Thermal radiative properties of electron-beam-melted and mechanically alloyed V-4Cr-4Ti based alloys between 200 and 750 °C

The directional spectral emissivities of two V-4Cr-4Ti family alloys, candidate structural materials for fusion first wall/blanket applications, were measured between 200 °C and their working temperatures (700–750 °C), with and without a high-temperature treatment. Besides showing the typical metallic behavior, an increase in the emissivity after the heat treatment (1000–1200 °C) was observed in both alloys. This has been attributed to several microstructural changes, which show the important role of microstructure in the thermal radiative properties of these alloys. In order to explain these mechanisms, the samples were analyzed using electron microscopy and X-ray diffraction. These measurements revealed differences in grain size, composition of the main phase and amount and distribution of dispersed secondary phases. X-ray diffraction and X-ray photoelectron spectroscopy were also used in order to check the extent of oxygen penetration. The results of directional spectral emissivity measurements were integrated to calculate the total hemispherical emissivity, the key heat transfer parameter in the high-temperature high-vacuum environments of fusion reactors. It is observed that the strategy of mechanical alloying with oxide and carbide dispersion to improve the mechanical properties also translates into an enhancement of the radiative refrigerating capability of these alloys.