Spray deposited 718 was evaluated and its characteristicswere compared with those of conventional as-cast and cast-wrought 718 material. General comparisons were made on the basis of microstructural features, microsegregation and fracture toughness.Spray forming via the Ospreya Process was also investigated through a computer model developed at Drexel University.
Triple melting (TM) by VIM+ESR+VAR has been highly successful for Alloy 718, large diameter ingots of Alloy 706, and high hardener alloys such as Alloy 720. Frequencies of ultrasonic indications for TM 718 are significantly lower than for VIM+VAR melt 718 because fewer clusters of inclusions are present, The cleanliness associated with TM 718 was verified by microscopy and by electron beam melting of buttons after VIM, VIM+ESR, and TM. Furthermore, white spot frequencies were found to be reduced for TM 718. Ultrasonic defect frequencies of Alloy 706 and Alloy 720 are also low. A major advantage of triple melting Alloy 706 is that ingots up to 36 inches (914mm) in diameter can be melted without freckles or positive segregation problems.
Clean Metal Spray Forming (CMSF) is a new process in which the melt pool from an Electroslag Refining (ESR) furnace is used as the source for a liquid metal stream to be directly processed via spray forming. The process takes advantage of the refining function of the ESR process and the economy of the spray forming process to yield material that is oxide-free, tinegrained, equiaxed, homogeneous, and thus acceptable for fatigue-life critical applications. The controlled transfer of liquid metal from the ESR pool to the spray forming system is performed using a ceramic-free cold-walled-induction guide, which is a segmented induction heated copper funnel. A pilot plant for development of the concept using nickel-based alloys has been constructed and is operational. Oxide cleanliness, microstructure, and mechanical properties of Alloy 718 processed through the system will be discussed.
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