Micro-Twinning in IN738LC Manufactured with Laser Powder Bed Fusion

The build orientation in laser powder bed fusion influences grain structures in nickel-based superalloys. Prior research has shown that equiaxed and textured microstructures form depending on orientation. It was already known that textured microstructures lead to anisotropic mechanical behavior. However, the creep performance of 45°-oriented samples remains unclear. No prior work had resolved why 45°-oriented samples show the lowest time to rupture. This gap motivated further investigation into microstructural effects. The solidification conditions of the PBF-LB/M process remain underexplored in relation to creep behavior. Understanding these effects is crucial for optimizing component design.

This study aimed to evaluate the tensile and creep properties of IN738LC samples built at 0°, 45°, and 90° orientations. The goal was to correlate microstructural features with mechanical performance. The researchers proposed to investigate why 45°-oriented samples show reduced creep resistance. They sought to link microstructure to heat-treated and as-built conditions. The motivation was to improve design practices for additive manufacturing. The focus was on the PBF-LB/M process and its impact on superalloy behavior. The study aimed to provide insights into orientation-dependent mechanical performance. The results could inform future additive manufacturing strategies.

The study used tensile and creep testing at 850 °C and 200 MPa on IN738LC samples. Samples were built at 0°, 45°, and 90° orientations using PBF-LB/M. Microstructural analysis was conducted to assess grain morphology and texture. The researchers compared mechanical properties across orientations. They examined solidification conditions and heat treatment effects. The study included post-build heat treatment to simulate service conditions. Data collection focused on time to rupture and tensile strength. The methods combined mechanical testing with microstructural characterization.

Tensile tests at 850 °C showed expected trends, with 45° samples between 0° and 90° in performance. Creep tests revealed that 45°-oriented samples ruptured fastest at 850 °C and 200 MPa. The 90° orientation demonstrated the longest time to rupture. The 0° orientation showed intermediate creep resistance. The researchers observed microstructural differences linked to build orientation. Textured grains in 45° samples correlated with reduced creep life. The study found that solidification conditions influence grain alignment. These findings suggest a strong orientation-microstructure-mechanical property relationship.

The study concluded that build orientation significantly affects the microstructure and mechanical behavior of IN738LC. The 45° orientation showed the lowest creep resistance due to microstructural effects. The researchers propose that solidification direction influences grain alignment and creep performance. The findings suggest that heat treatment can modify microstructure and improve properties. The authors emphasize the importance of orientation in component design. They recommend considering microstructural effects in additive manufacturing strategies. The results highlight the need for orientation-specific mechanical testing. The study provides insights into optimizing PBF-LB/M processes for superalloys.