RE: Cracks in abradable coatings
When diagnosing cracks, it is helpful to think about the cooling and contraction rates of both the substrate and the coating. Ideally, they should contract the same amount, leaving the coating in a state of neutral stress. When you get tension cracks in the coating, either during spraying or during machining, try to keep the coating cooler or allow the substrate to get hotter. If the substrate gets hotter, it has to cool more, and it will shrink more, canceling some of the tensile stress in the coating.
Personally, I try to avoid cooling a coating because of the thermal shock of the "cold" air flow on the "hot" coating, which can also cause cracks.
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