Korozijska odpornost kompozita Ti-6Al-4V/TiC izdelanega z aditivnimi tehnologijami : magistrsko delo

Močnik, Nejc (author), Medved, Jože (mentor), Kocijan, Aleksandra (comentor)

Cilj magistrske naloge je bil primerjati korozijsko odpornost različnih delov hibridnega materiala, razvitih za uporabo v vesoljski tehniki. Namen naloge je bil potrditi korozijsko odpornost tega materiala v slanem mediju s 3,5 mas. % NaCl. Hibridni material je sestavljen iz jedra, proizvedenega z metodo selektivnega laserskega taljenja iz zlitine Ti-6Al-4V. Površina hibridnega materiala je narejena iz kompozita zlitine Ti-6Al-4V s 5 mas. % TiC, ki služi kot armatura. Za analizo je bilo pripravljenih pet vzorcev. Vzorca J (jedro) in JH (jedro, toplotno obdelan) sta simulirala jedro hibridnega materiala in sta bila izdelana z metodo selektivnega laserskega taljenja. Vzorec J je bil analiziran v grajenem stanju, vzorec JH pa je bil toplotno obdelan na 800 °C za dve uri. Vzorca P (površina) in PH (površina, toplotno obdelan) sta simulirala površino hibridnega materiala in sta bila izdelana z metodo direktnega laserskega navarjanja. Vzorec P je bil analiziran v grajenem stanju, vzorec PH pa je bil toplotno obdelan na 800 °C za dve uri. Vzorec C1 je konvencionalna zlitina Ti-6Al-4V, ki je bila analizirana za primerjavo z vzorci, izdelanimi z metodami dodajne tehnologije. Vzorca P in PH, ki sta vsebovala TiC, sta v primerjavi z vzorci J, JH in C1 izkazala zmanjšano korozijsko hitrost v korozijskem mediju 3,5 mas. % NaCl, pridobljeno iz Taflovih diagramov. Hkrati pa sta izkazovala znatno nižji potencial za nastanek korozijskih jamic v primerjavi z vzorci brez TiC, kar kaže na negativne učinke TiC na nastanek jamic med dolgotrajno izpostavljenostjo korozivnemu mediju. Na vzorcih JH in PH, ki sta bila toplotno obdelana, je bila izvedena elektrokemijska impedančna spektroskopija v mediju 3,5 mas. % NaCl. Oba vzorca sta med izpostavljenostjo pokazala rast pasivnega sloja, vendar je pasivni sloj na vzorcu PH tvoril bolj porozno strukturo, kar razlaga padec upora prenosa naboja skozi čas. Kljub rahlo povečani korozijski hitrosti vzorca PH zaradi nastanka sekundarne Ti(?) med toplotno obdelavo, rezultati elektrokemijske impedančne spektroskopije potrjujejo nastanek stabilnega pasivnega sloja. Dodatek TiC sicer zniža potencial za nastanek jamičaste korozije, vendar ocenjujemo, da sta vzorca P in PH primerna za uporabo v predlaganih aplikacijah.

• Language: Slovenian
• Keywords: Ključne besede: selektivno lasersko taljenje, direktno energijsko navarjanje, Ti-6Al-4V/TiC, elektrokemijska impedančna spektroskopija, potenciodinamične meritve.
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Place of publishing: Ljubljana
• Publisher: N. Močnik
• Year: 2024
• Number of pages: XVII, 68 f.
• PID: 20.500.12556/RUL-161718
• UDC: 669
• COBISS.SI-ID: 212467203
• Publication date in RUL: 13.09.2024

Secondary language

• Language: English
• Title: Corrosion resistance of Ti-6Al-4V/TiC composite produced by additive technologies : master's thesis

Abstract

The goal of this master's thesis was to compare the corrosion resistance of various components of a hybrid material designed for aerospace applications. The aim was to verify the corrosion resistance of this material in a 3.5 wt.% NaCl saline environment. The hybrid material consists of a laser powder bed fusion manufactured core made from alloy Ti-6Al-4V. Its surface is made of a composite material created using direct energy deposition of Ti-6Al-4V with 5 wt.% TiC. Five samples were manufactured and prepared for evaluation. Samples J (core) and JH (core, heat treated) were simulating the core of the hybrid material and were manufactured using laser powder bed fusion technology. Sample J was analyzed in the as-built state, and sample JH was heat-treated for two hours at a temperature of 800 °C. Samples P (surface) and PH (surface, heat treated) were simulating the surface of the hybrid material and were manufactured using direct energy deposition technology. Sample P was analyzed in the as-built state, and sample PH was heat-treated at 800 °C for two hours. Sample C1, a conventionally built Ti-6Al-4V alloy, was used to compare the results of the additively manufactured samples. Samples P and PH, which contained TiC, showed a decreased corrosion rate in a corrosion environment of 3,5 wt.% NaCl obtained from Tafel plots compared to samples J, JH, and C1. However, they exhibited a significantly lower pitting potential than the samples without TiC, indicating the negative effects of TiC on the formation of pits during prolonged exposure to corrosive media. Electrochemical impedance spectroscopy was done on heat treated samples JH and PH in 3,5 wt.% NaCl. Both samples exhibited growth of the passive layer during exposure, but the passive layer formed on the sample PH formed a more porous structure, indicated by lower charge transfer resistance over time. Despite a marignal increase in the speed of corrosion of sample PH due to the formation of a secondary Ti(α) phase during heat treatment, the results of electrochemical impedance spectroscopy indicated the formation of a stable passive layer. The addition of TiC to the matrix lowered the pitting potential of the material; however, we assess that both samples P and PH are suitable for use in proposed applications.

• Keywords: Key words: laser powder bed fusion, direct energy deposition, Ti-6Al-4V/TiC, electrochemical impedance spectroscopy, potenciodynamic polarization.