Comparison of Microstructure and Mechanical Properties of K4169 Alloy Fabricated by Gravity Casting, Counter-Gravity Casting and Laser Powder Bed Fusion

This research conducts a comparative study on the microstructure and mechanical properties of K4169 superalloy prepared by gravity casting (GC), counter-gravity casting (CGC) and laser powder bed fusion (LPBF). In the LPBF manufacturing process, the high temperature gradient and large cooling rate result in fine grains in the prepared samples (19∼30μm), as well as fine and distributed precipitated phases. This significantly improves their mechanical properties, which are far superior to those of the GC samples and slightly better than those of the CGC samples. The grain size of the CGC samples (650μm) is smaller than that of the GC (380μm) samples, and the size of the precipitated phases is also smaller, so their mechanical properties are better. After the three types of samples undergo SA (solution + aging) heat treatment, the molten pool in the LPBF samples disappears, the average grain size increases (45∼63μm), and a large number of δ phases and carbides precipitate at the grain boundaries, which reduces the plasticity of the LPBF samples. However, their mechanical properties reach the level of forged K4169. The grain size of the CGC samples does not change much, and more spherical carbides precipitate at the grain boundaries, which further improves the strength, making it close to that of the forged K4169 alloy, but the plasticity is further reduced. In the GC samples, there are still coarse and irregular Laves phases, acicular δ precipitated phases, and spherical carbides between the dendrites, and their strength is slightly improved. The analysis shows that the δ phase precipitated in the matrix after heat treatment reduces the plasticity of the K4169 while improving the strength of the material.