PTt history from kyanite-sillimanite migmatites and garnet-staurolite schists from the Bayankhongor area, Mongolia indicates suprasubduction switching from extension to compression during Rodinia assembly

The tectonometamorphic evolution of the peri-Siberian tract of the Central Asian Orogenic Belt is mainly characterized by Baikalian Late Proterozoic - Early Cambrian cycle related to amalgamation of Proterozoic oceanic and continent fragments to Siberain landmass. Here we present in-situ monazite geochronology linked to P−T modelling of micashischsts and migmatite gneisses at the northern part of the Precambrian Baydrag block (central Mongolia) previously considered as a part of Baikalian metamorphic belt. Garnet-sillimanite-kyanite gneiss records first burial to the sillimanite stability at ~725 °C and 6.5 kbar, followed by burial to the kyanite stability at ~650 °C and ~8 kbar. The garnet-staurolite schist records burial to the staurolite-stability at ~620 °C and 6 kbar, followed by a nearly isothermal burial to ~580 °C and 9 kbar. The monazite data yield a continuum of 207Pb-corrected 238U/206Pb dates of c. 926−768 Ma in the Grt−Sil−Ky gneiss, and c. 937−754 Ma in the Grt-St schist. Based on monazite textural positon and internal zoning, the time of prograde burial and peak under a thermal gradient of 28-32 °C/km is estimated at c. 870−890 Ma. It is not clear whether such high grade conditions prevailed until a phase of further burial under a geothermal gradient of 18-22 °C/km and dated at 800−820 Ma. Additionally, monazite with dates of c. 568−515 Ma occurs as whole grains or as rims with sharp boundaries on Grenvillean monazite in Grt-St schist testifying for minor Baikalian overprint. Metamorphic zircon rims with Th/U ratio ~0.01-0.06 in Grt−Sil−Ky gneiss with 877 ± 7 Ma age, together with lower intercepts of zircon discordia lines in both Grt-Sil-Ky gneiss and Grt-St schist further support the Tonian age of high grade metamorphism. The P−T and geochronology data show anticlockwise P−T evolution from c. 930 to 750 Ma which is interpreted as a result of thickening of suprasubduction extensional and hot edifice - probably of back arc or arc type. This kind of prograde metamorphism was so far described only on the northern part of the Tarim block and interpreted as a result of initiation of peri-Rodinian subduction of Mirovoi Ocean. Here, we further discuss geodynamic consequences of a unique discovery of Tonian metamorphism in term of tectonic switch related to initiation of peri-Rodinian oceanic subduction during supercontinent assembly followed by strong mechanical coupling potentially related to onset of Rodinia splitting

Energy Reductions Using Next-Generation Remanufacturing Techniques

The goal of this project was to develop a radically new surface coating approach that greatly enhances the performance of thermal spray coatings. Rather than relying on a roughened grit blasted substrate surface for developing a mechanical bond between the coating and substrate, which is the normal practice with conventional thermal spraying, a hybrid approach of combining a focused laser beam to thermally treat the substrate surface in the vicinity of the rapidly approaching thermally-sprayed powder particles was developed. This new surface coating process is targeted primarily at enabling remanufacturing of components used in engines, drive trains and undercarriage systems; thereby providing a substantial global opportunity for increasing the magnitude and breadth of parts that are remanufactured through their life cycle, as opposed to simply being replaced by new components. The projected benefits of a new remanufacturing process that increases the quantity of components that are salvaged and reused compared to being fabricated from raw materials will clearly vary based on the specific industry and range of candidate components that are considered. At the outset of this project two different metal processing routes were considered, castings and forgings, and the prototypical components for each process were liners and crankshafts, respectively. The quantities of parts used in the analysis are based on our internal production of approximately 158,000 diesel engines in 2007. This leads to roughly 1,000,000 liners (assuming a mixture of 6- and 8-cylinder engines) and 158,000 crankshafts. Using energy intensity factors for casting and forgings, respectively, of 4450 and 5970 Btu-hr/lb along with the energy-induced CO2 generation factor of 0.00038 lbs CO2/Btu, energy savings of over 17 trillion BTUs and CO2 reductions of over 6.5 million lbs could potentially be realized by remanufacturing the above mentioned quantities of crankshafts and liners. This project supported the Industrial Technologies Program's initiative titled 'Industrial Energy Efficiency Grand Challenge.' To contribute to this Grand Challenge, we. pursued an innovative processing approach for the next generation of thermal spray coatings to capture substantial energy savings and green house gas emission reductions through the remanufacturing of steel and aluminum-based components. The primary goal was to develop a new thermal spray coating process that yields significantly enhanced bond strength. To reach the goal of higher coating bond strength, a laser was coupled with a traditional twin-wire arc (TWA) spray gun to treat the component surface (i.e., heat or partially melt) during deposition. Both ferrous and aluminum-based substrates and coating alloys were examined to determine what materials are more suitable for the laser-assisted twin-wire arc coating technique. Coating adhesion was measured by static tensile and dynamic fatigue techniques, and the results helped to guide the identification of appropriate remanufacturing opportunities that will now be viable due to the increased bond strength of the laser-assisted twin-wire arc coatings. The feasibility of the laser-assisted TWA (LATWA) process was successfully demonstrated in this current effort. Critical processing parameters were identified, and when these were properly controlled, a strong, diffusion bond was developed between the substrate and the deposited coating. Consequently, bond strengths were nearly doubled over those typically obtained using conventional grit-blast TWA coatings. Note, however, that successful LATWA processing was limited to ferrous substrates coated with steel coatings (e.g., 1020 and 1080 steel). With Al-based substrates, it was not possible to avoid melting a thin layer of the substrate during spraying, and this layer re-solidified to form a band of intermetallic phases at the substrate/coating interface, which significantly diminished the coating adhesion. The capability to significantly increase the bond strength with ferrous substrates and coatings may open new remanufacturing opportunities that were previously not considered due to concerns with the limits of the mechanical bonding of conventional TWA coatings. However, the limited results obtained within this one-year program are not sufficient to move the LATWA into a production environment. Additional work will be needed engineer the process to coat components with more complex geometries than the flat specimens studied in this work. In addition part-specific bench testing and relevant field tests will be required to fully establish the necessary confidence for introducing the LATWA process. These are typical constraints and requirements for most any new production process, and it is quite possible this new process will continue to be a viable approach for extending the usage of remanufacturing, and in turn capturing the resulting energy savings and green house gas emission reductions

The effect of YSZ microstructure on Young's modulus

The mechanical behavior of nanostructured yttria stabilized zirconia (YSZ) thermal spray deposits was examined and compared to conventional zirconia coatings. Young's modulus was measured using indentation techniques. The anisotropy of the deposits was estimated by indenting the deposits in the perpendicular and parallel directions to the substrate. Statistical distribution of the mechanical properties was correlated with the microstructure. The effective Young's moduli of nanostructured and standard YSZ were also modeled by means of 2D extended FEM; whereby actual microstructures were assessed. The simulation was based on micrographs by employing a standard meshing program combined with an in-house developed XFEM package, which incorporates the crack structure into the model. The effect of nano-scale features on the effective Young's modulus were predicted and compared to experimental observations

Nanophase partially stabilized zirconia intermediate layer for strain accommodation in a multi-layer thermal barrier coating

Applying an environmental barrier coating (EBC) and a thermal barrier coating (TBC) on the next generation gas turbine structural materials such as silicon carbide matrix composites will lead to large stresses due to thermal expansion mismatch; thereby limiting the coating's effectiveness and lifetime. Nanostructured materials possess a large volume fraction of grain boundaries and are conjectured to partially relieve the strain in the coating structure. A Triple Torch Plasma Reactor (TTPR) was used to spray multi-layered TBCs consisting of a mullite EBC deposited either on a silicon carbide or a mullite substrate, a nano-phase partially stabilized zirconia coating (n-PSZ), and a yttria stabilized zirconia coating (YSZ) as the TBC. The nanostructure of the n-PSZ could be maintained during the deposition process. The coatings were heat treated at 1300°C and the change in microstructure and mechanical properties were analyzed using scanning electron microscopy (SEM), micro-indentation and scratch testing applied to the coating cross section. While a change in the microstructure was observed, in particular grain growth, the hardness and elastic modulus appeared to be little affected by the heat treatment giving a preliminary validation of the multilayer concept