Microstructure and Oxidation Behavior of Fe-25Mn-9Al-8Ni-1C-xTi Alloy Prepared by Vacuum Arc Melting

In this study, Fe-25Mn-9Al-8Ni-1C-xTi alloy (x = 0, 0.1, 0.2, 0.3, 0.4 wt.%) was prepared by vacuum arc melting, and the corresponding microstructure and oxidation behavior at 600 °C were studied. The results show that Fe-25Mn-9Al-8Ni-1C-xTi alloy mainly contains austenite phase, ferrite phase and TiC phase. With Ti content increasing, the austenite phase content decreases, while the contents of ferrite phase and TiC phase increase. The oxidation performance test results show that the addition of Ti element greatly reduces the oxidation weight gain of the alloys at the initial oxidation stage. With the extension of the oxidation time and the further increase of the Ti content, the alloys oxidation weight gain shows a trend of first increasing and then decreasing. When the Ti content is 0.2 wt.%, the oxidation weight gain of this series of alloy reaches the lowest value during the stable oxidation period. Compared with Fe-25Mn-9Al-8Ni-1C alloy, its weight gain per unit area is reduced by 21.1%. Fe-25Mn-9Al-8Ni-1C-xTi alloy oxide layer exhibits a double-layer structure. The outer oxygen layer is mainly loose iron-oxides, while in the inner oxygen layer, the oxides are mainly composed of manganese-oxides and aluminum-oxides, which are relatively dense.

Oxidation Mechanism of Al-Sn Bearing Alloys

Oxidation of Al-Sn bearing alloy occurs during production, processing and use, which reduces both alloy performance and performance of coatings applied to the alloy surface. Therefore, the oxidation mechanism of Al-Sn bearing alloy is studied at 25, 180, 300, and 500 °C. The oxidation morphologies of the alloy were observed by scanning electron microscopy (SEM), and the oxidation products were determined by X-ray diffraction (XRD). The oxidation weight gain curves were obtained by thermogravimetric analysis. The experimental results show that: Al-Sn bearing alloy is oxidized quickly to form Al2O3. As the oxidation temperature increases, Sn phase start to precipitate along the grain boundary and form networked spheroids of Sn on the alloy surface. The amount of precipitation increases with further increase of the oxidation temperature. Cracks and holes are left in the alloy. The oxide layer is mainly composed of Sn, SnO2, and Al2O3. At 25 °C, oxidation rate of Al-Sn alloy approach zero. At 180, 300, and 500 °C, the oxidation rate increases quickly conforming to a power function, and eventually remains stable at about 3 × 10−6 mg·mm−2·s−1.

Effect of Y on the Oxidation Behavior of a Directionally Solidified Ni-based Single Crystal Superalloy

The effect of Y addition on the oxidation behavior of a Ni-based directionally solidified single crystal superalloy was investigated. Isothermal oxidation test for the samples with different-level Y addition was conducted at 1100℃ in air. The Y content of the samples was demarcated by the actual pickup amount resulted from ICP-AES test. It was found that the addition of Y increased the oxide resistance by an adhesive double-layer oxide scale which was composed of Al2O3 and spinel Ni(Cr,Al)2O4. With 70ppm Y addition, the oxidation weight gain was decreased from 12.6g/m2 for the alloy without Y addition to 5.3g/m2, and the oxidation rate was significantly decreased. Besides, the internal nitride also disappeared after Y doping because of the increasing oxidation scale adherence and the decreasing of oxidation products. In this study, 660ppm Y addition alloy showed the best oxidation resistance.

High-Temperature Oxidation Behavior of Fe–1Cr–0.2Si Steel

In the case of Fe–1Cr–0.2Si steel, tube furnace oxidation was carried out for 120 min and 30 min. These studies, along with the high-temperature oxidation behavior of Fe–1Cr–0.2Si steel, were examined from 700 to 1100 °C. It has been observed that with an increase in the oxidation time, the oxidation weight gain per unit area of Fe–1Cr–0.2Si steel changed from a linear to a parabolic relationship. The time was shortened when the oxidation phase was linear. When the oxidation temperature exceeded 900 °C, the value of WTransition decreased, and the oxidation rule changed. It could be considered that overall, the iron oxide structure of Fe–1Cr–0.2Si steel is divided into two layers. The formation of an outer oxide of iron is mainly caused by the outward diffusion of cation, while the inward diffusion of O ion forms the inner oxides of chromium and silicon. As the temperature increases, the thickness of the outer iron oxide gradually increases, and the thickness ratio of the inner mixed layers of chromium- and silicon-rich oxides decreases; however, the degree of enrichment of Cr and Si in the mixed layer increases. After high-temperature oxidation, Cr and Si did not form a composite oxide but were mechanically mixed in the form of FeCr2O4 and Fe2SiO4, and no significant delamination occurred.

Oxidation Kinetics of ZrB2 Ceramic Matrix Composite Materials

Zirconium diboride is widely applied because of some excellent performances. The oxidation kinetics of ZrB2-YAG-Al2O3 composite materials were researched, which helps to improve the performance of ultra-high-temperature composite materials. The results show the oxidation weight gain is decreased with increasing the content of YAG-Al2O3 and the molar ratio of Al2O3. The oxidation weight gain is increased with prolonging the oxidation time under 1300°Cæ, the oxidation weight gain ratio is decreased with prolonging the oxidation time. The effecting tendency of oxidation weight gain is not abvious with varying the contend of YAG-Al2O3 upon 1300°Cæ, however, the effecting tendency of oxidation weight gain is very abvious with varying the molar ratio of Al2O3.

Non-Isothermal Method for Charactering the Oxidation Resistance Property of SiAlON Materials

The oxidation resistance of SiAlONs is one important property. In our work we present a test method to characterize its anti-oxidation property with the non-isothermal oxidation process using Thermo Gravimetric Analyzer (TGA). The oxidation starting temperature (Ts), maximum oxidation rate temperature (Tm) and the value of the oxidation weight gain per unit area (Ga) are three key parameters to describe the antioxidant properties of the material. Experimental results prove this test method is easy and reasonable and it will be developed as the national standard of China.

Study of Thermal Diffusion on Oxidation Resistance of ZG40Cr24

Based on heat resistant steel ZG40Cr24, test alloys were cast by intermediate frequency induction furnace with non-oxidation method by alloying of aluminium and silicon. The oxidation resistance at 1100°C for 500 hours of test alloys was carried out according to oxidation weight gain method. The thermal diffusion were tested by Laser Heat Conductivity. The thickness of oxide scale was detected by Coating Thickness Meter. Experimental results showed that the thermal diffusion of oxide scale affected its oxidation resistance exactly, the lower thermal diffusion coefficient matched the higher oxidation resistance. The oxide scale thermal diffusion coefficient of ZG40Cr24+2%wt.Si+4%wt.Al was only 0.00092cm2.s-1, endowing itself 0.0633g.m-2.h-1 oxidation weight gain rate, reaching the complete oxidation resistance. The mechanism of the effect of thermal diffusion on oxidation resistance lay in that the lower thermal diffusion represented the inert inner particles of materials, the few quantity of diffusion particles, and lower transporting and moving rate. So the oxidation rate slowed down, realizing higher oxidation resistant property for oxide scales.

Study on Exfoliation Resistance of Ferro Superalloy Composite Oxide Scale

Based on ferro based superalloy K273 and heat resistant steel ZG40Cr24, test alloys were cast by intermediate frequency induction furnace with non-oxidation method by alloying of aluminium and silicon. The oxidation resistance at 1100°C for 500 hours of test alloys was carried out according to oxidation weight gain method. Experimental results show that the scale exfoliation resistance of K273 and ZG40Cr24 is reinforced greatly by Al2O3 and SiO2. The scale exfoliation weight gain rate at 1100°C descends from 1.2681g.m-2.h-1 to zero, reaching complete exfoliation resistance for ZG40Cr24 test alloy. Because of 1.5<PBR(Al2O3⁄Fe)<2 and the growing of Al2O3 and SiO2 from out side of scale-scale/oxygen interface, the composite scale grows intact and compact without accumulation of growing stress.

Effects of Nickel on Structure and Properties of Ferro Superalloy

The affecting law of nickel on structure and properties of ferro superalloy, which was cast by intermediate frequency induction furnace, were studied by orthogonal experimental method. The tensile strength and oxidation weight gain rate at 1000°C were tested. The matrix microstructure and scale morphologies and composition were studied using scanning electron microscope (SEM) and X-ray diffraction (XRD) respectively. It was found that the high temperature tensile strength went up with the increase of nickel by the forming of high temperature strengthening phase of γ’. After 100 hours aging at 1000°C, γ’ phase separated in blocks. Certain content of nickel improved the high temperature oxidation resistance of test alloys, but excess of it caused the higher oxidation weight gain rate and loose structure oxide scales with holes and exfoliating. In considering of high temperature tensile strength and oxidation resistance, the ideal content of nickel in ferro superalloy should be 9wt.%, with which at 1000°C the tensile strength of test alloys mostly exceeded 70MPa, and the average oxidation weight gain rate was only 0.55g.m-2.h-1, reaching the strong oxidation resistance. Such scale was compounded by Cr2O3 and Fe(Ni)Cr2O4 with compact structure, fine and even oxide grains.