Investigation of thermal diffusivity of Fe80Ni20 alloy by means of modified pulse method

Highlights: • The thermal diffusivity a(T) of the metastable Fe80Ni20 alloy was investigated. • The a(T) during heating and cooling of the sample investigated. • The occurrence of the hysteresis loop of the thermal diffusivity a(T) was proved. • The total error made while measuring thermal diffusivity was estimated. • The correctness of the modified flash method used in our study has been proved. The aim of this study is to present the research findings with regard to the characteristics of thermal diffusivity $a\left(T\right)$ of the metastable alloy Fe80Ni20. The modified pulse method has been applied for the $a\left(T\right)$ investigations. It allows to narrow down the interval of averaging the $a\left(T_i\pm 0.5\Delta T\right)$ in the interval lower than $\Delta T=1K$, whereas the estimated error of measurement of this quantity is below 4%. The temperature interval for the evaluation $a\left(T\right)$ for Fe80Ni20 alloy was established in the range of $20÷660\mathrm{°C}$. The $a\left(T\right)$ value was studied during both heating and cooling of the sample. For this alloy the authors confirmed the occurrence of the temperature hysteresis loop $a\left(T\right)$. It was established that during the sample's heating, the phase transition $\text{α}\to \text{γ}$ was initiated at the temperature $T_{\alpha \to \gamma }=T_{II}=586\mathrm{°C}$, and during its cooling we recorded the phase transition $\gamma \to \alpha$ successively in temperature $T_{III}=T_{\gamma \to \alpha }\cong 280\mathrm{°C}$, and again the overlapping of the characteristics $a\left(T\right)$ during its heating and cooling in temperature $T_I\cong 50\mathrm{°C}$.