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Research & Reviews: Journal of Material Sciences | ISSN: 2321-6212 | Volulme 6
November 07-08, 2018 | Atlanta, USA
Materials Science and Engineering
15
th
International Conference and Exhibition on
Applied Crystallography
3
rd
International Conference on
&
Microstructural evolution of nanocrystalline tungsten-25% rhenium-hafnium carbide composite
synthesized by spark plasma sintering technique for FSW tool application
Zafar Iqbal
Pakistan Institute of Engineering and Applied Sciences, Pakistan
D
evelopment of nanocrystalline tungsten-25% rhenium alloy reinforced with hafnium carbide is a challenging task as these alloys
are difficult to synthesize by conventional methods. The problem of these difficult to alloy elements can be addressed by using
a unique combination of mechanical alloying and spark plasma sintering (SPS) techniques via powder metallurgy route. Rhenium
was added to a lower ductile-to-brittle transition temperature and to increase recrystallization temperature of tungsten. SPS is a rapid
consolidating technique which prevents grain growth. These tool materials can withstand high temperatures and harsh conditions
in joining application such as Friction Stir Welding (FSW) of steel and titanium alloys. FSW is a green process which does not
emit fume and toxic fumes during the process. Sintering was carried between 1500-1800
o
c. Mechanically alloyed and spark plasma
sintered alloy and composite were characterized by optical microscopy, field emission scanning electron microscopy (FESEM) and
X-ray diffraction. Microstructural investigation of consolidated specimens was initially carried out by conventional etching and
metallography techniques. Optical micrographs showed no visible signs of grain boundary etching. Spark plasma sintered samples
were further electrochemically etched in one molar concentrated solution of NaOH. The positive terminal of the low voltage direct
current power supply was connected to the sample. The negative terminal was connected to a steel plate acting as a cathode. Both
electrodes were placed in the tank face to face with a gap of 6 to 10 centimeters between them. The voltage was kept constant at 5
volts during the etching process. The sample was etched for a short time interval from 1 to 5 seconds and microstructural analysis
was conducted after each etching step. The results of the FESEM images confirm microstructural revelation of these difficult to etch
alloy and composites.
zafariqbal@pieas.edu.pkRes. Rev. J Mat. Sci. 2018, Volume 6
DOI: 10.4172/2321-6212-C8-036