In this study the crack evolution and fracture toughness of HfO2/SiCN(O) ceramic nanocomposites were studied. These ceramics crack radially under indentation in contrast to Hertzian crack in SiOC ceramics. This difference was attributed to the variance in Poisson's ratio and elastic modulus to hardness ratio. Fracture toughness by crack opening displacement and radial crack length measurement was 0.8-1.2 MPa.m1/2 and 2.5-3 MPa.m1/2, respectively. The open network forming structure resulted in the over estimation of fracture toughness value by RCL. © 2015 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.

Ravi Kumar

Department of Metallurgical and Materials Engineering

Ravindran Sujith

Andre Zimmermann

Ceramic materials

Cracks

Hafnium oxides

Nanocomposites

Silicon compounds

CERAMIC NANOCOMPOSITES

CRACK EVOLUTION

CRACK OPENING DISPLACEMENTS

Fracture toughness values

HARDNESS RATIO

OVER-ESTIMATION

POLYMER DERIVED CERAMIC NANOCOMPOSITES

RADIAL CRACKS

Fracture toughness

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

Advanced Engineering Materials

Investigation on the room temperature strain rate sensitivity using depth sensing nanoindentation is carried out on precursor derived HfO 2/Si-C-N(O) ceramic nanocomposite sintered using pulsed electric current sintering. Using constant load method the strain rate sensitivity values are estimated. Lower strain rate sensitivity of ∼ 3.7 × 10 -3 is observed and the limited strain rate sensitivity of these ceramic nanocomposites is explained in terms of cluster model. It is concluded that presence of amorphous Si-C-N(O) clusters are responsible for the limited flowability in these ceramics. © 2014 Author(s).

Fulltext

AIP Advances

Room temperature strain rate sensitivity in precursor derived HfO 2/Si-C-N(O) ceramic nanocomposites

The deformation behavior of pulsed electric current sintered silicon oxycarbide ceramics produced by the solid-state thermolysis of polyhydridomethylsiloxane at small-scale is investigated. The ceramics remained X-ray amorphous after sintering at 1300 °C in vacuum and a high density of ≈2.35 g cm-3 is achieved. The elastic constants of these ceramics are determined using non-destructive ultrasonic testing method. The elasto-plastic deformation under contact loading is determined using depth sensing nanoindentation technique. An indentation hardness of ≈11 GPa and reduced elastic modulus of ≈105 GPa is observed. The load-displacement curves display significant elastic recovery with an elastic work ratio of ≈0.71. The evolution of Hertzian cone cracks upon microindentation indicates an anomalous deformation behavior. Small-scale deformation behavior of pulsed electric current sintered silicon oxycarbide ceramics is investigated. The ceramics remained X-ray amorphous after sintering at 1300 °C in vacuum and a high density of ≈2.35 g cm-3 is achieved. An indentation hardness of ≈11 GPa and reduced elastic modulus of ≈105 GPa is observed. The load-displacement curves display significant elastic recovery with an elastic work ratio of ≈0.71. The evolution of Hertzian cone cracks upon microindentation indicates an anomalous deformation behavior. © 2013 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.

Small-scale deformation of pulsed electric current sintered silicon oxycarbide polymer derived ceramics

The influence of pulsed electric current sintering on the structural evolution and indentation response of hafnia incorporated silicon carbonitride polymer derived ceramics was studied. Despite the absence of any sintering additives, appreciable sintering at 1400 C with a density of ∼2.7 g/cc was observed. Sintering beyond 1300 C resulted in the phase separation and nano-crystallization of amorphous Si-Hf-C-N-O ceramic. The crystallite coarsening was insignificant and thereby the tetragonal phase of hafnia was retained in the ceramic nanocomposite. A relatively high indentation hardness and elastic modulus of ∼18 GPa and ∼313 GPa were determined by depth sensing nanoindentation technique. © 2013 Elsevier Ltd and Techna Group S.r.l.

Ceramics International

Indentation response of pulsed electric current sintered polymer derived HfO2/Si-C-N(O) nanocomposites

Hafnium alkoxide modified polysilazane was synthesized by the drop-wise addition of hafnium tetra(n-butoxide) to polysilazane. The solid state thermolysis (SST) temperature and the ceramic yield for both the polysilazane and modified polysilazane were determined by performing thermogravimetry. Fourier transform infrared spectroscopy was performed to understand the polymer to ceramic conversion as well as the bonding characteristics of the ceramics. The modified polymer after crosslinking was subjected to SST at 800 °C at a constant heating rate of 5 °C/min for a dwell time of 2 h in atmospheric ambience. From the X-ray diffractograms, the as-thermolysed ceramics were observed to remain X-ray amorphous and on heat-treatment resulted in the crystallization of tetragonal hafnia. However, on heat-treatment at 1500 °C, reverse phase transformation from tetragonal to monoclinic hafnia was observed. Raman spectroscopy and transmission electron microscopy were employed to further understand the phase evolution. The thermal stability and the influence of amorphous matrix on the coarsening of HfO 2 were also evaluated. © 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Synthesis and phase stability of precursor derived HfO 2/Si-C-N-O nanocomposites

Acta Materialia

Composition dependence of indentation deformation and indentation cracking in glass

Crack Evolution and Estimation of Fracture Toughness of HfO2/SiCN(O) Polymer Derived Ceramic Nanocomposites

Journal	Data powered by TypesetAdvanced Engineering Materials
Publisher	Data powered by TypesetWiley-VCH Verlag
ISSN	14381656
Open Access	No