Search

Tensile behavior of titanium was studied at room temperature in the as-processed condition (using severe plastic deformation by high pressure torsion) and also in various annealed states. It was found that controlled annealing could lead to enhancement of both strength and ductility of this material. The origin of this phenomenon is discussed in the context of TEM/HREM and SEM observations. [Copyright &y& Elsevier]

In this work, a bulk gum metal (GM) was fabricated via arc melting from high purity powders. The ingots were first extruded using a conventional route followed by equal channel angular pressing (ECAP). The mechanical behavior of the extruded GM and ECAP-processed GM was studied under both quasi-static and high strain rate compression conditions to evaluate the influence of strain rate. In addition, the associated mechanical anisotropy, or the lack thereof, was investigated through loading in different orientations with respect to the extrusion or ECAP direction. Precipitous stress drops were observed under dynamic compression of both extruded and ECAP-processed GM specimens when loading perpendicular to the extrusion direction. Adiabatic shear banding (ASB) was found to be associated with the precipitous stress drops on the dynamic stress-strain curves. The details of the ASBs were characterized by optical and scanning electron microscopy, with emphasis on electron backscattered diffraction (EBSD). The mechanisms responsible for the formation of ASB were examined both from thermal softening and geometrical softening perspectives. Significant microstructure refinement within ASBs was established, and a possible grain refinement mechanism was proposed. [ABSTRACT FROM AUTHOR]

This paper reports on a study of the relationship between microstructure, mechanical behavior and impact toughness of the UFG Grade 5 Ti alloy. The mechanical behavior and impact toughness of the Grade 5 Ti alloy in a coarse-grained state, and in an ultrafine-grained (UFG) state produced by equal-channel angular pressing (ECAP) with subsequent deformation-and-thermal treatments via extrusion and warm upsetting in isothermal conditions, were studied extensively. It is shown that a strong refinement of α -grains (less than 250 nm) in the alloy by ECAP and extrusion leads to high strength but with low values of the uniform elongation and lower impact toughness. It is demonstrated that, in order to increase the impact toughness of UFG Ti alloys, it is possible to use approaches realizing ductility enhancement associated with an increase of the strain hardening capacity. An enhancement in the impact toughness of the UFG alloy through an increase in the uniform tensile elongation of the sample is achieved by the preservation of the ultrafine size of α -grains (about 800 nm) with predominantly high-angle boundaries and a decrease in the dislocation density due to recovery and dynamic recrystallization during warm upsetting. [ABSTRACT FROM AUTHOR]

The initial grain size of TWIP steel can affect the deformation mechanism during the HPT processes and the mechanical properties of severely deformed TWIP steels, contrary to the common belief that responses to the severe plastic deformation of metallic materials are not affected by initial grain size. [ABSTRACT FROM AUTHOR]

Different with common grain refinement dominated by dislocation activities, grain subdivision induced by sequential activation of multiple twinning was observed in a Mg-Gd-Y-Zr magnesium alloy via high-pressure torsion. Deformation bands were evolved from large primary twin bands, which contained refined grains through localized multiple twinning. Nanometer-scaled amorphous bands were also observed within deformation bands in Mg alloys for the first time. These observations indicate that localized deformation via multiple twinning and the consequent formation of deformation bands are potential routes to grain refinement in rare earth-magnesium alloys. [ABSTRACT FROM AUTHOR]

Abstract: In the current study the mechanical properties of ultra-fine grained low carbon steel processed by conventional equal channel angular pressing and a continuous equal channel angular pressing-Conform process were investigated. Both monotonic and cyclic properties were determined for the steel in either condition and found to be very similar. Microstructural analyses employing electron backscatter diffraction were used for comparison of the low carbon steels processed by either technique. Both steels feature very similar grain sizes and misorientation angle distributions. With respect to fatigue life the low carbon steel investigated shows properties similar to ultra-fine grained interstitial-free steel processed by conventional equal channel angular pressing, and thus, the general fatigue behavior can be addressed following the same routines as proposed for interstitial-free steel. In conclusion, the continuously processed material exhibits very promising properties, and thus, equal channel angular pressing-Conform is a promising tool for production of ultra-fine grained steels in a large quantity. [Copyright &y& Elsevier]

Abstract: Long-length ultrafine-grained (UFG) Ti rods are produced by equal-channel angular pressing via the conform scheme (ECAP-C) at 200°C, which is followed by drawing at 200°C. The evolution of microstructure, macrotexture, and mechanical properties (yield strength, ultimate tensile strength, failure stress, uniform elongation, elongation to failure) of pure Ti during this thermo-mechanical processing is studied. Special attention is also paid to the effect of microstructure on the mechanical behavior of the material after macrolocalization of plastic flow. The number of ECAP-C passes varies in the range of 1–10. The microstructure is more refined with increasing number of ECAP-C passes. Formation of homogeneous microstructure with a grain/subgrain size of 200nm and its saturation after 6 ECAP-C passes are observed. Strength properties increase with increasing number of ECAP passes and saturate after 6 ECAP-C passes to a yield strength of 973MPa, an ultimate tensile strength of 1035MPa, and a true failure stress of 1400MPa (from 625, 750, and 1150MPa in the as-received condition). The true strain at failure failure decreases after ECAP-C processing. The reduction of area and true strain to failure values do not decrease after ECAP-C processing. The sample after 6 ECAP-C passes is subjected to drawing at 200¯C resulting in reduction of a grain/subgrain size to 150nm, formation of (100) fiber texture with respect to the rod axis, and further increase of the yield strength up to 1190MPa, the ultimate tensile strength up to 1230MPa and the true failure stress up to 1600MPa. It is demonstrated that UFG CP Ti has low resistance to macrolocalization of plastic deformation and high resistance to crack formation after necking. [Copyright &y& Elsevier]

Abstract: Microstructure and mechanical properties of copper subjected to 1–10 ECAP passes via route Bc were compared with those for further cold rolled specimens. Microstructure was studied by means of TEM and EBSD analysis in three orthogonal sections. Rolling caused transformation of reasonably equiaxed structure after ECAP into lamellar one due to geometrical effect of deformation, but almost no additional grain refinement occurred during rolling. Significantly higher extent of HABs (about 20% irrespectively to passes number) was found after rolling. This was associated with more pronounced dynamic restoration process during rolling. Mechanical properties were estimated by tension testing at room temperature. Yield strength increased by ∼100MPa after rolling due to finer boundary spacing according to Hall–Petch relationship. [Copyright &y& Elsevier]

Abstract: NiTi alloy has a unique combination of mechanical properties, shape memory effects and superelastic behavior that makes it attractive for several biomedical applications. In recent years, concerns about its biocompatibility have been aroused due to the toxic or side effect of released nickel ions, which restricts its application as an implant material. Bulk ultrafine-grained Ni50.8Ti49.2 alloy (UFG NiTi) was successfully fabricated by equal-channel angular pressing (ECAP) technique in the present study. A homogeneous and smooth SrO–SiO2–TiO2 sol–gel coating without cracks was fabricated on its surface by dip-coating method with the aim of increasing its corrosion resistance and cytocompatibility. Electrochemical tests in simulated body fluid (SBF) showed that the pitting corrosion potential of UFG NiTi was increased from 393mV(SCE) to 1800mV(SCE) after coated with SrO–SiO2–TiO2 film and the corrosion current density decreased from 3.41μA/cm2 to 0.629μA/cm2. Meanwhile, the sol–gel coating significantly decreased the release of nickel ions of UFG NiTi when soaked in SBF. UFG NiTi with SrO–SiO2–TiO2 sol–gel coating exhibited enhanced osteoblast-like cells attachment, spreading and proliferation compared with UFG NiTi without coating and CG NiTi. [Copyright &y& Elsevier]

Abstract: Fully dense, nanocrystalline tantalum (average grain size as small as ∼40nm) has been processed for the first time by high-pressure torsion. High-resolution transmission electron microscopy reveals non-equilibrium grain boundaries and grains decorated with high-density dislocations. Microhardness measurements and instrumented nanoindentation experiments indicate that the mechanical property is quite uniform except for the central area of the disks. Nanoindentation experiments at different strain rates suggest that the strain rate sensitivity of nanocrystalline tantalum is increased compared to the coarse- and ultrafine-grained counterparts and is accompanied by an activation energy of the order of a few ∼b 3 (b is the magnitude of the dislocation Burgers vector), implying a shift in the plastic deformation mechanism from the screw dislocation dominated regime. We thus infer the plastic deformation mechanisms of nanocrystalline body-centered cubic (bcc) and face-centered cubic metals converge. To examine the stress–strain behavior, we have used microcompression to measure the compressive stress–strain curves on microscale pillars fabricated by focused ion beam technique. Yield strength as high as 1.6GPa has been observed. High-strain rate behavior has been investigated using a miniature Kolsky bar system. We have found that at high-strain rates the nanocrystalline tantalum specimens exhibit adiabatic shear banding, a dynamic plastic deformation mode common to many ultrafine-grained and all nanocrystalline bcc metals. [Copyright &y& Elsevier]

Commercially pure (CP) Ti was subjected to a complex severe plastic deformation (SPD) processing route consisting of equal channel angular pressing, swaging and drawing, resulting in the formation of a homogeneous ultra-fine-grained (UFG) microstructure showing a very high strength. The significant anisotropy of mechanical properties found in the processed rod is related to a very strong crystallographic texture developed during SPD processing. The features of plastic deformation of the UFG CP Ti are discussed with respect to its crystallographic texture. [ABSTRACT FROM AUTHOR]

Abstract: The microstructure and the mechanical properties of ultrafine grained Pd and Pd–x% Ag (x =10, 20, 40) alloys processed by high pressure torsion (HPT) were thoroughly investigated using transmission and high resolution electron microscopy, XRD analysis and tensile tests. The increased Ag content resulted in decrease of the stacking fault energy (γ SF), which made it possible to produce by means of HPT different ultrafine-grained structures in the alloys and to study their superior strength and ductility. The nature of such unique mechanical behaviour is discussed on the basis of analysis of strain hardening mechanisms and effect of stacking fault energy. [Copyright &y& Elsevier]

Abstract: An in situ tensile test with grey scale correlation has been performed to study the deformation process in ultrafine grained (UFG) Pd and Pd–x at.% Ag (x =5 or 20) alloys produced by high-pressure torsion. Shear band nucleation and propagation was found to be an important deformation mechanism after strain localization during the tensile test. The underlying microscopic mechanism is related to cooperative grain boundary sliding. Moreover, the additional influence of stacking fault energy was found to change the nature of the deformation mechanism from localized strain in Pd to more homogeneous deformation in Pd–20% Ag. In situ analysis and the findings are new and give innovative insight into the basics of deformation in UFG face-centred cubic metals. [Copyright &y& Elsevier]

Microstructures and mechanical properties of equal-channel angular pressing (ECAP) processed and naturally aged ultrafine grained (UFG) and coarse grained (CG) 7075 Al alloys as well as their evolutions during annealing were investigated. After the same natural aging, the tensile yield strength, ultimate strength, and microhardness of the UFG samples were 103%, 35%, and 48% higher, respectively, than those of the CG samples, because of higher densities of Guinier–Preston (G–P) zones and dislocations in the UFG sample. Upon annealing, the microhardness of the UFG sample decreased gradually, while a hardening peak appeared for the CG sample. The peak was caused by the precipitation hardening of the metastable η′ phase. For the UFG sample, the precipitation hardening was overcompensated by the significant decrease of microstrain (dislocation density) upon annealing, resulting in a lack of precipitation hardening peak. Differential scanning calorimetry indicates that the ECAP process only accelerated the phase precipitations, but did not change the sequence of phase precipitation. This study shows that severe plastic deformation has the potential to significantly improve the mechanical properties of age-hardening Al alloys. [Copyright &y& Elsevier]

Abstract: Evolution of the microstructure and mechanical properties of Al–30wt.% Zn alloy after the severe plastic deformation (SPD) by the high-pressure torsion has been investigated in detail in dependence on the increasing deformation degree. SPD leads to the gradual grain refinement and decomposition of the Al-based supersaturated solid solution. Measurements of the microhardness reveal a successive softening of the alloy with the increased deformation degree. [Copyright &y& Elsevier]

Abstract: A coarse-grained (CG) Al6061 alloy after solution treatment is subjected to high pressure torsion at room temperature resulting in the formation of a homogeneous ultra-fine grained (UFG) microstructure with average grain size of 170nm. Tensile tests are performed at room and liquid nitrogen temperatures for both CG and UFG conditions. Analysis of the surface relief of the tested specimens is performed. The effect of microstructure on the mechanical properties and on the deformation behavior of the material is discussed. [Copyright &y& Elsevier]