Effects Of Extrusion On Fe-16Cr-4Al-ODS Steel Nano Oxide Particles

Al-alloyed high-Cr oxide dispersion strengthened ferritic steels?ODS steels?are promising cladding material of Generation IV fission nuclear reactors such as SCPWR and LFR due to its superior high temperature strength and creep resistance,high resistance to irradiation damage and swelling and superior corrosion resistance.The excellent comprehensive properties of Fe–16Cr–4Al-ODS steel are derived from highly dispersed nano-oxide particles in the matrix.The nominal composition of this ODS steel is Fe–15.5Cr–2W–0.1Ti–4Al–0.35Y₂O₃.Materials Fe–16Cr–4Al-1150 and Fe–16Cr–4Al-1050 were used for the experiment of extrusion temperature of 1150°Cand1050°C respectively.In this research,the effects of extrusion temperature on the nano-oxide particles of the newly developed Fe–16Cr–4Al-ODS steels were investigated by the high resolution transmission electron microscopy?HRTEM?with a focus on the size,crystalline structure and interface structure of the dispersed oxide particles to correlate the nano-oxide particles with the overall macroscopic behavior of the ODS steels.The main results are as follows:?1?The maximum number of the nano-oxide particles in Fe–16Cr–4Al-1150 and Fe–16Cr–4Al-1150 was at a size of about 4-10 nm and 2-5 nm;respectively.The mean size of the nano-oxide particles in Fe–16Cr–4Al-1150 and Fe–16Cr–4Al-1050 was about 6.7 nm and 3.2 nm;respectively.?2?Y–Al–O,Y–Ti–O,Y₂O₃,TiO₂ and YCrO₄ oxides in Fe–16Cr–4Al-1150constitute⁷3.3%,¹2.1%,⁶.0%,⁶.0%and².6%of the particles,respectively.YAH,YAP,YAM and YAG in Y–Al–O oxides constitute⁴2.2%,¹4.7%,¹1.2%and⁵.2%of the particles,respectively.Y₂TiO₅ with the fraction of¹2.2%of the particles is only a Y–Ti–O oxide in Fe–16Cr–4Al-1150.?3?Y–Al–O and Y–Ti–O oxides in Fe–16Cr–4Al-1050 constitute⁹4%and⁶%,respectively.YAH and YAP in Y–Al–O oxides constitute⁸9.5%and⁴.5%,respectively.Y₂TiO₅ and YTiO₃ in Y–Ti–O oxides constitute⁴.5%and¹.5%,respectively.?4?Most of the nano-oxide particles in Fe–16Cr–4Al-1150 are semi-coherent with the ferritic matrix.Almost all the nano-oxide particles in Fe–16Cr–4Al-1050 are coherent with the ferritic matrix.The larger size?>20 nm?nano-oxide particles in the two ODS steels is almost incoherent with the ferrite matrix.?5?Compared with Fe–16Cr–4Al-1150,the nano-oxide particles in Fe–16Cr–4Al-1050 are smaller in size,more dispersed in particle distribution and better metal/oxide interface;The quantitative proportion of YAH in Fe–16Cr–4Al-1050increases significantly.The results show that the dispersion morphology and the crystalline structure of the nano-oxide particles in Fe–16Cr–4Al-ODS steel can be improved by decreasing the extrusion temperature.