Nagamani Jaya Balila | Max Planck Institute for Iron Research (original) (raw)
Supervisors: Vikram Jayaram
Phone: 349
Address: Structure and nano/micro-mechanics Department
MPIE GmbH
Dusseldorf, Germany
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Friedrich-Alexander-Universität Erlangen-Nürnberg
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Papers by Nagamani Jaya Balila
Materials Today Communications, 2021
Microscopy and Microanalysis, 2012
Journal of Materials Research
The influence of Pt layer thickness on the fracture behavior of PtNiAl bond coats was studied in-... more The influence of Pt layer thickness on the fracture behavior of PtNiAl bond coats was studied in-situ using clamped micro-beam bend tests inside an SEM. Clamped beam bending is a fairly well established micro-scale fracture test geometry that has been previously used in determination of fracture toughness of Si and PtNiAl bond coats. The increasing amount of Pt in the bond coat matrix was accompanied by several other microstructural changes such as an increase in the volume fraction of α- Cr precipitate particles in the coating as well as a marginal decrease in the grain size of the matrix. In addition, Pt alters the defect chemistry of the B2-NiAl structure, directly affecting its elastic properties. A strong correlation was found between the fracture toughness and the initial Pt layer thickness associated with the bond coat. As the Pt layer thickness was increased from 0 to 5 µm, resulting in increasing Pt concentration from 0 to 14.2 at% in the B2-NiAl matrix and changing α-Cr precipitate fraction, the initiation fracture toughness was seen to rise from 6.4 to 8.5 MPa.m1/2. R-curve behavior was observed in these coatings, with KIC doubling for a crack propagation length of 2.5 µm. The reasons for the toughening are analyzed to be a combination of material’s microstructure (crack kinking and bridging due to the precipitates) as well as size effects, as the crack approaches closer to the free surface in a micro-scale sample.
The field of micro-/nano-mechanics of materials has been driven, on the one hand by the developme... more The field of micro-/nano-mechanics of materials has been driven, on the one
hand by the development of ever smaller structures in devices, and, on the
other, by the need to map property variations in large systems that are
microstructurally graded. Observations of ‘smaller is stronger’ have also
brought in questions of accompanying fracture property changes in the
materials. In the wake of scattered articles on micro-scale fracture testing of
various material classes, this review attempts to provide a holistic picture of
the current state of the art. In the process, various reliable micro-scale
geometries are shown, challenges with respect to instrumentation to probe
ever smaller length scales are discussed and examples from recent literature
are put together to exhibit the expanse of unusual fracture response of
materials, from ductility in Si to brittleness in Pt. Outstanding issues related
to fracture mechanics of small structures are critically examined for plausible
solutions.
Philosophical Magazine Special Issue on Nanomech-IV, 2015
Journal of Materials Research, 2015
International Journal of Fracture, 2014
Microscopy and Microanalysis , 2013
Current Science-Special Section on Materials, 2013
Philosophical Magazine, 2012
A novel method is proposed for fracture toughness determination of graded microstructurally compl... more A novel method is proposed for fracture toughness determination of graded microstructurally complex (Pt,Ni)Al bond coats using edge-notched doubly clamped beams subjected to bending. Micron-scale beams are machined using the focused ion beam and loaded in bending under a nanoindenter. Failure loads gathered from the pop-ins in the load–displacement curves combined with XFEM analysis are used to calculate K c at individual zones, free from substrate effects. The testing technique and sources of errors in measurement are described and possible micromechanisms of fracture in such heterogeneous coatings discussed.
MRS Fall Meeting 2012 - Hysitron Related Technical Talks
Materials Today Communications, 2021
Microscopy and Microanalysis, 2012
Journal of Materials Research
The influence of Pt layer thickness on the fracture behavior of PtNiAl bond coats was studied in-... more The influence of Pt layer thickness on the fracture behavior of PtNiAl bond coats was studied in-situ using clamped micro-beam bend tests inside an SEM. Clamped beam bending is a fairly well established micro-scale fracture test geometry that has been previously used in determination of fracture toughness of Si and PtNiAl bond coats. The increasing amount of Pt in the bond coat matrix was accompanied by several other microstructural changes such as an increase in the volume fraction of α- Cr precipitate particles in the coating as well as a marginal decrease in the grain size of the matrix. In addition, Pt alters the defect chemistry of the B2-NiAl structure, directly affecting its elastic properties. A strong correlation was found between the fracture toughness and the initial Pt layer thickness associated with the bond coat. As the Pt layer thickness was increased from 0 to 5 µm, resulting in increasing Pt concentration from 0 to 14.2 at% in the B2-NiAl matrix and changing α-Cr precipitate fraction, the initiation fracture toughness was seen to rise from 6.4 to 8.5 MPa.m1/2. R-curve behavior was observed in these coatings, with KIC doubling for a crack propagation length of 2.5 µm. The reasons for the toughening are analyzed to be a combination of material’s microstructure (crack kinking and bridging due to the precipitates) as well as size effects, as the crack approaches closer to the free surface in a micro-scale sample.
The field of micro-/nano-mechanics of materials has been driven, on the one hand by the developme... more The field of micro-/nano-mechanics of materials has been driven, on the one
hand by the development of ever smaller structures in devices, and, on the
other, by the need to map property variations in large systems that are
microstructurally graded. Observations of ‘smaller is stronger’ have also
brought in questions of accompanying fracture property changes in the
materials. In the wake of scattered articles on micro-scale fracture testing of
various material classes, this review attempts to provide a holistic picture of
the current state of the art. In the process, various reliable micro-scale
geometries are shown, challenges with respect to instrumentation to probe
ever smaller length scales are discussed and examples from recent literature
are put together to exhibit the expanse of unusual fracture response of
materials, from ductility in Si to brittleness in Pt. Outstanding issues related
to fracture mechanics of small structures are critically examined for plausible
solutions.
Philosophical Magazine Special Issue on Nanomech-IV, 2015
Journal of Materials Research, 2015
International Journal of Fracture, 2014
Microscopy and Microanalysis , 2013
Current Science-Special Section on Materials, 2013
Philosophical Magazine, 2012
A novel method is proposed for fracture toughness determination of graded microstructurally compl... more A novel method is proposed for fracture toughness determination of graded microstructurally complex (Pt,Ni)Al bond coats using edge-notched doubly clamped beams subjected to bending. Micron-scale beams are machined using the focused ion beam and loaded in bending under a nanoindenter. Failure loads gathered from the pop-ins in the load–displacement curves combined with XFEM analysis are used to calculate K c at individual zones, free from substrate effects. The testing technique and sources of errors in measurement are described and possible micromechanisms of fracture in such heterogeneous coatings discussed.
MRS Fall Meeting 2012 - Hysitron Related Technical Talks