A dilution gas for use at {HEAD ~ the time} of forming {TAIL ~ the surface layer} is made of hydrogen , argon or helium or the like 
of forming
A dilution gas for use at { HEAD ~ the time } of forming { TAIL ~ the surface layer } is made of hydrogen , argon or helium or the like
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH