Characterization of Inconel and Stainless Steel Coatings Produced through Directed Energy Deposition Method Using Coarse Powders

In this work the laser cladding (LC) process was used to obtain a composite material consisting of a low-cost AISI 1020 substrate with a high-performance corrosion resistance coating. The coating materials included the AISI 304L stainless steel and the 625 and 718 Inconel alloys. The technique used was the pre-deposition of the alloy particles over the substrate with subsequent melting through laser using a Directed Energy Deposition (DED) machine. Focus was placed on evaluating the outcomes of using coarse and/or irregular powders for producing single-layer coatings. Firstly, single tracks were produced using different combinations of laser power and speed in order to determine the best conditions for each alloy. Secondly, the laser tracks were evaluated in relation to their geometric dilution and convexity. The AISI 304L alloy single layer displayed a dilution of 25% for the 500 W/300 mm/min combination while the 625 alloy processed under the same conditions exhibited a dilution of 88%. Finally, after selecting the best laser processing combinations, homogeneous coatings, free of cracks and with low porosity levels were obtained. The coatings were characterized by means of XRD, SEM-EDX, hardness and potentiodynamic polarization in 3.5% NaCl. The dilution of all coatings were also evaluated, with the AISI 304L samples showing the lowest dilution index. Such dilutions significantly influenced the coating corrosion resistances, as they decreased the contents of elements available to face the corrosion action. Considering the current adopted laser conditions, the AISI 304L showed the best corrosion performance, based on E-corr of -0.210 V and an i(corr) of less than 10(-7) A/cm(2). Moreover, the AISI 340L coatings exhibited intermediate surface hardness as compared to the Inconel alloys.