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Type Hetherly, J.; Martinez, E.; Di, Z.F.; Nastasi, M.; Caro, A.
  Publication Helium bubble precipitation at dislocation networks Volume Journal Article
Pages 2011
  Abstract Scripta Materialia  
  Corporate Author  
Publisher In Press  
Editor Uncorrected Proof
  Summary Language Series Editor Modeling; Precipitation; Grain boundary structure; He bubbles  
Abbreviated Series Title We report on a study of nanoscale He bubble precipitation and growth at a twist grain boundary in two face-centered cubic materials. Experimentally, the twist boundary in Au captures all the He in the sample, forming equal-sized bubbles at the dislocation intersection junctions. Simulations in Cu reveal a complex structure of the interface and different He pressure in the interface bubbles compared to bulk, providing an explanation for the high efficiency of the boundary to capture all the He in the sample.
  Series Issue ISSN  
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  Expedition Notes  
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1359-6462 no NU @ karnesky @ 11267
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Martin, M.L.; Somerday, B.P.; Ritchie, R.O.; Sofronis, P.; Robertson, I.M. Hydrogen-induced intergranular failure in nickel revisited Journal Article 2012 Acta Materialia In Press Corrected Proof Hydrogen embrittlement; Intergranular cracking; Transmission electron microscopy; Scanning electron microscopy; Nickel Using a combination of high-resolution scanning and transmission electron microscopy, the basic mechanisms of hydrogen-induced intergranular fracture in nickel have been revisited. Focused-ion beam machining was employed to extract samples from the fracture surface to enable the examination of the microstructure immediately beneath it. Evidence for slip on multiple slip systems was evident on the fracture surface; immediately beneath it, an extensive dislocation substructure exists. These observations raise interesting questions about the role of plasticity in establishing the conditions for hydrogen-induced crack initiation and propagation along a grain boundary. The mechanisms of hydrogen embrittlement are re-examined in light of these new results. 1359-6454 no NU @ karnesky @ 11313
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Mao, Zugang; Booth-Morrison, Christopher; Sudbrack, Chantal K.; Martin, Georges; Seidman, David N. Kinetic pathways for phase separation: An atomic-scale study in Ni–Al–Cr alloys Journal Article 2011 Acta Materialia 60 4 1871-1888 Nickel-based superalloys; Kinetic pathways; Atom probe tomography; Lattice kinetic Monte Carlo; Nanostructures The kinetic pathways involved in the formation of [gamma]'(L12 structure)-precipitates during aging of concentrated Ni–Al–Cr alloys at 873 K, for three distinct alloy compositions, are studied experimentally by atom probe tomography, and computationally with lattice kinetic Monte Carlo (LKMC) simulations using parameters deduced from first-principles calculations of cohesive energies, and from experimental diffusion data. It is found that the compositional evolution of the [gamma]'-precipitate phase does not follow the predictions of a classical mean-field model for coarsening of precipitates in ternary alloys. LKMC simulations reveal that long-range vacancy–solute binding plays a key role during the early stages of [gamma]'-precipitation. With the aid of Monte Carlo techniques using the parameters employed in the LKMC simulations, we compute the diffusion matrix in the terminal solid-solutions and demonstrate that key features of the observed kinetic pathways are the result of kinetic couplings among the diffusional fluxes. The latter are controlled by the long-range vacancy–solute binding energies. It is concluded that, because it neglects flux couplings, the classical mean-field approach to phase separation for a ternary alloy, despite its many qualitatively correct predictions, fails to describe quantitatively the true kinetic pathways that lead to phase separation in concentrated metallic alloys. 1359-6454 no NU @ karnesky @ 11306
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Stone, D.S.; Gao, H.; Chantharangsi, C.; Paksunchai, C.; Bischof, M.; Jaeger, D.; Martini, A.; Scharf, T.W.; Aouadi, S.M. Load-dependent high temperature tribological properties of silver tantalate coatings Journal Article 2014 Surface and Coatings Technology 244 37-44 Friction; Tribology; Silver tantalate; Molecular dynamics; Sputtering Abstract Silver tantalate coatings were produced by reactive unbalanced magnetron sputtering from silver and tantalum sources as potential high temperature solid lubricants. The films were wear-tested at 750 °C under normal loads of 1, 2, 5, or 10 N against a Si3N4 counterface. These sliding tests revealed that the friction monotonically increased as the load was increased. A systematic investigation of the surface and sub-surface regions of the wear track, using techniques such as Scanning Auger Nanoprobe, Atom Probe Tomography, and cross-sectional transmission electron microscopy, revealed the following trends with increasing load: (1) a decrease in the amount of Ag on the surface of the wear track; (2) a decrease in the thickness of the mechanically mixed layer that forms as a result of the reconstruction of AgTaO3 to form Ta2O5 and Ag; and (3) the formation of a porous structure throughout the tribofilm as a result of the segregation and migration of Ag from the original AgTaO3 matrix. These results were complemented by molecular dynamics simulations, which confirmed the increase of friction with load. Further, the simulations support the hypothesis that this trend can be explained in terms of decreased presence of Ag clusters near the sliding surface and the associated decreased porosity. 0257-8972 no NU @ karnesky @ 11490
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Martinez, E.; Ronsheim, P.; Barnes, J.-P.; Rochat, N.; Py, M.; Hatzistergos, M.; Renault, O.; Silly, M.; Sirotti, F.; Bertin, F.; Gambacorti, N. Lanthanum diffusion in the TiN/LaOx/HfSiO/SiO2/Si stack Journal Article 2011 Microelectronic Engineering Proceedings of the 17th Biennial International Insulating Films on Semiconductor Conference, 17th Bi 88 7 1349-1352 Metal/high-k stack; TiN; HfSiO; La; Interfacial dipole; Threshold voltage tuning; ToF-SIMS; Apt; Atr-Ftir; S-Xps Band edge Complementary Metal Oxide Semiconductor (CMOS) devices are obtained by insertion of a thin LaOx layer between the high-k (HfSiO) and metal gate (TiN). High temperature post deposition anneal induces Lanthanum diffusion across the HfSiO towards the SiO2 interfacial layer, as shown by Time of Flight Secondary Ions Mass Spectroscopy (ToF-SIMS) and Atom Probe Tomography (APT). Fourier Transform Infrared Spectroscopy in Attenuated Total Reflexion mode (ATR-FTIR) shows the formation of La-O-Si bonds at the high-k/SiO2 interface. Soft X-ray Photoelectron Spectroscopy (S-XPS) is performed after partial removal of the TiN gate. Results confirm La diffusion and changes in the La chemical environment. 0167-9317 no NU @ karnesky @ 11170
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Brechet, Yves; Martin, Georges Nucleation problems in metallurgy of the solid state: recent developments and open questions Journal Article 2006 Comptes Rendus Physique 7 9-10 959-976 Coherent precipitation; Recrystallisation; Precipitation coherente; Recristallisation Nucleation processes play a key role in the microstructure evolution of metallic alloys during thermomechanical treatments. These processes can involve phase transformations (such as precipitation) and structural instabilities (such as recrystallisation). Although the word `nucleation' is used in both cases, the situation is profoundly different for precipitation and for recrystallisation on which this article is focussed. In the case of precipitation, species are conserved and the underlying physics is stochastic fluctuations, allowing the apparition of critical germs of the new phase. In the case of recrystallisation, the underlying physical phenomenon is the progressive growth of subgrain structures leading to an unstable configuration, allowing a dislocation free grain to grow at the expense of a dislocated one. The two cases require different types of modelling which are presented in the article. To cite this article: Y. Brechet, G. Martin, C. R. Physique 7 (2006). no NU @ karnesky @ 9593
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Tang, Fengzai; Gault, Baptiste; Ringer, Simon P.; Martin, Phil; Bendavid, Avi; Cairney, Julie M. Microstructural investigation of Ti-Si-N hard coatings Journal Article 2010 Scripta Materialia 63 2 192-195 Titanium silicon nitride; Pulsed laser atom probe (PLAP); Nanostructure; Nanocomposite The microstructures of nanostructured Ti-Si-N hard coatings were investigated by transmission electron microscopy and pulsed laser atom probe. C and O impurities were detected. No evidence of increased Si levels at the grain boundaries was found, suggesting that Si is either in the form of a layer too thin to be detected using the techniques employed or in the form of a solid solution of SiN clusters. 1359-6462 no NU @ karnesky @ 10856
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Wu, Ling-Mei; Seyring, Martin; Rettenmayr, Markus; Wang, Wen-Hsiung Characterization of precipitate evolution in an artificially aged Al-Zn-Mg-Sc-Zr alloy Journal Article 2010 Materials Science and Engineering: A 527 1068-1073 Al-Zn-Mg-Sc-Zr alloy; age hardening; precipitation; transmission electron microscopy (TEM) The precipitates of an age hardenable Al-Zn-Mg-Sc-Zr alloy aged at 140 °C have been studied by transmission electron microscopy (TEM). The results are interpreted in terms of structural transformations that involve two types of Guinier-Preston (GP) zones (I and II), the metastable [eta]’ hardening precipitate and the stable phase [eta]-phase (MgZn2). At early stages of ageing, the GPI zones act as nucleation sites for the plate-like [eta]’ phase which precipitates on the 111Al plane. The transformation from [eta]’ to [eta] occurs gradually at longer ageing times. The [eta] particles mainly consist of [eta]1 and [eta]2 phase, with small amounts of [eta]4 type and minor quantities of [eta]’ type structures. Furthermore, while a fine dispersion of coherent Al3(Sc,Zr) precipitates is known to have a beneficial effect on the strengthening of the alloy, the formation of GPII zones is suppressed in the presence of zirconium that leads to a reduction in the amount of [eta]’ formed during subsequent ageing. 0921-5093 no NU @ karnesky @ Wu2009 10688
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Martin, G. A diffuse interface model for the interfacial transfer coefficient Journal Article 2005 Acta Materialia 53 9 2629-2632 Diffusion; Interfaces; Alloys; Kinetics; Phase field models; Theory Based on an extension to non-equilibrium problems, of Cahn's interface layer thermodynamics, we demonstrate that the matrix of transfer coefficients across a coherent interface between two phases, [alpha] and [beta], can be viewed as a correction to the Onsager's matrix of mobility coefficients along the continuous concentration profile. The latter coefficients are defined along the equilibrium concentration profile in the interfacial layer and in the [alpha]- and [beta]-phases. Combining the above definition with that of solute interfacial excess, we can define transfer coefficients relative to two components chosen arbitrarily, the values of which are intrinsic properties of the interfacial layer, independent of its precise location and thickness. no NU @ p-kolli @ 9702
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Soisson, F.; Barbu, A.; Martin, G. Monte Carlo simulations of copper precipitation in dilute iron-copper alloys during thermal ageing and under electron irradiation Journal Article 1996 Acta Materialia Acta Mater. 44 9 3789-3800 We propose a Monte Carlo simulation of the coherent precipitation of copper in [alpha]-iron using a vacancy diffusion mechanism. The only adjustable parameters are the vacancy concentration and the local vacancy jump frequencies. The latter are deduced from pair interactions restricted to nearest neighbour atoms. Precipitation kinetics are compared to recent experimental studies of precipitation in dilute Fe---Cu solid solutions during thermal ageing or electron irradiation (electrical resistivity measurements). The degree of advancement of the unmixing process as a function of time has the form of a stretched exponential, in good agreement with experiment. The simulation also provides interesting information on precipitate morphology and growth mechanisms which are useful for experimental data analysis. no NU @ karnesky @ 1917
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