Abstract
Powder bed fusion (PBF-LB) was developed to manufacture more complex parts than by conventional powder metallurgy processing, but its potential is limited by long part-fabrication times. New ring laser beam profiles were developed to reduce production time. However, the effects of the new ring profile and how it performs versus standard Gaussian laser profiles still requires additional research to optimize its performance. In this study, porosity, a critical factor in determining part quality, along with microhardness and microstructure were investigated for 17-4 PH stainless steel. Samples were printed with varying laser power (300 W to 1150 W) and scan speed (500 mm/s to 1200 mm/s). Six laser power and scan speed combinations were evaluated at an average linear energy density of 0.91 J/mm. In addition, the microstructures of both horizontal and vertical cross sections were characterized. For the six laser power and scan speed configurations analyzed, a lower scan speed resulted in a finer microstructure and maximum hardness values (362 HV / 37 HRC). Vertical cross sections exhibited higher percent porosity (~13%) with interconnected, elongated pores. A linear energy density of 1.00 J/mm with laser power of 900 W and scan speed of 900 mm/s was the optimal processing configuration that resulted in the maximum hardness values and a fine microstructure that correlated to desired Condition A hardness values (30-35 HRC) and microstructure (martensite). The hardness values and percent porosity of the six configurations were in the range of hardness values (26 HRC-34 HRC) and percent porosity values (1%-13%) reported in the literature.