Thermal Diffusivity of TiAlNb and AlNi Alloys - The European IMPRESS Project

Abstract

The thermal diffusivities of some industrially important alloys have been measured as a part of the EU funded Intermetallic Materials Processing in Relation to Earth and Space Solidification (IMPRESS) project which is coordinated by the European Space Agency (ESA). The thermal diffusivities of the alloys were measured by the Laser flash method with a carefully designed gas cleaning system to remove traces of oxygen from the argon atmosphere. In the present work, the thermal diffusivity of TiAlNb (Ti46.1Al45.9Nb8 at %) and AlNi alloy (Al-Ni31.5 at %) alloys have been measured independently at Royal Institute of Technology, Sweden (KTH) and National Physical Laboratory, UK (NPL). The results from both laboratories were consistent, and have been compared with predictions of phase transformation temperatures calculated using Thermo Calc and MTDATA software. Generally the variation of thermal diffusivity appears to be related to the phase transformation. However, one anomaly observed in the present work on TiAlNb was a maximum thermal diffusivity value at about 1100K. No corresponding peak was found for the density, ρ, the specific heat capacity, Cp, or the electrical resistivity, 1/σ, which were also measured as part of the project. In view of the fact that the thermal diffusivity could be related to electrical conductivity by the Wiedemann-Franz law describing electronic contribution to heat conduction, the present results indicate a non-electron contribution. This aspect is being currently investigated further. The recommended thermal diffusivity value of TiAlNb and AlNi alloys were obtained as follows. TiAlNb alloy: α = 3.75+ 5.16 ·10-3T+1.89·10-6 T2 – 2.69·10-9 T3 [10-6 m2 s-1] (293 K < T < 1573 K) AlNi alloy: α = 4.77+ 5.41·10-2T – 7.14·10-5T2 + 2.88·10-8T3 [10-6 m2 / s] (373K <T<943K)