Texas A&M Develop Method for 3D Printing Hard Steels Flawlessly
For millennia, metallurgists have been meticulously tweaking the ingredients of steel to enhance its properties. As a result, several variants of steel exist today; but one type, called martensitic steel, stands out from its steel cousins as stronger and more cost-effective to produce. Martensitic steels naturally lend themselves to applications in the aerospace, automotive and defense industries, among others, where high-strength, lightweight parts need to be manufactured without boosting the cost. However, for these and other applications, the metals have to be built into complex structures with minimal loss of strength and durability. Researchers from Texas A&M University, in collaboration with scientists in the Air Force Research Laboratory, have now developed guidelines that allow 3D printing of martensitic steels into very sturdy, defect-free objects of nearly any shape.
Although the procedure developed was initially for martensitic steels, researchers from the Texas A&M said they have made their guidelines general enough so that the same 3D-printing pipeline can be used to build intricate objects from other metals and alloys as well. The findings of the study were reported in the December issue of the journal Acta Materialia.
Steels are made of iron and a small quantity of other elements, including carbon. Martensite steels are formed when steels are heated to extremely high temperatures and then rapidly cooled. The sudden cooling unnaturally confines carbon atoms within iron crystals, giving martensitic steel its signature strength.
To have diverse applications, martensitic steels, particularly a type called low-alloy martensitic steels, need to be assembled into objects of different shapes and sizes depending on a particular application. That’s when additive manufacturing, more commonly known as 3D printing, provides a practical solution. Using this technology, complex items can be built layer by layer by heating and melting a single layer of metal powder along a pattern with a sharp laser beam. Each of these layers joined and stacked creates the final 3D-printed object.
However, 3D printing martensitic steels using lasers can introduce unintended defects in the form of pores within the material.
For their experiments, Karaman and the Texas A&M team first chose an existing mathematical model inspired from welding to predict how a single layer of martensitic steel powder would melt for different settings for laser speed and power. By comparing the type and number of defects they observed in a single track of melted powder with the model’s predictions, they were able to change their existing framework slightly so that subsequent predictions improved.
After a few such iterations, their framework could correctly forecast, without needing additional experiments, if a new, untested set of laser settings would lead to defects in the martensitic steel. The researchers said this procedure is more time-efficient.
Other contributors to the research include Austin Whitt and Raymundo Arróyave from the Department of Materials Science and Engineering; David Shoukr, Bing Zhang and Alaa Elwany from the Department of Industrial and Systems Engineering; and Sean Gibbons and Philip Flater from the Air Force Research Laboratory, Florida.
This research is funded by the Army Research Office and the Air Force Research Laboratory.
Source : Strategic Research Institute