Densification behavior of 316L-NiB stainless steel powder and surface morphology during selective laser melting process using pulsed Nd:YAG laser

Abstract

Purpose: This paper aims to report the production of 316L-1 Wt.% NiB cubes by using the selective laser melting (SLM) process. The laser used was pulsed, millisecond Nd:YAG system with maximum average power 100 W. Design/methodology/approach: Densification under different processing conditions (pulse energy, average laser power, laser scan speed, powder layer thickness, pulse frequency) was investigated. Morphology, macro and microstructure of laser melted samples were characterized by digital camera images and by scanning electron microscope. Density of the cubes was determined by Archimedes method in water. Vickers microhardness of samples was determined under the load of 25 g. Corrosion behavior of 316L and 316L-NiB samples was conducted in 5 per cent HCl solution at the testing temperature of 20°C during 240 h. Findings: Using laser power of ∼60-70 W, lower beam overlap and powder layer thickness of 200 µm, 3D cubical samples were obtained with significant balling in individual layers and an overall porosity being around 30 per cent. By increasing laser power to ∼80 W, with higher beam overlap and lower powder layer thickness of 100 µm, SLM parts with no balling and the presence of small pores of up to 4 per cent (20 Hz) and 9 per cent (40 Hz) were obtained. With further increase of laser power to 90 W, overall porosity rose to around 12 per cent. The addition of 1 Wt.% NiB to stainless steel negligibly lowered its corrosion resistance in 5 per cent HCl solution. Originality/value: A part from 316L stainless steel with balling-free structure and good density was successfully obtained through pulsed-SLM process with the aid of 1 Wt.% of NiB addition. Aside from significant influence on the improved structure of cubes, NiB had a favorable effect on microhardness values while practically not affecting the corrosion resistivity of the base material in an aggressive surrounding. © 2018, Emerald Publishing Limited.