Rhenium diboride (ReB2) exhibits high differential strain due to its puckered boron sheets that impede shear deformation. Here, we demonstrate the use of solid solution formation to enhance the Vickers hardness and differential strain of ReB2. ReB2-structured solid solutions (Re0.98Os0.02B2 and Re0.98Ru0.02B2, noted as “ReOsB2” and “ReRuB2”) were synthesized via arc-melting from the pure elements. In-situ high-pressure radial x-ray diffraction was performed in the diamond anvil cell to study the incompressibility and lattice strain of ReOsB2 and ReRuB2 up to ∼56 GPa. Both solid solutions exhibit higher incompressibility and differential strain than pure ReB2. However, while all lattice planes are strengthened by doping osmium (Os) into the ReB2 structure, only the weakest ReB2 lattice plane is enhanced with ruthenium (Ru). These results are in agreement with the Vickers hardness measurements of the two systems, where higher hardness was observed in ReOsB2. The combination of high-pressure studies with experimentally observed hardness data provides lattice specific information about the strengthening mechanisms behind the intrinsic hardness enhancement of the ReB2 system.
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Synthesis and Thermal Oxidation Resistance of Boron-Rich Boron–Carbide Material
A boron-rich boron–carbide material (B4+δC) was synthesized by spark plasma sintering of a ball-milled mixture of high-purity boron powder and graphitic carbon at a pressure of 7 MPa and a temperature of 1930 °C. This high-pressure, high-temperature synthesized material was recovered and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, Vickers hardness measurements, and thermal oxidation studies. The X-ray diffraction studies revealed a single-phase rhombohedral structure (space group R-3m) with lattice parameters in hexagonal representation as a = 5.609 ± 0.007 Å and c = 12.082 ± 0.02 Å. The experimental lattice parameters result in a value of δ = 0.55, or the composition of the synthesized compound as B4.55C. The high-resolution scans of boron binding energy reveal the existence of a B-C bond at 188.5 eV. Raman spectroscopy reveals the existence of a 386 cm−1 vibrational mode representative of C-B-B linear chain formation due to excess boron in the lattice. The measured Vickers microhardness at a load of 200 gf shows a high hardness value of 33.8 ± 2.3 GPa. Thermal gravimetric studies on B4.55C were conducted at a temperature of 1300 °C in a compressed dry air environment, and its behavior is compared to other high-temperature ceramic materials such as high-entropy transition metal boride. The high neutron absorption cross section, high melting point, high mechanical strength, and thermal oxidation resistance make this material ideal for applications in extreme environments.
more » « less- Award ID(s):
- 2148897
- NSF-PAR ID:
- 10467689
- Publisher / Repository:
- MDPI, Basel, Switzerland.
- Date Published:
- Journal Name:
- Materials
- Volume:
- 16
- Issue:
- 19
- ISSN:
- 1996-1944
- Page Range / eLocation ID:
- 6526
- Subject(s) / Keyword(s):
- ["Undergard Research Project","boron\u2013carbon system","thermal oxidation","extreme environments","mechanical properties","Raman spectroscopy"]
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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