Release Date: March 13, 2017
NETL’s Metallurgical Expertise Reaches New Heights
RS-25 rocket engine. Photo courtesy of NASA.
Extreme environments are everywhere. From the pressures of the ultradeep ocean to the inferno heat of a power plant, harsh conditions make scientific ingenuity a necessity. To operate technology in extreme environments, new materials that can withstand those environments need to be created. Scientists at NETL are known for their ability to do just that.
The three RS-25 engines used to propel NASA’s Space Shuttles are technological marvels. Fueled by liquid hydrogen, they generate intense heat and pressure to create the force necessary to escape the Earth’s atmosphere. During operation, an engine’s main combustion chambers can reach temperatures of 6,000 °F—far hotter than lava or molten steel.
Aerojet Rocketdyne, an American-based rocket and missile propulsion manufacturer, is NASA’s prime contractor for developing and building RS-25 engines. A critical component of the combustion system for this engine is an alloy called NARloy-Z, which is composed of copper, silver, and zirconium. The alloy has excellent heat transfer properties and is resistant to corrosion and oxidation, which make it ideal for use in spaceship design. In fact, the alloy has already been successfully used as a rocket nozzle liner for the Space Shuttle’s main engines and is slated for use in the next generation of launch vehicles.
However, there’s a serious catch. While Rocketdyne’s alloy is an optimal material for space applications, the manufacturing process to create it is extremely inefficient. Typical manufacturing of the alloy starts with 2,600 pounds of the source materials, but the resulting amount of alloy produced is less than 95 pounds—a 94 percent loss of material. One major reason for the loss is zirconium’s tendency to react during melting, causing the formation of inclusions. Inclusions are undesirable foreign particles that can impact alloy performance and must be machined out prior to final part manufacturing or the parts could potentially fail at critical moments.
Consequentially, representatives from Rocketdyne approached NETL and signed a Cooperative Research and Development Agreement to help develop a more efficient and cost-effective process for making NARloy-Z. Accepting the challenge, NETL’s advanced materials team set out to develop a solution to the alloy’s manufacturing flaws. The team began developing computational models to better understand material characteristics and process variables. Using this approach, the team determined that one of the original process steps had been contributing to the development of zirconium inclusions in the alloy.
Using these findings, the team developed a manufacturing process using vacuum induction melting. The process provides control over alloy composition and uniformity through reduced levels of nitrogen and oxygen in the melt, resulting in fewer contaminants being formed within the alloy. With careful control over the process, unwanted impurities could largely be avoided.
Armed with this information, the NETL team developed and optimized a fabrication process that eliminated the formation of inclusions, resulting in improved alloy yield and significant cost savings. The process has subsequently been scaled-up, and the produced alloy is currently undergoing extensive evaluation at Rocketdyne. To date, favorable performance characteristics have been reported—all systems go! NETL anticipates that Rocketdyne will use the new method to manufacture components for the next generation of rocket engines.
On land and in space, NETL’s high-performance materials capabilities are reaching new heights—enabling the deployment of transformational technologies capable of operating in extremely harsh conditions.