How to reduce the intersplat boundaries in thermal spraying

[hustzc]

Hi, dear all

It is always reported the intersplat boundaries have a negative effect on properties of thermally sprayed coating. I have a question on this issue that how can we reducing the intersplat boundary or amount ?


In one paper, it was said that the faster the powder feeding rate is, the lower of the intersplat boundries is, in HVOF process. I cannot understand why???

Any suggestion or comment on above-mentioned questions would be very appreciated.


zhang cheng

[Gordon]

Hi zhang cheng

The way I see it, the boundaries between splatted particles are a fact of life in thermal spray coatings. While these boundaries tend to be the weak link as far as strength and ductility are concerned, they are an important aspect in thermal spray coatings.

The qualities (bonding) of these boundaries I think is the important issue not the amount. Changing the amount or surface area of these boundaries will be dependent on the particle size and the degree of splatting. So does using coarser powders (larger spray particles) and or reducing splat size produce better coatings? Well it depends on what properties your after, but for strength I would say it would be a negative one. The reverse of what your question implies.

Post heat treatment sintering/fusing operations may reduce and strengthen these boundaries.

In one paper, it was said that the faster the powder feeding rate is, the lower of the intersplat boundries is, in HVOF process. I cannot understand why???

Neither do I

[hustzc]

Hi Gordon

Thanks for your reply. Your answer is somewhat similar to that of Prof. Pawlowski.
He also suggests to post-treatment.

Here, Must the post-treatment necessary for HVOF-sprayed coating ?

[Gordon]

Hi zhang cheng

Here, Must the post-treatment necessary for HVOF-sprayed coating ?

Not sure I understand your question.

Post heat treatment in most cases is not necessary and in many cases a big advantage as the coating can be applied without heating effects to the substrate.

In a few cases post heat treatment can be beneficial to the coating, but this has to be done with consideration to how this effects the substrate as well.