Dense (>98%) submicron sized monolithic zirconium diboride (ZrB<inf>2</inf>) was fabricated by reactive spark plasma sintering (RSPS) of 8 h ball milled Zr and B elemental mixtures at 1200 °C. During RSPS, ZrB<inf>2</inf> formed in-situ and the densification takes place by a two-step process. Plastic flow of ZrB<inf>2</inf> resulting from application of higher pressure enhanced densification significantly. Improvement in nanohardness, elastic modulus and indentation fracture toughness were observed with increased sintering pressure. © 2015 Acta Materialia Inc.

Budaraju Srinivasa Murty

Department of Metallurgical and Materials Engineering

Srinivasa Rao Bakshi

N. S. Karthiselva

Borides

Fracture toughness

Low temperature effects

Mechanical Alloying

Mercury (metal)

Milling (machining)

nanoindentation

Spark plasma sintering

Temperature

Zirconium

Zirconium compounds

INDENTATION FRACTURE TOUGHNESS

Low temperature synthesis

MECHANICAL MILLING

Mercury intrusion porosimetry

REACTIVE SPARK PLASMA SINTERING

SINTERING PRESSURE

ULTRA-FINE-GRAINED

ZIRCONIUM DIBORIDE

Sintering

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Scripta Materialia

In this paper, the effect of graphene nano-platelet (GNP) addition on the microstructure and sintering kinetics of ZrB2 during spark plasma sintering (SPS) is presented. SPS was carried out at 1800 °C temperature and 50 MPa pressure. GNP addition resulted in an increase in the relative density from 84% to 97%. Retention of GNPs after SPS was confirmed through Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) in conjunction with X-ray diffraction (XRD) and Raman spectroscopy. The effect of GNP reinforcement on sintering kinetics, microstructure and mechanical properties (Vickers micro hardness and indentation fracture toughness) are discussed. The ZrB2 -GNP samples showed different activation energies at different temperature ranges which are explained based on the likely processes that are involved during sintering. Final stage of sintering exhibited lower activation energy during which the GNP aided grain boundary sliding enhancing the densification. Several toughening mechanisms such as GNP fracture, GNP shearing, GNP bending and GNP pullout were observed. © 2019

International Journal of Refractory Metals and Hard Materials

Effect of graphene nano-platelet addition on the microstructure and spark plasma sintering kinetics of zirconium diboride

Diborides of Zr, Ti and Hf have potential applications as ultrahigh temperature ceramics, armor material, MEMS, substrates for optoelectronic applications and solar absorbers. Previous reports suggest that crystallographically textured diboride compacts have better mechanical and functional properties. Current methods of fabricating textured compacts are either cumbersome or energy and time intensive. We demonstrate a novel method for fabrication of bulk textured TiB2 by reactive spark plasma sintering (RSPS) of Ti-B mixtures having graphene nanoplatelets (GNP) as reinforcement. GNP acted as a template resulting in formation of large TiB2 grains with plate type morphology. X-ray diffraction and Electron backscattered diffraction analysis revealed presence of basal texture in TiB2 – GNP compacts. In comparison to GNP, carbon nanotube addition is shown to result in randomly oriented equiaxed grains. The improvement in indentation fracture toughness indicates GNP is better toughening additive compared to CNT. © 2018 Elsevier Ltd

Carbon

Graphene nanoplatelets induce crystallographic texturing during reactive spark plasma sintering of titanium diboride

In this study, dense fine-grained ZrB2 and TiB2 were fabricated using reactive spark plasma sintering (RSPS) of ball-milled Zr/B and Ti/B mixtures. Systematic investigations were carried out to understand the mechanisms of reactive sintering. Two densification mechanisms were found to be operating during RSPS. The first stage of densification was due to self-propagating high temperature synthesis reaction leading to formation of ZrB2 and TiB2 compacts having relative density of ~48 and ~65%, respectively. The second stage of densification occurred at temperatures more than 1100 °C and resulted in final relative density of more than 98%. Electron backscatter diffraction and electron microscopy studies on interrupted RSPS samples as well as dense samples showed deformed grains and presence of slip steps while grain orientation spread map and pole figure analysis confirmed plastic flow. Plastic flow-aided pore closure is shown as major mechanism during reactive sintering. © 2017 Informa UK Limited, trading as Taylor & Francis Group.

Philosophical Magazine

Densification mechanisms during reactive spark plasma sintering of Titanium diboride and Zirconium diboride

Hafnium carbide (HfC) along with sintering aids was consolidated at a relatively lower temperature i.e. 1600 °C (i.e. T=~0.41 Tm) under a uniaxial load of 50 MPa by spark plasma sintering. Two different sintering aids such as molybdenum disilicide (MoSi2) and carbon nanotube (CNT) were added to enhance the densification and lower the extent of grain growth in the sintered pellets. Density of the sintered pellet increased from 96.0±0.8% in HfC +5 wt% MoSi2 (HM) to 99.0±0.5% with the addition of 2 wt% CNT in HfC+5 wt% MoSi2 (HMC) at sintering temperature of 1600 °C. Further, the extent of grain growth drastically reduced from 204% in HM to 50% in HMC. Analysis of linear shrinkage during densification revealed that CNT addition increased densification rate and decreased the time required to reach the density of 99.0±0.5% at 1600 °C. Increased densification and lower degree of grain growth could be due to the synergistic effect offered by the CNT, which are as follows: (i) Lubrication effect of CNT, (ii) Lower activation energy for grain boundary diffusion (iii) Reduction in liquid phase sintering temperature and (iv) Grain boundary pinning. Fracture toughness of the sintered HM and HMC composite was obtained using indentation technique. By the addition of 2 wt% CNT in HM, drastic increase of 91% in fracture toughness was seen. This significant improvement in fracture toughness was due to the enhanced densification and relatively lower grain size of HMC. Also crack bridging, crack deflection, crack arrest, CNT and graphene sheet pull-out and swording played major role in toughening of HMC pellet. © 2016 Elsevier B.V.

Materials Science and Engineering A

Synergistic effect of carbon nanotube as sintering aid and toughening agent in spark plasma sintered molybdenum disilicide-hafnium carbide composite

Mechanically milled powder mixtures of Titanium and Boron containing 1, 2, 4 and 6 vol% multi-walled carbon nanotubes (CNT) were consolidated by reactive spark plasma sintering resulting in TiB2-TiC-CNT hybrid composites. Addition of CNT was found to affect the reaction rate for TiB2 formation which results in sudden volume shrinkage. Rod shaped TiC were formed due to reaction between Ti and CNT. TiB2-TiC-CNT hybrid composites having more than 96% relative density with nanosized TiB2 grains were obtained. XRD results revealed TiB2 and TiC as major and minor phases respectively. Unreacted CNT were observed in SEM and TEM. TiB2-TiC-CNT composites showed nanohardness of above 25 GPa and elastic modulus of 520 GPa. Indentation fracture toughness was improved by 55% (3.3±0.1 to 5.11±0.6) by the addition of 4 vol% of CNT. The effect of CNT addition on oxidation and co-efficient of thermal expansion is also presented. © 2016 Elsevier B.V.

Carbon nanotube and in-situ titanium carbide reinforced titanium diboride matrix composites synthesized by reactive spark plasma sintering

In this study, the low temperature synthesis of dense titanium diboride (TiB2) compacts by reaction spark plasma sintering (RSPS) of ball milled mixtures of titanium and boron powders is presented. The influence of milling time and sintering temperature on the in-situ reactive synthesis, densification, grain size and mechanical properties of TiB2 was investigated. TiB2 compacts with relative density above 99% have been obtained at a significantly low sintering temperature of 800 °C. X-ray diffraction analysis confirmed the formation of TiB2 along with a small amount of secondary TiB phase. The effect of TiB on the grain size and the hardness and fracture toughness was investigated. TiB2 compacts processed were found to have a nanohardness &gt; 26 GPa and an elastic modulus &gt; 570 GPa and indentation fracture toughness more than 3.30 MP a.m1/2. It is shown that RSPS can be an attractive route for synthesis of ultrahigh temperature ceramics at low temperatures. © 2014 Elsevier Ltd.

Low temperature synthesis of dense TiB2 compacts by reaction spark plasma sintering

Densification mechanisms during hot pressing of ZrB2–20vol.% SiC composite

Journal of the European Ceramic Society

Synthesis, consolidation and characterization of monolithic and SiC whiskers reinforced HfB2 ceramics

Spark-plasma sintering of ZrB2 ultra-high-temperature ceramics at lower temperature via nanoscale crystal refinement

Microstructure characterization of ZrB2–SiC composite fabricated by spark plasma sintering with TaSi2 additive

Low temperature synthesis of dense and ultrafine grained zirconium diboride compacts by reactive spark plasma sintering

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Publisher	Data powered by TypesetElsevier Ltd
Open Access	No