Measuring Sensible Specific Heat Capacity of In718plus Alloy by DSC AITranslate

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Basic Information:

DOI：10.13373/j.cnki.cjrm.XY24030027

Chinese Library Classification Number:TG146

Citation Information:

Specific heat capacity is a basic thermal physical parameter in the process of material temperature rise，and it is also a key physical quantity in material design and application. At present，the specific heat capacity of materials is tested mostly by the foreign standard ASTM E1269 "Standard test method for Measuring specific heat capacity by differential scanning calorimetry". The measured specific heat capacity is also called sensible specific heat capacity because the material only changes in temperature without phase transformation during the heating process. However，many metal materials are usually composed of a variety of phases at room temperature due to design and use requirements，and phase transformation will inevitably occur during the heating process，accompanied by obvious thermal response and directly reflected in the specific heat capacity curve. This part of the heat absorption or heat release due to phase transformation is called latent heat，and the specific heat capacity obtained by calculation is the specific heat capacity of latent heat. When the specific heat capacity of an unknown material is tested according to the standard test method，the actual specific heat capacity measured should be called the apparent specific heat capacity. That is because it contains both sensible heat capacity and latent heat capacity，and the current test standard does not mention how to distinguish between the two. When the material has no thermal effect，the apparent specific heat capacity measured is the sensible specific heat capacity. When the material includes thermal effect，the apparent specific heat capacity is greater than the sensible specific heat capacity. In many test cases，the apparent specific heat capacity was mistakenly considered as the sensible specific heat capacity of the material，which made the specific heat capacity data value too large，affecting the thermal conductivity characterization of the material. In this paper，the specific heat capacity of In718plus was tested，and the phase transformation in its curve was subjected to thermal insulation water quenching treatment and microstructure analysis，the specific reasons were identified and the data processing method for obtaining the sensible specific heat capacity was proposed. The specific heat capacity of In718plus superalloy was measured by differential scanning calorimetry （DSC）. An obvious heat absorption peak appeared during the heating process，resulting in an abnormal increase in the specific heat capacity. After the original microstructure was heated at 700 ℃ in Muffle furnace for 20 min，the η phase and the γ' phase in the grain boundary did not change much. After the original structure was kept at 900 ℃ in Muffle furnace for 20 min and water quenching，η phase on the grain boundary showed a tendency to grow，and the number of γ' phase decreased significantly. Therefore，it could be concluded that the main phase change occurring at the second peak on the DSC thermal analysis curve was the enhanced phase γ' dissolution reaction，which belonged to the first-order phase transition with latent heat. As reported in the literature，In718plus alloy was developed on the basis of In718 alloy by adjusting the chemical composition，and the strengthening phase was more stable γ' -Ni₃（Ti，Al，Nb），which increased its service temperature from 649 to 700 ℃. On the DSC curve，the phase transition peak started at 700 ℃ and ended at 900 ℃，which corresponded to the dissolution range of γ' phase. When the sensible specific heat capacity of In718plus itself was measured by DSC，the latent heat of γ' phase dissolution during the heating process had nothing to do with the sensible heat of In718plus itself，and should be distinguished in the test results. It was mentioned in literature that there was a functional relationship between the specific heat capacity and temperature of metal materials in a single-phase structure. Assuming that the material did not undergo phase transition，the specific heat capacity and temperature should meet the formula in the whole temperature range. The temperature points of In718plus alloy without phase transformation were 100，200，300，400，500 and 1000 ℃，and the corresponding specific heat capacity and temperature should meet the above functional relationship. In the case of first-order polynomial fitting，all the other points except the data points at 300 ℃ were distributed on both sides of the line，and the correlation coefficient R² at this time was 97.5%，with average effect. When quadratic polynomial fitting was used，all the data points were closer to the fitting curve，the fitting effect was better，and the correlation coefficient reached 99.7%. When the third and fourth order polynomials were used，the centers of all data points fell on the fitting curve，and the correlation coefficient was 100%，so the fitting effect was the best. It could be seen that the specific heat capacity of In718plus met the third-order polynomial relationship with temperature. The sensible specific heat capacity of the material was obtained by fitting the data of the temperature range of the phase transition with polynomial fitting. By comparing the correlation coefficient R²，it was found that the R² reached 100% when the fitting reached the cubic polynomial.