THE DEFORMATION OF AZ31 MAGNESIUM ALLOY DURING WARM CONSTRAINED GROOVE PRESSING

A magnesium alloy AZ31 as plate of dimensions (60 x 60 x 3) mm has been constrained groove pressed (CGP) four deformation passes (16 pressings) at 250 oC by simulation and experiments. On the basis of the analysis of calculation results about the deformation distribution in the alloy AZ31 workpieces, the mechanism for its microstructure evolution during the severe plastic deformation (SPD) process was partly clarified. On the other hand, deformation heterogeneity distribution developed in the workpieces by applying CGP caused the evolution of a non-uniform microstructure. The TEM microstructure analysis results provided clear evidence that across the plate both the banded deformed microstructure where dislocation cell structure and/or partially or fully recovered polygonized subgrain microstructure are present. The recovering dynamic and local polygonization process contributes significantly to the formation of ultra-fine materials (UFG) microstructure.

THE DEFORMATION OF AZ31 MAGNESIUM ALLOY DURING WARM CONSTRAINED GROOVE PRESSING

A magnesium alloy AZ31 as plate of dimensions (60 x 60 x 3) mm has been constrained groove pressed (CGP) four deformation passes (16 pressings) at 250 oC by simulation and expremental. On the basis of the analysis of calculation results about the deformation distribution in the alloy AZ31 workpiece the mechanism for its microstructure evolution during the severe plastic deformation (SPD) process was partly clarified. On the other hand, deformation heterogeneity distribution developed in plate by applying CGP caused the evolution of a non-uniform microstructure. The TEM microstructure analysis results provided clear evidence that across the plate both the banded deformed microstructure where dislocation cell structure and/or partially or fully recovered polygonized subgrain microstructure are present. The recovering dynamic and local polygonization process contributes significantly to the formation of ultra-fine materials (UFG) microstructure.

THE DEFORMATION OF AZ31 MAGNESIUM ALLOY DURING WARM CONSTRAINED GROOVE PRESSING

A magnesium alloy AZ31 as plate of dimensions (60 x 60 x 3) mm has been constrained groove pressed (CGP) four deformation passes (16 pressings) at 250 oC by simulation and experiments. On the basis of the analysis of calculation results about the deformation distribution in the alloy AZ31 workpieces, the mechanism for its microstructure evolution during the severe plastic deformation (SPD) process was partly clarified. On the other hand, deformation heterogeneity distribution developed in the workpieces by applying CGP caused the evolution of a non-uniform microstructure. The TEM microstructure analysis results provided clear evidence that across the plate both the banded deformed microstructure where dislocation cell structure and/or partially or fully recovered polygonized subgrain microstructure are present. The recovering dynamic and local polygonization process contributes significantly to the formation of ultra-fine materials (UFG) microstructure.

Microstructural Evolution and Deformation Behavior of Cold-Rolled Fe-Mn-Al-C Low-Density Steel

Low-density medium-manganese steels offer a vast development prospect for industrial application due to their outstanding combination of mechanical properties and density reduction. The microstructural evolution following tensile deformation of cold-rolled and annealed Fe-10Mn-10Al-0.7C steels was investigated by means of SEM and TEM microstructure analysis and XRD measurements. Annealing in the range of 700-1100 °C led to an austenite-ferrite dual-phase microstructure that was characterized by tensile strength of 700-1100 MPa and elongation of 6-34%. κ-carbides were observed in steels annealed at relatively low temperatures (700-850 °C). The steel exhibited the optimum combination of tensile strength of 930 MPa and elongation of 34% after annealing at 900 °C for 0.5 h. The stacking fault energy was estimated to be 69mJ/m2 considering the difference between average constituent and practical constituent of austenite caused by the high ferrite fraction. The deformed microstructures of the austenite exhibited the typical planer glide characteristics in sequence of dislocation array, Taylor lattice, Taylor lattice domain and microband. And the wavy glide occurs in ferrite was manifested by tangled dislocation and dislocation cells.

Ultra-Fine and Nano-Crystalline Structure Induced by Sliding Friction of Carbon Steel

Sliding friction is one of the most powerful processes for microstructural evolution in the sub-surface, including grain refinement and recrystallization of deformed structure. Pin-on-disc sliding tests were carried out for 0.45 mass % carbon steels, and TEM microstructure and hardness of the specimens were investigated. Particularly effects of friction conditions on the microstructure at the surfaces and wear properties of the friction induced microstructure were studied. It was found that ultra-fine equi-axed grains in the 30 - 50 nm size range were produced in the case of a high friction speed of 5.0 m/s in an air atmosphere. Moreover, nano-crystalline microstructure can be produced in a vacuum atmosphere even if the friction speed was low. The friction induced nano-crystalline surface layers, which exhibited significant high hardness, showed good wear resistance.

The Importance Of Surface Topography For The Biological Properties Of Nitrided Diffusion Layers Produced On Ti6Al4V Titanium Alloy

Diffusion nitrided layers produced on titanium and its alloys are widely studied in terms of their application for cardiac and bone implants. The influence of the structure, the phase composition, topography and surface morphology on their biological properties is being investigated. The article presents the results of a study of the topography (nanotopography) of the surface of TiN+Ti2N+αTi(N) nitrided layers produced in low-temperature plasma on Ti6Al4V titanium alloy and their influence on the adhesion of blood platelets and their aggregates. The TEM microstructure of the produced layers have been examined and it was demonstrated that the interaction between platelets and the surface of the titanium implants subjected to glow-discharge nitriding can be shaped via modification of the roughness parameters of the external layer of the TiN titanium nitride nanocrystalline zone.

Microstructure of CB2 Steel before and after Long-Term Creep Tests

A pilot 4t valve made of CB2 steel was produced in the frame of COST Action 522. Specimens for long-term creep tests were taken from positions with a wall thickness of 130 mm and 85 mm. Creep testing was carried out at 650°C and a stress range from 50 MPa to 120 MPa. The longest times to rupture of specimens in individual positions were 67,857 h and 82,649 h respectively. Ruptured samples underwent fractographic and microstructural analyses. Quantitative evaluation of substructure was performed using SEM and TEM. Microstructure consisted of tempered martensite with primary boron and niobium nitrides and secondary particles of M23C6 carbide, Laves phase and vanadium nitride. During creep tests coarsening of Laves phase occurred and new particles nucleated on the site of M23C6 carbides, NbN or BN nitrides. Significant increase in volume fraction of Laves phase was detected in specimens ruptured up to 20,000 hours in comparison to as received conditions; any further increase was found out after longer creep exposures. Concerning to M23C6 carbides any important changes were found out in their size and distribution. Density of fine MX nitride was higher after creep tests than in as received conditions with the exception of two longest creep exposures. Several Z-phase particles were also identified after these two exposures.

Deformation Mechanisms of Tandem Hot Rolled GH4169 Superalloy during Creep

By means of direct aged treatment, creep property measurement and high resolution TEM microstructure observation, the deformation mechanisms of Tandem Hot Rolled GH4169 superalloy during creep are investigated. Results show that, after direct aging treatment, fine γ″ particles with different sizes and shapes dispersedly precipitate in the alloy, which is one of important factors for the alloy possessing good creep resistance. And the deformation mechanisms of the alloy are that the deformed twinnings with different orientations are activated on {111} plane by pole mechanism, thereinto, the twinning dislocation may continuously slip around a pole axis dislocation on the twinning planes when the applied stress exceeds the critical value, and the twinnings may multiply by the dislocation reactions and mutual indemnification. As creep goes on, the denser dislocations with single or double orientations slip in the different twinnings, which play an important role of coordinating the grain deformation to enhance the creep resistance of the alloy.

A Strengthening Model of Cu-Cr In Situ Fibrous Composites Produced by Equal Channel Angular Pressing

The composite filament structure was produced in the Cu-5.7%Cr and Cu-12.4%Cr as-cast alloy ingots by using equal channel angular pressing (ECAP) at room temperature. Optical and TEM microstructure, micro-hardness, tensile strength and electrical conductivity of ECAPed samples were investigated. The rotation and spreading of Cr particles took place during ECAP, and resulted in long thin in-situ filaments. The tensile strength increased with the number of the ECAP passes. A strengthening model was recommended to predict the enhancement of the tensile strength in Cu-Cr in situ fibrous composites.