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郑亮,刘玉峰,刘杨,王悦,张轶波,刘娜,许文勇,袁华,李周,张国庆.高温合金差示扫描量热分析(DSC)的影响因素研究III:合金状态和升降温速率[J].稀有金属材料与工程(英文),2019,48(6):1944~1953.[Zheng Liang,Liu Yufeng,Liu Yang,Wang Yue,Zhang Yibo,Liu Na,Xu Wenyong,Yuan Hua,Li Zhou and Zhang Guoqing.Influencing Factors on Differential Scanning Calorimetry (DSC) Analysis of Superalloy III: Alloy state and Heating/Cooling Rate[J].Rare Metal Materials and Engineering,2019,48(6):1944~1953.]
Influencing Factors on Differential Scanning Calorimetry (DSC) Analysis of Superalloy III: Alloy state and Heating/Cooling Rate
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Received:November 22, 2018  Revised:February 21, 2019
DOI:
Key words: Ni-base superalloy  Alloy 625  DSC  powder  HIP  as-cast microstructure  segregation
Foundation item:国家重点研发计划(2016YFB0701404);国家科技支撑计划(2015BAE03B01);国家自然科学基金(51304177);国家国际科技合作专项2012DFA50240;重点实验室基金(9140C430202150C43200)
Author NameAffiliation
Zheng Liang,Liu Yufeng,Liu Yang,Wang Yue,Zhang Yibo,Liu Na,Xu Wenyong,Yuan Hua,Li Zhou and Zhang Guoqing  
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Abstract:
      Abstract: Differential scanning calorimeter (DSC) experiments were performed on solid-solution strengthening Ni-base superalloy 625, considering the effects of the alloy state (powder, powder+HIPed and as-cast) and heating/cooling rate (5-10°C/min) on the phase transformation temperatures. The alloys with different states were characterized by FESEM and EPMA. (1) The results indicate that the dendritic arm spacing of the as-cast alloy is 2 orders of magnitude higher than that of the 625 alloy powders, whereas the hot isostatically pressed (HIPed) alloys possess a fine equiaxed grain structures without dendritic segregation. (2) The heating/cooling rates have no significant influence on the onset of matrix melting ( equal to the incipient melting temperature for the solid-solution strengthening superalloy) and onset of solidification temperatures (inflection point), but have an obvious effect on the melting end, matrix mass solidification temperatures (peak position) and solidification end temperature (inflection point) of the alloy. Using the average phase change temperature on heating and cooling curve average method can reduce the influence of DSC experiment or sample conditions and obtain a relatively fixed and comparable phase transformation temperature. (3) The alloy state has obvious effect on incipient melting temperature and the arc shape near soidus temperature of DSC heating curve. The segregation tendency of alloy can be determined by the radian near the solidus reigion of DSC heating curve. The powders and HIPed PM625 alloys with weak segregation tendency exhibit a sharp inflection point in DSC heating curves in the region near solidus temperature, there is only a 5-6°C gap between the onset of matrix melting temperature of the alloy (deviation from the baseline inflection point) and the nominal solidus temperature (tangent-onset intersection). The DSC heating curve of the as-cast IN625 alloy with a high segregation tendency exhibit a larger radian near the solidus region, the difference between the onset of matrix melting temperature and the nominal solidus temperature (tangent-onset intersection) can reach 52°C. The onset of matrix melting temperatures of as-cast 625 alloys are 45°C and 40°C lower than that of the HIPed and powder 625 alloy respectively. The parameter of the process such as HT or HIP should be selected concerning the effect of the alloy state with large radian near solidus region of DSC heating curve on decreasing the incipient melting temperature. The DSC cooling curves for the different state of 625 alloys are similar, which all possess a large radian near the solidus region, because the alloys were completely remelted which eliminated the original microstructure features and re-solidified from the full liquid state.