 The nickel @-@ based superalloys have improved creep strength with the addition of rhenium . The alloys normally contain 3 % or 6 % of rhenium . Second @-@ generation alloys contain 3 % ; these alloys were used in the engines for the F @-@ 15 and F @-@ 16 , whereas the newer single @-@ crystal third @-@ generation alloys contain 6 % of rhenium ; they are used in the F @-@ 22 and F @-@ 35 engines . Rhenium is also used in the superalloys , such as <unk> @-@ 4 ( 2nd gen ) and <unk> @-@ 10 ( 3rd gen ) that are used in industrial gas turbine engines like the GE <unk> . Rhenium can cause superalloys to become <unk> unstable , forming undesirable TCP ( topologically close packed ) phases . In 4th- and 5th @-@ generation superalloys , ruthenium is used to avoid this effect . Among others the new superalloys are EPM @-@ 102 ( with 3 % Ru ) and TMS @-@ 162 ( with 6 % Ru ) , as well as TMS @-@ 138 and TMS @-@ 174 . 
