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