The dendrite morphologies and spacings of directionally solidified DZ125 superalloy were investigated under high thermal gradient about 500 K/cm. The results reveal that, with increasing cooling rate, both the spacings of primary and secondary dendrite arms decrease, and the dendrite morphologies transit from coarse to superfine dendrite. The secondary dendrite arms trend to be refined and be well developed, and the tertiary dendrite will occur. The predictions of the Kurz/Fisher model and the Hunt/Lu model accord basically with the experimental data for primary dendrite arm spacing. The regression equation of the primary dendrite arm spacings λ1 and the cooling rate Vc is λ1=0.013Vc-0.32. The regression equation of the secondary dendrite arm spacing λ2 and the cooling rate Vc is λ2=0.00258Vc-0.31, which gives good agreement with the Feurer/Wunderlin model.
ZHANG Weiguo LIU Lin ZHAO Xinbao HUANG Taiwen YU Zhuhuan QU Min FU Hengzhi
The primary dendrite morphology and spacing of DZ125 superalloy have been observed during directional solidification under high thermal gradient about 500 K/cm.The results reveal that the primary dendrite arm spacing decreases from 94μm to 35.8μm with the increase of directional solidification cooling rate from 2.525 K/s to 36.4 K/s.The regression equation of the primary dendrite arm spacingsλ 1 versus cooling rate is λ 1 =0.013(GV)-0.32.The predictions of Kurz/Fisher model and Hunt/Lu model accord reasonably well with the experimental data.The influence of directional solidi fication rate under variable thermal gradient on the primary dendrite arm spacing has also been investigated.
Zhang Weiguo Liu Lin Huang Taiwen Zhao Xinbao Qu Min Yu Zhuhuan Fu Hengzhi
The effect of solidification rate on the microstructure development of nickel-based superalloy under the temperature gradient of 500 K·cm-1 was studied. The results show that, with the increase of directional solidification rate from 50 to 800 μm·s-1, both the primary and the secondary dendrite arm spacings of the alloy decrease gradually, and the dendrite morphologies transform from coarse dendrite to superfine dendrite. The sizes of all precipitates in the superalloy decrease gradually. The morphology of γ' precipitate changes from cube to sphere shape and distributes uniformly in both dendrite core and interdendritic regions. MC carbide morphology changes from coarse block to fine-strip and then to Chinese-script and mainly consists of Ta, W, and Hf elements. The γ-γ' eutectic fraction increases firstly and then decreases, and similar regularity is also found for the variation of segregation ratio of elements.
