Sintering is the process of turning a powder material into a net-shaped component, that is, one that is close to its final shape, using heat and pressure. A new type of sintering, called Field Assisted Sintering Technology (FAST), uses a pulsed or continuous high density electric current delivered through the pressure mold and the powder to cause very rapid heating and dramatically shorter sintering times. The process can achieve new materials compositions and properties that could not previously be obtained.
The Penn State Applied Research Laboratory (ARL) has acquired three FAST units, likely the most of any academic institution in the country, according to Jogender Singh, senior scientist in ARL and professor of materials science and engineering who oversees the FAST machines and center of excellence. “I started the program in 2008, with a very small R & D unit with a 25-ton capacity,” Singh says.
As the value of the technology became apparent, Singh was able to obtain a larger unit with a 250-ton capacity. Later, with a grant from the Navy, he bought a 320-ton capacity hybrid machine that allows him to sinter parts up to 350 millimeters in diameter.
“The purpose of such a large machine is to let industry come and make a sub-scale or full-scale part and see if the technology is right for them before buying their own expensive machine,” he says. On a tour of the facility, which is part of the Applied Research Lab but located off campus, the industrial scope of the equipment was obvious. The hybrid unit is so large that it needed to be lowered by crane through a large hole cut in the roof. It stands two stories high.
Kennemetal, a powder-metal company based in Western Pennsylvania, was an early funder of his research. When he was able to demonstrate to them that the technology was capable of producing parts with good mechanical properties, they purchased a production unit for their UK branch and had Singh continue with R & D at Penn State. “The technology has been validated by the Navy and Department of Defense and directly transferred into manufacturing,” he says.
FAST could be considered a fusion of two prior technologies – arc welding and high current density diffusion bond welding. Developed and widely used in Japan since the early 1990s, the technology has now spread to Europe and the U.S. Singh convinced the Department of Defense to bring the technology to ARL-Penn State, which is now the leader in FAST R&D in the U.S.
Singh has funding from NASA to develop a prototype hybrid rocket nozzle/thruster, which is being tested for a potential Mars mission. NASA wants thrusters with twice the thrust-to-weight ratio of current components. To reach that goal the Penn State researchers are using FAST to sinter components with extraordinary thermal conductivity, good mechanical properties and light weight. For the Army, Singh is using the technology to make cheaper, lighter body armor composed of ceramic tiles.
“This technology is very effective at making body armor ceramic tiles cost effectively,” he says. “In addition, this allows us to make custom body armor for female soldiers cost effectively and in a very short time.” The process involves digitally scanning the soldier, creating a graphite mold via CNC machining, and sintering boron carbide powder into customized plates.
“We have developed a novel concept for making ceramic tiles with a new architecture,” he adds.
Singh was recently funded by the Army Research Lab to work on hybrid turbine disks. Aerospace engines with gas turbines can be made with lighter, stronger and faster rotating components to increase thrust using FAST.
“This is a revolutionary concept that allows us to make hybrid turbine disks that will allow the aerospace industries to operate the engine at a much higher thrust,” Singh says. “This will lead to lower fuel consumption, higher speed, and better performance.”
NASA has developed a low-density, single-crystal, nickel-based super alloy for turbine blades. However, normal methods of joining components could result in catastrophic failure of the parts due to micro-cracks, residual stress, and large grain size. With FAST technology, the ARL team joined the components with perfect bonding at the interfaces.
FAST has also been used to make highly reflective silicon carbide disks from powder materials for lightweight optics for space applications.
“Every material behaves differently under high pressure and high temperature conditions. So, we have to tailor our processing window for a given material and given net-shaped component. We have experts who design the molds for each component, and those designs are a challenge we are overcoming every day. It’s a team effort involving design engineers, technicians, students, and industry,” Singh concludes.
To learn more about Field Assisted Sintering Technology contact Prof. Jogender Singh at firstname.lastname@example.org.