N2O Decomposition over Fe-ZSM-5: A Systematic Study in the Generation of Active Sites

We have carried out a systematic investigation of the critical activation parameters (i.e., final temperature (673–1273 K), atmosphere (He vs. O2/He), and final isothermal hold (1 min–15 h) on the generation of “α-sites”, responsible for the direct N2O decomposition over Fe-ZSM-5 (Fe content = 1200–2300 ppm). The concentration of α-sites was determined by (ia) transient response of N2O and (ib) CO at 523 K, and (ii) temperature programmed desorption (TPD) following nitrous oxide decomposition. Transient response analysis was consistent with decomposition of N2O to generate (i) “active” α-oxygen that participates in the low-temperature CO→CO2 oxidation and (ii) “non-active” oxygen strongly adsorbed that is not released during TPD. For the first time, we were able to quantify the formation of α-sites, which requires a high temperature (>973) treatment of Fe-ZSM-5 in He over a short period of time (<1 h). In contrast, prolonged high temperature treatment (1273 K) and the presence of O2 in the feed irreversibly reduced the amount of active sites.

Metallurgical Interaction among BNi-9 and Waspaloy, FSX-414 or 304-Type Stainless Steel under TLP Cycle

The metallurgical interaction of BNi-9 filler metal paste with Waspaloy, Ni-coated Waspaloy, FSX-414, and 304-SS is studied in a brazing treatment under an argon atmosphere with an isothermal hold for one hour at 1150 °C. The Waspaloy alloys were brazed under both solubilized and aging conditions. Before brazing, some Waspaloy samples were electrochemically coated with an Ni layer 35-40 μm thick. The microstructures of the FSX-414 and 304-SS alloys showed that the thickness of the isothermal solidification zones was approximately 50 μm, while this thickness was not well defined in the Waspaloy samples. The Ni-coated solubilized Waspaloy showed a wider diffusive zone, which was associated with an increase in the penetration extension of the liquid films. The analysis of grain orientation in all brazed zones of the Waspaloy samples showed aleatory characteristics. Plastic factors in the different brazed zones were also obtained by nanoindentation under 350 mN loads. It was observed that the plastic factor was low when the width of the diffusive zone increased. The plastic factor in the Ni-coated Waspaloy was the lowest, while the diffusive zone in this sample had the largest width. The BNi-9 wettability is better in FSX-414, and 304-SS than in Waspaloy. Ni coating in Waspaloy improves BNi-9 wettability.

Sinthesis and Properties of Marble-Like Glass-Ceramics Using of Ash from Thermal Power Plants

Color marble-like glass-ceramic materials were obtained through thermal treatment of glasses of the system CaO-Al2O3-SiO2 by using natural materials with the introduction of waste materials - ash from thermal power plants (TPP). The melting of the glass batch was in corundum crucibles at 1450oC with an isothermal hold of 60 min. The glasses obtained was fritted in distilled water and dried for 6 hours at 100oC, then completely crushed and divided into fractions with grain size of 0.8 mm, 1.0 mm, 2 mm, 2.5 mm and over 2.5 mm. It was found that the use of ash from TPP lead to higher values of degree of transformation (crystallization) than using base composition. Values of Avramy parameter’s in the range n=1,0 ÷ 1,6 are showed that crystallization of the glass frit is largely heterogeneous and crystal growing starts from the surface. The introduction of ash from TPP to native glasses carry out to significant reduction of energy of crystallization by Ес=289 kJ/mol to Ec=221 kJ/mol. The glass-ceramic materials were obtained through a one stage crystallization - 1050÷1070оС and an isothermal hold of 60 min., colored white, yellow brown to dark brown. The main crystalline phase in glass-ceramics is β-vollastonite with needle habit, size of crystals - ĺ = 40 ÷ 120 μm and d <5 μm in quantities 37 ÷ 42%. As secondary phases depending on the amount of ash have been identified - the anorthite, gehlenite and α-quartz with prismatic habit were appeared. The obtained glass-ceramic materials have a marble-like effect and technical parameters compared with natural granite and marble and have higher values of density, micro hardness, speed grinding, bending strength and chemical resistance. That’s why they can be used in construction such as lining materials.

The Effect of Isothermal Hold Temperature on Microstructure and Mechanical Properties of TRIP Steel

TRIP (transformation induced plasticity) steels are low alloyed low carbon steels with complex microstructures consisting of ferrite, bainite and retained austenite. This complex microstructure provides them with excellent strength to ductility balance, making them a member of advanced high strength steels (AHSS) group. Suitable microstructure can be obtained by either heat or thermo-mechanical treatment. A hold in bainite transformation region is an integral part of any form of commercial TRIP steel processing route, as it enables formation of sufficient volume fraction of bainite and also stabilization of retained austenite in the final microstructure. Various bainitic hold temperatures ranging from 350 °C to 500 °C were tested within thermo-mechanical treatment of 0.2C-1.5Mn-0.6S-1.5Al steel and the final microstructures were evaluated with regard to the suitability to TRIP effect and achieved mechanical properties. The microstructures were analyzed by scanning electron microscopy and mechanical properties measured by tensile test.

Atomic Scale Investigation of Solutes and Precipitates in High Strength Steels

Two steels, ferritic, high strength with interphase precipitation and nanobainitic, were used to show the advances in and application of atom probe. The coexistence of the nanoscale, interphase Nb-Mo-C clusters and stoichiometric MC nanoparticles was found in the high strength steel after thermomechanical processing. Moreover, the segregation of carbon at different heterogeneous sites such as grain boundary that reduces the solute element available for fine precipitation was observed. The APT study of the solutes redistribution between the retained austenite and bainitic ferrite in the nanobainitic steel revealed: (i) the presence of two types of the retained austenite with higher and lower carbon content and (ii) segregation of carbon at the local defects such as dislocations in the bainitic ferrite during the isothermal hold.

Enabling the Double-C Curve in Pu-Ga Alloy Time-Temperature-Transformation Diagrams

Under ambient conditions, a Pu-2.0 at.% Ga alloy is retained in the metastable δ phase. Upon cooling to approximately -120 °C, the face-centered-cubic δ phase partially transforms to the metastable monoclinic α′ phase via a martensitic transformation. The kinetics of the δ⟶α′ transformation are reported to have double-C curve kinetics in a time-temperature-transformation (TTT) diagram, but the mechanisms responsible for this unusual behavior are not understood. Our work focuses on determining the underlying cause of the two noses. Optical microscopy has been used to investigate the role of “conditioning”—an isothermal hold at sub-anneal temperatures—on the δ⟶α′ transformation and to illuminate any disparities in transformation products. Conditioning was found to affect substantially the amount of transformation that occurs at particular points corresponding to both the upper- and lower-C of the TTT diagram.

Modelling the Precipitation of Al3X Dispersoids in Aluminium Alloys and their Effect on Recrystallization

A combined model is presented that predicts the non-uniform distribution of Al3X dispersoid particles in commercial aluminium alloys containing zirconium and scandium and uses these predictions as inputs to a simple recrystallization model. The recrystallization model relies on knowledge of the stored energy in the sub-structure after deformation and this has been measured using electron backscattered diffraction (EBSD) techniques. The recrystallization model is based on the concept that partial recrystallization results from the non-uniform distribution of dispersoid particles due to their precipitation from a segregated cast structure. The model has been used to devise an improved homogenization treatment for AA7050, which uses an isothermal hold during heat up to maximize dispersoid nucleation. It has also been applied to predict the effect of scandium additions on recrystallization, investigate the factors that control the through thickness variation in recrystallized fraction, and interpret the results of experiments where the effect of strain rate have been studied.

Morphology and Microstructure Evolution of Multilayer Au/Cr/Si Thin Films Subject to Annealing

ABSTRACTAu/Cr/Si microcantilevers were studied in their as-deposited condition and annealed state, with emphasis on a thermal treatment of 225 °C for 24 hours. Change in beam curvature was monitored during isothermal hold as a function of time. Secondary grain growth was observed in the gold, which contained non-uniformly distributed twins and dislocation defects. Diffusional transport of the chromium layer was observed during annealing. Nodules arranged in the “rolling hill” topography were observed at the free surface, both before and after annealing. Nanometer thick coatings of alumina grown by atomic layer deposition improved the uniformity of both microstructure evolution and curvature evolution during high-temperature annealing.