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Experimental investigation and modelling of nanoscale solid state reactions with high technological impact

Periodic Report Summary 1 - EXMONAN (Experimental investigation and modelling of nanoscale solid state reactions with high technological impact.)

The project EXMONAN focuses on the experimental investigations and modelling of materials already being used or are being considered as candidates for application in advanced technologies and is realized by a consortium of teams affiliated in 9 institutions: (i) Jagiellonian University in Krakow, Poland (UJ, the coordinator); (ii) Universite de Rouen, France (UR); (iii) University of Debrecen, Hungary (UD); (iv) Eidgenoessische Materialpruefungs und Forschungsanstalt, Switzerland (EMPA); (v) Bohdan Khmelnytskyy National University at Cherkasy, Ukraine (BKNUC); (vi) Institute of Strength Physics and Materials Science of the Siberian Branch of the Russian Academy of Sciences, Russia (ISPMS SB RAS); (vii) Institute of Solid State Physics, Russian Academy of Sciences, Russia (ISSP RAS); (viii) University of Newcastle, Australia (UN) and (ix) University of Waterloo, Canada (UW).
The progress of the realization of the EXMONAN is shown by indicating the results achieved within its particular objectives:
1. Elaboration of a new consistent methodology for atomistic simulation of interdiffusion in systems with different component diffusivities: from bulk to nanostructured samples (UJ – UN);
Results achieved within the reporting period: (i) Determination and explanation of the free surface effect on L10 ordering phenomena in nanoalloys; (ii) Determination of the atomistic origin of the relationship between the thermodynamic activation energies for self-diffusion and B2 ordering kinetics in intermetallics; (iii) Elaboration of a Monte Carlo algorithm for direct simulation of vacancy-mediated interdiffusion.
2. Elaboration of a model of time-dependent vacancy-mediated diffusion in intermetallic phase growing in a nano-couple (UJ – BKNUC);
Results achieved within the reporting period: (i) Comparative study of the competition between antiphase domains of the ordered intermediate phase A3B in FCC case and of AB for BCC case, growing in the process of interdiffusion. Indication that the mean domain size growth proceeds significantly faster within the intermediate phase layer during interdiffusion; (ii) Application of the Stochastic Kinetic Mean Field (SKMF) technique to simulate ordering and diffusion in L12 (Ni3Al), L10 (FePt) and B2 (NiAl) ordering bulk and nanostructured binaries.
3. Attainment of a fundamental understanding of (inter)diffusion and competing interface reactions during self-propagating high-temperature synthesis (SHS) in multi-layered Ni-Al and Ti-Al considered as model systems for benign joining processes for nanomaterials and other heat-sensitive materials (e.g. Polymers and amorphous alloys): modelling and experimental investigation (EMPA – BKNUC);
Results achieved within the reporting period: (i) Construction of an original device for direct measurements of SHS chracteristics. Indication that the phase formation sequences running in Ni-Al supplied by different producers substantially differ one from another. (ii) Development of a software for modeling the SHS reactions with arbitrary number of intermediate phases and arbitrary order of their formation.
4. Optimization of Pb-free soldering process for microelectronic components to improve the interconnect reliability: preventing (or postponing) the formation of the Cu3Sn phase due to the formation of Kirkendall voids (EMPA – BKNUC);
Results achieved within the reporting period: (i) First-time demonstration that, besides the common Zener pinning, voids can be additionally, kinetically pinned to the interface by the additional vacancy concentration gradient, existing due to inefficient vacancy sinks/sources at both sides of the interface. The kinetic pinning may explain the influence of copper substrate defect prehistory on the pinning behavior. (ii) New observation of the “enveloping” of the voids by the growing Cu3Sn phase due to the surface diffusion along the free surface of voids.
5. Determination of the diffusion rates and reaction kinetics of Ag nano-particles and -wires during low temperature sintering and ultrafast laser processing of Cu interconnects (EMPA – UW);
Results achieved within the reporting period: (i) Sinthesis of Ag nanoparticles and nanowires of different size and shapes (UW) and deposition of Ag nanomultilayers (Empa); (ii) Distribution of the specimens for a comparative characterisation. The experiments are in progress.
6. Determination of the thermodynamic driving forces and activation energies (i.e. the kinetic barriers) for interfacial segregation and grain-boundary wetting in the Ag-Cu, Al-Si and Al-Cu systems (ISSP RAS –EMPA);
Results achieved within the reporting period: (i) Observation and characterization of the interfacial segregation of Ag in Cu grain boundaries by comparison of lattice spacing in coarse-grained and nanograined solid solution Cu(Ag); (ii) Study of the grain boundary wetting in the Ag-Cu, Al-Cu, WC-Co and W-Ni systems.
7. Testing and optimization of developed nanostructured materials for advanced joining technologies (brazing, soldering, diffusion bonding), in particular, for the low-temperature joining of heat-sensitive nanomaterials (ISSP RAS – EMPA);
Results achieved within the reporting period: (i) Preparation of the nanograined solid solution Cu(Ag) by the severe plastic deformation (SPD) in the high pressure torsion (HPT) mode. (ii) Preparation of the copper-based Cu–Al–Ni shape memory alloy with high specific density of grain boundaries by means of SPD HPT.
8. Development of a 3D kinetic mean field model of chemical ordering in the FCC lattice and implementation of this model in a study of voiding. Understanding and analytical description of the competition between Kirkendall voiding and Kirkendall shift during interdiffusion in solid solutions and intermetallic phases (first of all, the B2 phase NiAl) (UD – BKNUC);
Results achieved within the reporting period: (i) Development of the method of Stochastic Kinetic Mean-Field (SKMF) implemented with the steady-state approximation for vacancy subsystem and extended upon the vacancy mechanism of atomic migration; (ii) SKMF modelling of the nucleation of FCC L12-ordered A3B phase from the supersaturated solid solution. Incubation time of the nucleation appeared to be the exponential function of the inverse squared noise amplitude; (iii) KMF investigation of the phase formation and competition during reactions of Self-Propagating High-Temperature Synthesis (SHS) in FCC lattice. The exponential dependence of the front velocity of SHS reaction on the mixing energy and a linear dependence of the front velocity on the asymmetry parameter was indicated.
9. Elaboration of the methodology for atomistic modelling of nanoscale structural transformations in solids at different temperatures using the phase field crystal, Monte-Carlo and ab-initio density functional methods (UR - ISPMS SB RAS – UJ).
Results achieved within the reporting period: (i) Application of the quasiparticle approach to describe the auto-organisation of graphene layers on the copper surface and to model the segregation phenomena at grain boundaries (GB) in alpha iron; (ii) Observation and description of point defect formation during the growth of graphene on a metallic surface. Analytical indication of the resulting degradation of the high electrical conductivity of this material.

Except for the research activities, the tasks related to the project management and the dissemination of the results are realized according to the original schedule.