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