Mohammad Dani

Time dependence of Mg-incorporation in alumina scales on FeCrAl alloys studied by FIB-prepared TEM cross sections

AbstractMinor alloying additions and alloy impurities can be of crucial importance for the protective properties of oxide scales on high temperature alloys. An example of an impurity is magnesium. In the present study, the effect of Mg impurity (concentration 80 ppm) on the oxidation behaviour of a commercial FeCrAl alloy at 1200°C was investigated. By a combination of various analysis techniques, such as optical metallography, SEM/EDX/WDX, X-ray diffraction and TEM, it was found that Mg appeared to become easily incorporated in the surface oxide already after relatively short exposure times.Comparison of the oxidation products showed a change in the scale growth mechanism to occur in course of the oxidation treatment. Magnesium was found to migrate through the alumina scale and it became enriched in the outer part of the oxide scale forming a layer of a (Mg,Mn)Al2O4 spinel. An important effect associated with the Mg-enrichment and spinel formation was the development of porosity within the scale which ma...

KETAHANAN OKSIDASI BAJA SUPER AUSTENITIK 15%CR-25%NI PADA TEMPERATUR 850 °C

ABSTRAK Ketahanan Korosi Temperatur Tinggi Baja Super Austenitik 15%Cr-25%Ni Pada Temperatur 850 °C. Ketahanan korosi temperatur tinggi atau ketahanan oksidasi merupakan prasyarat penting bahan logam yang akan diterapkan dilingkungan operasi bertemperatur tinggi.xa0 Pengujian ketahanan oksidasi baja super austenitik 15%Cr-25%Ni pada temperatur 850 °C selama 5 jam lebih telah dilaksanakan. Satu sampel as-cast sebagai acuan awal yang tidak diperlakukan panas dan dua (2) kelompok sampel (masing-masing 3 buah) disiapkan dalam eksperimen. Satu kelompok sampel as-cast setelah dipanaskan (pada 850 °C /5 jam lebih) dan didinginkan perlahan kemudian ditimbang. Satu kelompok sampel quench yang dilakukan penurunan cepat temperatur (dari 850 °C / 5 jam lebih) ke dalam air, kemudian ditimbang. Percobaan dilakukan selama 15 jam lebih pada masing-masing kelompok. Hasil memperlihatkan bahwa walaupun terjadi kenaikan berat sangat kecil pada sampel as-cast dan quench, tetapi foto morfologi mikroskop elektron (SEM) pada kedua sampel tersebut tidak memperlihatkan perubahan yang signifikan. Demikian pula hasil analisis fasa menggunakan difraksi sinar-X, tidak memperlihatkan pertumbuhan fasa produk oksidasi. Hasilxa0 pengamatan struktur mikro permukaan bahan menggunakan mikroskop optik (MO), juga tidak memperlihatkan kerusakan dan perubahan ukuran butir oleh proses oksidasi. Kebolehjadian pada fenomena ini adalah selain pembentukan spinel unsur Ni diperkuat juga oleh kemampuan unsur Cr untuk membentuk lapisan pasif (Cr2O3) dipermukaan bahan yang sangat besar dengan mengikat unsur O, sehingga bahan mampu menanggulangi produk oksidasi yang sangat kecil. Disimpulkan bahwa baja super austenitik memiliki ketahanan oksidasi yang baik pada temperatur 850°C. ABSTRACT High Temperature Corrosion Resistance of Super Austenite 15%Cr-25%Ni Steel at Temperature 850 °C. High temperature corrosion resistance so called oxidation resistance is an important prerequisite of a metal material that may be applied in a high-temperature operating environment. An oxidation test of super austenite steel 15% Cr-25% Ni at 850 °C for more than 5 hours has been performed. One as-cast specimen as an initial reference is not treated any heat and two (2) specimen groups (each of 4 pieces) were prepared in the experiments. One group of as-cast specimens after being heated at 850 °C for more than 5 hours and cooled slowly then weighed. Another group of quench specimens performed a rapid decrease of temperature (850 °C for more than 5 hours) into water, then weighed. The experiment was conducted for more than 15 hours in each group. The results show that there is a very small slight increase in weight on as-cast and quench specimens. However, electron microscope morphology (SEM) images on both specimens showed no significant changes. Similarly, the results of phase analysis using X-ray diffraction techniques also do not show the phase growth of oxidation products. In accordance with the observation of surface microstructures of materials by using optical microscope (OM), also did not show damage and changes in grain size by oxidation process. The likelihood of this phenomenon is that in addition to the formation of Ni element of spinels, it is also strengthened by the ability of Cr-elements to form a passive layer (Cr2O3) on a very large material surface by binding O-elements, so that the material can cope with very small oxidation products. It is concluded that the super austenitic steels has good oxidation resistance at 850°C.