Component Cr Ni Co Fe WMo Ti .lCb. C B Ta
Turbine Blades U500 18.5BAL 18.5 --4 3 3 --0.07 0.006 -RENE 77 (U700) 15 BAL 17 --5.3 3.35 4.25 --0.07 0.02 -IN738 16 BAL 8.3 0.2 2.6 1.75 3.4 3.4 0.9 -0.10 0.001 1.75 GTD111 14 BAL 9.5 -3.8 1.5 4.9 3.0 --0.10 0.01 2.8 Turbine Nozzles
.40 25 10BAL 1 8 -----0.500.01-
.45 25 10BAL 1 8 -----0.250.01-FS.414 28 10 BAL 1 7 -----0.250.01 -N155 21 20 20BAL 2.53 ----0.20 --GTD-222 22.5 BAL 19 -2.0 2.3 1.2 0.8 -0.10 0.008 1.00 -Combustors SS309 23 13 -BAL ------0.10 --HAST. 22 BAL 1.5 1.9 0.79 ----0.07 0.005 -N-263 20 BAL 20 0.4-6 2.10.4 --0.06 --HA-188 22 22 BAL 1.514.0 -----0.05 0.01 -Turbine认heels Alloy 718 19 BAL -18.5 -3.0 0.9 0.5 5.1 -0.03 --Alloy706 16BAL -37.0--1.8 -2.9-0.03 --Cr-Mo-V 1 0.5 -BAL -1.25 ---0.250.30 --A286 15 25 -BAL -1.2 2 0.3 -0.25 0.08 0.006 -M152 12 2.5 -BAL -1.7 ---0.30.12 --Compressor Blades AISI403 12 --BAL ------0.11 --AISI403.Cb 12 --BAL ----0.2-0.15 --GTD-450 15.5 6.3 -BAL -0.8 ----0.03 --
Materials 42.
nozzle and blade castings are made by using the conventional equiaxedinvestment casting process. In this process， the molten metal is poured intoa ceramic mold in a vacuum， to prevent the highly reactive elements in thesuper alloys from reacting with the oxygen and nitrogen in the air.认ith proper control of metal and mold thermal conditions the molten metalsolidifies from the surface to the center of themold， creating an equiaxed structure. Directional solidification (DS) is also being employed to produce advanced technology nozzles and blades. First used in aircraft engines morethan 25 yearsago， it was adapted for use in large airfoils in the early 1990s.By exercising careful control over temperature gradients， a planar solidifica-tion front is developed in thebade， and the part is solidified by moving this planar jront longitudinally through the entire length of the part. The result is a blade with an oriented grain structure that runs parallel to the majoraxis of the part and contains no transverse grain boundaries， as in ordinary blades. The elimination of these transverse grain boundaries confers addi-tional creep and rupture strength on the alloy， and the orientation of the grain structure provides a favorable modulus of elasticity in the longitudinal direction to enhance fatigue life. The use of directionally solidified bladesresults in a substantial increase in the creeplife， or substantial increase in tolerable stress for a fixed life. This advantage is due to the eliminationof transverse grain boundaries from the bucket， the traditional weak link in the microstructure. In addition toimproved creeplife， the directionally solidified blades possess more than 10 times the strain control or thermal fatigue compared to equiaxed blades. The impact strength of the DSblades is also superior to that of equiaxed， showing an advantage of more than 33%.
In the late1990s， single-crystal blades have been introduced in gasturbines. These blades offer additional， creep and fatigue benefits throughthe elimination of grain boundaries. In single-crystal material， all grain boundaries are eliminated from the material structure and a single crystal with controlled orientation is produced in an airfoil shape. By eliminating all grain boundaries and the associated grain boundary strengtheningadditives， a substantial increase in the melting point of the alloy can beachieved， thus providing a corresponding increase in high-temperaturestrength. The transverse creep and fatigue strength is increased， compared to equiaxed or DSstructures. The advantage of single-crystal alloys compared to equiaxed and DSalloys in low-cycle fatigue (LCF) life is increased by about 10%.
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