An instrument for <i>in situ</i> time-resolved X-ray imaging and diffraction of laser powder bed fusion additive manufacturing processes

Calta, Nicholas P.; Wang, Jenny; Kiss, Andrew M.; Martin, Aiden A.; Depond, Philip J.; Guss, Gabe; Thampy, Vivek; Fong, Anthony Y.; Weker, Johanna Nelson; Stone, Kevin H.; Tassone, Christopher J.; Kramer, M. J.; Toney, Michael F.; Buuren, T. van; Matthews, Manyalibo J.

doi:10.1063/1.5017236

Cited by 137 publications

(68 citation statements)

References 40 publications

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“…This X-ray probe position simplifies analysis by precluding diffracted intensity contributions from flying spatter or powder particles. At the same time, since the melt depression and melt pool extend up to at least 100 μm below the powder substrate interface 15,49 [Also see Supplemental Fig. S3], the volume probed provides relevant information about the phase and microstructural evolution within a localized region undergoing melting and resolidification.…”

Section: Resultsmentioning

confidence: 99%

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Subsurface Cooling Rates and Microstructural Response during Laser Based Metal Additive Manufacturing

Thampy

Fong

Calta

et al. 2020

Sci Rep

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Laser powder bed fusion (LpBf) is a method of additive manufacturing characterized by the rapid scanning of a high powered laser over a thin bed of metallic powder to create a single layer, which may then be built upon to form larger structures. Much of the melting, resolidification, and subsequent cooling take place at much higher rates and with much higher thermal gradients than in traditional metallurgical processes, with much of this occurring below the surface. We have used in situ high speed X-ray diffraction to extract subsurface cooling rates following resolidification from the melt and above the β-transus in titanium alloy Ti-6Al-4V. We observe an inverse relationship with laser power and bulk cooling rates. the measured cooling rates are seen to correlate to the level of residual strain borne by the minority β-ti phase with increased strain at slower cooling rates. the α-ti phase shows a lattice contraction which is invariant with cooling rate. We also observe a broadening of the diffraction peaks which is greater for the β-ti phase at slower cooling rates and a change in the relative phase fraction following LpBf. these results provide a direct measure of the subsurface thermal history and demonstrate its importance to the ultimate quality of additively manufactured materials. In LPBF, a common metal additive manufacturing (AM) process, a thin layer of precursor powder is selectively melted by tracing a high power laser to create a single, solid layer, followed by the spread of the next layer of powder for melting, and so on to build a part layer-by-layer 1-14. This approach offers a number of distinct advantages over conventional metal fabrication, including rapid prototyping, efficient material utilization, fabrication of complex geometries incompatible with machining or molding techniques, and applicability to materials which may exhibit machining difficulties, such as titanium 4,8-12,14. However, unlike conventional manufacturing techniques, the LPBF process is characterized by rapid melting and resolidification of small volumes of material that results in large thermal gradients both temporally and spatially, and consequently cooling rates that can be orders of magnitude higher than in conventional casting 10,15,16. Such large localized heating and cooling rates largely control the resulting microstructure, grain size and orientation, can lead to large residual stresses in some materials, and may also result in compositional segregation or formation of non-equilibrium trapped phases 4,17-20. Therefore quantifying these cooling rates and correlating them to the characteristics of the final build is an important step towards informing theoretical and process models that can predict and potentially control such stresses and inhomogeneities that are generally undesirable, especially in critical components. For this study, we focused on Ti-6Al-4V (Ti-64, 90%Ti, 6% Al, 4%V-by weight) as our material system. The high strength, light weight, and excellent corrosion resistance inherent to titanium and its ...

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Section: Resultsmentioning

confidence: 99%

“…The entire setup is enclosed in a vacuum chamber with beryllium windows to allow transmission of X-rays and is filled with argon to prevent oxidation of the powder during the LPBF process. Further details about the system can be found in Calta et al 49 .…”

Section: Methodsmentioning

confidence: 99%

Subsurface Cooling Rates and Microstructural Response during Laser Based Metal Additive Manufacturing

Thampy

Fong

Calta

et al. 2020

Sci Rep

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“…Please note that these are only rough estimates as heat fluxes continuously change with time-varying temperature fields. Moreover, this estimation of

is an underestimation as even higher temperature gradients are observed in the vicinity of melt zone by melt-pool simulation studies [ 37 ]. Nevertheless, it can be observed from these estimates that indeed heat losses through convection and radiation are orders of magnitude lower near the melt zone than those by conduction, as argued by Paul et al [ 19 ].…”

Section: Thermal Modeling Simplifications and Comparison Metricsmentioning

confidence: 99%

Fast Detection of Heat Accumulation in Powder Bed Fusion Using Computationally Efficient Thermal Models

et al. 2020

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The powder bed fusion (PBF) process is a type of Additive Manufacturing (AM) technique which enables fabrication of highly complex geometries with unprecedented design freedom. However, PBF still suffers from manufacturing constraints which, if overlooked, can cause various types of defects in the final part. One such constraint is the local accumulation of heat which leads to surface defects such as melt ball and dross formation. Moreover, slow cooling rates due to local heat accumulation can adversely affect resulting microstructures. In this paper, first a layer-by-layer PBF thermal process model, well established in the literature, is used to predict zones of local heat accumulation in a given part geometry. However, due to the transient nature of the analysis and the continuously growing domain size, the associated computational cost is high which prohibits part-scale applications. Therefore, to reduce the overall computational burden, various simplifications and their associated effects on the accuracy of detecting overheating are analyzed. In this context, three novel physics-based simplifications are introduced motivated by the analytical solution of the one-dimensional heat equation. It is shown that these novel simplifications provide unprecedented computational benefits while still allowing correct prediction of the zones of heat accumulation. The most far-reaching simplification uses the steady-state thermal response of the part for predicting its heat accumulation behavior with a speedup of 600 times as compared to a conventional analysis. The proposed simplified thermal models are capable of fast detection of problematic part features. This allows for quick design evaluations and opens up the possibility of integrating simplified models with design optimization algorithms.

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“…In this case, as the cavity is too deep and the pore fails to float up before solidification, the pore is retained deep in the base (King et al, 2014;Matthews et al, 2016). And also, Calta et al (2018) performed in-situ X-ray-based measurements of LPBF process using the synchrotron X-ray imaging and diffraction. They revealed the formation of keyhole pores along the melt track due to vapor recoil forces by imaging the melt pool dynamics.…”

Section: Melting-solidification Phenomena 31 Melting-solidification mentioning

confidence: 99%

A review of metal additive manufacturing technologies: Mechanism of defects formation and simulation of melting and solidification phenomena in laser powder bed fusion process

Kyogoku

Ikeshoji

2020

Mechanical Engineering Reviews

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In this review, the analysis of melting and solidification phenomena and the mechanism of the occurrence of defects as well as the analysis of melting and solidification using the numerical simulation in laser powder bed fusion (LPBF) process were introduced. In addition, the strategies of suppression of defects were described. The melting and solidification phenomena during LPBF process are relatively similar to those during welding.Since the plume brings about the strong recoil pressure on the melt pool, the keyhole takes place. And when the depth of keyhole becomes more than a threshold, the keyhole pore remains at the bottom of melt pool. Since the plume also brings about spattering and blows out powder, the gas pores are prone to occur easily. The micro-simulation of melting and solidification enables to reproduce the real phenomena. The macro-simulation of melting and solidification phenomena is one of the effective tools to predict the optimum fabrication condition. In order to prevent the occurrence of defects, it is significant not only to obtain the optimum fabrication condition using the process map but also to develop the simulation software. In addition, the use of the monitoring and feedback control system is greatly effective. Therefore the development of the cyber-physical system is needed.

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An instrument for in situ time-resolved X-ray imaging and diffraction of laser powder bed fusion additive manufacturing processes

Cited by 137 publications

References 40 publications

Subsurface Cooling Rates and Microstructural Response during Laser Based Metal Additive Manufacturing

Subsurface Cooling Rates and Microstructural Response during Laser Based Metal Additive Manufacturing

Fast Detection of Heat Accumulation in Powder Bed Fusion Using Computationally Efficient Thermal Models

A review of metal additive manufacturing technologies: Mechanism of defects formation and simulation of melting and solidification phenomena in laser powder bed fusion process

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