The preferred material for {TAIL ~ layers} 4 and 4′ are {HEAD ~ Ti alloys} or Ni alloys 
The preferred material for { TAIL ~ layers } 4 and 4′ are { HEAD ~ Ti alloys } or Ni alloys
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH