Fe‐Cr‐Mo based ODS alloys via spark plasma sintering: A combinational characterization study by TEM and APT

Abstract

Nanoscale oxides play an important role in oxide dispersion strengthened (ODS) alloys for improved high temperature creep resistance and enhanced radiation damage tolerance. In this study, transmission electron microscopy (TEM) and atom probe tomography (APT) were combined to investigate two novel Fe-16Cr-3Mo (wt.%) based ODS alloys. Spark plasma sintering (SPS) was used to consolidate the ODS alloys from powders that were milled with 0.5 wt.% Y 2 O 3 powder only or with Y 2 O 3 powder and 1 wt.% Ti. TEM characterization revealed that both alloys have a bimodal structure of nanometer-size (ß 100 -500 nm) and micronsize grains with nanostructured oxide precipitates formed along and close to grain boundaries with diameters ranging from five to tens of nanometers. APT provides further quantitative analyses of the oxide precipitates, and also reveals Mo segregation at grain boundaries next to oxide precipitates. The alloys with and without Ti are compared based on their microstructures.

Hot Deformation Behavior and Microstructure Evolution of 14Cr ODS Steel

“…The pre-alloyed powders are mechanically alloyed with the addition of nanosized oxides and other elements. Hot extrusion (HE), spark plasma sintering (SPS), and hot isostatic pressing (HIP) are the frequently used sintering methods for the consolidation of ODS steel [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ]. The final product of ODS steel is a cladding tube, which means that hot or cold working is inevitable during the fabrication process [ 1 , 5 ].…”

Bimodal Grain Size Distribution of Nanostructured Ferritic ODS Fe–Cr Alloys

“…Although basic recrystallization mechanisms are well studied, there are still effects in the microstructure evolution of particle‐strengthened alloys, which are not fully understood yet. One example is the formation of a bimodal grain size distribution which is observed in different ODS materials . A material with a well defined bimodal grain size distribution, consisting of nanograins and larger grains in the μm‐scale, is beneficial at low temperatures, because of its high strength caused by nanograins and the remaining dislocation‐mediated plasticity in larger grains.…”

“…A material with a well defined bimodal grain size distribution, consisting of nanograins and larger grains in the μm‐scale, is beneficial at low temperatures, because of its high strength caused by nanograins and the remaining dislocation‐mediated plasticity in larger grains. As at high temperatures the fine grain structure can be a drawback in terms of creep resistance, the bimodal grain size distribution is a compromise between a creep resistant coarse microstructure and radiation resistant fine‐grained material with high strength at lower temperatures . The following effects were found to contribute to the formation of a nonuniform grain structure in ODS steels: (1) a nonuniform distribution of oxide particles leading to a spatial variation in the pinning force, (2) inhomogeneous temperature distribution during sintering or (3) an inhomogeneous dislocation density after MA, leading to a variation in the driving force for recrystallization.…”

“…One example is the formation of a bimodal grain size distribution which is observed in different ODS materials. [21][22][23][24][25] A material with a well defined bimodal grain size distribution, consisting of nanograins and larger grains in the lm-scale, is beneficial at low temperatures, because of its high strength caused by nanograins and the remaining dislocation-mediated plasticity in larger grains. As at high temperatures the fine grain structure can be a drawback in terms of creep resistance, the bimodal grain size distribution is a compromise between a creep resistant coarse microstructure and radiation resistant fine-grained material with high strength at lower temperatures.…”

Sintering Behavior of Lanthana‐Bearing Nanostructured Ferritic Steel Consolidated via Spark Plasma Sintering

“…[5] Recently, spark plasma sintering (SPS), which is an advanced pressure-assisted sintering technique utilizing pulsed current (1 000-5 000 A), has been utilized by researchers to consolidate milled ODS powders. [6][7][8][9][10] Typical sintering time can be greatly reduced from several hours in conventional sintering to a few minutes in the SPS, thereby minimizing or eliminating propensity for grain growth. [8,11,12] One of the keys to preparing high performance NFSs lies in minimizing the precipitate size and improving the uniformity in their distribution.…”