I have a part made of Titanium that is peened with AWCR-14 to intensity range of .010-.015N” with 100% coverage.
We have been experiencing a phenomenon were small areas of the part are not being covered. The areas area full within the stream of peening media exiting the nozzle. There is no masking in or near the area. Visual inspection of the part under both white and black light reveal no foreign material on the part prior to shot peen. When we coat the part with a tracer dye all of the tracer is removed yet these isolated areas (approximately .125” diameter) remain un-peened and appear to be nearly black in color. Is it possible for Ti to have isolated areas that are harder than the remainder of the part?
Has anyone ever experienced this before?

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Sounds like a metallurgical problem. If the part is a titanium alloy then there could be hard precipitates at the surface that appear not to have been peened when actually they have been. Plastic stretching of the surface during peening temporarily removes the protective oxide coating. When this re-forms over a precipitate it could appear dark in color.

Thank you for the quick reply.

Socrates, How would one go about testing for this metallurgial problem?

First check that you can get a representative sample of the component’s surface – e.g. a cube of about 1cm side from a scrap component. Determine the chemical composition of the component and its thermo-mechanical history e.g. casting, forging, fabrication etc. Supply sample and details to a metallurgist requesting a metallographic examination of the sample’s surface region – before and after etching. Particular attention should be paid to the presence of inclusions and voids. Microphotographs should be supplied to verify any significant metallographic features.