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. 2017 Apr 27;10(5):461.
doi: 10.3390/ma10050461.

Effects of HfB₂ and HfN Additions on the Microstructures and Mechanical Properties of TiB₂-Based Ceramic Tool Materials

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Free PMC article

Effects of HfB₂ and HfN Additions on the Microstructures and Mechanical Properties of TiB₂-Based Ceramic Tool Materials

Jing An et al. Materials (Basel). .
Free PMC article

Abstract

The effects of HfB₂ and HfN additions on the microstructures and mechanical properties of TiB₂-based ceramic tool materials were investigated. The results showed that the HfB₂ additive not only can inhibit the TiB₂ grain growth but can also change the morphology of some TiB₂ grains from bigger polygons to smaller polygons or longer ovals that are advantageous for forming a relatively fine microstructure, and that the HfN additive had a tendency toward agglomeration. The improvement of flexural strength and Vickers hardness of the TiB₂-HfB₂ ceramics was due to the relatively fine microstructure; the decrease of fracture toughness was ascribed to the formation of a weaker grain boundary strength due to the brittle rim phase and the poor wettability between HfB₂ and Ni. The decrease of the flexural strength and Vickers hardness of the TiB₂-HfN ceramics was due to the increase of defects such as TiB₂ coarse grains and HfN agglomeration; the enhancement of fracture toughness was mainly attributed to the decrease of the pore number and the increase of the rim phase and TiB₂ coarse grains. The toughening mechanisms of TiB₂-HfB₂ ceramics mainly included crack bridging and transgranular fracture, while the toughening mechanisms of TiB₂-HfN ceramics mainly included crack deflection, crack bridging, transgranular fracture, and the core-rim structure.

Keywords: TiB2-HfB2 ceramics; TiB2-HfN ceramics; hot-pressed sintering; mechanical properties; microstructure.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
XRD patterns of TiB2-HfB2 and TiB2-HfN ceramic tool materials.
Figure 2
Figure 2
SEM-BSE photographs of the polished surfaces of TiB2-HfB2 and TiB2-HfN ceramic tool materials: (a) TiB2-10 wt % HfB2; (b) TiB2-20 wt % HfB2; (c) TiB2-30 wt % HfB2; (d) TiB2-10 wt % HfN; (e) TiB2-20 wt % HfN; (f) TiB2-30 wt % HfN.
Figure 3
Figure 3
EDS of the phases in the TiB2-HfB2 ceramic tool materials: (a) EDS of the dark phase; (b) EDS of the white phase, and EDS of the phases in the TiB2-HfN ceramic tool materials; (c) EDS of the dark phase; (d) EDS of the white phase; (e) EDS of the grey phase.
Figure 4
Figure 4
Fracture morphology of TiB2-HfB2 and TiB2-HfN ceramic tool materials: (a) TiB2-10 wt % HfB2; (b) TiB2-20 wt % HfB2; (c) TiB2-30 wt % HfB2; (d) TiB2-10 wt % HfN; (e) TiB2-20 wt % HfN; (f) TiB2-30 wt % HfN.
Figure 5
Figure 5
Relative densities of TiB2-HfB2 and TiB2-HfN ceramic tool materials.
Figure 6
Figure 6
Variation of the mechanical properties of TiB2-HfB2 ceramics with a change of the HfB2 content and variation of the mechanical properties of TiB2-HfN ceramics with a change of the HfN content.
Figure 7
Figure 7
Crack propagation path of the TiB2-HfB2 (a) and TiB2-HfN (b) ceramic tool materials.

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