Papers by Keyword: Severe Plastic Deformation (SPD)

Abstract: Composite materials were applied to meet the demands of production efficiency on industrial because they offered the superior properties both of aspects on mechanical and physical properties were constantly being refined and developed with several methods. Composite technology with aluminum as a matrix as well as ceramic materials as reinforcement was very dependent on a result of the perfection of the manufacturing process on the matrix material and reinforcement was used. Aluminum currently still dominates as a matrix because of its ductility, while reinforcing materials that are widely used are ceramic elements such as silicon carbide (SiC) and alumina (Al₂O₃). Using of SiC/Al₂O₃ has been widely studied because of the remarkable improvement of the mechanical properties it produces. The addition of number of SiC particles to Al₂O₃ was able to significantly increase the hardness properties. In this study, a number of composite manufacturing methods were compared from the results of properties by accumulative press bonding (APB), accumulative roll bonding (ARB), and repetitive press roll forming (RPRF). The mechanical properties of RPRF results are known to produce better properties, especially mechanical properties. Mechanical properties were observed from tensile and hardness tests. The finer grain size is produced by increasing the compression cycle and increasing the mechanical properties when adding double reinforcement of the SiC/Al₂O₃, which causes the strength and hardness of the RPRF results to increase. Whereas other methods such as APB and ARB it is not compatible with composite materials, this proves that the RPRF method was very suitable for processing composite materials compared to APB and ARB methods.

Abstract: Cyclic extrusion compression (CEC) is one of the well-known techniques in metal forming processes under the severe plastic deformation process (SPD) in which an ultra-large plastic strain is imposed on a bulk material in order to make ultra-fine grained (UFG) metals, alloys and composites. In this work, the mechanical properties of the aluminum alloy (6061) before and after CEC process were examined. A special CEC die was design and fabricated for the present work which achieved an effective plastic strain of about 0.62 after each separate cycle of CEC. The microstructure was effectively refined with increasing the number of CEC cycles as the grain size was reduced from ≈250μm to ≈30 μm after 6 cycles of CEC. The mechanical properties were tremendously increased in comparison with those of as cast and annealed condition. The micro-hardness increased from 25 Hv to 56 Hv, while the yield and the ultimate tensile strengths increased from 60 MPa to 198 MPa and 85 MPa to 204 MPa respectively, the ductility increased from 2.97% to 4.6% with the number of CEC cycles increasing up to six cycles.

Abstract: Preparation of aluminum substrates for surface segregation enhancement of insoluble lead deposition was achieved. Sever plastic deformation 'SPD' of Al sheets was done using surface mechanical attrition treatment 'SMAT' in air. Scanning electron microscope SEM of etched Al substrates cuts showed micro-cavities both on the surface and in-depth. Orientation effects and surface inclusions of Pb inside Al surface found at 40 and 50 Hz - SMAT Al by X-Ray diffraction and energy dispersive of X-Rays EDX. Concluding that SMAT frequency limits used enhanced surface inclusions without annealing that could improve adhesion of industrial protective Pb coatings.

Abstract: Repetitive continuous extrusion forming was employed as a continuous severe plastic deformation route and both Al-Fe-Cu alloy and Al-Mg-Si alloy were involved. Evolution of microstructures and properties during this process is investigated by optical microscope, electron-backscatter diffraction, transmission electron microscope, and tensile testing. The results show that in the Al-Fe-Cu alloy an obvious mechanical softening and grain refinement were observed, while in the Al-Mg-Si alloy it shows a slightly rising in strength and ductility as the extrusion passes increasing.

Abstract: Reverse transformation behavior of thermally-induced martensite phase (α’) in martensitic stainless steel by the shot-peening is investigated. It is found that volume fraction of austenite phase (γ) on the peened surface is increased by the shot-peening under elevated temperature. This means that reverse transformation from thermally-induced α’ to γ can be induced by the shot-peening. Moreover, with decreasing the distance between blast nozzle and specimen (blast distance), the reverse transformation occurs more remarkably. This is because that larger shear strain can be induced by the shot-peening with shorter blast distance. Furthermore, thickness of the deformation-induced layer becomes larger as the blast distance decreases. It can be concluded that the reverse transformation in SUS410S with thermally-induced α’ occurs by large shear strain during the shot-peening.

Abstract: The formation of nanocrystalline structures and mechanical properties were studied in a nitrogen-bearing 304-type stainless steel subjected to severe plastic deformation (SPD). The steel samples were processed at ambient temperature using three different methods, i.e., caliber rolling, multidirectional forging and high pressure torsion. All these techniques resulted in pronounced grain refinement. The microstructures consisting of austenite/ferrite crystallites with transverse dimensions of 50 and 30 nm evolved in the rolled and forged samples, respectively. The austenite fractions comprised approximately 0.4. In contrast, the microstructure consisted mainly of austenite with an average grain size of about 25 nm evolved after high pressure torsion. All samples of the stainless steel subjected to severe plastic deformation demonstrated significant strengthening. The ultimate tensile strengths of 2065 MPa and 1950 MPa, were obtained after rolling and high pressure torsion, respectively. The ultimate tensile strength of samples subjected to multidirectional forging was 1540 MPa.

Abstract: An Al-3% Mg-0.2% Sc alloy was subjected to annealing or solution treatment and further processed by HPT at room temperature. Microhardness measurements were taken along the middle-sections of the discs and they demonstrated that a very substantial hardening is achieved during HPT processing regardless of the initial heat treatment. Hardness values of ~200 Hv were recorded at the edge of the samples although the microhardness distribution remained inhomogeneous along the diameters of the discs after 20 turns of high-pressure torsion. In addition, the microhardness of the solution treated Al-Mg-Sc samples continued to increase with the equivalent strain imposed by the anvils even after 30 turns of HPT processing whereas the hardness at the edges of the annealed discs saturated after 10 turns. These differences in the hardness evolution are attributed to the higher Mg content in solid solution in the case of the solution treated samples and its influence on delaying the recovery rate of this aluminium alloy.

Abstract: Evolution of structure and properties of Ni under severe plastic deformation by equal-channel angular pressing (ECAP) and dynamic channel-angular pressing (DCAP) has been studied by transmission and scanning electron microscopy and microhardness measurements, and the differences in formation of submicrocrystalline structure under different deformation techniques have been revealed. The thermal stability of structure obtained by these methods is compared. It is demonstrated that under the DCAP processing the material is strengthened faster, by lesser number of passes, and microstructure’s thermal stability is somewhat lower after ECAP compared to that after DCAP, although after equal number of passes ECAP results in a more homogeneous microstructure.

Abstract: (α + γ) two phase stainless steel (Fe-21%Cr-4.8%Ni-1.5%Mo) powder was processed by high pressure torsion (HPT) and consolidation at room temperature. The received powder had fully α single phase due to the rapid cooling during gas atomizing process. Specimens after HPT process were heat treated at 1173K for 3.6ks. It was revealed that the decomposition of α phase to γ took place during the heat treatment. Detailed microstructure observation showed that an equiaxed (α + γ) micro-duplex structure was developed and its average grain size was approximately 3.2 micrometers. The same heat treatment given to the material without HPT resulted in a coarse two phase microstructure.Therefore, it is considered that an ultra fine grained microstructure was caused by increasing of nucleation sites for γ phase due to severe plastic deformation (SPD) of HPT process. Electron backscatter diffraction patterns (EBSD) analysis indicated that α phase has a {110}/ND strong texture, that is, the α phase seems to have single orientated coarse grain structure. The γ precipitates indicated a {111}/ND strong texture, and the crystallographic orientation relationship of Kurdjumov-Sachs was observed.

Abstract: The paper reports on the effect of severe plastic deformation on mechanical properties of an Al-4.57Mg-0.35Mn-0.2Sc-0.09Zr (in wt. pct.) alloy processed by equal channel angular pressing followed by cold rolling (CR). The sheets of the 5024 alloy with coarse grained (CG) structure exhibited a yield stress (YS) near 410 MPa and an ultimate tensile strength (UTS) of 480 MPa, while the YS and UTS of this material with ultrafine-grained (UFG) structure increased to 530 and 560 MPa, respectively. On the other hand, the elongation to failure decreased by a factor of 2 and 4 after CR and CR following ECAP, respectively. It was shown that dislocation strengthening attributed to extensive CR plays a major role in achieving high strength of this alloy. Besides these macroscopic characteristics, jerky flow caused by the Portevin-Le Chatelier (PLC) instability of plastic deformation was examined. The formation of UFG structure results in a transition from mixed type A+B to pure type B PLC serrations. No such effect on the serrations type was observed after CR.