Vljudno vabljeni na predavanje, ki bo potekalo v
petek, 23. avgusta, ob 11. uri na Fakulteti za strojništvo Univerze v Ljubljani v predavalnici II/3b
What we have learned in the last ten years of Additive Manufacturing of NiTi
Prof. Dr. Mohammad Elahinia
Mechanical, Industrial and Manufacturing Engineering Department
University of Toledo, USA
Shape memory alloys are a group of smart materials with two unique properties, i.e., shape memory effect and superelasticity, and are widely used in many biomedical and engineering applications. Since shape memory alloys are known as hard-to-machine materials, conventional manufacturing techniques thus have difficulties to produce advanced (e.g., porous) geometries as required in many applications. In the recent years, additive manufacturing of shape memory alloys (particularly NiTi alloy) has shown promising results for manufacturing of shape memory parts. Additive manufacturing (AM) of NiTi has been mainly studied with the laser powder bed fusion (LPBF) technique. At the early stage of these studies, the printability and processing of NiTi were investigated to produce dense parts. Building on the results of the printability map, the involved process parameters (PPs) have been optimized to improve the properties. While low volumetric energy density–the combined effect of laser power, scanning speed, hatch distance, and layer thickness– results in parts with a lack of fusion and formation of cracks, high volumetric energy density leads to element evaporation and unintended porosity. Other PPs, including scanning strategy and build direction, have shown an impact on the microstructure, texture, and thermomechanical response of the part. Recently, AM of NiTi has also been conducted in Direct Energy Deposition (DED) and Binder Jetting (BJ). In laser wire DED, laser power and scanning speed in the range of 400-1000 W and 300-900 mm/min, respectively, were evaluated to obtain optimized PP to print defect-free parts. The quality was assessed by lack of fusion, wire stubbing and dripping, melt pool characteristics, and hardness measurements. BJ, a more cost-effective method, holds the advantage of eliminating direct exposure to high temperatures and consequently reducing cracks, residual stress, and warping. Optimization of sintering of the green part has been studied by investigating the effect of chamber atmosphere (argon/vacuum) and sintering temperature (1250 – 1350 °C) for different binder saturation levels on density and dimensional accuracy.
Kratek CV predavatelja:
Prof. dr. Mohammad Elahinia, currently serving as Interim Dean of the College of Engineering, was most recently the Chair and a Professor in the Department of Mechanical, Industrial and Manufacturing Engineering (MIME). He serves as Director of the Dynamic and Smart Systems Laboratory at The University of Toledo. Dr. Elahinia’s research interests are in smart and active materials. His current research is focused on additive manufacturing of functional materials such as shape memory alloys for aerospace and biomedical application. At University of Toledo, he has served as an investigator on several funded projects with a total budget of more than $15 million.
Doc. dr. Jaka Tušek, Laboratorij za nelinearno mehaniko LANEM