Characterization of the Dendritic Microstructure of Investment Cast Alloy 718

Ko, Young-Bong; Berry, John T.

doi:10.7449/1994/superalloys_1994_201_212

Cited by 2 publications

(1 citation statement)

References 2 publications

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“…The fraction-solid versus temperature relationship presented by Ko and Berry from actual castings at similar cooling rates was used to deduce th.e enthalpy curve shown in Figure 2. [5] No attempt was made to model the development of the grain structure in the castings in these simulations.…”

Section: And Simulation Proceduresmentioning

confidence: 99%

Porosity in Cast Equiaxed Alloy 718

Overfelt¹,

Sahai²,

Ko³

et al. 1994

Superalloys 718, 625, 706 and Various Derivatives (1994)

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Alloy 7 18 is a widely used superalloy which shows excellent performance at moderate temperatures. This desirable performance originates from the composition and processing conditions. Many manufacturers choose to investment cast Inconel 7 18 for their components because of investment casting's ability to produce complex parts at reasonable costs. However, improper casting conditions can cause deleterious defects to occur such as porosity. The prediction of the porosity distribution in shaped castings is a popular research topic at the present time. A number of semi-empirical criteria functions have been proposed to assist in such predictions, the functions being generally obtained from computer modeling of casting solidification. Although considerable attention has been given to the use of porosity criteria functions with aluminum based alloys, only limited consideration has been given to superalloy castings. Four sets of plate castings were investment cast under varying foundry conditions and the porosity distributions metallographically characterized. The castings were top poured and contained vertical 50.8 mm by 50.8 mm plates of the following thicknesses: 2.54, 12.7, and 25.4 mm. A computer solidification model was developed for the castings and utilized to examine the effectiveness of various porosity criteria functions for predicting porosity. The computer model was shown to be effective in predicting unfed centerline shrinkage in the 25.4 mm thick plates. In addition, the predicted porosity trends of two widely used porosity criteria functions were shown to be consistent with the measured amounts of porosity in three of the four 12.7 mm thick plates. However, significant process variations, e.g. inclusion content, can dominate the development of porosity in castings and make the prediction of porosity an inexact science. These effects and the effective application of porosity criteria functions in predicting process parameters for alloy 7 18 casting are also discussed.

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Section: And Simulation Proceduresmentioning

confidence: 99%

Porosity in Cast Equiaxed Alloy 718

Overfelt¹,

Sahai²,

Ko³

et al. 1994

Superalloys 718, 625, 706 and Various Derivatives (1994)

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A model for prediction of pressure and redistribution of gas-forming elements in multicomponent casting alloys

Felicelli

Poirier

Sung

2000

Metall Mater Trans B

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A finite element model for simulating macrosegregation in multicomponent alloys is extended to include the calculation of pressure and redistribution of gas-forming elements during solidification. The model solves the conservation equations of mass, momentum, energy, and alloy components, including gas-forming elements such as hydrogen and nitrogen. The results of transport calculations are contrasted with thermodynamic equilibrium conditions to establish the possible formation of pores, assuming that there is no barrier to nucleation of the pores. By solving the transport of gaseous solutes and comparing their Sievert's pressure with the local pressure, the new model can predict regions of possible formation of intergranular porosity. Simulations were performed for a nickel-base alloy (INCONEL 718) in plate castings with equiaxed structure, and the evolution of microporosity for different initial concentrations of hydrogen and nitrogen was analyzed. The simulations showed that during solidification and cooling, a large fraction of the hydrogen escapes and a smaller fraction of nitrogen escapes from the casting. The initial gas concentration is an important factor in porosity formation, but the pressure drop due to shrinkage flow is not very significant. The resulting gas porosity is rather insensitive to initial nitrogen concentration, but sensitive to the concentration of hydrogen.

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Characterization of the Dendritic Microstructure of Investment Cast Alloy 718

Cited by 2 publications

References 2 publications

Porosity in Cast Equiaxed Alloy 718

Porosity in Cast Equiaxed Alloy 718

A model for prediction of pressure and redistribution of gas-forming elements in multicomponent casting alloys

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