Izboljšanje oksidacijske odpornosti volframovega kompozita s karbidnimi vključki z dodatkom kroma in itrija

Simonič, David (avtor), Iveković, Aljaž (mentor), Meden, Anton (komentor)

Za tehnološki razvoj na področju visokotemperaturnih procesov potrebujemo boljše termično odporne materiale. Na tem področju se je volfram izkazal kot potencialno primeren material. Čeprav ima mnogo pozitivnih lastnosti, ima tudi nekatere pomanjkljivosti, ena od teh je relativno slaba oksidacijska odpornost pri visokih temperaturah. V dosedanjih raziskavah se je izkazalo, da dodatek volframovega karbida prepreči oksidacijo med sintranjem in izboljša nekatere mehanske lastnosti materiala. Pri čistemu W pa dodatek kroma in itrija pripomore k izboljšanju površinske oksidacijske zaščite, zato bi bilo smiselno preveriti vpliv dodatka Cr in Y na kompozit volframa s karbidnimi vključki. Namen dela je bil izboljšati visokotemperaturno oksidacijsko odpornost volframovih kompozitov s karbidnimi vključki z dodatkom kroma in itrija. Različne količine Cr in Y sem dodal W in WC ter nato nastalo zmes sintral. Tako pripravljenim vzorcem smo z dinamično termogravimetrično analizo do temperature 1050 °C preverili oksidacijsko odpornost. Homogene mešanice prahov W, WC, Cr in Y sem pripravil z mokrim mletjem v planetarnem mlinu, nato sem suspenzijo zamrznil in topilo sublimiral pod znižanim tlakom. Prahove sem sintral na FAST način. Za sintranje sem moral določiti optimalno maksimalno temperaturo in tlak. Sintranim vzorcem sem z rentgensko analizo določil fazno sestavo in z vrstičnim elektronskim mikroskopom preveril njihovo mikrostrukturo. Na SEM sliki volframovega kompozita s karbidnimi vključki vidimo samo eno glavno fazo. Ko volframovemu kompozitu s karbidnimi vključki dodamo Cr, opazimo nastanek črnih zrn kromovih oksidov. Pri dodatkih 10 ut. % Cr in več poleg tega opazimo novo glavno fazo, strjeno tekoče omrežje. Pri vzorcu z 10 ut. % Cr v tej fazi opazimo z W bogate dendrite, ki pri večjem dodatku Cr izginejo. Obe glavni fazi sta z volframom bogati fazi. Dodatek Y na mikrostrukturo nima opaznega vpliva. S termogravimetrično analizo sem določil temperaturo, pri kateri se začnejo mase vzorcev povečevati. Ta temperatura se viša z večanjem količine dodanega Cr v vzorcih. Dodatek Y pa ni imel bistvenega vpliva na to temperaturo. Poleg tega sem primerjal povečanje celokupne mase vzorcev. Dodatek Cr ni sorazmeren povečanju mase. Najmanj se je povečala masa vzorca brez dodatka, ki je primerljiv vzorcu z najmanjšim dodatkom Cr. Tem sledi vzorec z največjim dodatkom Cr. Največje povečanje celokupne mase je nastopilo pri vzorcu z 10 ut. % dodatka Cr. Masa se veča z večanjem količine dodanega Y. Prav tako sem določil prisotne faze v oksidni plasti, ki nastane po oksidaciji vzorca ter preveril mikrostrukturo in stik z vzorcem.

• Jezik: Slovenski jezik
• Ključne besede: Oksidacijska zaščita, termogravimetrijska analiza, FAST, začetna temperatura naraščanja mase, neto povečanje mase.
• Vrsta gradiva: Magistrsko delo/naloga
• Tipologija: 2.09 - Magistrsko delo
• Organizacija: FKKT - Fakulteta za kemijo in kemijsko tehnologijo
• Leto izida: 2022
• PID: 20.500.12556/RUL-137993
• COBISS.SI-ID: 117040387
• Datum objave v RUL: 07.07.2022

SIMONIČ, David, 2022, Izboljšanje oksidacijske odpornosti volframovega kompozita s karbidnimi vključki z dodatkom kroma in itrija [na spletu]. Magistrsko delo. [Dostopano 26 april 2025]. Pridobljeno s: https://repozitorij.uni-lj.si/IzpisGradiva.php?lang=slv&id=137993

Sekundarni jezik

• Jezik: Angleški jezik
• Naslov: Improving the oxidation resistance of tungsten carbide composite with the addition of chromium and yttrium

Izvleček

Better heat-resistant materials for technological development in the field of high-temperature processes is needed. Tungsten has proven to be a potentially suitable material in this area. Although it has many positive properties, it also has some drawbacks, one of which is relatively poor oxidative resistance at high temperatures. Research to date has shown that the addition of tungsten carbide prevents oxidation during sintering and improves some mechanical properties of the material. In the case of pure W, the addition of chromium and yttrium helps to improve the surface oxidation protection, so it would make sense to check the effect of the addition of Cr and Y on the tungsten composite with carbide inclusions. The aim of the work was to improve the high temperature oxidation resistance of tungsten composites with carbide inclusions with the addition of Cr and Y. Different amounts of Cr and Y were added to W and WC then the resulting mixtures were sintered. Oxidation resistance was checked by dynamic thermogravimetric analysis of samples prepared in this way up to temperatures of 1050 °C. Homogeneous mixtures of powders of W, WC, Cr and Y were prepared by wet grinding in a planetary mill, then the suspension was frozen, and the solvent sublimated under reduced pressure. Powders were sintered using FAST method. For this the optimal maximum temperature and pressure was determined. The present phases of the sintered samples were determined by X-ray analysis and their microstructure with a scanning electron microscope. In SEM image of a tungsten composite with carbide inclusions, we see only one main phase present. When Cr is added to tungsten composite with carbide inclusions, the formation of black grains of chromium oxides is observed. With addition of 10 ut. % of Cr and more, a new main phase, solidified liquid network, is observed. In the sample with 10 wt. % Cr W-rich dendrites are observed in solidified liquid network, which disappear with greater addition of Cr. Both main phases are tungsten-rich phases. The addition of Y has no noticeable effect on the microstructure. The temperature at which the masses of the samples begin to increase was determined using thermogravimetric analysis. It increases with increasing amount of Cr added in the samples. The addition of Y did not have a significant effect on this temperature. In addition, the net increase in sample weights was compared. The addition of Cr is not proportional to the increase in net weight. The mass of the sample without the addition, which is comparable to the sample with the least addition of Cr, increased the least. This is followed by the pattern with the largest addition of Cr. The largest increase in net mass occurred in the sample with 10 wt. % addition of Cr. Mass increases with increasing amount of Y added. I also determined the phases present in the oxide layer formed after oxidation and checked the microstructure and contact with the sample.

• Ključne besede: Oxidation protection, thermogravimetric analysis, FAST, initial temperature of mass increase, net weight increase.