wherein {HEAD ~ the metal} is selected from the group consisting of: cobalt, {TAIL ~ nickel} or chromium, and a metal alloy of these metals 
wherein { HEAD ~ the metal } is selected from the group consisting of : cobalt , { TAIL ~ nickel } or chromium , and a metal alloy of these metals
OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH