Vpliv visokoaktivnega aluminiziranja na korozijske lastnosti jekel 16Mo3, 10CrMo9-10 in 13CrMo4-5 : magistrsko delo

Prijatelj, Klara (avtor), Bizjak, Milan (mentor), Kosec, Tadeja (komentor)

Procesi korozije so prisotni na vseh področjih industrije, zato je njihovo razumevanje pomembno za nadaljnji tehnološki napredek. Informacije, ki jih pridobimo z raziskovanjem korozijskih procesov, nam omogočajo načrtovanje korozijsko bolj odpornih zlitin. V magistrskem delu smo preučili vpliv oplemenitenja površine s postopkom aluminiziranja v zasipu na korozijske lastnosti izbranih jeklih. Izbranim jeklom 16Mo3, 10CrMo9-10 in 13CrMo4-5 smo s postopkom difuzijskega aluminiziranja v trdnem želeli povečati koncentracijo aluminija v površinski plasti. Postopek aluminiziranja je potekal v zasipu, ki je mešanica različnih prahov. Zasip je bil sestavljen iz difuzijskega elementa (6 mas. % Al), aktivatorja (3 mas. % NH4Cl) in inertnega polnila (91 mas. % Al2O3). Postopek je potekal pri dveh različnih temperaturah (900 in 730 °C) in dveh različnih časih žarjenja (2 in 4 ure). Za karakterizacijo modificirane površine smo po aluminiziranju izvedli mikrostrukturno analizo z uporabo svetlobnega in vrstičnega elektronskega mikroskopa. Z uporabo višje temperature difuzijskega aluminiziranja (900 °C) smo pridobili debelejšo plast od difuzijskega aluminiziranja pri 730 °C. Na podlagi rezultatov sklepamo, da so v modificirani plasti vzorcev aluminiziranih pri 900 °C intermentalne faze FeAl, Fe3Al in trdna raztopina ?. Pri vzorcih aluminiziranih pri 730 °C sklepamo, da je modificirana plast sestavljena iz intermentalnih faz FeAl2, Fe2Al5, FeAl, Fe3Al in trdne raztopine ?. Korozijske lastnosti modificirane površine smo določili z elektrokemijskimi meritvami. Lastnosti so bile določene z meritvami korozijskega potenciala, meritvami linearne polarizacije, potenciodinamskih meritev in elektrokemijske impedančne spektroskopije. Na podlagi rezultatov smo ugotovili, da modificirana plast izboljša korozijske lastnosti izbranim jeklom. S postopkom aluminiziranja smo jeklom korozijski potencial premaknili k bolj pozitivnim vrednostim. Povprečni korozijski potencial pri aluminiziranih vzorcih je bil bolj pozitiven kot pri osnovnih jeklih. Prav tako imajo aluminzirani vzorci za dva reda nižjo gostoto korozijskega toka v primerjavi z osnovnim jeklom, kar nakazuje na izboljšano korozijsko obstojnost. Za oceno korozijske hitrosti smo izračunali hitrost korozije za posamezno jeklo in aluminizirane vzorce. Postopek aluminiziranja na vseh jeklih zmanjša korozijske hitrosti za 55 do 241-krat.

• Jezik: Slovenski jezik
• Ključne besede: korozija, difuzijsko aluminizranje v zasipu, mikrostruktura, elektrokemijske meritve
• Vrsta gradiva: Magistrsko delo/naloga
• Tipologija: 2.09 - Magistrsko delo
• Organizacija: NTF - Naravoslovnotehniška fakulteta
• Kraj izida: Ljubljana
• Založnik: [K. Prijatelj]
• Leto izida: 2022
• Št. strani: XVIII, 95 str.
• PID: 20.500.12556/RUL-136086
• UDK: 669
• COBISS.SI-ID: 105552387
• Datum objave v RUL: 12.04.2022

Sekundarni jezik

• Jezik: Angleški jezik
• Naslov: Influence of high active aluminization process on corrosion properties of 16Mo3, 10CrMo9-10 in 13CrMo4-5 : master's thesis

Izvleček

Corrosion processes are found in all areas of industry. Understanding them is therefore important for further technical progress. With the information we obtain by investigated corrosion processes, we can develop more corrosion-resistant alloys and improve corrosion protection. In the master's thesis we studied the influence of surface refinement and how the modified layer affects the corrosion properties of selected steels. Selected steels 16Mo3, 10CrMo9-10 and 13CrMo4-5 were used to increase the concentration of aluminum in the surface layer by powder-pack aluminization. The aluminization process took place in a filling, which is a mixture of different powders. The filling consisted of a diffusion element (6 wt. % Al), an activator (3 wt. % NH4Cl) and an inert filler (91 wt. % Al2O3). The process took place at two different temperatures (900 and 730 °C) and two different annealing times (2 and 4 hours). In order to characterize the modified surface, a microstructural analysis was performed after aluminization using a light and scanning electron microscope (SEM). A thicker layer was obtained at a higher diffusion aluminization temperature (900 °C) than at 730 °C diffusion aluminization. From the results, we can conclude that in the modified layer in the sampels aluminized at 900 °C were obtained intermediate phases FeAl, Fe3Al and solid solution α. In the samples aluminized at 730 ° C, the intermediate phases FeAl2, Fe2Al5, FeAl, Fe3Al and solid solution α were obtained in modified layer. The corrosion properties of the modified surface were determined by electrochemical measurements. The properties were determined by corrosion potential measurements, linear polarization measurements, potentiodynamic measurements, and electrochemical impedance spectroscopy. Based on the results, it was determined that aluminide coating improved the corrosion resistance of selected steels. Aluminization brought the corrosion potential of the steels to more positive values. The average corrosion potential aluminized samples were in general more positive than potential for steels, showing at formation of more protective surface. We also reduced the corrosion current density of aluminized samples by two orders of magnitude compared to base steel, indicating improved corrosion resistance. To estimate the corrosion rate, we calculated the corrosion rate for individual steels and aluminized samples. The aluminizing process on all steels reduces corrosion rates by 55 to 241 times.

• Ključne besede: corrosion, powder pack aluminization, microstructure, electrochemical measurements