A study on the thermal expansion characteristics of a dissimilar fusion joint by high temperature X-ray diffraction

The lattice thermal expansion behaviour of the constituents of a dissimilar fusion joint between a magnetic iron alloy and Inconel-82®1 has been investigated by high temperature X-ray diffraction in the temperature range 300–1273 K. It is found that the thermal expansivity of the inconel phase in the fusion zone of the weld is considerably lower than that of pure Inconel-82® filler metal. On the other hand, the thermal expansivity of the soft-iron phase is rather close to that of the inconel phase in weld, at least up to moderate temperatures. In addition, the temperature sensitivity of its thermal expansion is also rather weak. It is found that in the temperature range 300–773 K, the thermal expansion mismatch between the weld constituents is not really drastic. Metallographic characterisation of the fusion zone of the weld using SEM-EDX and EPMA techniques revealed the presence of a compositionally modulated zone on the inconel side of the fusion line. It is reasoned that the change in composition of the inconel phase in weld as compared to pure Inconel-82® filler metal, is what is responsible for its reduced thermal expansivity in weldment.