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