In the present study, we have been focused on the failure phenomena of diesel engines glow plugs and attempts to extend their lifespan. The investigation revealed that the most sensitive element of the glow plug is a heating coil made of FeCrAl (Kanthal AF) wire. Despite excellent anti-oxidation properties of these alloys, provided by the formation of a protective alumina scale on the alloy surface, the oxidation resistance is limited when exposed to thermal cycling up to 1050 °C. The reason is cracking and constant re-formation of the alumina protective scale and consequent consumption of the aluminium in the subsurface area of the wire. To prevent premature failure of heating coils, powder pack aluminization was implemented to increase the aluminium content in the subsurface of the alloy and thus the possibility of easier re-formation of the protective alumina scale.
COBISS.SI-ID: 1850207
In the present study, the initial stages of oxidation/nitridation behavior of commercial FeCrAl alloy (Kanthal AF) during annealing at 900 °C and 1200 °C in an atmosphere of air or pure nitrogen are compared. Isothermal and thermocyclic oxidation tests with varying total exposure times and heating rates were performed. Scale characterization was carried out by scanning electron microscopy (SEM-EDX), Auger electron spectroscopy (AES), focused ion beam (FIB-EDX), and thermogravimetric analysis (TGA). Our results show significant formation of the AlN phase in subsurface region of Fe-Cr-Al alloy which reduces the aluminum activity and causes embrittlement and destruction of the alumina scale integrity. The processes of Al-nitride formation and Al-oxide scale growth depend on annealing temperature, heating rate and partial pressure of oxygen. We found that nitridation of Fe-Cr-Al alloy is a faster process than oxidation at temperatures below 1000 °C in atmospheres with low oxygen partial pressures.
COBISS.SI-ID: 1803871
In the present work we investigate the formation of tetragonal ZrO2 in Zr-Al and Zr-Cu thin films prepared by PVD process. The films with different composition were treated with inductively coupled oxygen plasma for a duration of only 5?s at pressure 0.5?mbar. This resulted in heating of the sample and in the penetration of the coatings with oxygen to a depth of approximately 100–200?nm. We found that the doping of Zr with Cu and subsequent treatment with oxygen plasma seems to be a promising method to stabilize tetragonal zirconia. No crystalized oxide phases were formed in the Al doped coatings. Plasma treatment times may remain extremely short, in the order of some seconds, and the method could also be scaled up by using larger samples and treatment chambers.
COBISS.SI-ID: 31436583
This study presents an analysis of the corrosion properties of laser treated surfaces that were exposed to aggressive environments. Different samples were prepared with laser light of various power intensities and processing speeds. The samples were prepared on low alloyed Ti. Electrochemical, spectroscopic and microstructural analyses were conducted in order to study the properties of the laser treated surfaces. Corrosion testing showed different effects of laser power and production speed on the properties of the laser treated surfaces. It was shown that a high intensity and slow processing rate affect the surfaces by forming oxides that are relatively stable in a corrosive environment of 0.1 M NaCl.
COBISS.SI-ID: 2463591