The tensile properties, high-cycle fatigue properties, and microstructure evolutions during fatigue process of asreceived and pre-strained Fe-30Mn-0.9C twinning-induced plasticity (TWIP) steel were investigated. It is found that the fatigue lives of the TWIP steel can be effectively improved through pre-straining, since the deformation twins induced by pre-straining could effectively lead to the improved yield strength and the homogenized deformation. This study may provide possible ways for improving the high-cycle fatigue properties of TWIP steels.In recent years, the advanced high-strength steels have been widely used in automobile industry to satisfy the weight reducing, energy saving, and security principles of new generation cars. [1] Twinning-induced plasticity (TWIP) steels have an excellent combination of high strength and good ductility, so that they are very attractive for automotive industry; therefore, much attention has been paid on the development of TWIP steels. So far, researchers mainly focus on the alloy designing, basic mechanical properties, and the corresponding microstructure evolution during deformation of TWIP steels. [2][3][4][5][6][7][8][9][10] Generally, most automobile parts are under cyclic loading condition during their service, thus, the fatigue resistance is one of the key factors for the practical utilization of TWIP steels. There are many reports about the low-cycle fatigue properties of TWIP steels, [11][12][13][14][15][16] and the pre-strain method was developed to improve their low-cycle fatigue properties. [11,16] As for the high-cycle fatigue, there have been some investigations about the bending fatigue properties of TWIP steels. [17][18][19][20] Hamada et al. [17][18][19] and Karjalainen et al. [20] showed that TWIP steels have quite high bending fatigue strength. However, there are no research findings on the high-cycle fatigue properties of the TWIP steels under axial loading, and the effects of pre-strain on the high-cycle fatigue properties are still not clear so far.In order to improve the fundamental understanding on the axial high-cycle fatigue behaviors of TWIP steels and supplement experimental data, the axial high-cycle fatigue tests of as-received and pre-strained Fe-30Mn-0.9C TWIP steel were performed and the corresponding microstructure evolutions were observed in the current study. The main goal of the current study is to explore further improvement of the high-cycle fatigue properties of TWIP steel via pre-straining.In this study, Fe-30Mn-0.9C (wt pct) TWIP steel was used. The cast ingot was austenized at 1473 K (1200°C) for 4 h, then immediately hot forged into plate with final dimension of 40 9 100 mm 2 at 1223 K to 1473 K (950°C to 1200°C), and finally cooled in air. The plate was annealed at 1323 K (1050°C) for 1 hour and water-quenched, and then dog-bone shaped tensile and fatigue specimens were cut into sectional dimensions of 15 9 3 9 3 and 10 9 5 9 4 mm 3 from the annealed plate, respectively; and the length direction of tensile and fatigue specimen...

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The isothermal-oxidation behavior of Al-rich TiAl alloys containing Y up to 1.0 at.% was studied in synthetic air with a flow of 200-250 mL/min at 800 and 900°C. Oxidation kinetics and scale adherence were studied in terms of the morphological features and microstructural evolution of the oxide scale. In the specimens oxidized at 800°C, all alloys containing 0.3-1.0 at.%Y showed reduced mass gain compared to the Y-free alloy, especially for the 0.3 at.%Y alloy. Under isothermal exposure at 900°C, the addition of small amounts of Y (0.1 and 0.3 at.%) was effective in enhancing the oxidation resistance. The alloys with higher Y contents (0.6 and 1.0 at.%), on the contrary, had a reverse effect on the oxidation resistance by providing rapid diffusion paths in the form of coarse Y 2 O 3 particles close to the substrate. The improvement of oxidation resistance of the alloy with Y additions was due partly to the improved adhesion of the scale and due partly to the formation of a continuous a-Al 2 O 3 layer in the outer scale. Y segregation and/or Y 2 O 3 precipitation at the oxide grain boundaries was effective in decreasing the oxidation rate and refining the oxide grains. The thinner scale was responsible for relaxing the thermal stress and, thus the cohesion between the scale and substrate was greatly improved in Y-containing alloys.

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