Papers by Keyword: Equal-Channel Angular Pressing (ECAP)

Abstract: The mechanical properties and fracture mechanisms of the 0.09%C-0.08%Mo-0.03%Nb- 0.06%V steel in the initial state and with the ultrafine-grained (UFG) structure obtained by equalchannel angular pressing (ECAP) have been estimated. The investigation included the static and cyclic tensile tests, the impact tests at room and lower temperatures with automatic recording of force-displacement diagram, and the analysis of both the fracture surface microrelief and the evolution of plastic deformation zone by replica method. It is established that the grain refinement increases the ultimate strength and yield strength, but decreases plasticity and impact toughness and raises fatigue growth rate and the critical temperature of ductile–brittle transition. The dynamic fracture toughness of the material after ECAP as compared with that of the material with the initial structure decreases due to the raising of the critical brittleness temperature.

Abstract: Commercial purity Ti is an important candidate material for orthopedic and dental implants because of its high specific strength, good corrosion resistance and excellent biocompatibility. However, for biomedical applications as a replacement for Ti-6Al-4V alloy that is currently used, improvement in strength of CP Ti is necessary. This can be achieved by using severe plastic deformation (SPD) processes like equal channel angular pressing (ECAP) at warm working temperatures followed by conventional processing at room temperatures. This requires adequate workability after ECAP. In this study, the workability of CP Ti after warm ECAP has been investigated. Specimens of CP Ti, 17 mm in diameter, were extruded using processing route Bc through an ECAP die with an angle of 120◦ between the two intersecting channels and at a temperature of approximately 400oC. Workability testing was carried out using collar type compression specimens by upsetting the specimens between flat platens till the onset of cracking. Workability diagrams have been plotted as a function of axial and hoop strains at failure. The results show that processing by ECAP lead to only minor reductions in workability of CP Ti. The tensile strength is enhanced considerably by this process.

Abstract: A commercially pure niobium has been subjected to SPD at room temperature ( ~0.11 TM) via ECAP (90º, route BC) up to 16 passes and via HPT up to shear strains γ =1000. ECAP-ed samples show an equiaxed structure after 8 and 16 passes with a decreasing average grain size. The results show that both the microstructure and mechanical properties of ECAP-ed samples do not reach a steady state up to at least 16 passes. HPT samples show at outer region a finer structural size but similar hardness values at similar equivalent strains. The nanoindentation results show an evident indentation size-effect even for the most deformed samples. The hardness values at the nano level converge for the recrystallized, the ECAP-ed and the HPT samples. This implies that, at the nano level, when the geometrically necessary dislocation density overcomes significantly the (initial) statistically stored dislocation density, hardness depends mainly on the physical intrinsic properties of the material (Burgers modulus, bulk modulus...) and the contribution of bulk mechanical properties (i.e., bulk yield strength) to hardness is smoothed down. Strain-rate sensitivity (SRS) of plastic strength has been also measured by means of rate-jump nanoindentation tests. The SRS is proportional to the inverse of hardness.

Abstract: Microstructure and mechanical properties of the ultrafine-grained (UFG) 1421 aluminum alloy processed by equal channel angular pressing (ECAP) have been studied. This UFG material was successfully rolled under the conditions of superplasticity. It was established that the rolled material exhibited not only the enhanced superplasticity, but also high strength retaining initial ductility at room temperature after additional short-term annealing and low-temperature aging.

Abstract: Tensile tests were carried out at 473 K with initial strain rate of 10-4 s-1 in samples of a ZK60 alloy (Mg-5.5% Zn-0.5% Zr) processed by different number of passes using Equal-Channel Angular Pressing (ECAP). The measured superplastic elongations ranged from ~930% to a record of ~3050%. The flow behavior was found to vary with the number of passes of ECAP. It is shown that strain-hardening due to grain growth and the evolution of the strain rate sensitivity with the strain determines the flow behavior and final elongations. The results are consistent with theories of plastic flow in tensile testing.

Abstract: Equal-channel angular pressing (ECAP) at 443 K was used to introduce an ultra-fine grained (UFG) microstructure to a Zr and Sc modified 7075 aluminum alloy. Using the methods of TEM and EBSD, an average grain size of 0.6 1m was recorded after the pressing. The UFG microstructure remained very stable up to the temperature of 723 K, where the material exhibited high strain rate superplasticity (HSRSP) with elongations to failure of 610 % and 410 % at initial strain rates of 6.4 x 10-2 s-1 and 1 x 10-1 s-1, respectively. A strain rate sensitivity parameter m in the vicinity of 0.45 was observed at temperatures as high as 773 K. At this temperature, the material still reached an elongation to failure of 430 % at 2 x 10-2 s-1. These results confirm the stabilizing effect of the Zr and Sc additions on the UFG microstructure in a 7XXX series aluminum alloy produced by severe plastic deformation.

Abstract: The stress-strain curves at high strain rate superplasticity were analyzed for Ti-6Al-4V and aluminum 1420 industrial alloys in ultra-fine grained state produced by severe plastic deformation. For both alloys the observed strengthening effect can be caused by grain growth under the above mentioned conditions resulting to increase of grain boundary sliding resistance. In the case of aluminum alloy the grain recovery can be accompanied by significant change in phase composition which is also stimulates the recrystallization process.

Abstract: Severe plastic deformation (SPD) has received considerable attention for its capability to produce ultrafine and nano structured materials. On the one hand, SPD, especially in the forms of equal channel angular pressing (ECAP) and high pressure torsion (HPT) is able to refine bulk materials with coarse grain structures. On the other hand, SPD has been used to synthesise bulk materials from particles. It enables particles from nano to micro scales to be consolidated into fully dense materials at much lower temperatures and shorter times, compared to the conventional sintering processing. It is particularly relevant to consolidating particles with non-equilibrium microstructures and to producing complex multiphase alloys. In this summary, ECAP as an effective process to synthesise a range of light metal based materials from particles with various sizes and structures, including aluminium and aluminium composites, titanium and magnesium, will be demonstrated. Full density and good bonding are achieved easily with the application of a back pressure. Microstructures from nano to ultrafine scales have been produced, resulting in significantly enhanced strength. Simultaneous increase in ductility has also been achieved in some alloys by virtue of multi-scale structures.

Abstract: Deformation methods of nanostructuring (DMNs) of materials are proposed to classify into severe plastic deformation (SPD) and mild plastic deformation (MPD) methods according to fundamentally different low- and high-temperature grain refinement mechanisms they exploit. A general analysis of the fundamentals and nanostructuring efficiency of three most developed DMNs, high pressure torsion (HPT), equal-channel angular pressing (ECAP), and multiple isothermal forging (MIF) is done with a particular attention to ECAP and MIF. It is demonstrated that MIF is the most efficient method of DMNs allowing one to obtain the bulkiest nanostructured samples with enhanced mechanical properties.

Abstract: Equal channel angular pressing (ECAP) is one of the most promising processes to fabricate ultra-fine grained materials. The material deformation is affected by die geometry, material behavior, friction and back pressure. The optimum back pressure for 1100Al during ECAP was studied. The effect of back pressure on deformation behavior, effective strain and deformation load were analyzed by using finite element software. The results show that the corner gap between the billet and the die in the external part of the deformation zone decreases and even disappears with the increase of back pressure, which can produce more uniform and larger strain in the billet. The deformation load enhances with the increase of back pressure. From the simulation results, it can be found out that the optimum back pressure for 1100Al pressed in the die of Φ=90° is about 30MPa.