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chroming is the finish on some hardsurfacings.
If its done poorly it peels off in sheets sort of like what you've got there. I dont know the manufacturing process of all of the components in the td5 so I mentioned it.
It looks a little off to me for machining swarf as its not discolored (I would have expected chunks that side to have some blueing) and its quite shiny,
You said you had the head replaced, may be they couldn't get the old head off due to a seized head bolt and drilled the head off and the drill swarf just fell down into the engine....... (don't you just hate it when they send the apprentices to do the mundane jobs)
I would be leaning towards what blacknight is saying, it is too shiny for a piece of machined alloy or steel, have you worked out if its steel or aluminium(use a magnet) and has he said it has no discolouration. If its very shiny and smooth it could be hard facing like of a cam shaft. Itsnotworthcomplaining has a good point about drilling out head bolts though.