Heat treatment of integrally bladed rotors (IBR) or bladed disks (blisk) is required to obtain appropriate material properties and to relieve residual stresses due to fusion welding processes such as, for example, electron beam welding, laser welding, or arc welding, as well as solid state bonding processes such as linear friction welding.
Heat treatment is typically performed by exposing the entire IBR or a portion of the IBR (e.g. the weld region) to a predetermined thermal cycle. The technique of heat treating the entire IBR is commonly known in the art of IBR manufacture.
During blade repair operations, it may be necessary to locally heat treat the repaired areas of the integrally bladed rotors that have been exposed to elevated temperatures resulting from repair operations. In the finished machine condition, conventional heat treatment is not always possible due to concerns with part distortion. Additional risk factors for conventional heat treatment, of a repaired finished machined integrally bladed rotor are, (a) it may create unnecessary risk due to the potential for surface contamination throughout the entire part and (b) some areas of the IBR should not be exposed to additional temperature exposure that results in material property debit. Because of these concerns, local heat treatment has been considered to be a preferred option.
IBRs are typically made of either titanium alloys such as Ti-6-4, Ti-6-2-4-2, Ti-6-2-4-6 alloys or nickel based alloys such as Alloy 718 alloy or IN-100. The IBR is a critical rotating component within an engine, and the engineering, materials, manufacturing, and quality requirements are extremely rigorous.
There are two major technical challenges associated with the local heat treatment of an IBR, in addition to the business challenge that the manufacturing process be affordable. First, the selected portion of the IBR receiving heat treatment must meet a prescribed thermal cycle and the remaining IBR component must not be exposed to temperatures that exceed a specific peak temperature to ensure that the material properties meet engineering requirements. Second, the selected portion of the IBR receiving localized heat treatment must be protected from oxidation due to exposure to high temperature.