Additive-free superhard B4C with ultrafine-grained dense microstructures |
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| Affiliation: | 1. Departamento de Física de la Materia Condensada, Universidad de Sevilla, 41012 Sevilla, Spain;2. Departamento de Ingeniería Mecánica, Energética y de los Materiales, Universidad de Extremadura, 06006 Badajoz, Spain;3. Instituto de Ciencia de Materiales, CSIC-Universidad de Sevilla, 41092 Sevilla, Spain;1. University Limoges, CNRS, ENSCI, SPCTS, UMR 7315, F-87000, Limoges, France;2. CEA Saclay, DEN, DANS, DMN, SRMA, LA2M, Université Paris-Saclay, Gif/Yvette, France;1. State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China;2. Graduate University of the Chinese Academy of Sciences, Beijing 100049, China;1. Department of Materials Science & Engineering, Rutgers University, New Brunswick, NJ, 08854, USA;2. Department of Chemical and Materials Engineering, University of Nevada, Reno, Reno, NV, 89577, USA;3. Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD, 21218, USA;4. U.S. Army Research Lab, Aberdeen Proving Ground, Aberdeen, MD, 21005, USA;5. Survice Engineering Company, Belcamp, MD, 21017, USA;6. Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, MD, 21218, USA;7. Materials and Process Simulation Center, California Institute of Technology, Pasadena, CA, 91125, USA;1. College of Mechanical and Equipment Engineering, Hebei University of Engineering, Handan 056038, China;2. College of Materials Science and Engineering, Hebei University of Engineering, Handan 056038, China;3. State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China |
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| Abstract: | A unique combination of high-energy ball-milling, annealing, and spark-plasma sintering has been used to process superhard B4C ceramics with ultrafine-grained, dense microstructures from commercially available powders, without sintering additives. It was found that the ultrafine powder prepared by high-energy ball-milling is hardly at all sinterable, but that B2O3 removal by gentle annealing in Ar provides the desired sinterability. A parametric study was also conducted to elucidate the role of the temperature (1600–1800 °C), time (1–9 min), and heating ramp (100 or 200 °C/min) in the densification and grain growth, and thus to identify optimal spark-plasma sintering conditions (i.e., 1700 °C for 3 min with 100 °C/min) to densify completely (>98.5%) the B4C ceramics with retention of ultrafine grains (∼370 nm). Super-high hardness of ∼38 GPa without relevant loss of toughness (∼3 MPa m1/2) was thus achieved, attributable to the smaller grain size and to the transgranular fracture mode of the B4C ceramics. |
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| Keywords: | Super-hard ceramics Ultrafine-grained ceramics High-energy ball-milling Spark-plasma sintering |
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