Effect of heat input on the subgrains of laser melting deposited Invar alloy

Invar alloys are widely used in the aerospace, but their manufacturability and mechanical properties are not well understood when they are employed in additive manufacturing. The laser melting deposition (LMD) technology is utilized to the surface repair of Invar alloys. In this work, the microstructure evolution, quantitive subgrain size, as well as the subgrain orientation are investigated using optical microscopy. Moreover, the effect of partially remelting of successive layers is exhibited. It is explicit that the cellular crystal orientation is strongly influenced by the heat flow which is subject to the scanning direction. Considering to the basic laws of Invar alloy microstructure evolution during LMD process, the relations between heat input and produced subgrain characteristics are further elucidated. The results show that a slight increase of λ from 4.4 μm to 5.2 μm at the function of heat input varied from 98.6 J/mm2 to 114 J/mm2. Moreover, it was notable that a reverse change in the dimension discrepancy of remelted and non-remelted subgrains occurred with two kinds of heat input.