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Needham, MA, United States

Hausild P.,Czech Technical University | Nohava J.,CSM Instruments Inc. | Pilvin P.,University of Southern Brittany
Strain | Year: 2011

Deformation-induced martensite in metastable austenitic steel was characterised by the grid nanoindentation method. Distribution of nanohardness was found out in specimens with different martensite volume fractions. Bimodal distribution of hardness was only slightly affected by the values obtained on or near γ-α' phase boundary. This approach was verified by independent phase identification using electron back scattered diffraction. © 2010 Blackwell Publishing Ltd.

Hausild P.,Czech Technical University | Materna A.,Czech Technical University | Nohava J.,CSM Instruments Inc.
Materials and Design | Year: 2012

The local stress-strain relations were characterized by instrumented indentation with spherical indenter. The results obtained by indentation with different indenter radii were compared with tensile stress-strain curves of two metastable austenitic stainless steels (grade A301 and A304) and analyzed using finite element model. A forward finite element analysis was also carried out with model material behavior (elastic-perfectly plastic, linear hardening, piece-wise linear hardening and power-law hardening). The limitations of identified stress-strain relations arising from the indenter shape, uneven contact and non-linear material behavior due to the deformation induced martensitic transformation are discussed. © 2012 Elsevier Ltd.

Li H.,Harvard University | Randall N.X.,CSM Instruments Inc. | Vlassak J.J.,Harvard University
Journal of Materials Research | Year: 2010

Indentation experiments on thin films are analyzed by using a rigorous solution to model elastic substrate effects. Two cases are discussed: elastic indentations where film and substrate are anisotropic and elastoplastic indentations where significant material pileup occurs. We demonstrate that the elastic modulus of a thin film can be accurately measured in both cases, even if there is significant elastic mismatch between film and substrate. © 2010 Materials Research Society.

Guldin S.,University of Cambridge | Guldin S.,Ecole Polytechnique Federale de Lausanne | Kohn P.,University of Cambridge | Stefik M.,University of South Carolina | And 6 more authors.
Nano Letters | Year: 2013

Low-cost antireflection coatings (ARCs) on large optical surfaces are an ingredient-technology for high-performance solar cells. While nanoporous thin films that meet the zero-reflectance conditions on transparent substrates can be cheaply manufactured, their suitability for outdoor applications is limited by the lack of robustness and cleanability. Here, we present a simple method for the manufacture of robust self-cleaning ARCs. Our strategy relies on the self-assembly of a block-copolymer in combination with silica-based sol-gel chemistry and preformed TiO2 nanocrystals. The spontaneous dense packing of copolymer micelles followed by a condensation reaction results in an inverse opal-type silica morphology that is loaded with TiO2 photocatalytic hot-spots. The very low volume fraction of the inorganic network allows the optimization of the antireflecting properties of the porous ARC despite the high refractive index of the embedded photocatalytic TiO2 nanocrystals. The resulting ARCs combine high optical and self-cleaning performance and can be deposited onto flexible plastic substrates. © 2013 American Chemical Society.

Agency: Cordis | Branch: FP7 | Program: CP-TP | Phase: NMP.2012.1.4-3 | Award Amount: 2.54M | Year: 2013

Optical coatings are commonly deposited over large areas on different substrates: glass, metals (steel, aluminium...) or polymeric foils (PET...). Production processes involve normally large machinery including many times roll-to-roll processes to deposit multilayers over several square meters of substrates. However, properties of these coatings depend strongly on nanometric properties: composition, crystallography, nanostructure, roughness, homogeneity... Solar selective coatings are considered a special case of optical coatings combining several layers with different properties, mainly: antireflection, solar absorbance and infrared mirror. Nowadays the most demanding solar selective coatings are those used in tubes of high temperature parabolic trough solar collectors. Coatings have to operate in an aggressive environment (temperatures above 400C, thermal cycling) during 20-25 years. Besides, further developments require higher temperatures, improved scratch resistance and working under oxidant atmospheres (small quantities of water vapour and oxygen). In order to get significant advances in this field it is essential to have: 1. Nanoscale structure related requirements (nanoroughness, nanohardness, crystallography, composition, vibrational modes) and the correlation with performance requirements: optical and, more important, life expectancy. 2. Standard characterisation and degradation protocols to serve as a powerful tool to coating developers, producers and end users for life prediction and to push the collector parameters (temperatures and environment) to higher efficiency parameters. The main idea behind this NECSO project is to provide tools to the end users namely solar plants builders, to guarantee that the selective coating will work properly during 20 to 25 years. Novel experimental methods for testing materials under extreme conditions (temperature and radiation) are needed providing a deeper understanding of the interaction of electromagnetic radiation with nanomaterials, as basis for design of new spectrally selective absorber coatings. Nanoscale characterisation (roughness, AFM, nanoindentation, scratch-adhesion, crystallography by FESEM-EBSD, Raman, RX, XPS, etc) will correlate the nanostructure parameters with coating performance. The resulting outcomes are expected to contribute significantly to the infrastructure of the solar energy research, development and industrial activities worldwide. Additionally, the designed testing protocols should help coating developers to compare available layers and newly designed ones, with standard procedures. Finally, testing procedures will also be of utter importance to have a fast quality control on the coatings, typically in 4 meter tubes, over some tens of kilometres in a common cylinder parabolic solar plant.

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