With new heat treatment, 3D printed metal can withstand extreme conditions

A new heat treatment method developed by MIT transforms the microstructure of 3D printed metals, making the material stronger and more resilient in extreme thermal environments. The technique could make it possible to 3D print high-performance propellers and vanes for gas turbines and power generation jet engines, enabling new designs with improved fuel consumption and energy efficiency.

Of today Gas turbines The blades are manufactured through conventional casting processes in which molten metal is poured into complex molds and solidified in a direction. These components are made from some of the most heat-resistant metal alloys on Earth, as they are designed to spin at high speeds in extremely hot gas, extracting work to generate electricity in electric Factory and push in jet engine.

There is growing interest in manufacturing turbine blades through 3D printing, which, in addition to the environmental and cost benefits, can allow manufacturers to rapidly produce more complex, more energy-efficient production. tongue geometry. But efforts to create 3D-printed turbine blades have yet to address one major obstacle: warping.

In metallurgy, creep refers to the tendency of metals to permanently deform in the face of persistent mechanical stress and high temperatures. While researchers have been exploring printed turbine blades, they have discovered that the printing process produces fine particles tens to hundreds of micrometers in size – a microstructure that is particularly susceptible to creep .

“In practice, this means gas turbines will have a shorter lifespan or be more fuel efficient,” said Zachary Cordero, Boeing Career Development Professor of Aeronautics and Astronautics at MIT. “These are costly, undesirable outcomes.”

Cordero and his colleagues have found a way to improve the structure of 3D printed alloys by adding an additional heat treatment step that turns the fine grains of a printed material into much larger “column” particles — a sturdier microstructure minimizes creep potential material, as the “columns” are aligned with the axis of maximum stress. The method outlined today in , the researchers say Additive productioncleared the way for industrial 3D printing of gas turbine blades.

“In the near future, we envision gas turbine manufacturers printing their blades and vanes at large-scale additive manufacturing plants, then processing them using heat treatment“Cordero said.” 3D printing will enable new cooling architectures that can improve the thermal efficiency of a turbine, so that it generates the same amount of electricity while burning less fuel and ultimately emitting less carbon dioxide. “

Cordero’s co-authors on this study are lead author Dominic Peachey, Christopher Carter and Andres Garcia-Jimenez at MIT, Anugrahaprada Mukundan and Marie-Agathe Charpagne of the University of Illinois at Urbana-Champaign, and Donovan Leonard of the Laboratory. Oak Ridge Country.

Activate a transformation

The team’s new method is a form of directed recrystallization — a heat treatment that sends a material through a hot zone at a precisely controlled rate to combine many of the material’s microscopic particles into crystals. larger, stiffer and more uniform body.

Directed recrystallization was invented more than 80 years ago and has been applied to wrought materials. In their new study, the MIT team adapted the direction recrystallization process for 3D printed superalloys.

The team tested the method on 3D-printed nickel superalloys — metals commonly cast and used in gas turbines. In a series of experiments, the researchers placed 3D-printed rod-shaped superalloy samples in a bath of room-temperature water, directly below an induction coil. They slowly pulled each rod out of the water and through the coil at various speeds, heating the rods dramatically to a temperature that varied from 1,200 to 1,245 degrees Celsius.

They found that drawing the bars at a specific speed (2.5 mm/hr) and through a specific temperature (1,235 degrees Celsius) created a steep thermal gradient that caused variation in the conformation. printed fine-grained microstructure of the material.

“The starting material is tiny grains with defects called dislocations, like a wilted spaghetti dish,” explains Cordero. “When you heat this material up, those defects can annihilate and restructure, and particles can grow. We continuously lengthen the particles by consuming the defective material and particles. smaller — a process called recrystallization.”

Climb

After cooling the heat-treated rods, the researchers examined their microstructure using optical and electron microscopes, and found that the printed microscopic particles of the material were replaced by “column” grains, or elongated crystal-like regions, that are significantly larger than the original grains.

Lead author Dominic Peachey said: “We completely changed the structure. “We show we can increase the particle size by orders of magnitude, into large columnar particles, which should theoretically lead to significant improvements in creep properties.”

The team also showed that they could control the tensile speed and temperature of the rod samples to tune the growing grain of the material, creating regions of specific grain sizes and orientations. This level of control could allow manufacturers to print turbine blades with site-specific microstructures that are resilient to specific operating conditions, says Cordero.

Cordero plans to test the heat treatment on 3D printed geometries that more closely resemble turbine blades. The team is also exploring ways to speed up suction, as well as testing the creep resistance of the heat-treated structure. They then envisioned that heat treatment could enable the practical application of 3D printing for manufacturing turbine tongue, with more complex shapes and patterns.

“The new wing and blade geometry will enable more energy-efficient land-based gas turbines, as well as ultimately aviation engines,” notes Cordero. “From a fundamental perspective, this could lead to lower carbon dioxide emissions, just through improving the efficiency of these devices.”

This story is republished with permission from MIT News (web.mit.edu/newsoffice/), a popular website that covers news about MIT research, innovation, and teaching.