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On November 14, 2022, the secretariat of the Yangtze River Delta G60 Laser Alliance learned that the Massachusetts Institute of Technology has developed a new heat treatment method that can change the microstructure of metal 3D printing, making the material stronger and more elastic in extreme heat environments . The technique could make it possible to 3D print high-performance blades for power-generating gas turbines and jet engines. At the same time, new design techniques can be promoted, which means that people can also obtain higher energy conversion efficiency. precision cnc customized CNC production machining
technical background
Today’s gas turbine blades are manufactured through a traditional casting process in which molten metal is poured into complex molds and directionally solidified. These components are made of some of the most heat-resistant metal alloys on Earth because they are designed to spin at high speeds in extremely hot gases, transferring kinetic energy to generate electricity for power plants or provide thrust for jet engines.
There is now growing interest in 3D printing to manufacture turbine blades, which, in addition to its environmental and cost advantages, will allow manufacturers to quickly produce more complex and more energy-efficient blades. But 3D printing turbine blades has always had a big and insurmountable obstacle: creep.
“In practice, that means the gas turbine will either have a shorter lifespan or be less fuel efficient,” said Zachary Cordero, the Boeing Career Development Professor of Aeronautics and Astronautics at the Massachusetts Institute of Technology. precision cnc customized CNC production machining
Cordero and his colleagues found a way to improve the structure of 3D printed alloys by adding an additional heat treatment step that converts the fine grains of the printed material into larger “columnar” grains, which are stronger The microstructure minimizes the creep potential of the material because the “pillars” are aligned with the axis of maximum stress. The method, the researchers say, could pave the way for industrial 3D printing of gas turbine blades.
“In the near future, we envision gas turbine manufacturers, who will print their blades in large 3D printing factories, post-process them by using our heat treatment. 3D printing will enable new cooling architectures, and the benefits of this are The thermal efficiency of the turbine can be increased so that it produces the same amount of power while burning less fuel and ultimately emitting less carbon dioxide.”
triggers microstructural transformations
The team’s new method is a form of directional recrystallization, a heat treatment that passes the material through a hot zone at a precisely controlled rate, fusing the material’s many microscopic grains into larger, stronger, more uniform crystals. precision cnc customized CNC production machining
Directional recrystallization technology was invented more than 80 years ago and has been applied to deformed materials. In their new study, the team used a method of directional recrystallization when 3D printing a nickel-based superalloy. The researchers placed 3D-printed samples of rod-shaped superalloys in a room-temperature water bath directly below an induction coil. They slowly pulled each rod out of the water and through the coils at different speeds, heating the rods significantly to between 1200 and 1245 degrees Celsius.
They found that drawing the rod at a specific speed (2.5 millimeters per hour) and through a specific temperature (1235 degrees Celsius) created a steep thermal gradient that triggered a transformation in the fine-grained microstructure of the printed material.
“The material starts out as small grains with defects called dislocations, like a broken piece of spaghetti,” Cordero explained. “When you heat the material, the defects disappear and reconfigure, and the crystals Grains are able to grow. We continually elongate the grains by consuming defective material and smaller grains, a process called recrystallization.” precision cnc customized CNC production machining
Research result
After cooling the heat-treated rods, the researchers examined their microstructure using optical and electron microscopes and found that the microscopic grains of the printed material were replaced by “columnar” grains, or long crystal-like regions much larger than the original grains.
Lead author Dominic Peachey said: “We have completely changed its structure. We can show that by increasing the grain size by several orders of magnitude, a large number of columnar grains are formed, which in theory should lead to a dramatic improvement in creep performance. “
The team also showed that they could control the speed and temperature at which rod samples were drawn to tune the material’s growing grains, creating regions of specific grain sizes and orientations. “This level of control could allow manufacturers to print turbine blades with position-specific microstructures that can be adapted to specific operating conditions,” Cordero said.
Cordero plans to test the heat treatment on 3D printed geometries closer to turbine blades. The team is also exploring ways to speed up the stretching rate, as well as testing the creep resistance of the heat-treated structures. Then, the practical application of 3D printing was realized through their heat treatment method to produce industrial-grade turbine blades with more complex shapes and patterns.
The research was supported in part by the U.S. Office of Naval Research, the team said. precision cnc customized CNC production machining