Papers by Keyword: Severe Deformation

Abstract: Equal Channel Angular (ECAP) pressing has been showed as an attractive route to produce fine and ultrafine-grained metals and alloys with high strength and fracture toughness. ECAP is a simple process for applying severe plastic deformation (SPD) to metals that can be done with common laboratory equipments (mechanical tests machines) and an adequate die. In the present work, an eutectoid steel was processed by ECAP in a 120° die. Mechanical behavior of samples deformed by ECAP was compared to the same material processed by rolling. The hardness level obtained after a single pass of ECAP was comparable to an 84% reduction by rolling in a single pass. The hardness level obtained after 1 ECAP pass on a patented steel was higher than 4 ECAP passes on the same steel without patenting. The metallographic analysis showed intense alterations on the microstructure by the ECAP processing.

Abstract: According to severe deformation of crossheading surrounding rock of Xinshun Mine 15102# roadway. Sight instrument method is adopted to loose circle test of crossheading surrounding rock, and study the damage range. The study result indicates that the loose circle is about 2.5m~3.0m of 15102# roadway. The loose circle of sides is about 2.4m~2.8m; belong to typical large loose circle. And roof loose circle is a little more than sides. Surrounding rock has some engineering characteristics of soft rock, leading to loose circle rock fragment and expand severely. Increase supporting difficulty. It adopts unite supporting form in the case of surrounding rock.

Abstract: In this study, the relationship between the structure and properties of commercial purityaluminium (AW-1199) was investigated by applying constrained groove pressing (CGP) method.The refinement of the coarse grain aluminium microstructure to submicrocrystalline size by largeplastic strain at room temperature defined. The impact of various strains upon microstructurechanges is investigated using transmission electron microscopy (TEM) and electron back scatterdiffraction (EBSD). A mixture of subgrains produced by grains subdivision and polygonizedsubgrains formed locally due to dynamic recovery was found in the deformed aluminium. Thetensile properties and resulting hardness are related to microstructural evolution induced by CGP. Asubstantial impact of straining upon the increasing in tensile strength was observed after the firstpass. Further strain increase had an insignificant effect on tensile strength but was accompanied byductility loss. The post deformation annealing effect was then explored with aim to increase theductility. The results indicate that changes in strength and ductility may be related to formation of abimodal structure.

Abstract: Ni-rich alloy (50.8at.%Ni) was plastically deformed by compression combined with reversion oscillating torsion. The compression rate was 0.05 mm/s and the torsion frequency and angle were 1,5Hz and ±3°. After the deformation process the specimens were annealed at 350°C/1h (623K/1h) and 400°C/1h (673K/1h). Their structure and transformation characteristic were studied with the use of TEM, X-ray phase analysis and DSC measurements. TEM observation of specimens after annealing at 350°C/1h (623K/1h) indicate presence of highly deformed B2 phase. In the specimen annealed at 400°C/1h (673K/1h) additionally Ni4Ti3 precipitates and the R-phase in the B2 matrix was found. DSC measurements show that the transformation sequence changes for the deformed and then annealed samples from single step B2  B19’ transformation to the B2  R  B19’ on cooling. Also increase of R-phase transformation temperature TR with the decrease of annealing temperature was observed.

Abstract: Microstructure evolution during annealing of a Ni-20%Cr alloy subjected to high-pressure torsion (HPT) at ambient temperature was examined. It was shown that discontinuous static recrystallization (DSRX) occurs in non-uniform manner under subsequent annealing in the alloy strained to ε<4. The material strained to ε6 or higher exhibits continuous grain growth (GG) under subsequent annealing. It is attributed to the fact that HPT led to the formation of nanoscale grains with an average size of 50 nm. Increasing fraction of these grains with strain leads to transition from DSRX to continuous GG under subsequent annealing. It was found that the main feature of recrystallization behavior of the Ni-20%Cr alloy subjected to HPT is simultaneous occurrence of short-range ordering and recrystallization processes under annealing conditions. As a result, despite the formation of recrystallized structure with an average grain size of 340 nm after annealing at 600°C (0.52 T_m), the material exhibits very high microhardness of 3.6 GPa.

Abstract: The structural changes in a 304-type austenitic stainless steel during large strain cold rolling and subsequent annealing were studied. The severe deformation resulted in the development of highly elongated grains/subgrains aligned along the rolling axis. The transverse grain/subgrain size rapidly decreased to its minimal value of about 50 nm at relatively small strains of ~1 and then hardly changed upon following deformation. Such a structural response on cold working was associated with multiple twinning resulting in fast grain subdivision. The processing was accompanied by a partial martensitic transformation resulting in a decrease of austenite volume fraction to about 0.35 after straining to ε = 4.0. Isochronal annealing for 30 min was characterised by a gradual coarsening of grains, the average size of which increased to about 200 nm after heating to 800°C. The high elongation of ferrite grains facilitated simultaneous homogeneous nucleation of austenite grains throughout the matrix upon heating; and, therefore, promoted the development of ultrafine grained structure with the size of structural elements well below 1 micron.

Abstract: In this paper a specific method of severe plastic deformation (SPD) applied to the NiTi shape memory alloy and the obtained structure and the alloy properties are presented. Cold rolling combined with transverse movement of the rolls was the method. The maximal strain obtained was ε_c ≈ 10.20 for the relatively large specimens. Then the alloy was annealed in order to obtain samples of a given grain size. In the paper the structure of the alloy annealed at 350°C was studied with the use of TEM equipped with Nanomegas attachment ASTAR allowing determination of the orientation of grains in nanoareas.

Abstract: Tensile behaviour of two steels with submicrocrystalline structures, i.e. a 304-type austenitic steel and an Fe-27%Cr-9%Ni austenitic-ferritic steel, was studied. The starting materials were subjected to large strain rolling and swaging to a total strain of ∼4 at ambient temperature. The severe deformation resulted in a partial martensitic transformation and the development of highly elongated austenite/ferrite (sub) grains aligned along the deformation axis. In the cold worked state, the transverse grain/subgrain size was about 100 nm in the 304-type steel and about 150 nm in the Fe-27%Cr-9%Ni steel. The grain refinement by severe plastic deformation resulted in increase of ultimate tensile strength to 2000 MPa and 1800 MPa in 304-type and Fe-27%Cr-9%Ni steels, respectively. The phase transformation and recrystallization took place concurrently upon annealing, leading to the development of submicrocrystalline structure consisting of austenite and ferrite grains. No significant softening took place under annealing at temperatures below 600°C. The tensile strength was 1920 MPa in 304-type steel and 1710 MPa in Fe-27%Cr-9%Ni steel after annealing at 500°C for 2 hours.

Abstract: Severe plastic deformation (friction, compression shear, filing or rolling) of Hadfield steel leads to the growth of the internal effective field on 57Fe cores, removal of the magnetic degeneracy in spectra, and the extension of the paraprocess up to room temperature. The observed change of the magnetic characteristics is explained by the deformation-induced redistribution of carbon and short-range ordering of carbon and manganese. Since the magnetic degeneracy is removed in the Hadfield steel upon deformation, it is possible to consider a mechanism of magnetic precipitation hardening, which is realized in local magnetically ordered regions of the structure containing Mn-C pairs.

Abstract: Thermomechanical treatment was applied to a binary NiTi alloy in order to improve its functional properties by forming nanocrystalline structure of the alloy. The alloy deformation was obtained by cold rolling combined with transverse movement of the rolls. This technique allowed us to obtain high strain (c ≈ 6) for the relatively large specimens. Subsequently, the samples were annealed in the temperature range 300 -500oC in order to form a nano-, submicro –and/or microcrystalline structure. The evolution of the structure and associated changes of the transformation sequences and functional properties were studied with the use of TEM, X-ray phase analysis, DSC and bend and free recovery ASTM tests. A mixed amorphous/crystalline structure was obtained after severe deformation, the martensitic transformation was completely suppressed in the sample. Annealing at lower temperatures caused formation of nanocrystalline structure that grew to the microcrystalline and finally well-defined polygonized structure in annealed at 500oC specimens.