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Effect of Ta-doped WC on the formation of graded cemented carbides
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
2013 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

One way of changing the hexagonal tungsten carbide crystal (WC) is to dope WC with transition metals. In this master thesis the influence of different levels of tantalum doping in the simple hexagonal WC-structure have been investigated focusing on the effects on the gamma-phase free gradient formation, the overall microstructure and the microhardness. Samples with tailored compositions have been designed with thermodynamic calculations and sintered in vacuum conditions in order to study the formation of the gradient surface layers. A number of different techniques have been used to characterize the sintered pieces. Light optical microscopy and scanning electron microscopy were applied to investigate the microstructure. Energy dispersive x-ray spectroscopy was used to determine element distribution and to carry out chemical analysis of phases. X-ray diffraction was applied to determine changes in lattice parameters of the WC phase. Microhardness profiles were determined by microindentation. Results show a remarkable influence of Ta-doped-WC on gradient layer thickness, volume fraction of gamma-phase and microhardness levels in the graded cemented carbides. By using Ta-doped-WC less gamma-phase volume fraction and an increased gradient layer thickness is obtained. Also, samples produced with Ta-doped-WC present lower microhardness values compared to samples produced with conventional undoped-WC.

Abstract [sv]

Ett sätt att ändra WC kristallen är att dopa WC med övergångsmetaller. I detta examensarbete har effekterna av dopning med olika mängder av tantal i den hexagonala WC strukturen undersökts med fokus på gradienten utan gamma-fas, mikrostrukturen samt mikrohårdheten. Prover med skräddarsydda sammansättningar har utformats med hjälp av termodynamiska beräkningar och sintrats under vakuum för att kunna studera gradienten. Ett antal olika metoder har använts för att karakterisera de sintrade proverna. Ljus-optisk-mikroskopi och svepelektron-mikroskopi användes för att karakterisera mikrostrukturen. Energi-röntgen-spektroskopi användes för element distribution och kemisk analys. Röntgen-diffraktion tillämpades för att fastställa förändringar i gitterparametrarna. Mikrohårdheten bestämdes genom mikrohårdhetsmätning. Resultaten visar en anmärkningsvärd påverkan av Ta-dopad-WC avseende på gradienttjockleken, volymandel gamma-fas och mikrohårdheten i de graderade hårdmetallerna. Genom att använda Ta-dopat-WC fås mindre gamma-fas och tjockare gradient. Dessutom visar Ta-dopade-WC prover längre mikrohårdhet jämfört med odopade-WC prover.

Place, publisher, year, edition, pages
National Category
Materials Engineering
URN: urn:nbn:se:kth:diva-127828OAI: diva2:646318
Subject / course
Materials Science and Engineering
Educational program
Master of Science in Engineering - Materials Design and Engineering
Available from: 2013-09-09 Created: 2013-09-08 Last updated: 2013-09-09Bibliographically approved

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