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 (101¯0) 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.
Microstructure and thermal stability of high chromium ferritic/martensitic steel 12Cr-2W-2Ni-0.5Mo processed by equal channel angular pressing (ECAP) has been investigated using electron back ...scattering diffraction (EBSD) and transmission electron microscopy. Volume fraction of α′ – martensite, the values of lattice parameter, dislocation density and a size of coherent scattering domains were determined using X-ray technique in conventional reflection mode. Phase composition and volume fraction of precipitates was investigated using transmission X-ray diffraction. Tensile tests were used to estimate the mechanical properties. The contribution of strengthening mechanisms to yield stress of steel is discussed. It was demonstrated that the ECAP processing in the ferrite region with subsequent quenching from the austenite region leads to both the formation of homogeneous UFG structure and the increase of a number of boundaries with the coincidence site lattice (CSL) relationships (the CSL boundaries) in ferritic/martensitic steel providing the enhanced mechanical properties.
In this work X-ray scattering techniques are used in full scale to characterize the microstructure of Al-2wt.%Cu alloy in order to state common and diverse features between artificial and dynamic ...ageing. Artificial ageing of the alloy is implemented via T6 regime, dynamic ageing occurs during high pressure torsion. X-ray phase analysis of diffraction patterns obtained in the transmission regime has for the first time identified and quantified the nanodisperse phases of precipitates in the both aged states. Lattice parameters, coherent scattering domains distribution over sizes, averaged dislocation density, fractions of edge and screw dislocations of Al phase after artificial and dynamic ageing are determined via the diffraction patterns obtained in the reflection regime. Small angle X-ray scattering (SAXS) technique has established quantitative characteristics of size, shape and distribution of precipitates in the mentioned states. In order to confirm the results of SAXS, transmission electron microscopy studies are performed on the same foils. Peculiarities of mechanisms of artificial and dynamic ageing in the studied alloy are discussed on the basis of the obtained data.
•X-ray phase analysis in the transmission regime enables analyzing precipitates.•During dynamic strain ageing transformation of precipitates θ″ → θ′→ θ takes place.•Dynamic strain aging occurs more completely and quickly.•Growth of precipitates is conditioned by diffusion along dislocations.
Special features of structural and phase transformations during the formation of bainitic steel structure were studied. The possibilities of identifying plate (PM) and lath (LM) martensite after ...quenching, and of tempered martensite (TM) along with upper (UB) and lower (LB) bainite after tempering of quenched steel are described. The morphology and specifics of the formation of UB, LB, and TM in the steel structure were studied. The x-ray phase analysis method was used to show the possibility of identifying phases (PM, LM, residual austenite (
A
res
), TM, UP and LB) and calculating their mass fractions in steel by decomposing the reflections into components. Quenching at 950°C was shown to produce PM and LM in steel with different morphologies and dislocation densities, contents of twins and carbon concentrations in the matrix. Tempering of the quenched steel at 500°C was shown to cause the following phase transition: PM + LM +
A
res
→ UB + LB + TM + PM+ LM+ cementite. The resistance of bainitic steel to sulfide corrosion cracking underloading and to hydrogen embrittlement was assessed.
This paper deals with a study of the structure and thermal stability of intermetallic TiAl-based alloys subjected to high-pressure torsion (HPT). The structural features of the HPT-processed samples ...have been studied by transmission electron microscopy and X-ray diffraction. In order to study the thermal stability of ultrafine-grained (UFG) structure, the dependence of microhardness on the annealing temperature in a temperature range of 150–1000°С has been investigated. The effect of heat treatment on the grain structure stability and microhardness of the HPT-processed samples is discussed.
Abstract
Within the framework of experimental investigations and computer modeling using the viscoplastic self-consistent (VPSC) model of a material plastic flow, the regularities of preferential ...orientations formation were established, the proportion of certain texture components was estimated, and existing slip systems (SS) and twinning systems (TS) were identified for equal-channel angular pressing (ECAP) of copper alloys depending on the stacking fault energy (SFE).
The structure and texture of the fatigue fracture of a tubing sub made of a ferritic–pearlitic steel are studied. The microstructure is found to be characterized by a small grain size, a high ...edge-dislocation density, and a developed crystallographic rolling texture with a tension texture superposed on it. The growth of grains with the {112}〈111〉 and {114}〈221〉 orientations and the suppression of the {001}〈110〉, {112}〈110〉, and {110}〈001〉 texture components are shown to accelerate fatigue fracture.
The effect of processing by accumulative high-pressure torsion on the structure of steel 10 is investigated. It is found that after processing by accumulative HPT, a stronger structure refinement ...takes place in steel 10 as compared to regular HPT processing for the same number of revolutions.
Abstract
A new efficient method was used to find that in the case of high-pressure torsion of commercially pure titanium, accumulation of shear strain in Ti does not occur due to slippage of anvils. ...Despite this, micro-hardness increases as the number of turns n increases, and Ti structure is refined more intensively. High-pressure torsion is accompanied by a high-pressure ω-phase formation. However, the content of ω-phase changes non-monotonously with an increase in the number of turns. First, while number of turns is less than n=5, the ω-phase content reaches 50%. Upon further deformation, the ω-phase content decreases to 15% for n=20. A new accumulative high-pressure torsion method is applied to commercially pure titanium for the first time. Accumulative high-pressure torsion leads to the strongest transformation of the structure and an increase in hardness, since stronger real deformation occurs due to composition of compression and torsion strain cycles.
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