On thermal expansion behavior of invar alloy fabricated by modulated laser powder bed fusion

Abstract

In the present research, structural analyses are conducted on Invar (64% Fe-36% Ni) samples manufactured by modulated laser powder bed fusion (LPBF) under different laser power regimes. Within the selected process window, the results obtained from X-ray computed tomography analysis indicate that the relative density of as-built samples increases with an increase in laser power. In addition, it is observed that irregular-shaped pores with the longest axis normal to the building direction are significantly reduced with increasing the laser power. Microstructural investigation suggests that with increasing the laser power, a transformation from conduction to transition and keyhole modes occurs. In X-ray diffraction patterns of the as-built samples, only fcc γ-phase is detected and no reflection of bcc α-phase is found. Texture measurements show that the intensity of 〈110〉 crystallographic orientation along the building direction of the as-built samples increases with increasing laser power. Coefficient of thermal expansion of the as-built samples is very low and comparable to that of conventionally manufactured Invar alloy. Furthermore, as-built samples fabricated at lowest (250 W) and highest (400 W) laser powers exhibit the lowest and highest thermal expansion displacement, respectively. Finally, the thermal expansion behavior and its correlation with structural integrity and texture are discussed.