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Toughening of Boron Carbide Composites with Hierarchical Microstructuring.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Toughening of Boron Carbide Composites with Hierarchical Microstructuring./
作者:	Dai, Jingyao.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2021,
面頁冊數:	182 p.
附註:	Source: Dissertations Abstracts International, Volume: 83-06, Section: B.
Contained By:	Dissertations Abstracts International83-06B.
標題:	Applied physics. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28929314
ISBN:	9798494497543

Toughening of Boron Carbide Composites with Hierarchical Microstructuring.
Dai, Jingyao.

Toughening of Boron Carbide Composites with Hierarchical Microstructuring. - Ann Arbor : ProQuest Dissertations & Theses, 2021 - 182 p.

Source: Dissertations Abstracts International, Volume: 83-06, Section: B.

Thesis (Ph.D.)--The Pennsylvania State University, 2021.

With a unique combination of properties including high hardness, high melting point, low density, neutron absorption capability, and semi-conductivity, boron carbide (B4C) is suitable for various structural and multi-functional applications. However, B4C's current applications are limited by its intrinsic brittleness. Previous studies on toughening B4C focused on mechanisms including crack deflection and micro-crack toughening by introducing secondary reinforcement such as titanium diboride (TiB2), zirconium diboride (ZrB2) and crack deflection/bridging by carbon-based nanofillers including carbon nanotubes and graphene nanoplatelets. More recent studies demonstrated novel toughening strategies including grain boundary sliding and nano-pore compression enabled by nanocrystalline, nano-porous B4C. This study pursued toughness enhancement of B4C composites through hierarchical microstructure designs that combine multiple microstructure features including TiB2 particles, graphite platelets, and nanocrystalline, nanoporous B4C phases. Using field assisted sintering technology (FAST) and starting powders of different compositions and particle sizes, three types of B4C composites were fabricated: micro/nano B4C with graphite platelets, micro B4C-TiB2 with in-situ formed micron-sized TiB2 particles, and micro/nano B4C-TiB2 with sub-micron sized TiB2 particles and graphite platelets. Hardness and fracture toughness of these B4C composites were characterized using indentation at micro scale and using four-point bending at macro scale. Fracture toughness enhancement was observed for fabricated B4C composites: 2.38 MPa∙m1/2 for the reference B4C sample, 2.85 MPa∙m1/2 for the micro/nano B4C with ~10 vol% graphite platelets, 3.32 MPa∙m1/2 for the micro B4C-TiB2 with ~15 vol% TiB2, and 3.65 MPa∙m1/2 for the micro/nano B4C-TiB2 with ~15 vol% TiB2 and ~8.7 vol% graphite platelets when measured by the four-point bending. The fabricated micro/nano B4C-TiB2 samples exhibited high fracture toughness while retaining high hardness (31.88 GPa with ~15 vol% TiB2) due to inhibited grain growth, despite the lower hardness of formed graphite platelets and TiB2 particles. Through post-testing microstructure inspection, toughening mechanisms for the fabricated B4C composites were identified as graphite delamination, crack deflection, bridging, and micro-crack toughening. To obtain more understanding about the toughening contribution from each mechanism, micromechanics modeling was conducted for the micro and micro/nano B4C-TiB2 composites which exhibited the highest fracture toughness enhancement. The thermal residual stress resulted from the coefficient of thermal expansion mismatch between B4C and TiB2, and the existence of weak interphases were found to be two main driving factors behind the observed micro-crack toughening behavior. This thesis work demonstrated fracture toughness enhancement, without degradation of hardness, can be achieved through multiple toughening mechanisms enabled by the hierarchical microstructure design with components including TiB2 grains, graphite platelets, etc. The basic process-microstructure-property relations established in this study for B4C composites with hierarchical microstructures will contribute to future microstructure designs of ceramic composites with enhanced fracture toughness.

ISBN: 9798494497543Subjects--Topical Terms:

3343996
Applied physics.
Subjects--Index Terms:

Boron carbide

Toughening of Boron Carbide Composites with Hierarchical Microstructuring.
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500 $a Source: Dissertations Abstracts International, Volume: 83-06, Section: B.
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520 $a With a unique combination of properties including high hardness, high melting point, low density, neutron absorption capability, and semi-conductivity, boron carbide (B4C) is suitable for various structural and multi-functional applications. However, B4C's current applications are limited by its intrinsic brittleness. Previous studies on toughening B4C focused on mechanisms including crack deflection and micro-crack toughening by introducing secondary reinforcement such as titanium diboride (TiB2), zirconium diboride (ZrB2) and crack deflection/bridging by carbon-based nanofillers including carbon nanotubes and graphene nanoplatelets. More recent studies demonstrated novel toughening strategies including grain boundary sliding and nano-pore compression enabled by nanocrystalline, nano-porous B4C. This study pursued toughness enhancement of B4C composites through hierarchical microstructure designs that combine multiple microstructure features including TiB2 particles, graphite platelets, and nanocrystalline, nanoporous B4C phases. Using field assisted sintering technology (FAST) and starting powders of different compositions and particle sizes, three types of B4C composites were fabricated: micro/nano B4C with graphite platelets, micro B4C-TiB2 with in-situ formed micron-sized TiB2 particles, and micro/nano B4C-TiB2 with sub-micron sized TiB2 particles and graphite platelets. Hardness and fracture toughness of these B4C composites were characterized using indentation at micro scale and using four-point bending at macro scale. Fracture toughness enhancement was observed for fabricated B4C composites: 2.38 MPa∙m1/2 for the reference B4C sample, 2.85 MPa∙m1/2 for the micro/nano B4C with ~10 vol% graphite platelets, 3.32 MPa∙m1/2 for the micro B4C-TiB2 with ~15 vol% TiB2, and 3.65 MPa∙m1/2 for the micro/nano B4C-TiB2 with ~15 vol% TiB2 and ~8.7 vol% graphite platelets when measured by the four-point bending. The fabricated micro/nano B4C-TiB2 samples exhibited high fracture toughness while retaining high hardness (31.88 GPa with ~15 vol% TiB2) due to inhibited grain growth, despite the lower hardness of formed graphite platelets and TiB2 particles. Through post-testing microstructure inspection, toughening mechanisms for the fabricated B4C composites were identified as graphite delamination, crack deflection, bridging, and micro-crack toughening. To obtain more understanding about the toughening contribution from each mechanism, micromechanics modeling was conducted for the micro and micro/nano B4C-TiB2 composites which exhibited the highest fracture toughness enhancement. The thermal residual stress resulted from the coefficient of thermal expansion mismatch between B4C and TiB2, and the existence of weak interphases were found to be two main driving factors behind the observed micro-crack toughening behavior. This thesis work demonstrated fracture toughness enhancement, without degradation of hardness, can be achieved through multiple toughening mechanisms enabled by the hierarchical microstructure design with components including TiB2 grains, graphite platelets, etc. The basic process-microstructure-property relations established in this study for B4C composites with hierarchical microstructures will contribute to future microstructure designs of ceramic composites with enhanced fracture toughness.
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653 $a Nanocrystalline, nanoporous B4C
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773 0 $t Dissertations Abstracts International $g 83-06B.
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