Dear colleagues,

Have one of you some ideas or solutions for solving the edge delaminations of HVOF-sprayed MCrAlYs on Ni-base alloys (i.e., IN738 and MarM247). The general quality of coatings is excellent (porosity and oxides both less than 1%), but some delaminations appear on the convex edges of turbine vanes or heat shields. The coatings are produced by a HVOF system using kerosene and oxygen.

I tried several solutions: pre-heating temperature variations (100 to 200°C), variations of coating gun speed and and coating sequences, grit blasting rougher the substrate to increase bonding. The problem is not solved yet. There was some improvement with rougher blasting and thinner coatings, but the delaminations are not completely eliminated.

The delaminations are not present on all edges. The coating thickness is about 200-350 micrometers. It seams that these delaminations appear during diffusion heat treatment. The powder size ranges mostly between 15-45 micrometers. During process development, the tensile strength of the coating (without heat treatment), sprayed with selected parameters, was typically 70-80 MPa.

The delaminations appear only on convex radius (external edge of parts) and only on some locations. Before we used another (old) HVOF system to spray the same powder onto same parts with quite similar robot program, but we did not have these delaminations, even if the coating was significantly more porous and presented less bonding strength than with the new gun giving delaminations on the edges.

On the other side, not all type of parts present such edge delaminations when sprayed with this new kerosene - oxygen gun. For some parts, the edges delaminations appear, on the others they don't appear.

Has somebody a solution or some ideas how we may solve this problem? Thank you very much!

Best regards,
Florin

Hi Florin

If your new HVOF system is much higher energy you may require increased cooling on part and coating. Hot spots close to the edge could cause these problems. My first thoughts anyway. Good luck with solving your problem.

What system are you using. Most HVOF systems apply MCrAlYs in tension. The JP 5000 does a very good job of maintaining residual compressive stresses in the coating (No I don't work for Praxair).

Its sounds like this is the basis of your problem, and would be helpful to know what system you are using.

Florin Wrote:Dear colleagues,

Have one of you some ideas or solutions for solving the edge delaminations of HVOF-sprayed MCrAlYs on Ni-base alloys (i.e., IN738 and MarM247). The general quality of coatings is excellent (porosity and oxides both less than 1%), but some delaminations appear on the convex edges of turbine vanes or heat shields. The coatings are produced by a HVOF system using kerosene and oxygen.

I tried several solutions: pre-heating temperature variations (100 to 200°C), variations of coating gun speed and and coating sequences, grit blasting rougher the substrate to increase bonding. The problem is not solved yet. There was some improvement with rougher blasting and thinner coatings, but the delaminations are not completely eliminated.

The delaminations are not present on all edges. The coating thickness is about 200-350 micrometers. It seams that these delaminations appear during diffusion heat treatment. The powder size ranges mostly between 15-45 micrometers. During process development, the tensile strength of the coating (without heat treatment), sprayed with selected parameters, was typically 70-80 MPa.

The delaminations appear only on convex radius (external edge of parts) and only on some locations. Before we used another (old) HVOF system to spray the same powder onto same parts with quite similar robot program, but we did not have these delaminations, even if the coating was significantly more porous and presented less bonding strength than with the new gun giving delaminations on the edges.

On the other side, not all type of parts present such edge delaminations when sprayed with this new kerosene - oxygen gun. For some parts, the edges delaminations appear, on the others they don't appear.

Has somebody a solution or some ideas how we may solve this problem? Thank you very much!

Best regards,
Florin

hello florin
delaminations can be result of irregularity in your colding or fast colding substrat.I know you speak french ,and it s easier for me to answer in french ,
delaminage des couches est le resultat d un refroidissement rapide et non homogene,verifie ton systeme de refroidissement de pieces
j espere que ca resoudra ton probleme