A study of WC-X systems for potential binders for WC

This work was done to select a possible replacement for cobalt as a binder through a phase diagram approach using selected WC-X systems. The study was in two parts; experimental and calculations using Thermo-Calc. Potential binders were identified by searching for solid solution formation, a similar...

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Main Author: Kumi, David Ofori
Format: Others
Language:en
Published: 2012
Online Access:http://hdl.handle.net/10539/11218
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spelling ndltd-netd.ac.za-oai-union.ndltd.org-wits-oai-wiredspace.wits.ac.za-10539-112182019-05-11T03:42:05Z A study of WC-X systems for potential binders for WC Kumi, David Ofori This work was done to select a possible replacement for cobalt as a binder through a phase diagram approach using selected WC-X systems. The study was in two parts; experimental and calculations using Thermo-Calc. Potential binders were identified by searching for solid solution formation, a similar melting point to cobalt, and a small solubility for WC as main requirements, from phase diagrams. The experimental samples were designed to be 50 at.% WC and 50 at.% binder for easy manufacturing and analysis, even though this is not an optimum amount for application. Twelve different alloy compositions were prepared and were analysed in both as-cast and heat treated conditions. The samples were annealed at 1000ºC for 168 hours under vacuum. Microstructure characterization was carried out on two scanning electron microscopes with EDX, and X-ray diffraction was done. Two sets of calculations were made, with one comprising the same composition studied experimentally (50 at.% WC and 50 at.% binder), and a more realistic composition comprising 90 at.% WC and 10 at.% binder. The latter was done to give a better understanding to the experimental microstructures. Most of the WC decomposed into W2C; this was attributed to the high temperature of the arc-melter and should not occur on normal hard metal preparation. Most of the compositions calculated had solid solution binders and WC. Thermo-Calc could not predict the decomposition of the carbide phase at high temperature. Some phases identified were similar in both the experiments and calculations. Sample W25:C25:Ni43:V7 had the binder phase initially solidifying as (Ni) but transformed into ~Ni2V on cooling; it was identified as the most likely alloy to replace cobalt but will still need further work such as preparing a more realistic composition, manufacturing by sintering, and comparing properties such as hardness with WC-Co. Thus, the binder composition was selected from the Ni-V binary system. 2012-01-31T11:24:00Z 2012-01-31T11:24:00Z 2012-01-31 Thesis http://hdl.handle.net/10539/11218 en application/pdf application/pdf
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language en
format Others
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description This work was done to select a possible replacement for cobalt as a binder through a phase diagram approach using selected WC-X systems. The study was in two parts; experimental and calculations using Thermo-Calc. Potential binders were identified by searching for solid solution formation, a similar melting point to cobalt, and a small solubility for WC as main requirements, from phase diagrams. The experimental samples were designed to be 50 at.% WC and 50 at.% binder for easy manufacturing and analysis, even though this is not an optimum amount for application. Twelve different alloy compositions were prepared and were analysed in both as-cast and heat treated conditions. The samples were annealed at 1000ºC for 168 hours under vacuum. Microstructure characterization was carried out on two scanning electron microscopes with EDX, and X-ray diffraction was done. Two sets of calculations were made, with one comprising the same composition studied experimentally (50 at.% WC and 50 at.% binder), and a more realistic composition comprising 90 at.% WC and 10 at.% binder. The latter was done to give a better understanding to the experimental microstructures. Most of the WC decomposed into W2C; this was attributed to the high temperature of the arc-melter and should not occur on normal hard metal preparation. Most of the compositions calculated had solid solution binders and WC. Thermo-Calc could not predict the decomposition of the carbide phase at high temperature. Some phases identified were similar in both the experiments and calculations. Sample W25:C25:Ni43:V7 had the binder phase initially solidifying as (Ni) but transformed into ~Ni2V on cooling; it was identified as the most likely alloy to replace cobalt but will still need further work such as preparing a more realistic composition, manufacturing by sintering, and comparing properties such as hardness with WC-Co. Thus, the binder composition was selected from the Ni-V binary system.
author Kumi, David Ofori
spellingShingle Kumi, David Ofori
A study of WC-X systems for potential binders for WC
author_facet Kumi, David Ofori
author_sort Kumi, David Ofori
title A study of WC-X systems for potential binders for WC
title_short A study of WC-X systems for potential binders for WC
title_full A study of WC-X systems for potential binders for WC
title_fullStr A study of WC-X systems for potential binders for WC
title_full_unstemmed A study of WC-X systems for potential binders for WC
title_sort study of wc-x systems for potential binders for wc
publishDate 2012
url http://hdl.handle.net/10539/11218
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