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The Effect of Some Production Parameters on Microstructure, Physical and Mechanical Properties of Powder Metallurgically Produced (90W-7Ni-3Fe) Heavy Alloy

Zarshenas Moghaddam, Saeed | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 46560 (07)
  4. University: Sharif University of Technology
  5. Department: Materials science and Engineering
  6. Advisor(s): PourAzarang, Kazem; Abachi, Parvin
  7. Abstract:
  8. In applications requiring high density and good mechanical properties, tungsten heavy alloys are of interest [1]. Due to lack of intermetallic phase in microstructure of 90W-7Ni-3Fe alloy, it is more attractive to use. At present work, the powder metallurgically produced specimens were cold swaged. At this work, during the production and swaging, some parameters were changed. Powders of tungsten, nickel and iron were milled for an hour with the speed of 50 rpm in Retsch Planetry/PM 400 MA ball mill. At the first route, elemental powders mixture after 1 minute were reached to 30MPa, after that were heated at rate of 50°C/min to 1500°C in vacuum (hot press or HP). At the second route, powders mixture were cold pressed with isostatic pressure and then sintered with two different procedures (The first and second routes were named CM and CS, respectively). The sintering temperature was 1480°C and holding time 30 minutes. The heating rate was selected as 50°C/min at hydrogen atmosphere. Pre-sintering temperature was performed at 700°C (for route 1) and 1200°C (for route 2) for 30 minutes to eliminate absorbed gases at specimens. The Cooling surfaces rate from sintering temperature for CM specimens was 5°C/min. The CS specimens cooled in turned off furnace.The Diameter of HP specimens, CM specimen and CS specimen were reduced from 5.5mm to 4.5mm, 10.1mm to 3.2mm and 5.3mm to 3.4mm respectively. The influences of this parameters on Microstructure, physical and mechanical properties were investigated. Microstructure of all specimens was investigated using VEGA/TESCAN-XMU SEM and Reicherd-Jung/MeF3A optical microscopy. Density of them was measured and then EDS and XRD was done. Microhardness and pressure tests, vertically and horizontally to the swage axis were done according to the standards.The microstructure of HP specimens showed that tungsten grains are near each other with long tungsten-tungsten interface and the microstructure of CS and CM specimens includes nearly spherical tungsten grains. The size of tungsten grains in CS specimens were smaller than that of CM. The relative density of hot pressed specimen (HP) was 99.7% which was more than other specimens. Microhardness of Ni-rich phase of CS specimen was more than that of CM, before and after the swage. According to compression test results, the yield stress of CS specimen were higher than that swaged and not swaged specimens. Also yield stress of CS specimen was more in comparison to previous studies
  9. Keywords:
  10. Microstructure ; Liquid Phase Sintering ; Powder Metallurgy ; Swage ; Cold Isostatic Press

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