Role of Cobalt in Waspaloy

Reduction of Strategic Elements in Turbine Disk Alloys.

“…An additional effect, which must be taken into consideration, is the decrease of solubility of C in the matrix phase with reduction of the Co level, which results in the formation of more carbide particles of M C type at intermediate temperatures. The present observation is cgsqstent with those in Nimonic alloys (18), Waspaloy (24), and cast MERL 76 (29). The predominant type of carbide in the 18% Co alloy is MC, which precipitate as cuboidal and equiaxed particles distributed intra-and intergranularly.…”

“…At temperatures below 760'C, cobalt has another beneficial effect, which is directly related to previous observations that cobalt lowers the solubility of Al and Ti in nickel solid solutions and results in a slightly larger volume fraction of Y' phase (18,24). However, in our study, the additional v' precipitation occurs during aging or testing at temperatures below 760 0 C. These /' particles are very fine and have a measurable effect on the yield strength and creep of the gamma alloys.…”

Effects of Cobalt in Nickel-Base Superalloys

“…No more than a 10% decrease in the strengths is observed when cobalt was removed completely from Waspaloy and from the disk heat treated Udimet 700 (2,4).…”

“…In Waspaloy, with a smaller y' volume fraction, Maurer et al (4) observed that the solvus temperature is unaffected by cobalt.…”

“…Particularattentionwill be given to two other very recent studies (3,4). The study by Nathal and Meier (3) concentratedon Mar-M247,which is representativeof the high strength cast alloys for high temperaturevane and blade applicationsand can be used in polycrystalline,directionally solidifiedand monocrystallineforms.…”