Study on variations of microstructure and metallurgical properties in various heat-affected zones of SLM fabricated Nickel–Titanium alloy

Farhang, Behzad; Ravichander, Bharath Bhushan; Venturi, Federico; Amerinatanzi, Amirhesam; Moghaddam, Narges Shayesteh

doi:10.1016/j.msea.2020.138919

Cited by 31 publications

(15 citation statements)

References 35 publications

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“…For the transversal cracks observed in all processing conditions, two aspects inherent to the process can be considered: the first is associated with the internal stresses (Ref 38,39) in the material arising from the abrupt heating and cooling conditions when the laser scans the material surface, in such a way that stress relief may have occurred with the propagation of cracks; and, the second aspect may be associated with the permanence of Ti-rich, Ni-free islands, which present themselves as regions of unfused material surrounded by the compositional gradient of the partially cast specimens based on Ni-Ti system. This region of non-cast material surrounded by partially cast material may contribute to the generation of cracks when understood as stress concentrating regions, due to contraction and dilatation effects between the solid and liquid phases that induce stresses, that can be intense, leading to crackÕs propagation.…”

Section: Resultsmentioning

confidence: 99%

Production of Cylindrical Specimens Based on the Ni-Ti System by Selective Laser Melting from Elementary Powders

Oliveira

Lima

Sallet

et al. 2021

J. of Materi Eng and Perform

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This study aimed to evaluate the potential use of elemental powders, Ni oxyreduction and Ti HDH (hydration-dehydration) to obtain the NiTi shape memory alloy in cylindrical specimens from additive manufacturing process by Selective Laser Melting with laser power and energy density under control (100 to 150 W and 25 to 40 J/mm 3 ). Scanning electron microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD) conjugated analyses showed that all processing parameters yield samples with Ti enriched regions surrounded by alloy layers associated to Ni 3 Ti, Ni 3 Ti 2 , and NiTi 2 intermetallic. This evidence suggests that the parameters applied were not enough to promote the complete fusion of Ti particles, indicating that the samples presented a melting microstructure with evidence of defects located due to lack of fusion due to the irregular voids and Ti islands that resemble the irregular morphology of the starting Ti HDH powder, and pores depending on the retention of gases in the fusion pool. Each explored condition presented in its structure a set of different phases in nature and proportion, without the NiTi intermetallic. Also, justifies the apparent and real density values not compatible with the NiTi intermetallic theoretical density, but the density resulting from the mixture of different Ni-Ti system phases formed. Observing the decrease in the cracks and pores, and the real densities measured, compared with the theoretical density of the NiTi intermetally, the specimens that represent the best conditions are those produced with 125 and 150 W with 30 J/mm 3 , in order not compromising the SMA properties, and would allow microstructural evolution for the formation of the NiTi through heat treatment. Although the most favorable parameters, the NiTi system did not exhibited an austenitic matrix, and then the adoption of the proposed elementary powders mixture will be promising when followed by solution heat treatment, which is one of the works under development by our research group.

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Section: Resultsmentioning

confidence: 99%

Production of Cylindrical Specimens Based on the Ni-Ti System by Selective Laser Melting from Elementary Powders

Oliveira

Lima

Sallet

et al. 2021

J. of Materi Eng and Perform

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“…As the compositional analysis revealed the presence of γ', γ" strength hardening phases in the heat-affected zones, the magnitude of the hardness can be associated with the presence of the aforementioned subsidiary phases. The presence of higher percentages of the strengthening phases shall result in an increase in the Vickers hardness values [34]. From the Pareto chart in Figure 11, it is clear that the hatch spacing is the dominant factor in determining the hardness of the SLM fabricated IN718 specimens.…”

Section: Discussionmentioning

confidence: 97%

“…Finally, the hardness, as a mechanical property, was considered, as it correlates the laser process parameters and the chemical composition [34]. For instance, as the energy density increased from the Ev = 75.0 J/mm 3 to Ev = 91.6 J/mm 3 , with a decrease in the hatch spacing values from 121 µm to 99 µm, the Vickers hardness of the samples increased from 273.813 HV to 308.584 HV.…”

Section: Discussionmentioning

confidence: 99%

Study on the Effect of Powder-Bed Fusion Process Parameters on the Quality of as-Built IN718 Parts Using Response Surface Methodology

Ravichander

Amerinatanzi

Moghaddam

2020

Metals

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Inconel 718 (IN718) is a nickel-based superalloy which is widely used in aerospace, oil, and gas industries due to its outstanding mechanical properties at high temperatures, corrosion, fatigue resistance, and excellent weldability. Selective laser melting (SLM), one of the most used powder-bed based methods, is being extensively used to fabricate functional IN718 components with high accuracy. The accuracy and the properties of the SLM fabricated IN718 parts highly depend on the process parameters employed during fabrication. Thus, depending on the desired properties, the process parameters for a given material need to be optimized for improving the overall reliability of the SLM devices. In this study, design of experiment (DOE) was used to evaluate the dimensional accuracy, composition, and hardness corresponding to the interaction between the SLM process parameters such as laser power (P), scan speed (v), and hatch spacing (h). Contour plots were generated by co-relating the determined values for each characteristic and the process parameters to improve the as-built characteristics of the fabricated IN718 parts and reduce the post-processing time. The outcome of this study shows a range of energy density values for the IN718 superalloy needed to attain optimal values for each of the analyzed characteristics. Finally, an optimal processing region for SLM IN718 fabrication was identified which is in accordance with the values for each characteristic mentioned in literature.

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“…One major challenge associated with fabricating IN718, however, is the low machinability arising from its high hardness value (372 HV for wrought IN718 based on AMS 5663 and 350 HV for cast IN718 based on AMS 5383) and low thermal conductivity (11.2 W.m −1 .K −1 ) [9], which, in turn, leads to extreme tool wear and unsatisfactory workpiece surface integrity [10,11]. In recent years, additive manufacturing technology has attracted great attention for the fabrication of IN718 since it minimizes the need for machining [12]. Amongst all available AM techniques, laser powder bed fusion (LPBF) has widely been adopted within the industry due to the overall cost and fabrication advantages [3,[13][14][15].…”

Section: Introductionmentioning

confidence: 99%

Cost-Aware Design and Fabrication of New Support Structures in Laser Powder Bed Fusion: Microstructure and Metallurgical Properties

et al. 2021

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This study investigates the effect of support structures on the properties of Inconel 718 (i.e., IN718) parts produced by the laser powder bed fusion (LPBF) additive manufacturing process. Specifically, the effects of support structure shape (i.e., pin-type, angled-type, cone-type) and geometry (i.e., support wall thickness, and gap) on their composition, hardness, microstructure, and material/time consumption are investigated and compared to the conventionally fabricated Inconel 718. From the microstructural analysis, the deepest melt pools appeared to be formed in the sample fabricated on top of the pin-type support structure having a relatively low wall thickness. The XRD results conveyed that a proper selection of geometrical variables for designing support structure results in elevated levels of the strengthening phases of IN718. The sample fabricated on top of the pin-type support structure showed the highest Vickers hardness value of 460.5 HV, which was even higher than what was reported for the heat-treated wrought Inconel 718 (355–385 HV). Moreover, for the thinner support wall thickness, an improvement in the hardness value of the fabricated samples was observed. This study urges a reconsideration of the common approach of selecting supports for additive manufacturing of samples when a higher quality of the as-fabricated parts is desired.

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Study on variations of microstructure and metallurgical properties in various heat-affected zones of SLM fabricated Nickel–Titanium alloy

Cited by 31 publications

References 35 publications

Production of Cylindrical Specimens Based on the Ni-Ti System by Selective Laser Melting from Elementary Powders

Production of Cylindrical Specimens Based on the Ni-Ti System by Selective Laser Melting from Elementary Powders

Study on the Effect of Powder-Bed Fusion Process Parameters on the Quality of as-Built IN718 Parts Using Response Surface Methodology

Cost-Aware Design and Fabrication of New Support Structures in Laser Powder Bed Fusion: Microstructure and Metallurgical Properties

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