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Analysis

Summary

Metallurgical examination of the failed blade (refer to ATSB Technical Analysis Report No.3/01) indicated that the loss of the blade section was due to the progression of fatigue cracking into the blade section from an area of cracking and notching on the blade tip. The cracking was found to have progressed into the blade parent Rene 125 material through an extensive Inconel 625 weld repair beneath the tip notching.

The Inconel 625 alloy is inferior to the Rene alloys in terms of its fatigue strength. Cracks within the Inconel 625 alloy will develop and propagate much more rapidly than equivalent cracks developed within the Rene alloys.

The Rene alloys are successfully weldable only under tight procedural control and require high levels of preheat to reduce hot cracking. Under conditions of restraint, such as deep crack repairs, the use of a ductile Inconel 625 alloy as a filler improves the success rate in producing sound repairs. The latest revisions of the appropriate repair documents that came into affect on 19 October 2000, cautioned the repairers that certain cracks are not repairable with Inconel 625 weld filler and that Rene 80 or 142 alloys are necessary for trailing edge welds below the blade tip shelf. The documents did not prohibit the use of Inconel 625 alloy.

 
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