Effects Of Cr And Al Content On Microstructure And Mechanical Properties Of ODS-FeCrAl Alloys

ODS-FeCrAl alloy has excellent radiation tolerance and high temperature strength,which is considered to be one of the main candidate materials for the Generation ? fission reactors fuel cladding and accident-tolerant fuel cladding.The research showed that when Cr content of in ODS alloys exceeds 16 wt%,high temperature aging embrittlement may occur.Recently radiation embrittlement phenomenon was also observed in ODS alloys with Cr content below 16 wt%.The corrosion resistance of ODS alloys decreases as the Cr content decreases,while increasing Al content is necessary to ensure corrosion resistance.Therefore,many researches are focusing on low Cr/high Al ODS alloys.In this thesis,nine kinds of ODS-FeCrAl alloys with different Cr and Al contents were prepared by mechanical alloying and hot isostatic pressing method.The effects of Cr and Al contents on the microstructure and mechanical properties of ODS-FeCrAl alloy were systematically investigated.The main conclusions are as follows:(1)In the 9Cr-xAl(x=4.5,5.0 and 5.5)alloys,with the increasing of Al content,the average grain size of the alloys decreases first and then increases,and the proportion of ultrafine grains(100-500 nm)first increase after reduction.In the 12Cr-xAl and 15Cr-xAl alloys,as the Al content increases,the average grain size of the alloy continuously increases,and the proportion of ultrafine grains decreases.In the yCr-4.5Al(y=9,12 and 15)alloys,as the Cr content increases,the average grain size of the alloys decreases and the ultrafine grain ratio increases.For yCr-5.0AI alloys,the average grain size of the alloys increases with the increase of Cr content,and the proportion of ultrafine crystal decreases.In the yCr-5.5Al alloys,as the Cr content increases,the average grain size of the alloy increases first and then decreases,and the proportion of ultrafine grains decreases first and then increases.(2)The large oxides of nine kinds of ODS-FeCrAl alloy are Al2O3,and the size is mainly distributed in the range of 20-80 nm.The average size of large oxides in nine kinds of ODS-FeCrAl alloys is not much different which is around 40 nm.The effect of Cr content on the density of large oxides is not significant.In 9Cr-xAl,12Cr-xAl and 15Cr-xAl alloys,the density of large oxides increases in the alloys when the Al content increases;(3)The nanoscale oxides of nine kinds of ODS-FeCrAl alloy are mainly Y₄Zr₃O₁₂,Y₂TiO₅(?2-5 nm)and slightly larger YAlO₃(-5-20 nm).In the 9Cr-xAl alloys,the size of the nanoscale oxides increases with the increasing of the Al contents,while the number density first increases and then decreases.The number density of the nano scale oxides in the 9Cr-5.0Al alloy reaches 2.3×10²³/m³;The size of nanoscale oxides in 12Cr-xAl and 15Cr-xAl alloys increases with the increasing of Al content,and the number density decreases.When the A1 content is fixed,the number density of the nanoscale oxides increases with the increasing of Cr content in the yCr-4.5Al alloys,and the number density of nanoscale oxides in the 15Cr-4.5A1 alloy reaches 2.2×10²³/m³;The density of the nanoscale oxides in yCr-5.OAl alloy decreases first and then increases with the increasing of Cr content;The size of nanoscale oxides in yCr-5.5Al alloy increases first and then decreases with the increasing of Cr content,and number density first decreases and then rises;(4)The nine kinds of ODS-FeCrAl alloys exhibit excellent high temperature strength at 600? and 700?.When the Cr content is fixed,in the 9Cr-xAl alloy,as the A1 content increases,the tensile strength increases first and then decreases,and the elongation rate first decreases and then increases.The ultimate tensile strength of 9Cr-5.0Al alloy reaches 864 MPa and 569 MPa,respectively;In 12Cr-xAl and 15Cr-xAl alloys,the ultimate tensile strength decreases with the increase of A1 content while the elongation rate increases.When the Al content is fixed,the ultimate tensile strength and the elongation of yCr-4.5Al alloys increases with the increasing of the Cr content.The ultimate tensile strength of 15Cr-4.5Al alloy is 855 MPa and 552 MPa,respectively;The ultimate tensile strength of yCr-5.0Al alloys decreases with the increasing of Cr content,and the elongation first rises and then decreases;The ultimate tensile strength of yCr-5.5A1 alloys decreases as the Cr content increases,and the elongation increases.