Grain boundary segregation in UFG alloys processed by severe plastic deformation

Grain boundary segregations were investigated by Atom Probe Tomography in an Al-Mg alloy, a carbon steel and Armco\trademark Fe processed by severe plastic deformation (SPD). In the non-deformed state, the GBs of the aluminium alloy are Mg depleted, but after SPD some local enrichment up to 20 at.% was detected. In the Fe-based alloys, large carbon concentrations were also exhibited along GBs after SPD. These experimental observations are attributed to the specific structure of GBs often described as "non-equilibrum" in ultra fine grained materials processed by SPD. The grain boundary segregation mechanisms are discussed and compared in the case of substitutional (Mg in fcc Al) and interstitial (C in bcc Fe) solute atoms

Effects of the Tempering and High-Pressure Torsion Temperatures Onmicrostructure of Ferritic/Martensitic Steel Grade 91

Grade 91 (9Cr-1Mo) steel was subjected to various heat treatments and then to high-pressure torsion (HPT) at different temperatures. Its microstructure was studied using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Effects of the tempering temperature and the HPT temperature on the microstructural features and microhardness in the ultrafine-grained (UFG) Grade 91 steel were researched. The study of the UFG structure formation takes into account two different microstructures observed: before HPT in both samples containing martensite and in fully ferritic samples

Enhanced Fatigue Limit in Ultrafine-Grained Ferritic–Martensitic Steel

The influence of the ultrafine-grained (UFG) structure on the fatigue endurance limit and the nature of fatigue failure have been studied. It is shown that the formation of the UFG structure containing carbides and the coincidence site lattice relationship (CSL) and twin boundaries leads to an increase in the fatigue endurance limit. To study the mechanisms of fatigue failure, scanning and transmission electron microscopy and X-ray diffraction analysis were used. Studies have shown that the formation of the UFG structure as a result of rolling and subsequent heat treatment above the temperature of the ferrite/austenite phase transition leads to an increase in the fatigue endurance limit by more than 70%, from 475 to 800 MPa, compared to coarse-grained samples. The dynamic aging observed during fatigue tests was more pronounced in materials with a UFG microstructure. The influence of the CSL and twin boundaries on the nature of the fatigue failure of ferritic–martensitic steel is discussed

Microstructure and Properties of the 308LSi Austenitic Steel Produced by Plasma-MIG Deposition Welding with Layer-by-Layer Peening

This paper investigates the effect of cold working via layer-by-layer peening on the microstructure and properties of a 308LSi steel workpiece produced by the wire deposition welding with a consumable electrode following the principle of 3D printing. The microstructure, phase composition and mechanical properties of the metal are studied before and after the workpiece synthesis. In the microstructure of the workpieces produced by peening, there is, in addition to austenite, a small quantity of fine-dispersed carbides and residual δ-ferrite in the interdendritic spaces. It is demonstrated that the use of layer-by-layer cold working in the process of deposition welding enables eliminating transcrystallization of the deposited metal, promotes an increase in the microstructure’s degree of dispersion and a more uniform distribution of fine-dispersed carbides in the volume of the dendrites. It is found that these structural features of the deposited metal in the additive manufacturing of a workpiece with layer-by-layer peening lead to an enhancement of the strength characteristics as compared to the material produced by the conventional wire deposition welding. Meanwhile, the level of the ductility characteristics remains high

Grain boundary segregation in UFG alloys processed by severe plastic deformation

International audienceGrain boundary segregations were investigated by Atom Probe Tomography in an Al-Mg alloy, a carbon steel and Armco® Fe processed by severe plastic deformation (SPD). In the non-deformed state, the GBs of the aluminium alloy are Mg depleted, but after SPD some local enrichment up to 20 at.% was detected. In the Fe-based alloys, large carbon concentrations were also exhibited along GBs after SPD. These experimental observations are attributed to the specific structure of GBs often described as "non-equilibrum" in ultra fine grained materials processed by SPD. The grain boundary segregation mechanisms are discussed and compared in the case of substitutional (Mg in fcc Al) and interstitial (C in bcc Fe) solute atoms