my customer needs to repair of hard chromed defect area in Landing Gear Boeing 737-400 , should be use HVOF process or others like Selective plating ? does anyone has any experiences ?
Your customer should really refer to the relevant Boeing OEM manuals to see if there's a repair OR contact a Boeing representative to check what is permissable.
Don't even think about asking for advice on how to make this repair. Boeing and all other aircraft OEMs specify how to repair their parts. They specify everything including, in some cases, the brand of spray gun which must be used to make the repair. If you do it differently, you will never work for your customer again, and if something bad happens to that plane, even if it was not related to your repair, you can be sure that you will be talking to some government officials. If you are lucky, only your business will be shut down.
The first thing would be you would have to be MRO or Approved Maintenance Repair and Overhaul Centre and probably cost a million bucks in licensing fees. Then you can read their repair manuals lol.