Enhanced densification and mechanical properties of β-boron by in-situ formed boron-rich oxide

Haibo Zhang, Metin Örnek, Simanta Lahkar, Shuangxi Song, Xiaodong Wang, Richard A. Haber, Kolan Madhav Reddy

Research output: Contribution to journalArticlepeer-review


We report nearly full densification of polycrystalline rhombohedral beta (β)-boron without the addition of sintering aids via spark plasma sintering (SPS). The analytical aberration corrected transmission electron microscope observations have revealed in-situ growth of nanocrystalline boron-rich oxide precipitates that contain approximately 4 at.% of oxygen and beget the densification of β-boron. Further electron energy loss spectroscopy and diffraction analysis confirmed that the newly formed boron-rich oxide (nominally B96O4) structure with B-O σ-bonding belongs to space group R3¯m. Depth sensitive nanoindentation showed boron-rich oxide phase has a hardness of about 41 ± 2 GPa, which is 10% higher than that of β-boron matrix. The estimated hardness and fracture toughness of β-boron were approximately 31 GPa and 2.2 MPa m1/2, respectively, using Vickers microindentation, which falls in the range of those commercially used boron carbides. These results suggest that the enhanced densification and mechanical properties arise from the newly formed boron-rich oxide in β-boron during SPS experiments.

Original languageEnglish (US)
Pages (from-to)148-160
Number of pages13
JournalJournal of Materials Science and Technology
StatePublished - Feb 10 2022

All Science Journal Classification (ASJC) codes

  • Ceramics and Composites
  • Mechanics of Materials
  • Mechanical Engineering
  • Polymers and Plastics
  • Metals and Alloys
  • Materials Chemistry


  • Boron
  • Mechanical properties
  • Precipitates
  • Sintering
  • Transmission electron microscopy


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