Kinetika difuzijskog stvaranja karbidnih slojeva

Matijević, Božidar (1997) Kinetika difuzijskog stvaranja karbidnih slojeva. = Doctoral thesis , Sveučilište u Zagrebu, Fakultet strojarstva i brodogradnje, UNSPECIFIED. Mentor: Stupnišek, Mladen.

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Abstract (Croatian)

Karbidni slojevi dobiveni difuzijskim procesima imaju visoku otpornost prema različitim mehanizmima trošenja, posebno abrazijskom mehanizmu trošenja zbog njihove visoke tvrdoće. U radu je istraživana kinetika stvaranja sloja vanadijeva karbida u rastaljenoj solnoj kupki boraksa s dodatkom karbidotvornog elementa vanadija. \Na temelju raščlambe postojećih saznanja o procesima stvaranja karbidnih slojeva postavljen je fizikalni model koji stvaranje karbidnog sloja raščlanjuje u četiri koraka. Izrađen je matematički model procesa stvaranja karbidnih slojeva koji se temelj na činjenici da je pokretačka sila procesa gradijent kemijskog potencijala difundirajućeg elementa, tj. ugljika. \Na osnovu termodinamičkih ovisnosti matematičkog modela, tijek procesa je u direktnoj vezi s termodinamičkom aktivnošću ugljika u čeliku. Termodinamička aktivnost ugljika uzima u obzir sadržaj ugljika i legirajućih elemenata u čeliku pri odgovarajućoj temperaturi procesa. Za provođenje eksperimentalnog rada konstruirana je i izrađena nova namjenska ped. Na temelju dobivenih rezultata debljine sloja vanadijeva karbida na ugljičnim čelicima s različitim sadržajem ugljika određena je matematička ovisnost aktivacijske energije procesa i faktora frekvencije o termodinamičkoj aktivnosti ugljika i temperaturi procesa. Valjanost modela provjerena je eksperimentalno i pri legiranim čelicima. Dobivena je dobra korelacija između analitici određene debljine sloja vanadijeva karbida i kemijskog sastava čelika, odnosno termodinamičke aktivnosti ugljika. Izrađen je također program za izračunavanje tehnoloških parametara procesa stvaranja sloja vanadijevog karbida koji uzima u obzir kemijski sastav čelika preko termodinamičke aktivnosti ugljika.

Abstract

The carbide layers produced by diffusion processes have high resistance to the different wear mechanisms, in particular towards the abrasion wear due to their high hardness. Kinetics of formation of the vanadium carbide layer in a molten borax salt bath with addition of vanadium as the carbide-forcing element has been studied. Based on the analysis of existing knowledge on the processes leading to formation of carbide layers, a physical model has been set, according which the formation of layer is divided into four steps. A mathematical model of carbide layer formation has been designed, founded on the fact that the driving force of the process is gradient of the chemical potential of diffunding element, ie. carbon. Depending on the thermodynamic relationships of the model, course of the process is directly proportional to the thlermodynamic activity of carbon in steel. The thermodynamic activity of carbon takes into account content of carbon and alloying elements in steel at the given temperature of the process. The experimental work has been carried out in an oven specially designed and produced for the job. Based on the measured values of thicknesses of the vanadium carbide layer on carbon steels containing different carbon contents, mathematical relationship of the process activation energy and frequency factor toward the thermodynamic activity of carbon and temperature of process. Validity of the model has been tested experimentally for alloyed steels. A good correlation between analytically calculated thickness of the vanadium carbide layer. and chemical composition of steel, ie. thermodynamic activity of carbon. A computer program for determination of technological parameters of the process for producing the vanadium carbide layer, which takes into account the chemical composition of steel through thermodynamic activity of carbon, has been created.

Item Type: Thesis (Doctoral thesis)
Uncontrolled Keywords: difuzijski procesi; kinetika stvaranja karbidnih slojeva; karbidni slojevi; vanadijev karbid; rendgenska difrakcija; spektografska analiza; metalografska analiza; fizikalni model stvaranja karbidnih slojeva; matematički model
Divisions: 1000 Department of Materials > 1020 Chair of Heat Treatment and Surface Engineering
Date Deposited: 22 Sep 2014 18:00
Last Modified: 16 Oct 2015 13:20
URI: http://repozitorij.fsb.hr/id/eprint/131

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