University of Wolverhampton
Browse
Collection All
bullet
bullet
bullet
bullet
Listed communities
bullet
bullet
bullet
bullet
bullet
bullet
bullet
bullet
bullet
bullet
bullet
bullet
bullet

Wolverhampton Intellectual Repository and E-Theses > E-Theses > E-Theses > Consolidation of WC-Co nanocomposites synthesised by mechanical alloying

Please use this identifier to cite or link to this item: http://hdl.handle.net/2436/106834
    Del.icio.us     LinkedIn     Citeulike     Connotea     Facebook     Stumble it!



Title: Consolidation of WC-Co nanocomposites synthesised by mechanical alloying
Authors: Hewitt, Stephen A.
Advisors: Kibble, Kevin A.
Publisher: University of Wolverhampton
Issue Date: 2009
URI: http://hdl.handle.net/2436/106834
Abstract: The influence of mechanical alloying (MA) milling time, temperature, sintering method and microstructure on the mechanical properties of a tungsten carbide-cobalt (WC-Co) hardmetal, based on 10wt% Co, has been established. The effects of high-energy milling for 30, 60, 180 and 300 min and the interrelation between milling time and powder properties, and the resultant effects on the mechanical properties of the consolidated WC-10Co material, has been obtained for a horizontally designed ball mill. Nanostructured WC-10Co powder was synthesised after 60 min cyclic milling at room temperature with an average WC domain size of 21 nm. In direct comparison, a WC-10Co composition MA at -30°C for 60 min produced an average WC domain size of 26 nm with a higher lattice strain. WC domain size showed a slight increase with milling time, measured at 27 nm after 300 min ball milling. Extended ball milling (300 min) reduced the mean particle size from 0.148 μm for 60 min milling to 0.117 μm. Thermal analysis showed that the onset temperature of the WC-Co eutectic was related to particle size with increased milling time reducing the onset temperature from 1344°C after 60 min milling to 1312°C after 300 min milling. Onset temperature was further reduced by the addition of vanadium carbide (VC), reducing the onset temperature to 1283°C after 300 min milling. Powder contamination increased with increased milling time with Fe content measured at ~ 3wt% after 300 min ball milling. Milling at -30°C reduced Fe contamination to an almost undetectable level. Increased ball milling time resulted in decreased levels of green density with the powders milled for 30 and 300 min achieving 62.5% and 59.5% TD, respectively. Relative density increased for the powder milled at -30°C compared to the RT milled powder due to its flattened, slightly rounded morphology. A large difference in VC starting particle size compared to WC and Co led to non-uniform dispersion of the inhibitor during milling. Densification and hardness reached optimum levels for the 60 min milled powder for both pressureless sintering and sinter-HIP. Both properties decreased with increased milling time, regardless of the sintering method. Low temperature milling resulted in a higher hardness value of 1390 HV30 compared to 1326 HV30 for the 60 min, RT milled material after pressureless sintering. Densification levels of the doped materials were restricted to < 90% TD for both sintering methods due to inhomogeneity in the microstructures. Palmqvist fracture toughness (WK) of the RT milled powders increased with increased milling time and increasing WC grain size for both sintering methods. WK reached 11.6 MN.m3/2 with 300 min milling after pressureless sintering but reached 16.1 MN.m32 for the same material after sinter-HIP due to the effect of mean WC grain size and binder phase mean free path. The -30°C milled powder exhibited higher fracture toughness for both sintering methods than the 60 min, RT milled material. Spark plasma sintering (SPS) showed that the onset of densification was dependent upon particle size with the powder from 300 min milling showing an onset temperature of ~ 800°C compared to ~ 1000°C for the 60 min milled powder. The low temperature milled powder showed an onset temperature of ~ 980°C, which suggested that low temperature milling provided enhanced densification kinetics.
Type: Thesis or dissertation
Language: en
Description: A thesis submitted in partial fulfilment of the requirements of the University of Wolverhampton for the degree of Doctor of Philosophy
Keywords: Tungsten carbide
Cobalt
Mechanical alloying
Nanostructured
Milling time
Sintering
Appears in Collections: E-Theses

Files in This Item:
File Description Size Format View/Open
SA Hewitt e-thesis.pdf16029KbAdobe PDFThumbnail
View/Open

All Items in WIRE are protected by copyright, with all rights reserved, unless otherwise indicated.

 

Fairtrade - Guarantees a better deal for Third World Producers

University of Wolverhampton, Wulfruna Street, Wolverhampton, WV1 1LY

Course enquiries: 0800 953 3222, General enquiries: 01902 321000,
Email: enquiries@wlv.ac.uk | Freedom of Information | Disclaimer and copyright | Website feedback | The University as a charity

OR Logo Powered by Open Repository | Cookies