John J. deBarbadillo

Computational Modeling of Electroslag Remelting (ESR) Process Used for the Production of High-Performance Alloys

This paper presents a comprehensive computational model for the prediction of the transient Electroslag Remelting (ESR) process for cylindrical ingots based on axisymmetric two-dimensional analysis. The model analyzes the behavior of the slag and growing ingot during the entire ESR process involving a hot-slag start with an initial transient, near-steady melting, hot-topping and subsequent solidification of the slag and ingot after melting ends. The results of model application for an illustrative ESR process for Alloy 718 and its validation using results from an industrial trial are presented. They demonstrate the comprehensive capabilities of the model in predicting the behavior of the ingot and slag during the entire process and properties of the final ingot produced. Such analysis can benefit the optimization of existing process schedules and design of new processes for different alloys and different ingot sizes.

Long Term Thermal Stability of INCONEL Alloy 783

Recently developed INCONEL® alloy 783 (nominal composition of Ni-34Co-26Fe-5.4Al-3Nb-3Cr) is precipitation strengthened by Ni3Al-type Gamma Prime and NiAl-type Beta Phases. Due to its low co-efficient of thermal expansion (CTE), high strength, and good oxidation resistance alloy 783 has been specified for use in aircraft gas turbine components such as rings, casings, shrouds, and seals and has been considered for use in a number of other critical industrial turbine components.In this study, commercially produced alloys 783, 718, and 909 were annealed and aged following recommended heat treatments. The materials were then isothermally exposed at 1100°F (593°C) for times up to 10,000 hours. At 1000 hour intervals, specimens of these alloys were removed from the furnace and subjected to room temperature tensile (RTT) and high temperature tensile (HTT) testing at 1200°F (649°C). The microstructure of as-produced and exposed materials was characterized using optical microscopy, Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). Variation in tensile properties with isothermal exposure time was correlated with the microstructure.Copyright

Superalloy 718: Evolution of the Alloy from High to Low Temperature Application

Alloy 718 (UNS N07718) was the culmination of a research project started in the mid-1950s to develop a stronger pipe alloy for coal-fired power plants. It was never used for that application, but it was quickly adopted for aircraft turbine engines because of its very high strength, thermal stability, formability and weldability compared to the γʹ-strengthened alloys available in the 1960s. Alloy 718 derives its unique combination of strength and fabricability from a coherent ordered tetragonal phase γʺ and the slow diffusion rate of its main constituent, niobium. Very early in its commercial life, alloy 718 was recognized as having attributes for both ambient and cryogenic temperature uses as well. Impact toughness, aqueous corrosion resistance, and non-ferromagnetic properties were important attributes. Alloy 718 replaced established age-hardened iron/nickel-base alloys such as A-286, K-500 and X-750 as well as martensitic steels in a wide range of components in the space launch, oil and gas, marine, nuclear and superconducting magnet industries. As the applications became more specialized, so did the heat treatments and microstructures to accentuate specific properties. A common thread through these low temperature applications has been hydrogen embrittlement and a substantial body of literature documents our increasing awareness of its role in service performance. In recent decades, new alloys based on alloy 718 and the γʺ strengthening phase have been introduced, especially for oil and gas production equipment. This paper describes the early development of alloy 718 for these important applications, along with alloy, microstructure and heat-treatment evolution and current status.

Characterization of structure and thermophysical properties of three ESR slags

The structure and properties of electroslag remelting (ESR) slags were characterized. Slags samples of three compositions were obtained from industrial remelting processes at Special Metals Corporation and from casting in a laboratory vacuum induction melter. The structure of the slag samples was observed using optical and electron microscopy, and phases were identified and their relative amounts quantified using X-ray diffraction. Laser flash thermal diffusivity, density, and differential scanning calorimetry measurements for specific heat were performed to determine the bulk thermal conductivity of the samples. Sample porosity was measured as a function of depth using a serial sectioning technique, and a onedimensional computational model was developed to estimate the thermal conductivity of the fully dense slags. These results are discussed in context with previous studies, and opportunities for future research are identified. AFRL Case Number: 88ABW-2015-1871.