Influence of LP-DED speed (LMD vs EHLA) on corrosion behavior of single layer CRA overlays in marine environments

Corrosion Resistant Alloys (CRA) are high-cost materials but very useful in aggressive environments because of their excellent corrosion resistance, thanks to passivity.

Nowadays, surface modification technology is very useful for the designing of specific surfaces and get multifunctional material in competitiveness price. A growing technology for this application is Laser based Powder Direct Energy Deposition (LPDED) -also known as laser cladding or Laser Metal Deposition (LMD)-. This technology offers a welding speed similar to that of arc welding, leading to dilution of the substrate.

Extreme High Speed Laser application (EHLA) is a novel type of LP-DED and is applied at speeds 10 to 100 times faster than LMD. The aim of this research is to assess the impact on corrosion behavior in 3,5 wt% NaCl of the EHLA speed increase from LMD, when CRA overlays are applied with graded Pitting Resistance Equivalent Number (PREN). The results obtained are the followings: the chemical composition of coating is more similar to cladding powder with EHLA than with LMD, in terms of the microstructure the grain size is bigger with EHLA, induced by thick monolayer welding strategy. From the corrosion point of view and despite harmful phases like iron oxides, laves phases, carbides, etc. There are few interesting things to point out: firstly, corrosion potential has presented different results for each alloy, 316L powder has a more positive value with EHLA technology but with Inconel 625 the corrosion potential is more negative with EHLA. Regarding Pitting potential, in case of 316L there is an improvement comparing with LMD but in case of INCONEL 625 a contradictory effect is observed. The EIS measurements in layers manufactured with EHLA has showed that the 316L capacitive behavior and passive resistance is better than INCONEL 625, affected by the process parameters.

The main conclusion is that EHLA is beneficial for 316L. However, the corrosion resistance of the INCONEL 625 superalloy has worsened.