Influence Of Zr Addition On The Microstructures Of 14Cr-ODS Steels And The Investigation Of Strengthening Mechanism

Oxide dispersion strengthened?ODS?steels are considered as the best candidates of structural materials for nuclear systems due to their excellent high temperature mechanical properties and superior radiation resistance.The strengthening mechanism of this kind of new material is the introduction of stable,dispersed and nanoscaled oxide particles into the matrix and then form a dispersion strengthening effect.Two compositions of ODS steels of 14Cr-ODS and 14Cr-Zr-ODS were prepared by mechanical ball mill and hot isostatic pressing?HIP?sintering in this work.And the influence of Zr addition on the microstructures and the strengthening mechanism were studied.The conclusions are as follows:The oxide particles in 14Cr-Zr-ODS are smaller,more homogeneous and dispersed than those in 14Cr-ODS.The characterizations on these particles suggest that the particles with smaller sizes tend to exist as rhombohedral Y₄Zr₃O₁₂,while the particles with larger sizes generally exist in the form of monoclinic Y₂O₃.The calculation on the misfit of the interfaces between matrix and particles with different sizes reveal that,the coherency of the particles decreases with the increasing of the particles'sizes.And when the particle size reaches to 14 nm,the lattice planes of matrix and particles begin to losing their parallel relationships under the direction of vector g.What's more,due to the well coherency of the fine Y₄Zr₃O₁₂2 particles with matrix,the interfaces have lower energy and these particles have higher stability under high temperature.So the fine particles will possess higher coarsening resistance and dissolving resistance and can cause an intense pinning effect on the migration of grain boundaries during the sintering process and eventually refine the grains of14Cr-Zr-ODS alloy.The tensile tests suggest that the strength and plasticity of14Cr-Zr-ODS alloy are all superior to those of 14Cr-ODS alloy,and the strengthening mechanism of Zr addition on the ODS steels mainly include:?1?the oxide particles become more fine and dispersed after Zr addition and the pinning effects of particles on dislocations become stronger;?2?the Y₄Zr₃O₁₂2 particles are more coherent with the matrix,and the interfaces between them are more ordered and have lower energy,so the interface bonding force is stronger and can prevent the fracture of the interfaces according to load partition phenomenon;?3?the Y₄Zr₃O₁₂2 particles have excellent coarsening resistance and dissolution resistance because the interface structure between them and the matrix is more ordered,so they can pinning the migration of grain boundaries during sintering and refine the grains.