Fracture Analysis of Blade of an Integrated Compressor Impeller
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During a trial test of a ZL104 al-alloy impeller, one of its blades experienced sudden catastrophic failure. Fractographic investigation indicates that the fracture mode of the blade is of instantaneous fracture. Metallurgical observation indicates that the fractured blade had been repair-welded on the sides of the lower and upper surfaces of blade before fracture. Multiple crack origins were found at the interface between the substrate and the repair welding layer at the side of the lower surface of the fractured blade. The defective casting process caused at least four shrinkage cavities in the substrate region at the side of the lower surface of blade, from which crack origins were initiated. The crack propagated from the lower surface toward the upper surface of blade. The presence of original casting defect of shrinkage cavities in the substrate at the side of the lower surface of blade which act as “stress raiser” is mainly responsible for the instantaneous fracture of the blade. Imperfect removal of original casting defects before repair-welding and the occurrence of numerous blowholes on the repair-welding layer can aggravate the problem, aiding in the crack propagation.
KeywordsBlade Repair-welding Shrinkage Blowhole Instantaneous fracture
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