Fracture Toughness of Cold Sprayed Pure Metals
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Fracture Toughness of Cold Sprayed Pure Metals Ondrej Kovarik1
•
Jan Siegl1 • Jan Cizek2,3 • Tomas Chraska2 • Jan Kondas4,5
Submitted: 28 June 2019 / in revised form: 16 October 2019 ASM International 2019
Abstract The study of fracture toughness of pure Al, Cu, Ni and Ti deposited by cold spray was performed in order to obtain a fundamental understanding of the damage process and quantify the material performance. Rectangular specimens cut from self-standing deposits with fatigue pre-cracks were tested in three-point bending. The KIC values were obtained from J-R curves following the ASTM E1820 standard. The stress–strain behavior of the tested material was obtained from supplementary four-point bending. The cold spray deposits exhibited significantly lower fracture toughness than the corresponding wrought materials. The reduction was more pronounced for coatings with limited ductility (Ti and Cu), where the fracture toughness reached less than 12% of the wrought counterpart only. The higher ductility coatings of Al and Ni possessed fracture toughness of 18–25% of the wrought reference materials. The performed fractographic analysis
This article is an invited paper selected from presentations at the 2019 International Thermal Spray Conference, held on May 26–29, 2019, in Yokohama, Japan, and has been expanded from the original presentation. & Ondrej Kovarik [email protected] 1
Department of Materials, Faculty of Nuclear Science and Physical Engineering, Czech Technical University in Prague, Prague, Czech Republic
2
Institute of Plasma Physics, The Czech Academy of Sciences, Prague, Czech Republic
3
Institute of Materials Science and Engineering, Brno University of Technology, Brno, Czech Republic
4
Impact Innovations GmbH, Rattenkirchen, Germany
5
Department of Mechanical Engineering, Politecnico di Milano, Milan, Italy
revealed inter-particular decohesion as the major failure mode. Keywords cold spray fracture toughness Processing stress–strain
Introduction Cold spray is increasingly used to dimensionally restore worn components in, e.g., aerospace, power or paper industry. Using the technology, mission critical components are frequently repaired (Ref 1), naturally drawing focus to the essential material properties such as strength, yield stress or ductility, as well as fracture mechanical and fatigue properties. Also the emerging application of both thermally and cold sprayed coatings serving as smart materials (Ref 2) enabling, i.e., large area heating, sensing or similar tasks, is demanding reliable estimation of the coating material properties. One of the most important material properties is fracture toughness. It can be characterized by critical value (e.g., KIC or JIC) of the corresponding fracture mechanical parameter (e.g., K or J). The critical value marks a loading at which an existing crack starts to propagate. Most commonly used fracture mechanical parameters include the stress intensity factor K (Ref 3) describing the magnitude of the linear elastic c
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