 10mm each side) on an x-y manipulator and were seam welded under argon shielding, to prevent oxidation during welding process. The beam was focused between the overlapped wires using build in camera. Fig. 2 shows the schematic of the laser welding set-up used in this study. Silver tapes were used to hold the wire in place during the welding process. Mechanical tests of the laser micro welded Nitinol wires were carried out using uniaxial tensile testing procedure. The tests were carried out on a Zwick Roell machine with a cross-head speed ...
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... In order to create a complex, three-dimensional structure of an implant, an appropriate method of forming and connecting elements or their fragments is necessary. There are several techniques of joining NiTi alloys, including: plasma welding [11], vacuum brazing [12], resistance welding [13], tungsten inert gas [14], friction welding [15,16], microplasma arc welding [15], capacitor discharge welding [15], explosive welding [16], ultrasonic welding [16], adhesives joining [16], and laser welding [15][16][17][18][19][20][21]. However, most of these methods are used to join sheets, tubes, tapes, or strips. ...
... However, most of these methods are used to join sheets, tubes, tapes, or strips. For thin wires, the laser welding is an efficient, economical, and uncomplicated technique that can join particularly thin wires applied in medical procedures [20,22]. Thanks to this method, one can control the size of the welded area on a micro-scale. ...
... The papers reported the possibility of butt welding of NiTi wires of 100 µm whose strain was 3% at a tension of 500 MPa [17]. In work [20], the welding parameters for a 0.5 mm wire were optimized by selecting the power range of 54 W-72 W. The welding time was relatively long (85-115 ms), but the authors did not analyze the influence of welding conditions on pseudoelasticity. Chan et al. [23] showed the cycling repetition of pseudoelasticity for butt welded 0.5 mm wires whose maximum strain was 4%. ...
Abstract
Joining wires made of NiTi alloys with shape memory effect and pseudoelasticity causes many technical and structural problems. They result from unwanted phase interactions that occur in high temperatures and negatively affect the characteristics of these materials. Such obstacles are challenging in terms of welding. Hence, an attempt was made to join NiTi wires via an economical and reliable basic laser welding technique which does not require complicated equipment and gas protection. The parameters such as spot diameter and pulse time were constant and only the laser power, calculated as a percentage of the total power, was optimized. The wires were parallelly connected with overlapping seam welds 10 mm long. The welds were examined regarding their microstructure, chemical and phase composition, reversible martensitic transformation, microhardness, and pseudoelasticity. The obtained results showed that the joint was completed at the 12–14% power. The weld revealed good quality with no voids or pores. As the laser power increased, the microhardness rose from 282 (for 4%) to 321 (for 14%). The joint withstood the stress-inducing reversible martensitic transformation. As the transformation was repeated cyclically, the stress value decreased from 587 MPa (initial wire) to 507 MPa (for the 14% power welded wire).
Keywords: NiTi shape memory alloy; welding; microhardness; pseudoelasticity
... The consideration of the microstructure of the HAZ and FZ regions are similar to those made in the previous section. As visible, the FZ (right side) shows some significant coarse grains, while fusion boundary (left side) indicates epitaxial crystallization of the grains induced by the laser welding process [50]. ...
... As can be seen, the microhardness value in the BM is near 400 HV, while the values decrease around 280 HV approaching the FZ due to the re-solidification structure. In fact, the generated heat conduction in the NiTi wire causes the effect of grain growth and recrystallization of the BM during the welding process [129]. Nevertheless, the size of the locally softened region has the minimum influence on JBFs when the laser power is between 0.85 and 1.7 kW [41]. ...
NiTi shape memory alloys (SMA) are broadly employed in multifunctional systems in several industrial
domains, like aerospace, automotive, biomedical and power plants. Their functional properties, which
include shape memory effect (SME) and superelasticity (SE), offer a particular flexibility to design many
smart components. However, scientists and practitioners are still facing some restrictions in machining
processes and joining techniques of NiTi SMAs to both similar and dissimilar materials. Compared to other
procedures, laser welding is an economical and reliable joining technique for NiTi SMAs. Nevertheless,
it is considered a challenging technique, with many obstacles still to overcome to achieve welded joints
characterized by the necessary strength and the required functionalities. In this respect, the present
work investigates the effects of laser welding process on the functional properties of NiTi and related
alloys. Mechanical, microstructural, and metallurgical effects of the process are reported, as well. Lastly,
the impact of the post-weld heat treatment (PWHT) is studied as an effective solution to improve the
downsides of the laser welding process.
... As a result, sample 9NA shows remarkably a higher hardness values compare to sample 10NA. It might be due to the higher laser power (450 N) of sample 10 NA which leads to enlarging the grain size and subsequently decrease the hardness rate [159]. ...
... As can be seen, the microhardness value in the BM is near 400 HV, while the values decrease around 280 HV approaching the FZ due to resolidification structure. In fact, the generated heat conduction in the NiTi wire causes the effect of grain growth and recrystallization of the BM during the welding process[159]. Nevertheless, the size of the locally softened region has the minimum influence on JBFs when the laser power is between 0.85 and 1.7 kW[101]. ...
... The consideration of the microstructure of the HAZ and FZ regions are similar to those made in the previous section. As visible, the FZ (right side) shows some significant coarse grains, while fusion boundary (left side) indicates epitaxial crystallization of the grains induced bythe laser welding process[159]. ...
NiTi shape memory alloy (SMA) are widely applied in many industrial domains, such as biomedical, aerospace, automotive and power plants, due to its outstanding functionality including superelasticity (SE) and shape memory effect (SME). The machining process of this material is really challenging with a lot of barriers. Accordingly, joining techniques can be an alternative approach to design shape memory components with more flexibility.
Among all methods, laser welding process is a reliable and economic technique for joining of NiTi alloys. However, thermal process influences strongly on the strength and functionality of the NiTi welded joints in the Heat Affected Zone (HAZ) and the Fusion Zone (FZ). Indeed, the transformation temperature of NiTi alloy can be altered due to varying in the material composition.
Therefore, controlling the operational parameters, including laser power, scan speed or focal distance lead to effectively improve the mechanical and the functional behavior of NiTi joints. It consequently enhances the weldability of this material. This current study investigates the laser welding of NiTi shape memory sheets and reports the effect of laser parameters on microstructural, functionality, and mechanical properties of the welded joints. Also, this study is employed a numerical model to estimate the optimum laser parameters, including laser power and scan speed, which can reduce the Heat Affected Zone (HAZ) and the Fusion Zone (FZ) and therefore result in a better weld. The simulation results, including the transient temperature, welding penetration, and the dimension of HAZ and FZ, show a good accuracy compared to the experimental results.
Emerging trends in laser cladding procedure of welding by nitinol wire is finding its prominence in aviation, automotive, biomedical and thermal power plants as well as in precise repair work. Various parameters like range of applicability for laser deposition process along with new techno advent in additive manufacturing processes are making researchers to work in this domain. This paper focuses on the performance of the repaired component and economic efficiency of laser cladded welding by nitinol wire with the parameters ranging from micro to macro aspect, from low voltage to high voltage in hybrid environment procedure. Experimental analysis by Compressive and Impact test on repaired parts by Nitinol Wire through non-destructive testing machines is clearly discussed. This paper also gives briefly information regarding several methods used by additive manufacturing of different welding techniques by nitinol wire on base material. The properties of the repaired materials strength have also been discussed. Envision of this paper is to reconnoiter Additive Manufacturing, prevalently known as 3D printing. It is emerging in today’s development in manufacturing & repair techniques with advent procedure as a standard porter of the next generation industry to produce radical changes and consequently decreases the expenses in repair work & also enhances productivity. This paper also focuses on Additive technology by Laser Cladding technique which can successfully repair parts used in gas turbine engines such as vanes, stators, seals and rotors, and even geometrically complex parts such as airfoils, blisks, ducts and diffusers through different repair applications using LMD, AFM including repair of high-pressure turbine case and compressor front drum.
