electron beam additive manufacturing of Ni-Ti alloy (original) (raw)
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Journal of Materials Engineering and Performance, 2021
The electron beam additive manufacturing (EBAM) method was applied in order to fabricate rectangular-shaped NiTi component. The process was performed using an electron beam welding system using wire feeder inside the vacuum chamber. NiTi wire containing 50.97 at.% Ni and showing martensitic transformation near room temperature was used. It allowed to obtain a good quality material consisting of columnar grains elongated into the built direction growing directly from the NiTi substrate, which is related to the epitaxial grain growth mechanism. As manufactured material showed martensitic and reverse transformations diffused over the temperature range from −10 to 44 °C, the applied aging at 500° C moved the transformation to higher temperatures and transformation peaks became sharper. The highest recoverable strain of about 3.5% was obtained in the as-deposited sample deformed along the deposition direction. In the case of deformation of the alloy aged at 500 °C for 2h, the formation o...
MRS Bulletin, 2016
NiTi shape-memory alloys Shape memory is a fascinating material property, enabled by complex deformation mechanisms that create the "shape memorizing" ability in specifi c metallic and polymeric materials. Shape-memory materials can recover their primary shape after deformation (applied under specifi c temperature/ stress conditions) as a response to a thermal or mechanical command. This capacity of shape-memory materials allows for a wide range of applications, from biomedical implants and devices to sensors, actuators, aerospace components, and even fashion items. 1-6 This article focuses on NiTi (nickel titanium or nitinol) intermetallics, since they are the most utilized shape-memory alloy. NiTi intermetallics are ductile in contrast to commonly known brittle intermetallics, hence they are commonly referred to as alloys. NiTi alloys regain their original shape through a reversible martensitic transformation (i.e., low-temperature martensite ↔ high-temperature austenite) (see Figure 1). 7-9 The low-temperature martensite deforms through reorientation and detwinning of martensite lattice structure. Subsequent heating transforms the martensite (monoclinic with low symmetry) to austenite (body-centered cubic with high symmetry) and recovers the original shape. This type of shape-memory effect is also known as a thermal-memory effect. Conversely, when the austenite is stressed within a specifi c temperature range, it transforms to martensite. Since martensite is unstable without stress at those temperatures, it transforms back to austenite upon unloading, reversing the deformation. This results in a large elastic response, called superelasticity. 10-13 Accordingly, the martensite ↔ austenite transformation temperature is the most important factor in NiTi alloys; it defi nes the application at an intended working condition. Besides the shape-memory ability of NiTi alloys, they exhibit other valuable characteristics (e.g., good biocompatibility [comparable to conventional stainless steel and titanium, despite some existing concerns]), 14-17 low stiffness (important for biomedical applications where bone stress shielding or bone healing is an issue), 18 , 19 good corrosion resistance (similar to 300 series stainless steel or titanium alloys), 20 , 21 superb wear resistance, 22-24 high strength, and excellent ductility. 22 , 25 These characteristics broaden the applications and performance of NiTi devices.
Tensile actuation response of additively manufactured nickel-titanium shape memory alloys
Scripta Materialia, 2018
In the present work, we characterize the tensile shape memory actuation behavior of NiTi shape memory alloys (SMAs) fabricated using laser powder bed fusion (L-PBF) additive manufacturing process. The samples were fabricated using two different sets of processing parameters. While reversible tensile shape memory behavior was observed in both cases, the samples fabricated with a shorter hatch spacing exhibited higher transformation temperatures, lower actuation strain, and lower irrecoverable strain compared to the samples fabricated with wider hatch spacing. The actuation strain and ductility of the L-PBF samples were lower than that of the conventionally manufactured NiTi SMA samples.
Journal of Alloys and Compounds, 2021
The gas metal arc welding (GMAW) based wire arc additive manufacturing (WAAM) process has been employed to deposit 5-layered NiTi alloy on the Titanium substrate using Ni 50.9 Ti 49.1 wire as the feedstock. The heterogeneity of the piled up layers has been evaluated in terms of the variation in microstructure, composition and phases present. The melting of the Ti substrate under the first layer led to a substantial increase in Ti concentration in the melt during the deposition of the first layer and facilitated the formation of Ti-rich NiTi/Ti 2 Ni mixture during the solidification. In the 2nd e 5th layers columnar grains appeared in the inner space, whereas equiaxed grains formed on the top of the layers. The chemical composition of the 1st e 3rd layers differed from the nominal composition of the feedstock wire i.e. the layers in proximity of the substrate had lesser Ni concentration. As the result, the temperatures of the B2 4 B19' martensitic transformation were different across the layers and the start temperature of the forward transformation changed from 73 C (1st layer) to À16 C (5th layer). Using the EDX and calorimetric data, the Ni distribution in each layer was determined and its influence on the martensitic transformation temperatures was discussed in detail. The difference in Ni concentration has made various layers to be present in different states (martensite or austenite) at room temperature. In this case, the layers (2e4) were deformed by different mechanisms during tension at room temperature. The deformation of the layers by reversible mechanisms was confirmed by the shape memory effect on heating of the pre-deformed NiTi sample produced by WAAM.
Journal of Manufacturing Processes, 2021
Additive manufacturing has been adopted to process nickel-titanium shape memory alloys due to its advantages of flexibility and minimal defects. The current layer-by-layer method is accompanied by a complex temperature history, which is not beneficial to the final characteristics of shape memory alloys. In this study, a continuous directed energy deposition method has been proposed to improve microstructure uniformity. The spatial characterization of nickeltitanium shape memory alloy fabricated by continuous directed energy deposition is investigated to study the temperature history, phase constituent, microstructure, and mechanical properties. The results indicate that the fabricated specimen has a monotonic temperature history, relatively uniform phase distribution and microstructure morphology, as well as high compressive strength (2982 MPa~3105 MPa) and strain (37.7%~41.1%). The reported method is expected to lay the foundation for spatial control during the printing of functional structures.
Mechanical properties of Ti-(∼49at%) Ni shape memory alloy: Part I. Effect of cold deformation
Materials Science and Engineering: A, 2013
The present investigation aims to study the effect of cold deformation on the mechanical properties and shape recovery behavior of the Ti-rich Ti-Ni alloy. The micrographic investigations and XRD analyses have revealed that the microstructure of the homogenized and quenched samples comprises austenite (B2) and martensite (B19 0) phases. Significant enhancement of martensite volume fractions in the microstructure has been achieved after 30% cold deformation. The effect of deformation has also been manifested in terms of the sloping tensile curve in the region of shape memory strain. The shape recovery experiment has indicated improved shape recovery ratio in the case of the deformed samples owing to the delay in onset of the plastic straining during the shape deformation.
STUDY OF NANOMECHANICAL PROPERTIES OF Ni-Ti SHAPE MEMORY ALLOY BY INSTRUMENTED INDENTATION TECHNIQUE
2011
An attempt has been made to correlate shape memory behavior and the micromechanical characteristics of the martensite crystals in the polycrystalline microstructure of thermally and thermo mechanically processed nearly equi-atomic NiTi shape memory alloy. The nanoindentation measurements have shown that suitable schedule of thermo mechanical treatment improves the hardness of the martensite phase. The recovery index parameter obtained from the load depth profile illustrates the recovery of the indentation strain of the martensite phase.
Textural Evolution by Multiple Steps of Marforming in Ti-Rich Ni-Ti Shape Memory Alloy
Esomat 2009 - 8th European Symposium on Martensitic Transformations, 2009
The Nickel-Titanium (Ni-Ti) alloys are the most attractive amongst shape memory alloys (SMA) due to their good functionality properties coupled with high strength and good ductility. The transformation temperatures in Ti-rich NiTi SMA can be altered with suitable thermal and/or mechanical treatments to obtain martensitic Ti-Rich Ni-Ti SMA (Ni-51at%Ti) that will contribute to different phase transformation sequences (one, two and 300 minutes in vacuum), (ii) followed by multiple steps of marforming (30% thickness reduction by cold rolling), (iii) four distinct final thermal treatments (400,-Ray Diffraction (XRD) at room (ER) and X-Ray Diffraction (XRD) were used to identify the transformation temperatures and the phases that are present after all steps of thermomechanical treatments.