Processing and characterization of high density tungsten-nickel-iron alloys

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2013

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Çalışkan, Necmettin Kaan

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In the present study, processing of W-Ni-Fe alloys by liquid phase sintering technique has been investigated. Effect of sintering atmospheres (hydrogen and vacuum), tungsten content altering from 90 to 97 wt.%, Ni/Fe ratio varied from 2 to 4 and post sintering treatments (heat treatment and swaging) on the microstructure and mechanical properties of W-Ni-Fe alloys have been analyzed. Liquid phase sintered alloys were characterized by mechanical tests, electron microscopy and XRD studies, thermal analyses and quantitative metallographic methods. An optimum sintering cycle was investigated and applied to the W-Ni-Fe alloys. It has been observed that reduction under hydrogen led to superior mechanical properties due to better wetting of the surface oxide layer free tungsten particles by the binder phase. After characterization studies, it was found that ductility degrades significantly with the increase in contiguity upon an increase in tungsten content which also induces the transformation of dominant fracture mechanism from transgranular to intergranular fracture. Moreover, liquidus temperatures and tungsten solubility of the binder phase were found to increase with an increase in the Ni/Fe ratio which resulted in higher volume fraction of binder phase and better mechanical properties. It was also found that subsequent heat treatment also results in increase in volume fraction of the binder phase and reduction in contiguity which lead to better ductility. Tensile strength and hardness of the alloys increased after deformation due to higher dislocation density which but this also leads to an increase in the matrix failure as well as number of transgranular failure.

Subject Keywords

Sintering., Sinter (Metallurgy)., Powder metallurgy., Iron, Tungsten, Nickel

URI

http://etd.lib.metu.edu.tr/upload/12616169/index.pdf
https://hdl.handle.net/11511/22833

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Graduate School of Natural and Applied Sciences, Thesis

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Citation Formats

N. K. Çalışkan, “Processing and characterization of high density tungsten-nickel-iron alloys,” Ph.D. - Doctoral Program, Middle East Technical University, 2013.