素材表面严重粗糙，镀层无法覆盖平整。
The material surface coarse, coating can't cover serious level.
因为阴极极化作用超过一定范围，会导致氢气的大量析出，从而使镀层变得多孔、粗糙、疏松、烧焦，甚至是粉末状的，质量反而下降。
Because the cathode polarization effect more than a range, will lead to a large number of hydrogen, and separation coating becomes porous, rough, loose, scorched, even the powder, quality just drop.
化学气相沉积的碳化物镀层一般很耐磨，但这些表面层镀后的粗糙度较高，会使与之相配的试件受到剧烈磨损。
In general, the carbide coating of chemical vapour deposition resists wear. But these surface coatings have a high roughness, which causes violent wear in the matched test pieces.
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