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| AN INVESTIGATION OF FRECKLES IN AN IRON-NICKEL BASE WROUGHT SUPERALLOY |
| Wang Yunshi;Hou Cuiping;Wang Mingxian Institute of Metal Research; Academia Sinica |
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Cite this article:
Wang Yunshi;Hou Cuiping;Wang Mingxian Institute of Metal Research; Academia Sinica. AN INVESTIGATION OF FRECKLES IN AN IRON-NICKEL BASE WROUGHT SUPERALLOY. Acta Metall Sin, 1980, 16(1): 22-128.
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Abstract Investigation of freckles observed in Fe-35Ni-15Cr-2. 4Al-2. 3Ti-2W-2Mowrought superalloy has been carried out. The freckles were actually dendrites whichmay appear as small spots or streaks depending on whether cross- or longitudinalsections of the bar are taken. Enrichment of Ti, Al, Si, Mo, Ni and minute C, B,S, etc. in interdendritic spaces in the freckles' region may result in the formationof γ', Ti(C,N) and M_3B_2 as well as in the growth of σ-phase which was observedonly in the freckle areas. In the case of the freckles' region, the temperature offusion would be low, being probably about 1190℃ which is nearly 40℃ belowthat of the matrix. If the hot working of the alloy is carried out at 1190℃ orthereabout, microcracks may be formed in such freckles' region. The freckles cannot be eliminated completebly even after soaking for a long time at elevated tem-peratures. The higher hardness associated with the freckles can be troublesome inmachining and in giving a rough machined surface. In vie of the fact that the', the brittle intermetallic σ-phase and the non-metallic inclusions are somewhatlocally concentrated, the mechanical properties of such an alloy might be expectedto be adversely affected. The freckle segregation is essentially associated with gravity segregation. It iscaused by upward movement of jets of liquid metals enriched with light elementsin the mushy zone during solidification. The tendency of forming freckles seemsto be related to the melting rate of the consumable electrode as well as to thedepth of the liquid metallic pool.
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Received: 18 January 1980
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[1] #12
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