Internal convective effects on the lifetime of the metastable phase undercooled Fe–Cr–Ni alloys

A new hypothesis has been developed to explain the effect of internal fluid flow on the lifetime of a metastable phase in solidifying Fe-Cr-Ni alloys. The hypothesis shows excellent agreement with available experimental results, but microgravity experiments are required for complete validation. Certain Fe-Cr-Ni stainless steel alloys solidify from an undercooled melt by a two-step process in which the metastable ferrite phase forms first followed by the stable austenite phase. Recent experiments using containerless processing techniques have shown that the lifetime of the metastable phase is strongly influenced by flow within the molten sample. Simulations using a commercial computational fluid dynamics (CFD) package, FIDAP, were performed to determine the time required for collision of dendrites and compared to experimental delay time. If the convective velocities are strong enough to bend the primary arms, then the secondary arms of adjacent dendrites can touch. The points of collision form low-angle boundaries and result in high-energy sites that can serve as nuclei for the transformation to the stable phase. It has been determined that the convective velocities in electrostatic levitation (ESL) are not strong enough to cause collision. However, in ground-based electromagnetic levitation (EML), the convective velocities are strong enough to cause the dendrites to deflect so that the secondary arms of adjacent dendrites collide. There is quantitative agreement between the numerically determined time to collision and the experimentally observed delay time in EML. The strong internal velocity due to convection within the EML samples is the reason for the observed difference in delay times between ESL and EML. Microgravity testing is essential because the significant change in nucleation behavior occurs between the ranges accessible by ground-based ESL and EML. Testing in microgravity using EML will permit a large range of internal convective velocities including those that are inaccessible in 1 g.

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“…Experiments have shown that the delay time is approximately 0.19 ± 0.074 msec. Our calculation is within the scatter of the experiments 14 …”

Section: Resultssupporting

confidence: 54%

“…Our calculation is within the scatter of the experiments. 14 In ESL, the time to collision was calculated to be 0.29 msec. The ESL simulations were run assuming a convective velocity of 0.04m/sec, which is the velocity present when the heating laser is on.…”

Section: Comparison Of Numerical Time To Collision With Experimental mentioning

confidence: 99%

Microgravity Experiments on the Effect of Internal Flow on Solidification of Fe‐Cr‐Ni Stainless Steels

Hanlon

Matson

Hyers

2006

Annals of the New York Academy of Sciences

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“…[5] Hanlon et al [4,6] tested the hypothesis by investigating the deformation of metastable dendrites due to melt convection. Their numerical results show that the deformation of the tips of neighboring dendrites by drag forces due to convection causes the collision of the secondary dendritic arms.…”

Section: Introductionmentioning

confidence: 99%

Numerical Prediction of the Accessible Convection Range for an Electromagnetically Levitated Fe50Co50 Droplet in Space

Lee

Xiao

Matson

et al. 2014

Metall Mater Trans B

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a series of space experiments will be performed to investigate the influence of the convection on the multiphase solidification phenomena of metallic alloys. For the success of the mission, it is of critical importance to predict the convection in molten samples under given test parameters. In this research, the convection induced in the molten Fe 50 Co 50 alloy was predicted numerically. The magnetohydrodynamic model for the ground-based electromagnetic levitator developed in the previous research was extended to the space application. The same modeling strategies were applied to the electromagnetic levitator in space. Using the numerical model, the convection under various test conditions was predicted: The flow pattern was characterized as a function of the heating current. The maximum convection velocity at various temperatures was estimated with the increasing heating current. Finally, the range of accessible convection velocity was predicted as a function of the critical undercooling of the sample, the minimum positioner control voltage, and the undercooling of the sample. The results are expected to provide critical information for the design of the space experiments and the interpretation of the results.

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“…19 For rapid solidification processing, of particular interest is the observation that the delay time is a weak function of primary undercooling and a strong function of melt stirring, 21 and this article provides a coherent dataset from a single experimental platform on a single sample to allow new theories to be tested.…”

Section: Introductionmentioning

confidence: 99%

Use of Thermophysical Properties to Select and Control Convection During Rapid Solidification of Steel Alloys Using Electromagnetic Levitation on the Space Station

Matson

Xiao

Rodriguez

et al. 2017

JOM

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A major reason to conduct solidification experiments in space is that the unique conditions accessible in reduced-gravity allow investigation of fundamental questions while limiting the influence of sedimentation or buoyancyinduced convection. When processing metallic alloys using containerless electromagnetic levitation, convection may be controlled over a wide range, spanning the laminar-turbulent transition, by proper selection of facility operating conditions. By measuring key thermophysical properties such as density, viscosity, and electrical resistivity on-orbit, the specific sample being processed may be characterized and the results used to update pre-mission magnetohydrodynamic model predictions of induced stirring within the droplet. Thus, convection becomes a controlled experimental parameter that can be applied to an investigation of how stirring influences the metastable-tostable transformation during rapid solidification of FeCrNi alloys. For these alloys, the incubation or delay time is observed to be a weak function of undercooling and a strong function of applied convection.

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Internal convective effects on the lifetime of the metastable phase undercooled Fe–Cr–Ni alloys

Cited by 17 publications

References 10 publications

Microgravity Experiments on the Effect of Internal Flow on Solidification of Fe‐Cr‐Ni Stainless Steels

Microgravity Experiments on the Effect of Internal Flow on Solidification of Fe‐Cr‐Ni Stainless Steels

Numerical Prediction of the Accessible Convection Range for an Electromagnetically Levitated Fe50Co50 Droplet in Space

Use of Thermophysical Properties to Select and Control Convection During Rapid Solidification of Steel Alloys Using Electromagnetic Levitation on the Space Station

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