Electron beam freeform fabrication of NiTi shape memory alloys: Crystallography, martensitic transformation, and functional response

Li, Binqiang; Wang, Liang; Wang, Binbin; Li, Donghai; Oliveira, J.P.; Cui, Ran; Yu, Jianxin; Luo, Laihui; Chen, Ruirun; Guo, Jingjie; Fu, Haipeng

doi:10.1016/j.msea.2022.143135

Cited by 74 publications

(20 citation statements)

References 60 publications

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“…[ 13 ] NiTi alloys fabricated by AM technology have successfully achieved microstructural dimensions and superior performance. [ 14 ] Furthermore, the martensitic transformation temperature of NiTi alloys is affected by composition, microstructure, and thermomechanical state, which are closely related to the process parameters of AM Technology. [ 15 ] Therefore, under the optimized process, metallurgical defects such as sphericity, porosity, insufficient fusion, and cracks in NiTi alloys can be eliminated.…”

Section: Introductionmentioning

confidence: 99%

Microstructure and Mechanical Properties of NiTi Shape Memory Alloys by Laser Engineered Net Shaping

Fei

Liu

et al. 2023

Adv Eng Mater

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Herein, NiTi alloys are prepared by laser engineered net shaping (LENS) technology. By exploring the mechanical properties and microstructures of NiTi samples under different laser powers, it is concluded that NiTi alloys with a laser power of 350 W have better tensile strength (783 MPa) and strain recovery rate (59.01%). In addition, the mechanical properties and microstructure of NiTi samples with a laser power of 350 W at different aging temperatures (400–800 °C) are also explored. It is found that NiTi alloys aged at 600 °C had better tensile strength (729 MPa) and strain recovery rate (92.85%). In addition, the phase‐transition temperature and endothermic enthalpy and exothermic enthalpy of the NiTi samples after thermal treatment increased, which is attributed to the formation of stable martensite (B19′) inside the NiTi samples after thermal treatment, and the type of internal NiTi phases structure change significantly. Thermal treatment can generate Ni4Ti3, NiTi2 precipitates, and martensite (B19′) with high density of dislocations inside the NiTi samples. Herein, it is showed that LENS can prepare NiTi alloys with excellent mechanical and structural properties by controlling the equipment parameters and aging temperature.

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Section: Introductionmentioning

confidence: 99%

Microstructure and Mechanical Properties of NiTi Shape Memory Alloys by Laser Engineered Net Shaping

Fei

Liu

et al. 2023

Adv Eng Mater

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“…[14] The fabrication of specific products made from Ni-Ti alloys by processes such as machining, casting, and metal forming poses challenges due to the difficult processability of these alloys, [15][16][17][18] which limits possible innovative applications. It must be pointed out, however, that promising progress has been made in the field of additive manufacturing of Ni-Ti alloys, e.g., for wire-based additive techniques such as electron-beam free forming and ultra-high-frequency pulsed gas tungsten arc welding, which has led to improved process understanding [19,20] and new strategies for components with outstanding properties. [21] Although these additive processes already enable high building speeds and comparatively large workpieces, challenges for the application of additive manufacturing processes with Ni-Ti alloys still consist in anisotropy, very thin cross sections, surface quality, and costs.…”

Section: Introductionmentioning

confidence: 99%

Laser Welding of Nitinol Thin Foils: Mechanical Properties and Microstructure Depending on Process Parameters

Katrakova-Krüger

Pegoraro

Salmaso

et al. 2023

Metall Mater Trans A

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Ni–Ti alloys are used as functional materials in numerous sectors such as aerospace, automotive engineering, medical technology, and consumer goods. Their properties in terms of shape memory effect and superelasticity offer a great potential for innovative smart products. However, forming and machining of these alloys into concrete products is challenging. Assembling plain structures by laser welding to complex product shapes offers an economical alternative in many cases, but can be associated with negative effects, such as reduction of strength, development of brittle intermetallic compounds, alteration of transformation temperatures, and modification of shape memory effects and superelastic behavior. Against this background, investigations on laser welding of Ni55/Ti45 foil with a thickness of 125 µm by a fiber laser were conducted. Supported by methods of design of experiments, optimal parameters were determined with respect to laser power, welding speed, focus position, and beam oscillation, and the welding results were analyzed concerning the microstructure and mechanical characteristics of the welded joints. The effect of laser beam oscillation was investigated for the first time for the welding of this alloy. Due to the very low thickness, the preparation of the foils for the microstructure characterization is quite demanding. Best results were obtained by ion milling. Fracture surfaces and the influence of the welding were also investigated.

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“…These kinds of materials that possess shape recoveries are called shape memory alloys (SMAs). SMAs possess shape memory effect (SME), pseudo-elasticity, superior biocompatibility, and super-elasticity [4,5]. Nickel-titanium SMA, commonly referred to as Nitinol SMA, have gained a lot of popularity owing to their unique characteristics and acceptability for a wide range of applications [6,7].…”

Section: Introductionmentioning

confidence: 99%

Effect of Near-Dry WEDM Process Variables through Taguchi-Based-GRA Approach on Performance Measures of Nitinol

Vora

Shah

Khanna³

et al. 2022

JMMP

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The machining of Nitinol shape memory alloys (SMA) through conventional machining techniques imposes several challenges due to the alloys’ comprehensive mechanical qualities. Wire electrical discharge machining (WEDM) process is a non-conventional machining technique that is suitable mainly for producing complex shape geometries with excellent surface features for difficult-to-cut materials. The current study attempted the use of a near-dry WEDM process for Nitinol SMA with the consideration of multiple response variables. The studied literature and machine capabilities have identified input factors of pulse-on-time (Ton), pulse-off-time (Toff), and current and output factors of MRR, SR, and RLT. Through the Taguchi approach, a total of nine experimental trials were designed to analyze the performance of the process. The statistical significance of input factors on the performance measures was studied with the help of ANOVA techniques. Statistical analysis for all the output measures has shown that the generated regression terms had a significant influence. For single output measures, the current was found to have a substantial effect on both MRR and SR, while Toff was the most significant contributor in the case of RLT. The obtained results of residual plots for all performance measures implied good ANOVA results. The effect of near-dry WEDM variables was studied on output measures through main effect plots. Grey relational analysis (GRA) has been employed to attain optimal parametric settings of multiple performance measures. GRA technique for the optimal parametric settings of simultaneous performance measures of MRR, SR, and RLT was found to have a Ton of 30 µs, Toff of 24 µs, and current of 4 A. Validation trials were conducted to check the adequacy of the GRA technique. The minor acceptable deviation was recorded among the anticipated and recorded values. This clearly reveals the acceptability of the integrated approach of the Taguchi–Grey method. The surface morphology for the near-dry and wet-WEDM has also been investigated through scanning electron microscopy (SEM). The author considers that the present study will be beneficial for users working in WEDM and near-dry WEDM processes for hard machining materials.

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Electron beam freeform fabrication of NiTi shape memory alloys: Crystallography, martensitic transformation, and functional response

Cited by 74 publications

References 60 publications

Microstructure and Mechanical Properties of NiTi Shape Memory Alloys by Laser Engineered Net Shaping

Microstructure and Mechanical Properties of NiTi Shape Memory Alloys by Laser Engineered Net Shaping

Laser Welding of Nitinol Thin Foils: Mechanical Properties and Microstructure Depending on Process Parameters

Effect of Near-Dry WEDM Process Variables through Taguchi-Based-GRA Approach on Performance Measures of Nitinol

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