Characterization of bulk bimodal polycrystalline nickel deformed by direct impact loadings

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 601; pp. 48 - 57
• Main Authors: Dirras, G., Tingaud, D., Csiszár, G., Gubicza, J., Couque, H., Mompiou, F.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 17.04.2014; Elsevier
• Subjects: Applied sciences; Bimodal microstructure; Condensed matter: structure, mechanical and thermal properties; Defects and impurities in crystals; microstructure; Dislocations; Exact sciences and technology; Hardness; Impact; Linear defects: dislocations, disclinations; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Nanohardness; Nickel; Physics; Spark plasma sintering; Structure of solids and liquids; crystallography; Impact; Nanohardness; Spark plasma sintering; Nickel; Bimodal microstructure; Dislocations; Line shape; Volume fraction; Polycrystal; Hardness; Composite material; Dislocation; Fragmentation; Dislocation density; Dislocation velocity; Crystallites; Dual phase structure; Fine grain structure; Microstructure; Crack; Recovery (properties); X-ray line profile analysis; Dislocations (crystals); Micrometer sized particles; Velocity; Bi-modal microstructures; Cracks; Dislocation densities; Grain fragmentation; Micro-structure evolutions; Polycrystalline nickels
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2014.02.043

Spark plasma sintering of a blend of powders with nanometer and micrometer sized particles yielded to a composite-like nickel microstructure consisting of ultrafine-grained (UFG) and coarse-grained (CG) volumes with the fractions of 36% and 64%, respectively. Microstructure evolution and nanohardness distributions of specimens submitted to impact loading at various velocities between 12 and 50ms−1 were determined. At a velocity of 12ms−1, cracks were formed in the UFG regions but they were stopped by the CG entities. Higher velocities resulted in crack-free microstructures and considerable grain fragmentation within CG regions. X-ray line profile analysis investigations showed a decrease of mean crystallite size from ~104 (initial state) to ~41nm (highest velocity). The dislocation density first increased up to 20ms−1 then it decreased considerably with increasing impact velocity, indicating recovery in the microstructure due to the conversion of plastic work into heat. Accordingly, the average nanohardness decreased with increasing the velocity from 20 to 31ms−1. No difference between the microstructures impacted at 31 and 50ms−1 was observed.