A comparative study of Cu-15Ni-8Sn alloy prepared by L-DED and L-PBF: Microstructure and properties

In this paper, dense Cu-15Ni-8Sn alloy blanks were fabricated by laser-directed energy deposition (L-DED). Then, we systematically compared the L-DED sample with the laser-powder bed fusion (L-PBF) Cu-15Ni-8Sn alloy sample prepared in our previous work in terms of their building rate, microstructure, and performance. The average grain size of the L-DED sample was about 23.3 +/- 16.7 mu m, and its microstructure mainly included fine dendrites with a width of 5.6 +/- 1.2 mu m. The Vickers hardness, yield strength, and elongation at break of the L-DED sample were 166 +/- 5HV1, 327 +/- 9 MPa and 23.9 +/- 3.2%, respectively. The building rate of L-DED was about 16 times that of L-PBF. Due to the different laser power densities and different melting modes of L-DED and L-PBF, there were various preferred orientations along the laser scanning direction. Compared with the L-PBF sample, the sizes of grains, dendrites, and segregated phases of the L-DED sample coarsened, and its dislocation density decreased. Combined, these factors decreased its yield strength and were primarily responsible for the lower cooling rate of L-DED. The slow cooling rate alleviated the local thermal deformation in the L-DED sample, which reduced the possibility of stress concentration and increased its plasticity and work hardening rate.