Jul 10, 2017 | By Tess

Researchers from the Oak Ridge National Laboratory (ORNL) and Rice University in Houston, Texas have developed a novel process for creating “damage-tolerant components” made from multiple materials. The innovative process combines 3D printing with traditional casting methods.

Model of a 3D printed preform structure

The research project, entitled “Damage-tolerant metallic composites via melt infiltration of additively manufactured preforms,” shows how the combination of 3D printing with casting can result in optimized parts that are stronger than if they were 3D printed or casted. As the researchers explain, the novel two-step process helps to overcome “issues with intermetallic formation, cracking, and poor resolution” that are endemic of most 3D printing technologies.

The first step of the process developed by ORNL consists of producing a lattice preform structure using selective laser melting (SLM) technology. This lattice functions as a sort of skeleton for the final component. The second step of the process involves infiltrating the preform with a “liquid metal that had a melting temperature lower than that of the reinforcement.”

In their example, the researchers poured an aluminum alloy (A356) over a 3D printed steel lattice made from 316L. The produced part, an “interpenetrating phase composite” (or IPC), was shown to have a higher damage tolerance than a part made purely from aluminum.

Compression tests conducted on the 3D printed composite part showed that the stress-strain response of the part could actually be controlled by simply adjusting the volume fraction and topology of the steel lattice reinforcement. Similarly, tension tests on composites with a 39 vol% of steel demonstrated “an order of magnitude improvement over the strain to failure” compared with the aluminum alloy on its own.

“Inspection of the as-tested tensile specimens suggested that this exceptional damage tolerance is a result of the interpenetrating structure of the constituents,” reads the paper’s abstract. “These results together demonstrate that this infiltration processing route avoids problems with intermetallic formation, cracking, and poor resolution that limit current fusion-based additive manufacturing techniques for printing metallic composites.”

According to the research team, its hybrid manufacturing process could have applications in the automotive industry, which demands parts with optimal thermal and mechanical properties. The composite parts made using the 3D printing-casting combo could meet these required standards.

“This scalable processing strategy can be used to fulfill specific component functions, giving materials designers unprecedented control over both microstructure and material properties,” explained Amit Shyam, an ORNL researcher and author on the study.

“The key advantage of this processing strategy over other fusion-based metal additive manufacturing techniques is that in this two-step process, liquid-phase mixing of the constituents is excluded. As a result, we are able to overcome problems with cracking and poor resolution that limit most of the other fusion-based additive manufacturing techniques for printing composites,” says the report.

The ORNL study was recently published in the journal Materials and Design.



Posted in 3D Printing Technology



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