Influence of pulsed laser scanning patterns on microstructural evolution and mechanical properties of Inconel 718 in direct laser deposition

The mechanical properties of direct laser deposition (DLD) parts are crucial for engineering applications, which are determined by the microstructure and texture. To achieve fine microstructure and higher mechanical performance, pulsed laser deposition is used to generate less heat accumulation and a higher cooling rate. However, the relationship between microstructure and thermal history is difficult to investigate due to the transient temperature change. In this work, a three-dimensional numerical model is developed to study the thermal behavior of the molten pool in the continuous laser deposition (CLD), the continuous pulsed laser deposition (CPLD), and the interval pulsed laser deposition (IPLD) processes. The microstructure of the deposition samples is investigated by optical microscope and electron back-scattered diffraction. The mechanical response of the deposition samples is investigated by tensile test and microhardness test. Compared with the CLD, CPLD, and IPLD result in higher temperature gradient and cooling rate, long columnar grains, and a strong fiber texture. However, grains with larger sizes and a texture with a herringbone pattern due to the change of heat flow are obtained in CLD samples. The test values of IPLD samples show higher tensile strength, higher yield strength, lower ductility, and higher hardness values. This research brings about a perspective for studying the thermal effects of deposition layers and a novelty deposition process to obtain specific microstructures and better mechanical properties.