Microstructure of severely deformed metals from X-ray line profile analysis

Two essentially different materials, cubic Ti(49.8)Ni(50.2) shape memory alloy and hexagonal AZ91 Mg alloy, were deformed by equal channel angular pressing (ECAP). The microstructure developed as a result of severe plastic deformation was studied by X-ray line profile analysis. The correlation between the microstructure and the mechanical behavior was also investigated. Below 100 degrees C the tensile strength of the Mg alloy increased as a consequence of the increase of the dislocation density owing to ECAP. Above 200 degrees C the strength decreased and the ductility increased as a result of the breakage of the Al(12)Mg(17) precipitates due to ECAP. The analysis of the dislocation contrast factors of Ti(49.8)Ni(50.2) revealed that {110} dislocations with line vector formed during ECAP

Microstructure and mechanical properties of severely deformed AX41 magnesium alloy

The object of the present paper is the study of mechanical properties and microstructural evolution of AX41 magnesium alloy, severely deformed using a combination of hot extrusion and equal channel angular pressing. Equal channel angular pressing processing was performed at 250°C following route Bc. Mechanical properties of the ultrafine-grained alloy were investigated in tension at a constant strain rate of 10-4 s-1 at room temperature and 100 °C. The dislocation density was determined by X-ray line profiles analysis. Microstructural observations performed by electron backscattering diffraction after 8 passes of equal channel angular pressing revealed very fine and homogeneous microstructure with a grain size of 0.3-6 μm. It has been found that the room temperature mechanical properties such as yield stress and tensile strength reach their maximum value even after the first pass which is in good agreement with the evolution of the dislocation density. Further processing by equal channel angular pressing led to the decrease in both the yield strength and the dislocation density, despite the slight grain size refinement

Neutron Diffraction Study and Deformation Behavior of a Composite Based Mg Alloy Reinforced by Short Saffil Fibers

In the present work neutron diffraction has been applied for ex situ investigation of residual stresses in Mg-4%Al-1%Ca (AX41) magnesium alloy reinforced with short Saffil fibers. Samples were deformed in compression at room temperature. Two types of fiber arrangement were investigated. In both samples the fibers were homogeneously distributed and arranged in parallel planes with a random fiber orientation. In the first sample these planes were parallel with the loading axis and in the second one they were perpendicular to the loading direction. Significant dependence of both the mechanical properties and residual strains on the fibers orientation was observed. Sample with parallel fiber arrangement showed higher hardness and lower ductility. Further the increment of residual tensile lattice strain in the matrix with a macroscopic deformation is much higher than in the other case. It was found that the residual strain evolution strongly depends on the orientation of grains in the matrix

Twinning Evolution as a Function of Loading Direction in Magnesium

The twinning activity in random textured cast magnesium during monotonic, room temperature tension and compression tests was monitored by neutron diffraction. Decrease of integrated intensity which characterizes the twinned volume fraction of selected reflections was compared to its Schmid factor. The comparison shows that twinned fraction correlates with the maximum value of the Schmid factor with high precision during tensile test and with the average value of the Schmid factor during compression test

Characterization of active deformation mechanisms in Mg alloys with LPSO phase

The WZ21 and the WZ72 magnesium alloys containing long period stacking ordered (LPSO) phase extruded with an extrusion ratio of 4:1 at 350C. The microstructure was analyzed by scanning electron microscopy using electron backscattered diffraction. Both alloys exhibit bimodal microstructure of the Mg matrix and elongated LPSO phase along the extrusion direction. Using kernel average misorientation (KAM) maps it was shown that the dynamic recrystallization starts at the grain boundaries of the initial coarse grains. Both alloys exhibit fiber basal texture. The maxima of the basal planes are reduced by increasing content of alloying elements. Uniaxial compression tests along extrusion direction with concurrent acoustic emission measurements were performed to reveal mechanical properties and active deformation mechanisms of the studied alloys. The acoustic emission source mechanisms were identified by statistical analysis of the raw acoustic emission signal.The authors are grateful for support from the Czech Science Foundation under grant No. 16-12075S; the Grant Agency of the Charles University under grant No. 1262217; the grant SVV-2017- 260442; the Operational Programme Research, Development and Education, The Ministry of Education, Youth and Sports (OP RDE, MEYS) under the grant CZ.02.1.01/0.0/0.0/16_013/0001794 and the Spanish Ministry of Economy and Competitiveness under the grant number MAT2012-34135.Peer Reviewe

Acoustic Emission Study of High Temperature Deformation of Mg-Zn-Y Alloys with LPSO Phase

Magnesium alloys with different content of zinc (Zn) and yttrium (Y) were extruded at an extrusion ratio of 18:1 at 350 °C. The alloying elements in both Mg alloys formed a long period stacking ordered (LPSO) phase, which during the extrusion process was elongated along the extrusion direction (ED). The magnesium matrix has bimodal character composed by fine dynamically recrystallized (DRX-ed) grains and initial coarse grains elongated along ED. Compression tests with concurrent acoustic emission (AE) measurements were performed along ED at 200, 300, and 400 °C. The deformation mechanisms and the mechanical properties at 200 °C are very similar to those obtained at ambient temperatures, i.e. in the alloy with low volume fraction of the LPSO phase (<10%) twinning controls the yielding, while in the alloy with high volume fraction of the LPSO phase (around 35%) dislocation slip and kink formation are dominant. At 300 °C the reinforcing effect of the LPSO phase is reduced and at 400 °C it is not effective anymore.The authors are grateful for support from the Czech Science Foundation under grant Nr. 16-12075S; the Grant Agency of the Charles University under grant Nr. 1262217; the grant SVV-2017-260442; the Operational Programme Research, Development and Education, The Ministry of Education, Youth and Sports (OP RDE, MEYS) under the grant CZ.02.1.01/0.0/0.0/16_013/0001794 and the Spanish Ministry of Economy and Competitiveness under the grant number MAT2012-34135.Peer Reviewe

Evolution of dislocation density during compression of a Mg-Zn-Y alloy with long period stacking ordered structure

An extruded Mg-Zn-Y alloy with long period stacking ordered (LPSO) structure was compressed in two different loading directions. The LPSO phase in the initial extruded material exhibited strong texture and elongated grain morphology which resulted in different dislocation densities and plastic behaviors during compression parallel and perpendicular to the extrusion direction.The authors are grateful for the support of the Czech Science Foundation under the contract no. 16-12075S, the Hungarian Scientific Research Fund, OTKA, Grant no. K-109021 and the Spanish Ministry of Economy and Competitiveness under project number MAT2012-34135.Peer Reviewe

Influence of Volume Fraction of Long-Period Stacking Ordered Structure Phase on the Deformation Processes during Cyclic Deformation of Mg-Y-Zn Alloys

Deformation mechanisms in extruded Mg-Y-Zn alloys with different volume fractions of the long-period stacking ordered (LPSO) structure have been investigated during cyclic loading, i.e., compression followed by unloading and reverse tensile loading. Electron backscattered diffraction (EBSD) and in situ neutron diffraction (ND) techniques are used to determine strain path dependence of the deformation mechanisms. The twinning-detwinning mechanism operated in the α-Mg phase is of key importance for the subsequent hardening behavior of alloys with complex microstructures, consisting of α-Mg and LPSO phases. Besides the detailed analysis of the lattice strain development as a function of the applied stress, the dislocation density evolution in particular alloys is determined.This research was funded by the Czech Science Foundation under grant 20-07384Y (D.D., G.F., K.F.); by Spanish Ministry of Economy and Competitiveness under project number MAT2016-78850-R; and by the Operational Programme Research, Development and Education, The Ministry of Education, Youth and Sports (OP RDE, MEYS) under the grant CZ.02.1.01/0.0/0.0/16_013/0001794.Peer reviewe

Evolution of the dislocation structure during compression in a Mg-Zn-Y alloy with long period stacking ordered structure

Evolution of the dislocation structure in Mg97Y7Zn5 (at. %) alloy having long period stacking ordered (LPSO) structure was studied during compression tests. Two materials, an as-cast and an extruded one were deformed up to the applied strain of ~25%. The evolution of the crystallite size, the dislocation density and the population of the particular slip systems were determined by the evaluation of the X-ray diffraction peak profiles. A very low dislocation density with the order of magnitude 1012–1013 m−2 was detected in the compressed specimens. This dislocation density did not increase considerably with increasing strain. At the same time, a significant decrease of the crystallite size occurred during compression. These observations can be explained by the arrangement of dislocations into low energy dipolar configurations, such as kink walls, which do not contribute to the dislocation density measurable by X-ray diffraction peak profile analysis, however they yield a fragmentation of the crystallites.The authors are grateful for the support of the Czech Grant Agency under grant Nr. 16-12075S. This work was supported by the Hungarian Scientific Research Fund, OTKA, Grant no. K-109021.Peer Reviewe

Characterization of Hot Deformation Behaviour of Extruded Mg-Y-Zn Alloys with LPSO Phase

18th International Conference on the Strength of Materials (ICSMA 18)Magnesium alloys with various content of zinc (Zn) and yttrium (Y) were extruded with an extrusion ratio of 1:18 at 350 °C. The alloying elements in these Mg alloys formed a long period stacking ordered (LPSO) phase, which was characterized by transmission electron microscopy (TEM). The microstructure of the alloys was further examined by light microscopy and scanning electron microscopy (SEM), where LSPO phase in all alloys was found to be elongated along the extrusion direction (ED). Mechanical properties of the extruded alloys were investigated during compression loading at various temperatures between room temperature and 350 °C at a constant strain rate of 10-3 s-1. Concurrently with the deformation tests, the acoustic emission (AE) response of the specimens was recorded, in order to reveal the active deformation mechanisms. The conclusions of the AE experiments were proved by the microstructure investigations