Recently, the American Oak Ridge National Laboratory (ORNL) has developed a heat-resistant molybdenum alloy formula called "Mighty Mo" (super strong molybdenum), which can be used with electron beam melting (EBM) 3D printing. This alloy can withstand Extreme temperatures can even meet the demanding requirements of aerospace applications.
According to reports, this super strong molybdenum is composed of a mixture of molybdenum and titanium carbide (TiC) powder, which overcomes the brittleness and easy oxidation of this type of alloy. After (EMD) printing, the metal matrix composite material will produce dense, crack-free parts that can withstand extreme temperatures. Mike Kirka of ORNL said: "Our results show that it is feasible to use mechanically alloyed metal matrix composite powders." "The structure formed by the molten powder can withstand high temperatures, which indicates that molybdenum and its alloys can be used in aerospace. And energy conversion applications."
As a refractory metal, molybdenum has multiple properties that make it an attractive choice for deployment in ultra-temperature sensitive areas. The characteristic of this alloy is that the melting point rises to 2622°C, and the coefficient of thermal expansion, thermal conductivity and corrosion resistance are low, but its toughness is also poor at certain temperatures. In addition, molybdenum is extremely sensitive to nitrogen and oxygen contamination during processing, which can cause segregation of its grain boundaries and cause cracking of parts. In the limited research that has been conducted in this field, scientists have mixed metals with other materials in an attempt to better control their recrystallization and grain size, but with little success.
As early as 2017, researchers from the Austrian powder manufacturer Plansee Group tried to use simulation data to quantify how the particle size of molybdenum contributed to its SLM printing sensitivity, but did not completely solve the problem. In contrast, the ORNL team has now discovered that by adding TiC particles to the alloy and converting to EBM, it is possible to create a microstructure with a higher level of robustness and rigidity.
To formulate the material, the scientists mixed Mo and TiC powder in a 60:40 ratio in a graduated cylinder filled with argon to prevent oxidation. Then, a planetary ball mill is used to mechanically alloy the resulting metal matrix composite material for 8 hours until it can be 3D printed. In order to process their new powder, the ORNL team developed a customized ArcamS12 EBM 3D printer, which features an improved build chamber consisting of a piston, feeder, rake, and table powder bed conveying system. The upgrade of the machine effectively optimizes its small batch production, while realizing advanced process monitoring and auxiliary material feeding.
Using their machine, the researchers chose to 3D print six parts measuring 12 mm (D) x 13 mm (H). They have a sandwich-like structure, which contains a layer of strong molybdenum wrapped between two layers of pure molybdenum. . Interestingly, SEM imaging showed that none of the pure samples showed any cracks, but they did have some surface inconsistencies due to the powder dispersion. Later, the research team performed thermodynamic modeling, which also showed that the process is still extremely sensitive to changes in composition and temperature. As a result, ORNL scientists speculate that strict management of process inputs will be the key to the use of molybdenum to manufacture future microstructures without causing changes in the consistency or temperature gradients of the part layers during processing.
In the end, the researchers also concluded that they proved the feasibility of 3D printing pure crack-free molybdenum, and with perfect parameter settings, the alloy can find new applications in the fields of aerospace or energy conversion, such as heat transfer components. .