Role of hydrogen on adhesion of NiCr thermal sprayed coatings

Hydrogen embrittlement was known for many years. Different theories explain how hydrogen plays the role of an accelerator for fracture when it was int roduced into the material either during its elaboration or during its servi ce as a mechanical part. In this latter case, the presence of a barrier to introduction of hydrogen into the material may delay or even impede the emb rittlement process. The present study was devoted to the mechanical aspects of hydrogen contamination of this type of a NiCr thermal sprayed coating a nd in particular to the influence of hydrogen on the coating adhesion on a low carbon steel substrate. It was found that, besides the embrittlement of the coating, adhesion was also affected since the critical load necessary to initiate a crack at the interface was reduced in the presence of hydroge n. Using an apparent interface toughness concept it was also possible to po int out the effect of the residual stresses in relation to the coating thic kness as well as surface effects on the apparent interface toughness value. (C) 2000 Elsevier Science B.V. All rights reserved.