Browsing by Subject "Alloying elements"

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    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.
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    Microstructural association between mechanical behavior with bending fracture surfaces in Astaloy CrA sintered parts alloyed by Cu and C
    (Elsevier Ltd, 2014) Khorsand H.; Ghaffari, M.; Ganjeh, E.
    Application of powder metallurgy technique, a method presenting both economic and technical concepts for producing sintered parts, has been expanding in automobile and other engineering industries. Powder metallurgy parts usually possess residual porosity in their microstructures deteriorating mechanical performance. There have been many solutions to increasing of strength in these parts such as applying different heat treatment or adding alloying elements. It is well known that Fe-Cu-C is the one of main alloying system for both increasing the strength and decreasing cost of them. In this study, the microstructure, mechanical properties (transverse rapture strength and hardness), crack behavior and fracture modes of a low alloy Fe-Cr powder (Astaloy CrA) with different amount of copper (0, 1 and 2. wt.%) and carbon, in form of graphite (0.45, 0.6 and 0.8. wt.%) sintered at conventional condition have been investigated. Microstructural evolution showed adding copper and graphite as alloying elements could generate widespread of strength (857-1380. MPa) and hardness (170-295 HV5). Developing different phases in microstructure was the main reason for various mechanical properties. Crack coalescence phenomenon leads to fracturing with ductile (at sinter-necks) and brittle morphology. Micro-mechanism of fracture related to transparticle and interparticle crack propagation. © 2013 Elsevier Ltd.