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Binder Migration in Double Pressed Drill Bit Inserts

Bjerke, Axel LU (2018) FYSM30 20172
Department of Physics
Solid State Physics
Abstract
It is possible to produce functionally graded cemented carbides on a large scale by double pressing. Being able to predict the binder migration in WC-Co cemented carbides during the sintering is essential to the design of such cemented carbides. The cobalt content is one of the main factors determining the hardness gradient. The cobalt binder migrates from large to small grains, from high cobalt concentrations to low and from high carbon concentrations to low. This has been shown qualitatively and quantitatively. However, the models and theory is not developed enough to be able to accurately predict and design hardness gradients in cemented carbides.

This research begins by investigating past experiments and models. Then proceeds by... (More)
It is possible to produce functionally graded cemented carbides on a large scale by double pressing. Being able to predict the binder migration in WC-Co cemented carbides during the sintering is essential to the design of such cemented carbides. The cobalt content is one of the main factors determining the hardness gradient. The cobalt binder migrates from large to small grains, from high cobalt concentrations to low and from high carbon concentrations to low. This has been shown qualitatively and quantitatively. However, the models and theory is not developed enough to be able to accurately predict and design hardness gradients in cemented carbides.

This research begins by investigating past experiments and models. Then proceeds by producing and investigating double pressed drill bit inserts for top hammers. Lastly, the research made new and further develop earlier migration equilibrium models and diffusion simulations. This research shows that the migration pressure models are reasonably accurate for certain grain size ranges. A modified version of a surface/interface energy minimization model without any fitting was also used. Which can predict the migration to a similar extent and it can be applied to a larger range of grain sizes. It also provides a maximum gradient in cobalt due to a grain size gradient. This paper also shows that diffusion simulations alone cannot adequately explain the migration, and that some type of bulk flow is likely to occur during sintering.

Some double pressed drill bit inserts with hardness gradients can be designed using these models of binder migration. More theoretical development and experiments are suggested to test and develop our understanding of binder migration in WC-Co cemented carbides. (Less)
Popular Abstract
Hard materials do not wear down, they break. Take diamond for example, the hardest natural material, which still breaks with the strike of a hammer and turns in to graphite at around 800 C. Hence using a pure diamond tool for drilling in rock is then as effective as trying to drill with your office pencil.

This is not the case for cemented carbides (hard metals). They are almost as hard as diamond, but they do not break as easily and do not turn in to dust at high temperatures. Cemented carbides are therefore one of the best materials for drilling in rock, cutting in steels, pressing other hard metals and actually any other application where a hard and tough material is needed.

Cemented carbides contain grains almost as hard as... (More)
Hard materials do not wear down, they break. Take diamond for example, the hardest natural material, which still breaks with the strike of a hammer and turns in to graphite at around 800 C. Hence using a pure diamond tool for drilling in rock is then as effective as trying to drill with your office pencil.

This is not the case for cemented carbides (hard metals). They are almost as hard as diamond, but they do not break as easily and do not turn in to dust at high temperatures. Cemented carbides are therefore one of the best materials for drilling in rock, cutting in steels, pressing other hard metals and actually any other application where a hard and tough material is needed.

Cemented carbides contain grains almost as hard as diamond and a couple of micro meters in diameter. These grains are held together by a tough binder. The focus here is on grains of tungsten and carbon, in a cobalt binder, used for inserts in rock drilling bits.

Simply put, more binder makes the material tougher but softer, smaller grains makes the material harder but more brittle. Making a material with a hard shell and a tough core, would be a possible solution to prevent wear without making it brittle. Like an armadillo or cell phone case.

Cemented carbides are produced from a powder which is pressed and then heated. The tough binder distributes itself through the piece during heating. Hence, binder concentrations will differ before and after heating. The distribution depends largely on the initial binder distribution, grain sizes and the initial carbon distribution.

This general idea has been known for more than fifty years, but there has been an increase in published research in the last decade. Today the tools for manufacturing such pieces are now available. But the theory is not fully developed and modeling efforts are just starting to take place.

This research reviews past theory and experiments to further develop it. Inserts are also manufactured, tested and the binder migration is modeled. Leading to a better understanding of the material and the ability to make new harder, better and stronger materials. (Less)
Popular Abstract (Swedish)
Hårda material slits inte, de knäcks. Diamant är ett bra exempel eftersom det är det hårdaste naturligt förekommande materialet. Diamant slits inte, men det knäcks om man slår det med en hammare och det blir till grafit vid cirka 800◦ C. Att försöka använda diamant till bergborrning är alltså lika effektivt som att borra med en blyertspenna.

Så är inte fallet för hårdmetall. Hårdmetall är nästan lika hårt som diamant, men det knäcks inte lika lätt och det omvandlas inte till ett pulver vid höga temperaturer. Detta gör hårdmetall till ett av de bästa materialen för bergborrning, skärande bearbetning, pressverktyg eller vilket område som helst där ett hårt och segt material behövs.

Hårdmetall innehåller små korn som är nästan lika... (More)
Hårda material slits inte, de knäcks. Diamant är ett bra exempel eftersom det är det hårdaste naturligt förekommande materialet. Diamant slits inte, men det knäcks om man slår det med en hammare och det blir till grafit vid cirka 800◦ C. Att försöka använda diamant till bergborrning är alltså lika effektivt som att borra med en blyertspenna.

Så är inte fallet för hårdmetall. Hårdmetall är nästan lika hårt som diamant, men det knäcks inte lika lätt och det omvandlas inte till ett pulver vid höga temperaturer. Detta gör hårdmetall till ett av de bästa materialen för bergborrning, skärande bearbetning, pressverktyg eller vilket område som helst där ett hårt och segt material behövs.

Hårdmetall innehåller små korn som är nästan lika hårda som diamant och de är bara ett par mikrometer i diameter. Dessa korn hålls ihop av en seg bindemetall. Detta arbete rör korn gjorda av volfram och kol i en bindemetall av kobolt, vilket används till bergborrstift.

Mer bindemetall gör materialet segare men mjukare och små korn gör det hårdare men sprödare, för att enkelt sammanfatta egenskaperna. Ett hårt skal och ett segt inre är en möjlig lösning, om man vill skapa ett material som är hårt men inte sprött. Ungefär som ett bältdjur eller ett mobilskal.

Hårdmetall tillverkas från ett pulver som pressas och sedan värms. Den sega bindemetallen sprider sig genom hårdmetallen under upphettningen. Detta leder till att kompositionen av bindefas och korn förändras under upphettningen. Hur bindemetallen då sprider sig beror på kornens storlek, koncentrationen av bindemetall och kolhalten.

Denna idén som ett koncept har funnits i mer än femtio år och forskningen har tilltagit de senaste tio åren. Maskiner för att skapa sådana hårdmetaller blev också nyligen tillgängliga. Men det finns fortfarande många glapp i teorin och försök att moddlera processen har just börjat.

Den här forskningen undersöker tidigare teori och experiment för att bygga vidare på den. Framställning och karakterisering av bergborrstift och modellering av bindemetallspridningen görs också. Detta leder till en bättre förståelse av materialet och en möjlighet att skapa nya hårdare, bättre ochstarkare material. (Less)
Please use this url to cite or link to this publication:
author
Bjerke, Axel LU
supervisor
organization
course
FYSM30 20172
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
8934205
date added to LUP
2018-02-05 11:57:07
date last changed
2018-02-05 11:57:07
@misc{8934205,
  abstract     = {{It is possible to produce functionally graded cemented carbides on a large scale by double pressing. Being able to predict the binder migration in WC-Co cemented carbides during the sintering is essential to the design of such cemented carbides. The cobalt content is one of the main factors determining the hardness gradient. The cobalt binder migrates from large to small grains, from high cobalt concentrations to low and from high carbon concentrations to low. This has been shown qualitatively and quantitatively. However, the models and theory is not developed enough to be able to accurately predict and design hardness gradients in cemented carbides.

This research begins by investigating past experiments and models. Then proceeds by producing and investigating double pressed drill bit inserts for top hammers. Lastly, the research made new and further develop earlier migration equilibrium models and diffusion simulations. This research shows that the migration pressure models are reasonably accurate for certain grain size ranges. A modified version of a surface/interface energy minimization model without any fitting was also used. Which can predict the migration to a similar extent and it can be applied to a larger range of grain sizes. It also provides a maximum gradient in cobalt due to a grain size gradient. This paper also shows that diffusion simulations alone cannot adequately explain the migration, and that some type of bulk flow is likely to occur during sintering.

Some double pressed drill bit inserts with hardness gradients can be designed using these models of binder migration. More theoretical development and experiments are suggested to test and develop our understanding of binder migration in WC-Co cemented carbides.}},
  author       = {{Bjerke, Axel}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Binder Migration in Double Pressed Drill Bit Inserts}},
  year         = {{2018}},
}