Many of us can relate to the dreaded experience of dropping our smartphone and desperately hoping the screen doesn’t break as we watch the precious device crash onto the ground.
But if that phone’s screen happened to be made of sapphire, it would be practically shatterproof. That’s just one example of the ways that ceramic materials such as sapphire and zirconia, which boast many superior mechanical, chemical and optical properties, could enable innovative products and new applications.
Ceramic materials are exceptionally strong; sapphire, for instance, is the second-strongest material after diamond. But that strength, as well as the materials’ brittleness, presents some challenges to overcome.
“Ceramic materials have a lot of potential, but the reason they are not widely used by industry is because of limitations with the processing technology,” says Sangkee Min, an assistant professor of mechanical engineering at the University of Wisconsin-Madison. “It’s not possible to fabricate these materials in mass quantities using conventional manufacturing technologies.”
Min seeks to develop new machining strategies for ceramics that would enable companies to adopt these materials for a wide variety of applications.
First, Min needs to deal with the problem of cracks. Conventional machining creates cracks on ceramic surfaces because the crystal structure of the material is prone to fracture.
With support from a prestigious CAREER Award from the National Science Foundation, Min will explore how the forces generated from cutting cause cracks in ceramic materials. Then, with this understanding, he will devise new strategies for machining that will avoid creating those cracks in the first place.
Min says an earlier breakthrough from his lab points to a promising approach for achieving this goal: He made cuts in a ceramic material at a depth of mere nanometers, and he identified certain machining parameters that enabled very smooth cuts, creating super-fine surfaces without any cracks.
Essentially, at that super-small scale, ceramics can be machined like metals—although we don’t yet know the reasons why.
“Why does a brittle, strong ceramic material behave like a soft, ductile material that we can nicely cut in some circumstances?” Min says. “I’m trying to understand the fundamental mechanism for when this material behaves differently than the conventional way. Once we know that, we can come up with different strategies to enable ceramic materials in many industry applications.”
Min’s groundbreaking work in this area is made possible by the unique ultra-precision ROBONANO machine in his lab. The 3D nanoscale milling machine, which Min acquired from the Japanese robotics manufacturer FANUC, is the only machine of its kind in the United States.
In fact, the ROBONANO is so astoundingly precise that Min can make nanoscale cuts through areas where the bonds between individual atoms are weaker. This is a key advantage, he says, because these types of cuts allow him to shape the material without generating the kind of forces that will cause it to fracture.
“Depending on the material’s crystalline structure, and which direction you cut it, sometimes it’s easier to cut, and sometimes it’s more difficult to cut,” says Min, who is also an affiliate of the college’s Grainger Institute for Engineering. “When we understand the circumstances that cause fractures, we can develop mathematical formulas to make predictions and come up with a new strategy of cutting.”
Min is not only excited about the fundamental science he’s investigating with this project but also about the ways his work could benefit industry. He notes that companies are eager to use ceramic materials because of their highly desirable properties.
“For example, the medical industry is very interested because ceramic materials are biocompatible,” Min says. “So you can put them inside the body and their lifespan is going to be much longer than implants made out of titanium or other materials. There is huge potential.”
In addition to sharing the results from this research in journal publications and integrating the knowledge into undergraduate and graduate courses, Min plans to help enhance the training of Wisconsin’s advanced manufacturing workforce. He will work with instructors around the state who lead advanced computer numerical control machine training and help them to integrate this knowledge into their training programs.