Researchers from Oak Ridge National Laboratory (ORNL)’s Spallation Neutron Source (SNS) have recently utilized neutron imaging to examine the cooling channels and other inner workings of Inconel 718 turbine blades. The blades were created using additive manufacturing, and the neutron imaging provides a way to nondestructively study the internal structure of the blades in order to improve their design.
Turbine blades are complicated and delicate pieces of engineering. Each blade has cooling channels that allow air to flow through and exit the porous shell of the blade, maintaining a stable temperature for the assembly. Due to their nature, each turbine blade requires a series of rigorous testing procedures in order to verify their structural integrity.
Visually observing the exterior casing of the blades is a simple matter, but capturing images of their internal structure (without physically cutting the turbine blades open) is no easy task. Bernie Riemer, senior research engineer at ORNL, gave a presentation about this topic on the last day of Dassault Systèmes’ Science in the Age of Experience in Chicago. Riemer explained that building a neutron imager is difficult and that the imager at ORNL functions by moving mercury at speeds that are high enough to cause cavitation.
According to Riemer, “A short-pulse proton beam generates an intense pressure wave in the mercury that drives high-cycle fatigue in the target vessel and cavitation of the mercury.” The proton beam initiates a rise in temperature of approximately 107 K/s. Once the beam pulse is finished, pressure interacts with the target, generating a dynamic response. The mercury is also bombarded by neutron flashes at a rate of 60 times per second.
Visual demonstration of a turbine blade flythrough using neutron imaging. The interior surface roughness, as measured with neutrons, can be modeled to study the changes in airflow. (Video courtesy of Oak Ridge National Laboratory.)
The team at ORNL is excited by these breakthroughs in neutron imaging methods and technology. “Neutron sources at ORNL are providing world-class capabilities for characterizing materials,” Riemer said. “The SNS first-of-a-kind mercury target is setting performance records, but we are working hard to increase power and improve reliability.”
Interested in learning more about neutron imaging? Take a look at how Neutron Holograms Reveal Hidden Interiors of Solid Objects.