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Adjusting the microchemistry of alloys for flawless metallic 3D printing – sciencedaily

By on September 28, 2021 0


Over the past decades, metal 3D printing has spearheaded efforts to create custom parts with complex shapes and high functionality. But as additive makers have included more alloys for their 3D printing needs, so too has creating uniform, flawless parts.

A new study by researchers at Texas A&M University has further refined the process of creating high-quality metal parts using powder-bed laser fusion 3D printing techniques. Using a combination of machine learning and single-channel 3D printing experiments, they identified favorable alloy chemistries and process parameters, such as laser speed and power, needed to print parts. with uniform properties at the microscopic scale.

“Our initial challenge was to make sure that there are no pores in the printed parts, as this is the obvious killer to create objects with improved mechanical properties,” said Raiyan Seede, doctoral student in the Department of materials science and engineering. “But after addressing this challenge in our previous work, in this study we dive deep into fine-tuning the microstructure of alloys so that there is more control over the properties of the final printed object at a scale. much thinner than before. “

The researchers published their results in the journal Additive manufacturing.

Like other 3D printing methods, powder bed laser melting also makes it possible to build 3D metal parts layer by layer. The process begins by rolling a thin layer of metal powder onto a base plate and then melting the powder with a laser beam along tracks that outline the cross-sectional design of the intended part. Then another coat of powder is applied and the process is repeated, gradually building up the final piece.

Metal alloy powders used for additive manufacturing can be very diverse, containing a mixture of metals, such as nickel, aluminum and magnesium, in different concentrations. When printing, these powders cool quickly after being heated by a laser beam. Since the individual metals in the alloy powder have very different cooling properties and therefore solidify at different rates, this shift can create a type of microscopic defect called microsegregation.

“When the alloy powder cools, individual metals can precipitate,” Seede said. “Imagine pouring salt into water. It dissolves immediately when the amount of salt is low, but when you pour in more salt, the excess salt particles that do not dissolve start to precipitate out as crystals. This is basically what happens in our metal. alloys when they cool rapidly after printing. “

He said this defect shows up as tiny pockets containing a slightly different concentration of the metallic ingredients compared to other regions of the printed part. These inconsistencies compromise the mechanical properties of the printed object.

To rectify this micro-defect, the research team studied the solidification of four alloys containing nickel and another metallic ingredient. In particular, for each of these alloys, they studied the physical states or phases present at different temperatures for increasing concentrations of the other metal in the nickel-based alloy. Thus, from detailed phase diagrams, they could determine the chemical composition of the alloy that would lead to minimal microsegregation during additive manufacturing.

Then they melted a single track of the alloy metal powder for different laser settings and determined the process parameters that would result in parts without porosity. Then, they combined the information gathered from the phase diagrams with that from the single lane experiments to get a consolidated view of the laser parameters and nickel alloy compositions that would produce a printed part without porosity and microsegregation.

Finally, the researchers took it a step further and trained machine learning models to identify patterns in their single track experimental data and phase diagrams to develop a microsegregation equation applicable to any other alloy. Seede said the equation is designed to predict the extent of segregation given the solidification range, material properties, and laser power and speed.

“Our methodology facilitates the successful use of alloys of different compositions for additive manufacturing without worrying about introducing defects even at the microscopic scale,” said Dr Ibrahim Karaman, Professor Chevron I and Head of the Department of materials science and engineering. “This work will be of great benefit to the aerospace, automotive and defense industries which are constantly on the lookout for better ways to manufacture custom metal parts.”

Research collaborators Dr Raymundo Arroyavé and Dr Alaa Elwany added that the uniqueness of their methodology is its simplicity, which can easily be adapted by industries to build strong and flawless parts with a choice alloy. They noted that their approach contrasts with previous efforts which relied mainly on expensive and time-consuming experiments to optimize treatment conditions.

Arroyavé is Professor in the Departments of Materials Science and Engineering and Elwany is Associate Professor in the Department of Industrial and Systems Engineering at Wm Michael Barnes ’64. Other contributors to this research include Austin Whitt and William Trehern from the Department of Materials Science and Engineering and Jiahui Ye from the Department of Industrial and Systems Engineering.

The research is supported by the United States Army Research Office and the National Science Foundation.