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

Çalışkan, Necmettin Kaan
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.


Production and characterization of porous titanium alloys
Esen, Ziya; Bor, Şakir; Department of Metallurgical and Materials Engineering (2007)
In the present study, production of titanium and Ti6Al4V alloy foams has been investigated using powder metallurgical “space holder technique” in which magnesium powder were utilized to generate porosities in the range 30 to 90 vol. %. Also, sintering of titanium and Ti-6Al-4V alloy powders in loose and compacted condition at various temperatures (850-1250oC) and compaction pressures (120-1125 MPa), respectively, were investigated to elucidate the structure and mechanical properties of the porous cell walls...
Sinter-hardening studies distaloy DH powders with varying carbon contents
Kılıç, Gülten; Ögel, Bilgehan; Durlu, Nuri; Department of Metallurgical and Materials Engineering (2013)
In this study, the effect of sinter-hardening on the mechanical properties of Distaloy DH (Fe-2Cu-1.5Mo) powder with 0.4%, 0.6%, and 0,8% graphite additions, was investigated. Powder samples were pressed under 600 MPa, and sintered at 1120°C under endogas from methane for 20 minutes in an industrial sintering furnace. After sintering the samples were cooled with three different cooling rates (0.5°C/sec,1.5°C/sec, and 3°C/sec). Microstructural characterization of samples were done with optical and electron m...
Investigation of the effect of orientation and heat treatment on the stress corrosion cracking susceptibility of 7050 aluminium alloy
Çevik, Gül; Doruk, Mustafa; Department of Metallurgical and Materials Engineering (2004)
In the present work, the effect of variation in specimen orientation and heat treatment on the Stress Corrosion Cracking (SCC) susceptibility of 7050 aluminum alloy was investigated in 3,5% NaCl solution and under freely corroding conditions. For this purpose, Constant Extension Rate Tests (CERT) was performed on precracked Compact Tension (CT) specimens and the Direct Current Potential Drop technique was applied to measure the crack lengths. In addition to crack length versus time curves, the relationship ...
Synthesis and characterization of nickel based bulk amkorphous alloys
Arslan, Hülya; Mekhrabov, Amdulla O.; Department of Metallurgical and Materials Engineering (2004)
The aim of this study is to synthesize and characterize new bulk amorphous alloys in the Ni- based systems. Theoretical studies on the basis of semi-empirical rules and the electronic theory of alloys in pseudopotential approximation has been provided in order to predict the impurity elements that will lead to an increase in the glass forming ability of Ni-based alloy systems. Glass forming ability of ten different compositions of alloys of Ni-Nb, Ni-Fe, Ni-B, Ni-Hf and Ni-Cr was simulated by using FORTRAN ...
Characterization of Ti-6Al-4V alloy foams synthesized by space holder technique
ESEN, ZİYA; Bor, Sakir (2011-03-25)
Ti-6Al-4V foams, biomedical candidate materials, were synthesized by powder metallurgical space holder technique as a result of evaporation of magnesium to achieve desired porosity content. Final products contained porosities in the range similar to 43-64% with an average macropore size between 485 and 572 mu m and a lamellar type Widmanstatten microstructure composed of alpha-platelets and beta-laths. Unlike the case of bulk Ti-6Al-4V alloy tested under compression loading, compression stress-strain curves...
Citation Formats
N. K. Çalışkan, “Processing and characterization of high density tungsten-nickel-iron alloys,” Ph.D. - Doctoral Program, Middle East Technical University, 2013.