Browsing by Subject "XRD analysis"

Now showing 1 - 2 of 2

Open Access
Increasing Ti-6Al-4V brazed joint strength equal to the base metal by Ti and Zr amorphous filler alloys
(2012) Ganjeh, E.; Sarkhosh H.; Bajgholi, M.E.; Khorsand H.; Ghaffari, M.
Microstructural features developed along with mechanical properties in furnace brazing of Ti-6Al-4V alloy using STEMET 1228 (Ti-26.8Zr-13Ni-13.9Cu, wt.%) and STEMET 1406 (Zr-9.7Ti-12.4Ni-11.2Cu, wt.%) amorphous filler alloys. Brazing temperatures employed were 900-950 °C for the titanium-based filler and 900-990 °C for the zirconium-based filler alloys, respectively. The brazing time durations were 600, 1200 and 1800 s. The brazed joints were evaluated by ultrasonic test, and their microstructures and phase constitutions analyzed by metallography, scanning electron microscopy and X-ray diffraction analysis. Since microstructural evolution across the furnace brazed joints primarily depends on their alloying elements such as Cu, Ni and Zr along the joint. Accordingly, existence of Zr 2Cu, Ti 2Cu and (Ti,Zr) 2Ni intermetallic compounds was identified in the brazed joints. The chemical composition of segregation region in the center of brazed joints was identical to virgin filler alloy content which greatly deteriorated the shear strength of the joints. Adequate brazing time (1800 s) and/or temperature (950 °C for Ti-based and 990 °C for Zr-based) resulted in an acicular Widmanstätten microstructure throughout the entire joint section due to eutectoid reaction. This microstructure increased the shear strength of the brazed joints up to the Ti-6Al-4V tensile strength level. Consequently, Ti-6Al-4V can be furnace brazed by Ti and Zr base foils produced excellent joint strengths. © 2012 Elsevier Inc. All rights reserved.
Embargo
Phase transformation and structural development in mechano-synthesized calcium-copper-titanate electroceramics
(Elsevier Ltd, 2024-11-27) Alizadeh, M.; Ardakani, H.A.; Amini, R.; Ghaffari, Mohammad; Pashangeh, S.; Vincenzini, P.
This research focuses on the mechano-synthesis of synthesizing calcium-copper-titanate (CCTO) powder through mechanical alloying of the respective oxides aiming to optimize the production of nanoscale electroceramics with high dielectric properties. Structural characterization was carried out using X-ray diffraction with Rietveld refinement (phase identification and quantification), while transmission electron microscopy was employed to observe particle size changes including the reduction of particle size to nanometric scales (10–35 nm). The mechano-synthesis process involving CaO, CuO, and $TiO_2$ resulted in the creation of perovskite CCTO, with minimal contamination observed from the milling process. Significant particle size reduction, nanostructure formation, and a high level of amorphization, alongside polymorphic transitions in $TiO_2$ during milling that played a critical role in achieving full amorphization, which was essential for the formation of high-purity CCTO. The study demonstrates that after 256 h of milling, 88 wt% of the powder consisted of crystalline CCTO, highlighting the potential for enhanced performance in dielectric and microelectronic applications. There was no detection of either stoichiometric CCTO or any non-stoichiometric phases prior to the complete amorphization of the powders. Therefore, results revealing significant advancements in particle size reduction, nanostructure formation, and amorphization, which influence enhanced material performance. Nucleating and growing the CCTO phase directly from an amorphous state without the formation of intermediate crystalline phases clears the potential for optimizing CCTO production processes.