Effect of Additional Heating of the Substrate on the Phase Composition of Inconel 718 Obtained by Direct Metal Deposition

This work investigates the effect of the temperature of the substrate additional heating on the structural-phase composition of an Inconel 718 coating obtained by direct laser growth. Using synchrotron radiation diffraction in the Debye-Scherrer geometry, it was shown that an additional heating temperature of the substrate of $750{ }^{\circ} \mathrm{C}$ leads to a more intense formation of the strengthening $\gamma^{\prime \prime}$ phase, as well as Laves phases with the stoichiometry ($\mathbf{N i}, \mathbf{C r}$, $\mathrm{Fe}) \mathbf{2}(\mathbf{N b}, \mathrm{Mo}, \mathrm{Ti})$. Also, as a result of a decrease in the temperature gradient formed during laser cladding and a decrease in the cooling rate of the melt pool, the structure of the formed material changed. The material obtained without additional heating is characterized by the presence of columnar dendrites in the structure located towards the substrate. Additional heating of the substrate up to $750{ }^{\circ} \mathrm{C}$ contributed to a change in the structure of the sample and the formation of larger dendrites without a preferred direction. In both cases, at the boundaries of the dendrites, segregation of a large number of elements forming the Laves phases occurred: $\mathrm{Nb}, \mathrm{Mo}, \mathrm{Ti}$. The internal material of dendrites is characterized by a high content of $\mathrm{Al}, \mathrm{Cr}, \mathrm{Fe}$ and Ni.