Equiatomic NiTi Research Articles

Thermodynamic Investigation of Propagating Behavior in SHS for Equiatomic and Non-Equiatomic NiTi Alloys Using Factsage Software

Thermodynamic Investigation of Propagating Behavior in SHS for Equiatomic and Non-Equiatomic NiTi Alloys Using Factsage Software

On the effect of the processing parameters in microstructure and thermomechanical properties of LPBF NiTi shape memory alloys

Recent studies have shown that variations in the parameters of the laser powder bed fusion (LPBF) process significantly impact the microstructure and thermomechanical properties of NiTi shape memory alloys (SMAs). Understanding how parameter selection influences the final NiTi SMA properties enables the strategic design of additively manufactured (AM) components with tailored mechanical and transformation behavior, suitable for specific applications in a plethora of scientific fields. However, the connection between processing and thermomechanical properties of NiTi SMAs is still not completely understood. This study investigates the effects of AM parameters laser power (72–185 W), scanning speed (668-1739 mm/s), and hatch spacing (28–85 μm) on a near equiatomic NiTi powder. Low porosity levels are found in the samples additively manufactured (AM) with the different LPBF parameter combinations. The findings also reveal that transformation temperatures and nickel evaporation trends correlate directly with volumetric energy density (VED). Additionally, the amount of Ti2Ni precipitates increases with higher VED. Thermal cycles under constant stress, training, and two-way shape memory effect tests have been performed; the results demonstrate a strain recovery ratio of 2–3.5% for most of the samples. The results arising from this study pave the way for the engineering of customized materials with tailored properties from the same alloy metal powder.

An Investigation on Microstructural Characteristics and Comprehensive Performances of Equiatomic Ratio NiTi Shape‐Memory Alloy Produced by Selective Laser Melting

The present study utilizes selective laser melting (SLM) technology to fabricate NiTi alloy and investigates the deposition quality, microstructure, mechanical performances, and functional properties of the as‐deposited parts. The NiTi component is fabricated by SLM at a suitable energy density (60.61 J cm−3), resulting in favorable surface forming quality and only micron‐sized porosity defects present in the interior. Dense and fine B19’ martensite is distributed within the epitaxial B2 austenite matrix that grows in the height direction through the melt pool boundary, along with the nanoscale Ti2Ni precipitates dispersedly distribute at B19’ grain interiors and grain boundaries. Both tensile and compressive results indicate that the as‐deposited NiTi components acquire slightly inferior ductility but superior strength than that of traditionally manufactured NiTi alloys. The shape‐memory effect of NiTi components is significantly influenced by holding temperature, exhibiting good and stable shape‐memory effect above a holding temperature of 75 °C. Simultaneously, the compressive superelastic behavior of the NiTi component exhibits favorable stability, with a recoverable strain of ≈5.5%. Overall, the NiTi component fabricated in the present study exhibits favorable mechanical properties and functional performance attributed to its excellent deposition quality and dense microstructure.

3D printing of shape memory Alloys for complex architectures of smart structures

Shape Memory Alloys (SMA) are materials used to design smart structures with intrinsic functional properties and improved efficiency. This is a key aspect of aerospace industry and makes SMA good candidates in this field. One of the most widespread SMA is the equiatomic NiTi alloy which, however, has the strong limitation of poor machinability, so only simple shapes can be obtained. Additive Manufacturing processes allow to overcome this limit and to design complex shapes. Compared to other metallic materials, the optimization of the process for NiTi alloy is complicated because, beside mechanical properties and presence of defects, considerable attention needs to be dedicated to the material functionality. The high temperatures involved in the additive process significantly affect the material properties due to possible evaporation of Ni and formation of precipitates that enable a shift of the phase transformation temperatures. This paper is focused on the optimization of the process parameters of the NiTi alloy printed through the Laser Powder Bed Fusion (L-PBF) to ensure optimal pseudo-elastic behaviour, which is essential for the design of structural dampers. This was accomplished starting from simple structures and then designing a damper that couples the pseudoelasticity of NiTi with load support capacity.The L-PBF is a powder-bed technique that selectively melts layers of micrometric metal powder. A pseudoelastic NiTi powder with 50.8 at. % of Ni content was selected and characterized through scanning electron microscope (SEM) and observations connected to an Energy Dispersive X-ray Spectroscopy (EDX) probe. After that, some cubic samples were manufactured, with the dimension of 3 × 3 × 15 mm3. A set of different laser powers and scanning speeds were used to find the set of process parameters that optimize the functional properties of the printed parts. Near fully dense specimens with density higher than 99.5 % were selected for further investigations. Differential scanning calorimetry (DSC) and mechanical tests were performed on as-built and heat-treated samples.Quasi-static mechanical tests were accomplished in compression mode, at different strains, up to 8 %. It was observed that the residual strain for cyclic loading at 4 % is lower than 1 %, so good recovery of the deformation was shown. Moreover, numerical analyses that mimic the pseudoelastic behaviour in compression tests were implemented.Finally, the best set of parameters was selected on the basis of the material's ability to recover deformations and its loss factor.

Characteristic variations in a pulsed‐anodized NiTi alloy surface by the lower voltage setting

Pulsed anodization of a nearly equiatomic NiTi alloy in HNO3 leads to the formation of a nearly Ni‐free oxide layer, resulting in the suppression of Ni‐ion release from the alloy surface. The core technology involves introduction of a lower‐voltage period, which promostes chemical reactions between the alloy and electrolyte, to obtain a surface layer with better corrosion protection. In this study, a higher voltage of 3.5 V was applied, and the lower voltage was varied within 0–3.5 V. As the lower voltage was increased, nanometer‐sized pores present on the anodized surface gradually expanded, while the layer thickness decreased. Although the corrosion protectivity of the layer did not change significantly during the electrochemical experiments, the amount of Ni‐ion released into the physiological solution significantly decreased when the voltage was below 1.8 V. X‐ray photoelectron spectroscopy analyses revealed the presence of Ni (OH)2 on the topmost surface, and its concentration decreased at a voltage <1.8 V. Lower voltages affected the concentration of Ni (OH)2 on the topmost surface and thus considerably influenced the Ni‐ion release behavior. These findings will contribute to the production of NiTi alloys with improved biocompatibility.

Crystal-to-amorphous phase transformation in ternary shape memory alloys

This systematic study evaluates the role of important factors in crystal-to-amorphous phase transformation during severe plastic deformation in ternary shape memory alloys. Experiments coupled with thermodynamic calculations to obtain comprehensive interpretation on the amorphization in ternary shape memory alloys. Equiatomic binary NiTi together with ternary Ni–45Ti–5Hf and Ti–45Ni–5Cu (at%) alloys as alloy models were processed by high-pressure torsion (HPT) at room and cryogenic temperatures. The binary and Hf-added alloys revealed an amorphous structure with a few remaining nanocrystals, however, Cu-added ternary alloy showed resistance to the amorphization after HPT processing. The results revealed two key factors of preventing martensite-to-austenite transformation during deformation and the intrinsic potential of the material for amorphization drive crystal-to-amorphous phase transformation. Higher transformation temperatures, enthalpy and thermal hysteresis prevented martensite-to-austenite transformation, which therefore encouraged amorphization. In addition, a large negative heat of mixing, Gibbs energy for amorphization and a large atomic size mismatch are important factors in implementing crystal-to-amorphous phase transformation. This investigation is a step forward to a fundamental understanding of ternary or even compositionally complex shape memory alloys for microstructural engineering by providing a homogeneous ultrafine-grained structure due to amorphization and subsequent heat treatment to achieve superior shape memory effect and superelasticity.

A comparative study of the amorphization of NiTi-B2 structure by anti-site defects

This paper reports a comparative study of the amorphization of B2 structure of near-equiatomic NiTi and three other equiatomic binary B2 alloy systems, including AlFe, CuZr and FeTi. The study was conducted by means of molecular dynamics simulation on the effects of anti-site defects within the B2 structure. It was found that anti-site defects cause severe random distortions to the B2 structures, lowering their crystalline ordering. Among the four B2 systems studied, equiatomic AlFe and FeTi cannot be fully amorphized by anti-site defects but NiTi and CuZr can become fully amorphous at above a threshold concentration of the defects, as compared to the structure of quenched liquid. It is also found that the threshold anti-site concentration for amorphization decreases with increasing temperature. In comparison between the two, NiTi is easier to be amorphized than CuZr by anti-site defects, both in terms of the threshold anti-site defect concentration required and the temperature range within which it is possible. These findings may help to explain the long-observed phenomenon of the easiness of equiatomic NiTi to become amorphous during cold working and the new observation of third element substitutional diffusion caused amorphization.

Elastic and transformation behaviour of equiatomic NiTi shape memory alloys fabricated at different sintering temperatures

The growing demand for bulk Nitinol in ball and roller bearing applications is focused on in this article. The uniaxial compaction and sintering process is considered for the fabrication of the alloys where the sintering temperatures vary from 950 ℃ to 1150 ℃. Better homogenisation and diffusion are achievable except for the 950 ℃ sintered sample. The results of XRD of 950 ℃ and 1050 ℃ sintered samples show the presence of the Ni3Ti phase but in all the Samples sintered above 950 ℃, NiTi is the major phase, unlike Ni3Ti in 950 ℃. The TEM analysis shows a trace amount of TiO2 which comes from the impurity of the purged Ar gas. The O2 in the samples can be accommodated inside a few Ti2Ni phases to form Ni2Ti4O phases. Ni4Ti3 precipitates formed at higher temperatures help in precipitation strengthening. At room temperature, both austenitic B2 and martensitic B19′ coexist. The DSC analysis shows that an increase in the sintering temperature increases the response time by consuming more energy. The elastic modulus and hardness have been increased up to 1100 ℃ and then decreased. Above Af temperature successful transformation of B2 to B19′ takes place.

Role of Zr and thermomechanical treatment on phase transformation and functional properties of NiTi-based shape memory alloys

A systematic investigation was conducted to evaluate the role of Zr addition on the martensitic phase transformation behavior and properties of NiTi-based shape memory alloys. Equiatomic binary NiTi alloy and ternary Ni50Ti45Zr5 and Ni50Ti40Zr10 alloys (at.%) were processed by a simple thermomechanical treatment including cold rolling followed by post-deformation annealing at 450 °C for 30 and 60 min. The microstructural investigation and thermal analyses reveal that martensitic phase transformation is suppressed by adding Zr. Solid solution strengthening due to Zr addition, strain hardening due to cold rolling and formation of (Ti,Zr)2Ni precipitates in a dual-phase microstructure during annealing leads to a significant increase in hardness in the thermomechanically treated alloys (e.g., up to 550 Hv for Ni50Ti45Zr5 alloy). The stress-strain curve of martensitic Ni50Ti50 alloy reveals the essential characteristics of shape memory effect, however, Ni50Ti45Zr5 alloy shows typical features of pseudoelasticity with significantly high stress plateau (∼600 MPa) and remarkable recovered strain of 3.5% during unloading.

Endothelium Cell Responses on Pulsed-Anodized NiTi Alloy with HNO<sub>3</sub>, NH<sub>4</sub>NO<sub>3</sub>, H<sub>2</sub>SO<sub>4</sub>, and (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub> as Electrolytes

Pulsed anodization allows to form a Ni-free TiO2 layer on an almost equiatomic NiTi alloy. The surface is then hydrophilized and impedes the release of Ni ions from the alloy. This study aimed to assess the suitability of electrolytes used in the pulsed anodization process with the view of application as a biomaterial. Toward this end, the NiTi alloy was pulsed-anodized in four different aqueous electrolytes, HNO3, NH4NO3, H2SO4, and (NH4)2SO4, after which the endothelium cell behavior was compared. The use of H2SO4 as the electrolyte resulted in the formation of a TiO2 layer with a groove-like structure of several tens of nanometers wide, and this surface inhibited the activity of endothelium cells. The ability to prevent the release of Ni ions was diminished when using the HNO3 electrolyte, resulted in inferior cell proliferation. The other two electrolytes, NH4NO3 and (NH4)2SO4, formed a Ni-free TiO2 layer with a comparatively smooth surface, which more effectively suppressed the release of Ni ions; thus, the cell attachment as well as proliferation were superior to that of the other two electrolytes. The surface smoothness and Ni suppression were thus concluded to be the factors governing the selection of an electrolyte.

Synthesis and characterization of novel NiTi–Ni3Ti/SiC nanocomposites prepared by mechanical alloying and microwave-assisted sintering process

Equiatomic Ni–Ti alloy reinforced with 0, 2.5, 5, and 10 vol % SiC nanoparticles was synthesized through mechanical alloying and microwave sintering process. In this method, a mixture of Ti and Ni powders and SiC nanoparticles (0–10 vol%) were mechanically milled for 30 h, compressed under 1 GPa pressure, and then sintered at 900–1100 °C by microwave heating. Microstructural analysis of the synthesized samples was performed using X-ray diffraction and scanning/transmission electron microscopy, and their hardness was determined using a Vickers microhardness tester. Structural studies revealed the formation of a complex phase structure consisting of the austenite (B2–NiTi), the martensite (B19′-NiTi), and the nickel-rich (Ni3Ti) and titanium-rich (NiTi2) phases. HR-TEM investigations confirmed an increased Ni3Ti phase in the austenitic NiTi matrix nearby the martensitic NiTi phase. It was found that adding SiC nanoparticles to Ni–Ti increased the amount of hard Ni3Ti phase, promoted the stability of the martensite phase at room temperature, and retarded the matrix grain growth during the sintering process. Microhardness tests showed that when the content of SiC nanoparticles increased up to 5 vol %, the microhardness increased considerably to 9 GPa and then declined. The high microhardness of synthesized nanocomposites is due to the formation of Ni3Ti and NiTi martensitic phases and their nanocrystalline structure.

Depth distribution analysis of alloying and impurity elements in Ni-Ti alloy thin films using secondary ion mass spectrometer

Ni-rich Ni-Ti thin films of various compositions and thickness (69 nm - 141 nm) were deposited on Si (111) substrate by magnetron sputtering system using equiatomic NiTi alloy sputtering target. X-ray reflectivity analysis of the thin films deposited at room temperature showed the presence of a layered structure as: NiO/Ni-Ti/NiO/SiO2 on Si substrate. Secondary ion mass spectrometry (SIMS) was used to determine the qualitative (intensity) depth distribution of elements Ni, Ti, O and Si in the films using MCs+ approach. Relative sensitivity factor values were utilized to convert the qualitative depth profiles to concentration depth profiles. Surface and depth distribution of alloying elements in the deposited films were investigated. It was observed that the films deposited at high sputtering power and working pressure resulted in more non-uniform depth distribution of alloying elements compared to films deposited at low sputtering power and working pressure. SIMS depth profile data showed the presence of high oxygen contaminations at the surface and at the interface of the films. The Ti concentration in the deposited films depends upon the background oxygen contamination present in the deposition chamber during sputtering process. The concentration of Ni in the films deposited under similar working pressure increases with increase in the sputtering power. However, with increase in working pressure during deposition process results in decrease in the concentration of both Ni and Ti in the deposited films. In order to study the effect of insitu substrate heating on the distribution of alloying and impurity elements, one of the film was deposited on heated Si substrate. The film deposited on heated substrate represents the layer structure as NiTiO3 on Si substrate. The concentration of oxygen in the film deposited on heated substrate is comparatively higher than those deposited at room temperature.

Effect of carbon addition on the microstructure and mechanical behavior of near equiatomic NiTi alloy wire

According to the phase diagram, 0.03 wt% (C0.03) and 0.05 wt% (C0.05) carbon were added to Ni50.2Ti49.8 alloy, and the alloy wires with a diameter of 1.2 mm were prepared by vacuum induction melting and drawing. The results show that during melting and solidification, C combines with Ti in C0.03 and C0.05 to form eutectic TiC and primary TiC, respectively. Compared with the NiTi alloy wire without C, the tensile fatigue life (22866 cycles under 700 MPa tensile stress) and tensile strength (1536 MPa) of the alloy were increased by 39 % and 22 % respectively when 0.03 wt% C was added. With the further increase of C content to 0.05 wt%, the two properties began to deteriorate. This is mainly related to the changes of matrix phase composition, second phase morphology and internal microstructure caused by the addition of different amounts of C. The research results show that on the premise of following the requirements for C content (C ≤ 0.04 wt%) in the international standard ASTM F2063-18 for medical NiTi alloy composition, adding a certain amount of C (such as 0.03 wt%) to NiTi alloy is beneficial to improving the tensile strength and tensile fatigue life of wire.

Study on phase transformation behavior and mechanical properties of equiatomic ratio NiTi alloy formed by selective laser melting

PurposeThis paper aims to better control the mechanical properties and functional properties of NiTi alloy.Design/methodology/approachNiTi alloy samples with equal atomic ratio were formed by selective laser melting (SLM). X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy and tensile testing methods were used to study the effects of different laser power and scanning speed on the densification behavior, phase transformation characteristics and mechanical properties of NiTi alloy.FindingsCompared with the laser power, the variation of the keyhole effect caused by the change of scanning speed is more intense, which has a greater effect on the densification behavior of SLM NiTi alloy. The effect of the laser power on the phase transition temperature is small. The increase of scanning speed weakens the burning degree of Ni element, so phase transition temperature decreases. The results of DSC test and tensile test show that the scanning velocity can significantly change the phase transition temperature, martensite twins reorientation and stress–strain behavior of SLM NiTi alloy.Originality/valueThis study provides a potential method to regulate the mechanical properties and functional properties of NiTi shape memory alloy in the future and NiTi alloys formed by SLM with good elongation were obtained because the Supercellular crystal structure formed during the nonequilibrium solidification of SLM and the superfine precipitates dispersed in the alloy prevented the dislocation formation.

Influence of local thermal cycle on the lattice and microstructure evolution of twin-wire directed energy deposition-arc fabricated equiatomic NiTi alloy

In the present work, the authors wish to investigate the effect of repeated heating cycles on the phase and crystal structure few layers at a time. Equiatomic NiTi alloy is additively manufactured using twin-wire directed energy deposition-arc (TW-DED-arc) in an in-situ alloying process from pure Ni and Ti wire feedstocks. The central region is wide enough for the extraction of several metallographic and tensile specimens away from dilution zones. Microstructure characterization reveals the incorporation of silicon preventing the formation of NiTi2 and the existence of two types of B2 austenite in the matrix, which has a composition of 50.2 at.%Ni-49.8 at.%Ti. The lattice is observed to dilate near the top regions under tensile thermal stress with no contribution from Ni-rich precipitates. Mechanical test gives a maximum ultimate tensile stress of 782.5 MPa with a fracture surface indicative of quasi-cleavage failure. The results show TW-DED-arc is able to produce fully dense, chemically homogenous NiTi alloys without detrimental phases. In addition, the local thermal cycles experienced by the samples gradually promote the nucleation of Ti5Si3 precipitates and lead to a preferential growth of NiTi grains along the (0 0 1) direction.

The effect of copper on phase transformation, microstructure and mechanical characterization of Ni50-xTi50Cux shape-memory alloy

This research is related to the investigation of the influence of copper additions on phase transformation, microstructure and mechanical characterization of equiatomic NiTi shape-memory alloys. A typical vacuum arc melting furnace was used in the preparation of Ni50-xTi50Cux (x = 2, 5, 10, and 15 at.%) shape-memory alloys. The crystalline phase formation and phase transformation temperature were studied using X-ray diffraction and a differential scanning calorimeter. The morphology and chemical composition of the annealed samples were investigated using a field emission scanning electron microscope and energy-dispersive X-ray spectrometer analysis. The Vickers microhardness test was utilized in the analysis of the homogeneity of the alloy. The experimental results obtained from X-ray diffraction confirmed the coexistence of austenite and martensite phases along with the presence of a Ti2Ni and minor rutile phases. The crystalline sizes of the alloys were in the range of 42 to 78nm. An energy-dispersive spectrometer validated the distinct phases and precipitates in the alloys. The size and dispersion of the secondary phase in the alloy showed a significant influence on the increased hardness from 407HV to 470HV. The following NiTiCu alloy compositions were employed for low-temperature applications since their transition temperatures were below 100°C.

Investigation of the orientation dependence of marforming on superelasticity and shape memory effect in equiatomic TiNi single crystals under compression

The shape memory effect (SME) and superelasticity (SE) after marforming (deformation in the martensitic phase at 203 K, followed by annealing at 713 K, 0.5 h) were studied in the equiatomic TiNi crystals under compression. Marforming was carried out along [0 0 1]B2 and [0 1 1]B2 directions of B2-phase after strain of ε = 1.5ε0 (ε0 is the lattice deformation, which depends on the crystal orientation). SME and SE after marforming were studied along [0 0 1]B2 direction. It was shown that the maximum stress level of B2-phase σcr(B2) = 750 MPa, the lowest values of mechanical Δσ = 100 MPa and thermal ΔTh = 32 K hysteresis and the maximum temperature range of SE ΔTSE = 77 K were observed when marforming under compression was realized along the [0 0 1]B2 direction.

Effect of substrate temperature on the surface and interface properties of NiTi atmospheric plasma sprayed coating

Atmospheric plasma spraying (APS) is one of the most preferred coating processes, which comes under thermal spraying technology. It has a wide range of applications due to its versatility in surface modifications. By the APS technique, different high-temperature application materials like cermets, and ceramics, can be coated on a substrate whose surface properties have to be modified in an extreme environment. Ni50Ti50 (at.%) alloy became more focus of interest for researchers and industrialists due to their two extraordinary smart properties such as shape memory effect (SME), and superelasticity (SE) which can protect any structural materials from catastrophic failure. Compared to various deposition routes, APS is an economical process to apply NiTi on mild steel. NiTi smart alloy also exhibits good wear resistance, corrosion resistance, damping behaviour, and high load-bearing capacity. In terms of mechanical properties, it has high strength and hardness at high temperatures. Owing to these properties, NiTi alloy can be used to protect structural materials such as mild steel from catastrophic failure. In this study, mild steel was coated at 100 °C, 200 °C, 300 °C and 400 °C preheating temperatures by APS techniques using an equiatomic NiTi alloy. The surface and interface characterization were performed using an optical microscope, SEM, XRD, Hardness test and 3D optical profilometer. It was found that along with the desired NiTi phase, some of the intermetallic and oxide phases are responsible for the mechanical strength. The surface and interface morphologies show that NiTi splat formation by APS results in better surface bonding and dense coating. With increase in the substrate temperature, the hardness of a coating interface increases with decrease in the number of pores at coating interface.

Effect of volume energy density on selective laser melting NiTi shape memory alloys: microstructural evolution, mechanical and functional properties

Equi-atomic NiTi shape memory alloy (SMA) samples were manufactured by selective laser melting (SLM) with different laser volume energy densities via synchronously varying laser power and scanning speed. The processing quality, phase transformation, and microstructural evolution were investigated to explore the mechanisms that are responsible for mechanical and functional properties. The results showed scattered micro-sized spherical gaseous defects inside the deposit. One-stage phase transformation occurred without intermediate R-phase transition, and the temperature of both endothermic and exothermic peaks was lower than that of the ingot. The microstructure initially grew along the building direction, but displayed different crystal orientations between coarse columnar grains and refined irregular sub-grains. The micro-hardness mapping revealed that homogenous anti-indentation properties were acquired independent of location variations. While the anisotropic behavior in tensile properties occurred due to the passive effect of columnar B2 austenitic grains, a synergistic effect of strength and plasticity was acquired primarily due to the combined effect of sub-grain refinement strengthening and transformation-induced plasticity. The pre-deformed NiTi samples recovered to their original shape when heated above its critical phase transition point. This work demonstrated that the crack-free NiTi SMA with exceptional comprehensive performances could be fabricated by SLM through the control of energy density.

Study on laser beam butt-welding of NiTinol sheet and input-output modelling using neural networks trained by metaheuristic algorithms

Though NiTinol, the equiatomic Ni-Ti alloy, is revolutionizing different fields of engineering, manufacturing and medicine since its discovery as a functionally advanced material, poor formability and machinability, and the limitations of available fabrication techniques applied for this alloy are restricting its applications in the form of various desired products. Now-a-days, laser welding is the mostly reported joining technique applied to the alloy. Though the difficulties associated with fabrication method and the cost of the alloy are high enough, a computationally efficient model for quick and precise prediction of operating parameters in order to obtain the specified attributes of the laser welded NiTinol sheets is significantly missing in the literature. In the present work, basic metallographic study related to laser welding of NiTinol sheets in butt-joint configuration was investigated. At the same time, an efficient forward and reverse model had been developed with the help of artificial neural network (ANN). These ANNs were trained with the help of regression equation model using five different metaheuristic techniques separately for the development of both forward and reverse models. Laser power, scan speed, frequency, duty factor and focal positions were treated as the input process variables and three different weld attributes, namely bead-area, micro hardness of the bead and tensile strength of the bead were considered as output variables of the process. The developed model was capable enough of predicting the outputs, which were in good agreement with the experimental data, for both forward and reverse models. The novelty of this study deals with the development and testing of feed-forward neural network and recurrent neural network trained using five different metaheuristic techniques for both the forward and reverse modelling of fibre laser welding of NiTinol alloys.