Adding new fused coating to old
05-17-2017, 03:55 PM,
#1
Adding new fused coating to old
Have any of you had or heard of success in repairing a worn Ni-base spray+fuse coating by suitable surface preparation---but leaving some remnant coating---and preheating, followed by spraying and fusion of additional coating? I'd be interested in the details. Thanks!
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05-17-2017, 05:07 PM, (This post was last modified: 05-17-2017, 05:23 PM by Vadim Verlotski.)
#2
RE: Adding new fused coating to old
(05-17-2017, 03:55 PM)RAM Wrote: Have any of you had or heard of success in repairing a worn Ni-base spray+fuse coating by suitable surface preparation---but leaving some remnant coating---and preheating, followed by spraying and fusion of additional coating? I'd be interested in the details. Thanks!
Bad idea. New layer is peeling off while sintering. It is because the old layer gets a dense Cr2O3 layer when heated, which prevents adhesion. So, remove the old layer completely!

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05-17-2017, 11:48 PM,
#3
RE: Adding new fused coating to old
(05-17-2017, 05:07 PM)Vadim Verlotski Wrote:
(05-17-2017, 03:55 PM)RAM Wrote: Have any of you had or heard of success in repairing a worn Ni-base spray+fuse coating by suitable surface preparation---but leaving some remnant coating---and preheating, followed by spraying and fusion of additional coating? I'd be interested in the details. Thanks!
Bad idea. New layer is peeling off while sintering. It is because the old layer gets a dense Cr2O3 layer when heated, which prevents adhesion. So, remove the old layer completely!

Was the original coating preheated in air? How much time between preheating and spraying the new coating?
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05-18-2017, 07:31 AM,
#4
RE: Adding new fused coating to old
(05-17-2017, 11:48 PM)RAM Wrote:
(05-17-2017, 05:07 PM)Vadim Verlotski Wrote:
(05-17-2017, 03:55 PM)RAM Wrote: Have any of you had or heard of success in repairing a worn Ni-base spray+fuse coating by suitable surface preparation---but leaving some remnant coating---and preheating, followed by spraying and fusion of additional coating? I'd be interested in the details. Thanks!
Bad idea. New layer is peeling off while sintering. It is because the old layer gets a dense Cr2O3 layer when heated, which prevents adhesion. So, remove the old layer completely!

Was the original coating preheated in air? How much time between preheating and spraying the new coating?

It does not matter. Even without preheating, the old layer will oxidize. You want to melt the new layer or not? During this remelting, the old layer oxidizes under the new.
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