Repeatability Analysis of 304L Deposition by the LENS® Process

Sandia National Laboratories is currently engaging in an effort to qualify Laser Engineered Net Shaping™ (LENS®) as a repair and modification process for high rigor metal components. As part of that effort, the LENS team has conducted a process repeatability test to help identify variation within the system. This test utilized 304L stainless steel which is a commonly used material at Sandia. Over the course of 12 weeks, 3/8”x3/8”x2” towers were built in sets of 3 with a total of 30 towers completed. A random sampling of 10 of these towers (1 from each set of 3) had been identified before depositing the towers, and these towers were used for tensile testing and metallographic testing. The testing showed the ultimate and yield strengths of all samples to be well above those of annealed 304L. This is expected because of the rapid melt pool solidification present in the LENS process and the resulting grain refinement. The ductility, which usually remains on par with annealed 304L, was found to be lower. The final cause of this loss of ductility was determined to be inter-layer separation due to loose wires in the closed loop melt pool control system.