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Abstract
This study aims to improve the corrosion resistance of the low carbon steel by cladding it with super duplex stainless steel using laser powder bed fusion process. Critical process parameters such as laser power, laser scan speed, hatch spacing, and powder layer thickness were optimized to achieve the best possible metallurgical bonding between the clad and the substrate. The evaporative losses experienced during the laser melting process resulted in clad layers with lower chromium content (12–25 wt. %) as compared to 26 wt. % of the feedstock powder. A clad thickness of 65.8 µm was achieved after melting ten 50 µm thick powder layers. The higher cooling rates associated with laser powder bed fusion resulted in fine high aspect ratio columnar grain structures with predominantly ferrite grains; however, widmanstätten austenite needles were observed with increasing laser scan speeds. Increasing scan speed had a negative impact on the thickness, corrosion resistance, and the pitting potential of the clads exposed to 3.5 wt.% NaCl aqueous solution. Clads produced at the lowest scan speeds showed comparable corrosion resistance to rolled and annealed super duplex stainless steel.
Highlights
It was observed that the corrosion resistance and other electrochemical properties of the clads produced at lower scan speeds (e.g., 100 mm/s) were comparable to the wrought alloy[20], establishing the feasibility of laser powder bed fusion (LPBF) process for cladding operations to produce corrosion and wear-resistant surfaces
The minor balling around the perimeter is attributed to the changes in melt orientation causing excessive melt splashing and discontinuity in powder spreading at the edge of the clads
The balling phenomenon occurs due to a combination of factors including capillary instability, high scan speeds resulting in melt splashing, little liquid content in melt pools resulting from low or inadequate laser volumetric energy density (VED), and Plateau-Rayleigh instability[35]
Summary
LENS and DED are not suitable for producing clads with micron-level thickness, primarily owing to its powder feed mechanism These methods result in lower-dimensional accuracy, higher material consumption per unit volume of print, and higher surface roughness of the components produced. The LPBF process has considerable advantages over DED/LENS with respect to energy consumption, powder recyclability, dimensional tolerance and defect count in the built parts[11,23,24]. Among these benefits, those related to corrosion performance are important to highlight. It is widely recognized that surface imperfections are detrimental to corrosion properties, for localized corrosion issues such as pitting and crevice corrosion[26]
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