Crack on WC/Co

[Met.Eng.]

Hi SEF members ,

I have some crack problem with NiCr 200 mic bond coat an 400 mic Wc/co coating. We have top gun hvof system. We preheat our carbon steel 70 C and spray 200 m NiCr 10 mic per pas. After than we apply carbide 45 +20 mic 88/12 (7-10 mic per pas) whan we spray 4x 4 pass the max temp is 125 C on coating line. When we coatin we also cooling dry air as same time and whan we see 125 C we stop the operation and wait to decries tem. 60 C.

We use all recommended parameters but we can't take crack ness surface.

What can we do? Can we use Ni 5Al with our hvof or can we spray Ni Al 200 - 300 mic with Metco 6-pII after Hvof system? For ex 300 - 500 mic NiAl with 6P-II and apply 200 300 mic WCCo 88/12

We clean solvent and blasting 24 grit alumina grit after coating proses.

Is anybody help us?

Thanks and have a nice day

[Alberto Villalobos]

HI.

WHEN YOU HAVE CRACKS IN YOUR COATING, YOU HAVE TO CHECK THE NEXT POINTS:

1. MAX PROCESS TEMPERATURE IS HIGHER THAN NEEDED, TRY TO KEEP IT LOW, MORE THAN 150F BUT LESS THAN 250F.

2. YOUR COOLING RATE IS SO FAST, YOU TOLD THAT YOU STOP YOUR PROCESS WHEN TEMPERATURE IS INCREASING, BUT YOU HAVE TO BE CAREFUL BECAUSE IF YOU GET HIGH TEMPERATURE AND THEN YOU COLD QUICKLY YOU WILL GENERATE CRACKS. YOU NEED PAY ATTENTION IN:
-- THE TEMPERATURE OF AIR COOLING SYSTEM IS SO COLD
-- DISTANCE BETWEEN AIR SIPHON AND PART
-- PRESURE AND FLOW OF THE AIR IN THE COOLING SYSTEM
-- NUMBER OF AIR SIPHONS

3. YOU SHOUL CHECK IF YOUR THICKNESS IS CORRECT. ALL THE COATINGS HAVE THICKNESS LIMITATION, WHEN YOU EXCEDEED THIS LIMITS YOU INCREASE INTERNAL STRESSES AND YOU WILL GET CRAKS IN COATING.

i HOPE THAT THIS INFORMATION HELP YOU WITH YOUR PROBLEMS. IF YOU HAVE MORE DOUBTS YOU CAN SEND A EMAIL TO alberto.villalobos@honeywell.com

BEST REGARDS