Abstract
Vacuum Are Remelting (VAR) is one of the state-of-the-art secondary re-melting processes that are now routinely used to improve the homogeneity, purity and defect concentration in modern turbine disc alloys. The last is of particular importance since, as the yield strength of turbine disc alloys has progressively increased to accommodate increasingly stringent design requirements, the fracture of these materials has become sensitive to the presence of ever smaller defects, particularly inclusions. During the manufacture of these alloys extrinsic defects can be introduced in the primary alloy production stage from a variety of sources; these include ceramic particles originating from crucibles, undissolved tungsten (or tungsten carbide) and steel shot. In addition intrinsic inclusions can be produced during the VAR process itself such as those originating from the crown and shelf, often termed 'white spot'. VAR has proven to be effective in controlling inclusion content but optimization of the process, particularly for a new alloy composition, is a difficult and expensive exercise. Therefore, there is considerable interest in the use of numerical models to relate the process control variables to the final microstructure.A transient macroscopic model of the VAR process has been developed and applied to simulate inclusion motion in the melt pool and the dissolution of these thermodynamically unstable phases in a liquid metal environment. The model has been applied to determine the trajectories, thermal history and dissolution of intrinsic particles for typical melt conditions of INCONEL 718(R).
Original language | English |
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Title of host publication | host publication |
Pages | 29-37 |
Number of pages | 9 |
Publication status | Published - 2000 |