Materials Science Forum Vols. 667-669

Abstract: Equal channel angular pressing (ECAP) is the most popular severe plastic deformation process used to refine grain structure of metals. However, its application exhibits inherent problems of low productivity and poor utilization of material. In order to address these problems, the ECAP channel with two-turns can be used. Historical examples and current applications of this configuration are provided including route BC version of the process. Route C version of two-turn ECAP is illustrated with a scaled-up process used for processing square inch cross section aluminium billets. To address another problem, that of short billets, it is suggested that future applications of two-turn ECAP are based on the new process of incremental ECAP; it enables decoupling feeding of the material and its deformation and thus reduces dramatically the feeding force for billets, plates and sheets.

Abstract: A new continuous severe plastic deformation (SPD) procedure integrating conventional rolling with equal-channel angular deformation (designated CR-ECA deformation procedure) was investigated. Experimental results show that the SPD procedure has the capacity of realizing continuous SPD processing of long-size work-pieces with good surface qualities. Numerical simulations by using finite element code DEFORM-3D show that the number of roller pairs had significant influences on the the CR-ECA deformation procedure. As the number of roller pairs changed from 1 to 2, 3 and 4, the effective strain increased by 10.1 %, 10.1 % and 16.1 %; the output velocity increased by 10.8 %, 15.9 % and 14.4 %; the torque of the primary feeding roller decreased by 19.0 %, 34.7 % and 45.6 %; the total torque increased by 7.0 %, 11.8 % and 13.4 %; and the energy consumption used for making unit volume work-piece subjected to unit effective straining decreased by 12.2 %, 15.0 % and 19.4 %.

Abstract: The influence of severe plastic deformation (SPD) on distribution of effective stresses, effective strains and temperatures during equal channel angular rolling (ECAR) process is mathematically simulated. Effect of ECAR processing on substructural and mechanical properties of oxygen free high conductivity (OFHC) Cu material is investigated too. Mathematical simulations in software DEFORM-3D, ECAR technology, tensile tests, EBSD analysis were used as experimental methods. Mathematical simulations of first ECAR pass referred on following results: effective normal stress had low heterogeneity with value 385 MPa, effective strain was distinguished with high heterogeneity in cross section of sample (φ=1,5-3) and temperature in deformation zone achieved value 150 °C. Mechanical properties after cold drawing were: Rp0,2 = 217 MPa, Rm = 260 MPa, Z = 63 % and after sixth ECAR pass were: Rp0,2 = 412 MPa, Rm = 426 MPa, Z = 72 %. From experiments is resulting the stabilization of mechanical properties after fourth ECAR pass were obtained.

Abstract: Asymmetric rolling (ASR) is one of the severe plastic deformation (SPD) processes which are prominently used to reduce grain size and refine grain structure of the metals and alloys of commercial interest. In this work, commercial purity iron processed by asymmetric rolling was experimentally studied by means of optical microscopy and transmission electron microscopy (TEM). Tensile tests were performed on the samples under different treatment conditions and the experimental results were compared with the output from the modelling analysis. Modelling results of the mechanical properties of this type of material are in accordance with the grain refinement mechanism.

Abstract: CEC has unique characteristic. These are applicability of very large strain and deformation under high hydrostatic pressure. Due to these abilities of CEC, several unique phenomena have been observed. One of them is the possibility of consolidation of metallic powders in room temperature to the form of bulk material. In the present paper the consolidation of AgSnBi and AgNi to bulk composites was presented. Applying the deformation of  = 0.42 in the single cycle of CEC, under high hydrostatic pressure, the samples without pores and discontinuities were fabricated. The microstructure observations were performed by optical microscopy (MO), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). They show refinement of microstructure at all levels of observation. The nanometric-size subgrains/grains were found inside consolidated granules. The microhardness level of AgSnBi in average achieved level 110 μHV100, and AgNi of about 90 μHV100. The AgSnBi samples consolidated by CEC and additional hydrostatically extruded to wires with 3 mm in diameter average showed 500 MPa yield point.

Abstract: Precompacts out of immiscible systems CuCr (75/25 wt%) and WCu (80/20 wt%), respectively, were made by pressing mixed powders and sintering. By applying different strains and hydrostatic pressures of HPT at room temperature, disc-shaped samples with a diameter of 8 mm were produced. They were investigated by Light Microscopy, Scanning-Electron Microscopy using Back-Scattered Electrons, and X-ray Line Profile Analysis. In addition, Vickers microhardness data were collected. Both systems showed the highest microhardness at a shear strain of about γ = 170. The density (for the case of Cu25Cr) of the consolidated material could be increased to the theoretical value. Microhardness and grain sizes were studied individually for each of the phases, too.

Abstract: In this paper, the process of severe cold-rolling and annealing for Q235 steel with lath martensite has demonstrated a new promising technique for producing in-situ composite multi-nanolayer steel. Cold rolling and subsequent annealing have great impact on microstructure evolution as well as mechanical properties. In the as-rolled state, the strength (b 2112 MPa) is approximately four times increased than as-received material, which is attributed to work hardening and grain refining during cold rolling. As cold-rolled sample subjected to further annealing below 500 °C, deformed microstructure underwent further recovery and recrystallization and finally became refined equiaxed grains; ultrafine ferrite grains, nano-carbides precipitated uniformly were seen in the specimen annealed at 500 °C, and the phenomenon of fracture delamination was observed from the specimens, the delamination plane was parallel to the rolling plane, in-situ composite weak interfaces effect has great impact on the fracture surface. Annealing at and above 600 °C resulted in coarse ferrite grains with spheroidized coarse carbides, causing grain growth.

Abstract: This article focuses on the effect of combine rolling processes on structure and mechanical properties of the commercially pure Ti rods. The finite element model had being made. The analysis of strain state at the screw and shape rolling was done. The analysis of microstructure evolution at the warm rolling was completed.

Abstract: Some nanocrystaline Ni was prepared by repeated cold rolling with intermediate folding (F&R). The material was then processed by High Pressure Torsion (HPT) to study the grain evolution under additional Severe Plastic Deformation (SPD). Microstructures were characterized by Transmission Electron Microscopy (TEM) and the impurity distribution was analyzed by Atom Probe Tomography (APT). In this paper, we discuss about the influence of impurities on the grain growth during HPT and on the grain size reduction mechanism during SPD.

Abstract: A gradient nanostructured layer (GNsL) was generated on the two sides of bulk sample in 304L stainless steel by means of the surface mechanical attrition treatment. The microstructure of the GNsL was characterized via TEM observation. The prominent microstructural features involve the intersection of multi-system twin operation, subdividing the original grains into blocks, a martensite transformation mainly occurring at the interface of the twins as well, and the randomly orientated nanocrystallites at the top of surface. After annealing at 750°C for 10 min, recovery had occurred and the dislocation density was much reduced. The vast majority of the grains at the top surface were in the nanocrystalline/ultrafine range, with some recrystallization regions. The uniaxial tensile tests were performed to obtain the mechanical property of bulk samples with GNsL. The yield strength was about 2 times higher than that of the coarse-grained counterpart, but with a decrease in uniform elongation and elongation to failure as well. The relationship between the microstructure and mechanical property was discussed in detail.