Mechanism research on black fleck characteristic in TC18 titanium alloy
The mechanism of the black fleck defect in TC18 titanium alloy was studied by surface morphology observation,metallographic microstructure analysis and SEM/EDS analysis.It is indicated that the black fleck defect area,which is dark and continuously distributed,is isolated by the surrounding boundary line.It is proved that the defect area is actually α-β dual phase which is left over to the finished product due to a failure phase transition.Additionally,it was found through SEM/EDS and EPMA/WDS analyses that the oxygen content of the black fleck defect was higher,resulting in a higher β transus temperature.Consequently,the defect area did not undergo phase transition and was present in the finished products.
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