In a technology business, it’s generally out with the old, in with the new, right? Well, in the case of measuring part oxidation, not so fast, my friend!
Aviation’s mach 1 oxidation facility in Lynn, Massachusetts is a unique and significant operation that still utilizes the original test cell that validated America’s first jet engine (the GE 1-A, circa 1940) to help determine what coatings and alloys are best suited for today’s engine parts.
Over the years, nearly all alloys and coatings applied to GE hot-section components have been tested in the Bldg. 34 north test cell (code named “Fort Knox” during WWII).
This test cell was repurposed in the 1960s with equipment that simulates conditions in an engine. As jet engines operated at increasingly higher temperatures, traditional materials proved unequal to the task and the business needed a better way to quickly characterize a material’s environmental durability before committing to production.
The equipment subjects test specimens to high-velocity air (near mach 1) at temperatures as high as 2,250°F. In 2006, the facility was further contemporized with digital capability to evaluate material loss as a function of exposure.
A carousal of 24 pins comprised of various alloy/coating combinations is loaded onto a test rig that replicates the conditions within the hot section of a jet engine. The cell is directly linked to a computer system that controls and monitors key test parameters.
The pins are taken back to the Materials & Process Engineering Department where they are individually assessed further using a sophisticated, high-powered 3D digital macroscope that uses high-intensity LED light and a monochrome device to capture the specimen’s surface topography. This system generates a staggering amount of data that is analyzed by computer scripts and then coupled with a sophisticated measurement tool to make 3D digital maps of oxidized test samples that better quantifies rates of degradation of hot-section parts.
“Environmental durability is a key metric for our customers. Using alloys and coatings that resist oxidation mean an engine can stay in service longer. More time on wing translates to better value,” said John Graves, principal engineer in the materials & process engineering department who helped develop the new methods.
This testing has also helped prove the viability of CMCs for use in GE engines.
“While there’s no substitute for extensive qualification testing, putting new alloys and coatings directly into an engine is a time consuming and expensive approach,” added Andy Perry, subsection manager for materials application engineering in Lynn. “This test enables us to compare alloys and coatings under conditions that simulate the engine hot section at a fraction of the cost. So we can pick and choose the appropriate combination to meet the customer’s needs.”
In laymen’s terms, this testing helps determine that alloy “A” is better suited than alloy “B/C/D” for a particular part, and also produces a comprehensive data set to document why and by how much. This also helps the business and its customers determine more precisely when to replace a part based on oxidation of materials.
The data generated by this test is now being used as the foundation for oxidation curves that design engineers can use to better assess environmental durability of hot section components.