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鈷基高溫合金GH5605鑄態組織及高溫擴散退火過程中元素再分配

As-cast microstructure and redistribution of elements in high-temperature diffusion annealing in cobalt-base superalloy GH5605

  • 摘要: 利用光學顯微鏡(OM)、場發射掃描電子顯微鏡(FESEM)、能譜分析(EDS) 并結合熱力學及動力學計算結果對采用真空感應熔煉和電渣重熔二聯工藝生產的GH5605合金電渣錠的枝晶形貌、元素偏析和析出相進行分析.探索了合金的高溫擴散退火制度并結合差示掃描量熱儀(DSC) 和熱壓縮模擬實驗分析高溫擴散退火前后的合金特征.結果表明: GH5605合金中的枝晶和元素偏析情況較輕, 主要偏析元素是Cr和W并在枝晶間處偏聚, 電渣錠中的主要析出相包括奧氏體、晶界M23C6以及晶內和晶界處的奧氏體與M23C6板條狀共晶相.經1210℃/8 h擴散退火處理后枝晶和元素偏析基本消除, 共晶相基本回溶.

     

    Abstract: The dendritic morphology, elements segregation index, precipitates morphology, and precipitates types in GH5605 ingot produced by vacuum induction melting and electroslag remelting were investigated by using optical microscopy (OM), field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS) spectrum analysis and the results of thermodynamic and kinetic calculations by Thermal-Calc and JMatPro sofeware. To study the effects of high-temperature diffusion annealing on GH5605 ingot, the annealing system was investigated and the microstructure and macrostructure characteristics of GH5605 ingot were analyzed before and after the diffusion annealing by differential scanning calorimetry (DSC) and thermal compression simulation tests in Gleeble 3800 test machine. In the OM results, dendrites are not obvious, and secondary dendritic arms cannot be distinguished in the GH5605 surface but they are gradually clearer toward the center area. The EDS results show that element segregation index is comparably small in GH5605 ingot; every element segregation index is in the range of 0. 9-1. 4 which is not as large as those of nickelbased superalloy. The main segregating elements during solidification are Cr and W which mainly segregate in the dendritic regions.According to the FESEM results, the precipitate phases include austenite and grain boundary carbide M23C6 and because of the Cr and W segregation at dendritic arms, an unexpected eutectic phase comprising austenite and M23C6 appears, and the alternating lamellae of austentite and M23C6 develop a lathlike morphology. Different macrostructure and microstructure characteristics including the morphology of dendritic, elements segregation index, grain size, morphology and the amount of eutectic phase were analyzed and compared in different annealing times. The high-temperature diffusion annealing system is optimal at 1210 ℃/8 h, at which the dendrites and elemental segregation are substantially eliminated, and the eutectic phase is almost dissolved.

     

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