Materials Science Forum Vols. 503-504

Abstract: Development of high strength I/M Mg alloys has been tried by ECAE processing. The mechanical properties and microstructure of ECAE-processed Mg97Zn1Y2 alloy with LPSO (long-periodic stacking ordered) structure were investigated. The tensile yield strength and elongation of as-cast Mg97Zn1Y2 were improved substantially by ECAE process. ECAE-processed with yield strength of 290 MPa and elongation of 22 % was obtained. The microstructure of ECAE-processed Mg97Zn1Y2 alloy consisted of refined α-Mg with the grain size around 6.5 μm and finely dispersed LPSO phase. Furthermore, the some texture was formed by ECAE process. The improved mechanical properties seem to be originated by the microstructure refinement and texture.

Abstract: In order to make the effect of processing clear, AM50A magnesium casting alloys were extruded at various extrusion conditions such as extrusion temperature and extrusion ratio. The mechanical properties of AM50A alloy increased with decreasing extrusion temperature. Tensile yield strength and tensile strength of extruded AM50A alloy were 389MPa and 420MPa respectively when the extrusion temperature was 348K. The microstructure of the extruded magnesium alloy showed large grains stretched to the extrusion direction and fine recrystallized grains. Decreased extrusion temperature resulted in improved strength and decreased elongation with increasing of the degree of work hardens and extrusion force. When the extrusion ratio is high, improvement of strength is prevented by rycrystallization and it was observed as crystal orientation by XRD. The elongation of the extrusion increased with the recrystallization of grains. Every magnesium alloy extruded at low temperature has high strength.

Abstract: The dependence of the strain rate sensitivity (SRS) of α-Fe and Al 99.5, as typical representatives of fcc- and bcc-type metals, on the testing temperature and with respect to the microstructure is investigated. In particular, the differences between conventional grain size (CG) and ultrafine grain size (UFG) are pointed out. UFG Al 99.5 generally shows an elevated SRS compared to CG Al 99.5. In case of α-Fe the SRS of the UFG state is decreased at room temperature, but increased at 200 °C, compared to the CG state. It is shown that the SRS also influences the ductility of UFG-metals in tensile tests.

Abstract: Severe plastic deformation (SPD) techniques are the best for producing of massive nanostructured materials. The methods of equal channel angular pressure (ECAP) and twist extrusion (TE) are realized by simple shear uniform deformation without change of cross-section sizes of sample. In the case of roll forming (RF) the shear strain is localized in the near-surface layer of metal. Intensity of shear strain in the near-surface layer depends on variation of parameters of deformation and conditions of friction in a contact. Steel 65G (0.65C, 0.3Si, 0.6Mn, 0.3Cr, and 0.3Ni) was deformed by roll forming. Transmission electron microscopy (TEM) of “cross-section” samples was used for studying of gradient structure of deformed material. TEM investigation shown that cell substructure in a near-surface layer have been formed. The depth of deformed layer is approximately 40 micrometers. Average cell size in cross-section direction is about 100 - 200 nm. Thin nanostructure layer with cell size about 20-30 nm was detected. In our opinion such substructure formed due to effect of “good” impurities.

Abstract: This paper discusses the development of a novel processing route to produce ultra finegrain bulk alloy forgings; the microstructural response of these forgings to thermal exposure; and the comparison of mechanical properties to those from conventionally processed material. A Ni- 20Cr [wt%] alloy was processed by near-isothermal multi-axis forging to a grain size of approximately 1 μm. A heat-treatment study over the range 900 to 1200°C was conducted to determine the resultant grain size as a function of time and temperature. Tensile properties were measured at room temperature, 500°C, and 930°C. High-cycle fatigue properties were measured at room temperature. The room-temperature tensile strength was approximately 2.5 times greater than that of conventionally processed Ni-20Cr. Fatigue data showed that the room-temperature highcycle fatigue run-out stress was greater than 100% of the yield stress.

Abstract: Copper single crystals were subjected to equal-channel angular pressing (ECAP) via the so-called route A and Bc, in order to examine the influence of initial crystallographic orientation and processing route on microstructure development and grain fragmentation. Microstructural changes were examined by transmission electron microscopy (TEM). The pressing via the route Bc resulted in finer microstructure for all orientations in terms of grain size, equiaxiality and orientation scattering after four passes. Effect of initial crystallographic orientation on the grain refinement was also recognized, and it might be attributed to heterogeneous deformation such as shear bands, whose formation is strongly orientation dependent. After eight passes, however, the effect of processing route and initial orientation cannot be recognized.

Abstract: Conventional coarse grained (CG) commercial pure (CP) Ti Grade 2 was studied after cold rolling (CR) at room temperature, and after equal channel angular pressing (ECAP) at 450° C followed by CR, by transmission electron microscopy (TEM) methods. CR of the CG material leads to a microstructure showing initially twins with (0112) type and later subgrains separated by lowangle grain boundaries. CR carried out after ECAP yields the fragmentation of fine grains (300 – 800 nm) mostly bounded by high-angle boundaries into elongated subgrains (~ 100 nm). It was shown with in-situ annealing experiments in the TEM that this microstructure is thermally stable up to a temperature of 450° C. Tensile tests showed that the combination of ECAP with CR has the potential to produce at the same time high strength (941 MPa) and high ductility (16.7%).

Abstract: Anisotropy of mechanical properties, fatigue and fracture resistance of precipitation hardened CuCrZr alloy ultrafine (UFG) grained by equal-channel angular pressing (ECAP) is in focus of the present communication. Fracture toughness was estimated in terms of J-integral and the fatigue crack growth rate was quantified. It was found that although the estimated JIC-value appeared lower than that reported in the literature for a reference alloy, the ductility, fracture and crack growth resistance remained satisfactory after ECAP while the tensile strength and fatigue limit improved considerably. The stable crack growth rate did not differ very much for ECAP and reference conventional CuCrZr and no remarkable anisotropy in the stable crack growth was noticed.

Abstract: Copper-carbon composites (where carbon can be graphite, carbon-fibers, fullerenes and carbon nanotubes) are used and under investigations for various applications. The reported manufacturing methods are diverse, but, to our best knowledge, no process is available to fabricate a multifilamentary Copper-Graphite wire with a large number of graphite filaments. We describe a new processing route, which allows the fabrication of such composite by severe plastic deformation. The resulting microstructures and electrical properties are presented and discussed.

Abstract: Effect of equal-channel angular pressing (ECAP) on the corrosion and mechanical properties of Cu-35%Zn alloy were studied. Two types of feed direction were selected. One is parallel pass and the other is 180°degree rotated ECAP pass after each pass. Both ECAP passes made texture in each specimen in which shear band with 45 degree on transverse direction and twins exist. The specimen prepared by parallel ECAP pass has finer shear band. Relative amount of twins to shear band on the microstructure becomes decrease with number of ECAP pass. Microhardness increased from 75 Hv to 210 Hv by ECAP. The corrosion potential and rate of the ECAPed Cu-35%Zn alloys in aerated aqueous 1 M-H2SO4 solution were –92.3 mVSHE and 3.72x10-2 A/cm2 for route- A and –38.6 mVSHE and 5.08x10-2 A/cm2 for route-C, respectively. The corrosion potential and rate of depended on the feed direction and number of pass.