Tribological comparison of Inconel 625 coatings deposited via laser metal deposition and tungsten inert gas welding process

Abstract

Although different forms of renewable energy sources are in expansion, the oil and natural gas industry remains essential, maintaining its demand for more efficient methods for product transportation. The most productive and safe way is the flow through pipelines. However, pipeline usage directly involves several wear mechanisms, which contribute to pipeline degradation and, consequently, the need for repairs and maintenance shutdowns, implying in heavy financial impact in the entire industrial chain of supply. An economical and feasible solution to mitigate wear is to protect equipment with metallic coatings. Through this technique, engineers can keep the more noble—and expensive—metals only in regions where their chemical and mechanics proprieties are needed. Various processes may be industrially used for coating, presenting different levels of productivity, quality, and required investment. Among the arc welding processes, the most used for coating applications against wear and corrosion is the tungsten inert gas (TIG) process. The laser coating process, or laser metal deposition (LMD), a process concurrent to TIG, can apply such coatings with high precision and reproducibility, minimizing dilution, distortions, lack of fusion, and the formation of a large heat affected zones; however, results may vary. The present work evaluates two dilution-equivalent Inconel 625 coatings through rubber disk tribological testing, microhardness measurements, and worn surface analysis by scanning electron microscopy via energy dispersive x-ray analysis. Each coating was manufactured by one of the mentioned processes, LMD or TIG, with three replicates of each process to observe its repeatability. For the laser manufactured coating, microhardness values averaged to 247 HV, while TIG's average stayed at 218 HV. Volumetric loss due to wear testing behaved differently, with higher values about 16.3% more for TIG when compared to laser coating. The differences between microhardness values and volume losses are explained by crossing information from each coating's cross-section microscopy and worn surface, as well as each process parameterization and nature. In conclusion, LMD coating presented itself as the more efficient process; such a result, in parallel with the continuous advance in laser sources technology, makes a significant contribution to LMD consolidation as the pipeline coating process and a case study with a tribological comparison between two frequently applied processes.