Effects of titanium substitutions for aluminum and tungsten in Co-10Ni-9Al-9W (at%) superalloys
Effects of titanium substitutions for aluminum and tungsten in Co-10Ni-9Al-9W (at%) superalloys
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DOI：
10.1016/j.msea.2017.08.034
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发表时间：
2017-09-29
期刊：
影响因子：
6.4
通讯作者：
Seidman, David N.
中科院分区：
文献类型：
--
作者：
Bocchini, Peter J.;Sudbrack, Chantal K.;Seidman, David N.
Polycrystalline Co-10Ni-(9 - x)Al-(9 - x)W-2xTi at% (x = 0, 1, 2, 3, 4) alloys with gamma(f.c.c.) plus gamma'(L1(2)) microstructures are investigated, where the gamma'(L1(2))-formers Al and W are replaced with Ti. Upon aging, the initially cuboidal gamma'(L1(2))-precipitates grow and develop a rounded morphology. After 256 h of aging at 1000 degrees C, the precipitates in the 6 and 8 at% Ti alloys coalesce and develop an irregular, elongated morphology. After 1000 h of aging, replacement of W and Al with Ti increases both the mean radius, < R >, and volume fraction, phi, of the gamma'(L1(2))-phase from < R > = 463 nm and phi = 8% for 2 at% Ti to < R > = 722 nm and phi = 52% for 8 at% Ti. Composition measurements of the gamma(f.c.c.)-matrix and gamma'(L1(2))-precipitates demonstrate that Ti substitutes for W and Al in the gamma'(L1(2))-precipitates, increases the partitioning of W to gamma'(L1(2)), and changes the partitioning behavior of Al from a mild gamma'(L1(2))-former to a mild gamma(f.c.c.)-former. The grain boundaries in the aged alloys exhibit W-rich precipitates, most likely mu(Co7W6)-type, which do not destabilize the gamma(f.c.c.) plus gamma'(L1(2)) microstructure within the grains. Four important benefits accrue from replacing W and Al with Ti: (i) the alloys' mass density decrease; (ii) the gamma'(L1(2))-solvus temperature increases; (iii) the gamma'(L1(2)) volume fraction formed during aging at 1273 K (1000 degrees C) increases; and (iv) the 0.2% offset flow stress increases.
