Delta phase precipitation in Inconel 718

Azadian, Saied; Wei, Liu-Ying; Warren, Richard

doi:10.1016/j.matchar.2004.07.004

Cited by 466 publications

(190 citation statements)

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“…δ phase is incoherent with γ matrix, conferring rarely strength to the matrix when present in large quantities; on the contrary, the precipitation of δ phase would be at the expense of Nb, which associates with the loss of γ ′′ and therefore strength [7,16]. The conversion from γ ′′ to δ is accelerated when the thermal exposure is over 650 • C, which limits the main applications of IN718 under 650 • C [17,18].…”

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confidence: 99%

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

Deng

2018

Linköping Studies in Science and Technology. Licentiate Thesis

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Linköping 2018Cover image: A fracture surface of EBM IN718 after tensile test at room temperature.During the course of research underlying this thesis, Dunyong Deng was enrolled in Agora Materiae, a multidiciplinary doctoral program at Linköping University, Sweden. Printed by LiU-Tryck 2018 © Dunyong Deng AbstractAdditive manufacturing (AM), also known as 3D printing, has gained significant interest in aerospace, energy, automotive and medical industries due to its capabilities of manufacturing components that are either prohibitively costly or impossible to manufacture by conventional processes. Among the various additive manufacturing processes for metallic components, electron beam melting (EBM) and selective laser melting (SLM) are two of the most widely used powder bed based processes, and have shown great potential for manufacturing high-end critical components, such as turbine blades and customized medical implants. The futures of the EBM and SLM are doubtlessly promising, but to fully realize their potentials there are still many challenges to overcome.Inconel 718 (IN718) is a nickel-base superalloy and has impressive combination of good mechanical properties and low cost. Though IN718 is being mostly used as a turbine disk material now, the initial introduction of IN718 was to overcome the poor weldability of superalloys in 1960s, since sluggish precipitation of strengthening phases γ ′ /γ ′′ enables good resistance to strain-age cracking during welding or post weld heat treatment. Given the similarity between AM and welding processes, IN718 has been widely applied to the metallic AM field to facilitate the understandings of process-microstructure-property relationships.The work presented in this licentiate thesis aims to better understand microstructures and mechanical properties EBM and SLM IN718, which have not been systematically investigated. Microstructures of EBM and SLM IN718 have been characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and correlated with the process conditions. Monotonic mechanical properties (e.g., Vickers microhardness and tensile properties) have also been measured and rationalized with regards to the microstructure evolutions before and after heat treatments.For EBM IN718, the results show the microstructure is not homogeneous but dependant on the location in the components, and the anisotropic mechanical properties are probably attributed to alignment of porosities rather than texture.iii Post heat treatment can slightly increase the mechanical strength compared to the as-manufactured condition but does not alter the anisotropy. SLM IN718 shows significantly different microstructure and mechanical properties to EBM IN718. The as-manufactured SLM IN718 has very fine dendritic microstructure and Laves phases in the interdendrites, and is "work-hardened" by the residual strains and dislocations present in the material. Mechanical properties are different between horizontally and vertically built samples, and heat treatment can m...

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confidence: 99%

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

Deng

2018

Linköping Studies in Science and Technology. Licentiate Thesis

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“…It was heat-treated at 980°C for 1 h and water-quenched followed by an aging treatment at 720°C for 8 h. The billet was then furnacecooled to 620°C, aged for a further 8 h, and finally aircooled. [2], a single value for the solvus temperature is difficult to determine [4]. The equilibrium delta solvus calculated using thermodynamic software JMatPro was 1033°C.…”

Section: Materials and Experimental Methodologymentioning

confidence: 99%

“…However, for simplicity, it can be assumed that a particular d microstructure is associated with a characteristic back stress that varies with the temperature-dependent d phase volume fraction. In fact, the d content of IN718 decreases approximately linearly as the apparent solvus temperature is approached [2,4] and so r b can be taken to be proportional to the difference between the d solvus temperature, T solv , and the deformation temperature, T:…”

Section: Deformation Behaviormentioning

confidence: 99%

“…Significant research has been directed toward characterizing the precipitation and dissolution kinetics of the d phase in IN718 during heat treatment and aging, e.g., [1][2][3][4][5], and several experimental investigations have explored recrystallization associated with high-temperature compressive flow in solution-treated material, e.g., [6][7][8][9][10], but there has been rather less focus on the specific role of d precipitates during hot deformation. However, it is known that prior aging in the d stability field can have a significant effect on stress-strain response [11,12] and recent studies have highlighted the complexity of the mechanisms involved, including dynamic dissolution and reprecipitation [13], sub-grain formation [14], and platelet spheroidization [15].…”

Section: Introductionmentioning

confidence: 99%

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Hot Forging of IN718 with Solution-Treated and Delta-Containing Initial Microstructures

Lalvani

Brooks

2016

Metallogr. Microstruct. Anal.

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A systematic study of the effect of d phase precipitate morphology on the hot deformation behavior and microstructural evolution in nickel superalloy Inconel 718 is presented. Isothermal compression tests at fixed nominal strain rates and temperatures relevant to industrial forging (0.001-0.3 s -1 and 990-1040°C) were used. Three distinct initial microstructures have been examined: (I) solution treated, (II) a microstructure with finely dispersed particulate d precipitates, and (III) a microstructure containing dense network of intragranular and grain boundary d platelets. The peak flow stress associated with these various microstructures has been rationalized using a single, temperature-compensated power law. This clearly demonstrates opposition of the external applied stress by an internal back stress related to the initial d phase morphology and apparent delta solvus temperature. Post-peak flow softening is attributed to dynamic recrystallization, aided by the dissolution of finer precipitates in material containing particulate d phase, and to a certain degree of mechanical grain refinement caused by distortion and offsetting of grain segments where a dense d-platelet structure exists.

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“…At temperatures slightly above the upper recommended temperature the δ-phase, of body centered tetragonal (BCT) crystal structure, precipitates and growths into platelets [2]. The chemical composition of the γ" and the δ-phase is identical, Ni 3 Nb, although with the different crystal structures and the latter can thus not precipitate without the dissolution of former -the δ−phase is the stable one.…”

Section: Introductionmentioning

confidence: 99%

Effect of δ-Phase on the Weldability and the Hot Ductility of Alloy 718

Sjöberg¹,

Antonsson²,

Azadian³

et al. 2005

Superalloys 718, 625, 706 and Various Derivatives (2005)

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In the weld repair cycles of alloy 718 the solution temperature is usually selected low enough to avoid grain growth in wrought material. At such low temperatures, however, δ-phase also precipitates and the amount increases with each repair cycle.It is well understood that the overall ductility is reduced by the presence of the δ-phase in alloy 718 and, as such, may reduce the weldability. But it is also reported that the δ-phase may cause incipient melting in grain boundaries at the heat affected zone, HAZ, through a niobium rich melt fed by the local abundance of this element from attached δ−platelets. The purpose of the present work is to shed light on this issue on the one hand through practical weld experiments under heavily constrained circumstances and on the other through high temperature ductility testing in special hot tensile test equipment by which the hot ductility of re-melted material also was possible to examine. Materials with two levels of δ-phase and with two grain sizes were included.Contrary to what was anticipated it was extremely difficult to provoke cracking even in inhomogeneous cast material at the highest δ−levels in heavily constrained TIG-weld experiments. Also the hot ductility test results, measured as the high temperature ductility recovery temperature and range, indicated that there is no or very limited deterioration by the presence of δ-phase. Anomalous results, however, much lower ductility recovery temperatures, were found in samples with large grain size and a small amount of δ-phase. For re-melted samples several hundred degrees lower recovery temperatures were measured.

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Delta phase precipitation in Inconel 718

Cited by 466 publications

References 5 publications

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

Hot Forging of IN718 with Solution-Treated and Delta-Containing Initial Microstructures

Effect of δ-Phase on the Weldability and the Hot Ductility of Alloy 718

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Delta phase precipitation in Inconel 718

Cited by 466 publications

References 5 publications

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

Hot Forging of IN718 with Solution-Treated and Delta-Containing Initial Microstructures

Effect of &#948;-Phase on the Weldability and the Hot Ductility of Alloy 718

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Effect of δ-Phase on the Weldability and the Hot Ductility of Alloy 718