scholarly journals The Interdependence of the Degree of Precipitation and Dislocation Density during the Thermomechanical Treatment of Microalloyed Niobium Steel

Metals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 294
Author(s):  
Stoja Rešković ◽  
Ljerka Slokar Benić ◽  
Martina Lovrenić-Jugović
Keyword(s):  
Dislocation Density ◽  
Thermomechanical Processing ◽  
Cold Deformation ◽  
Industrial Process ◽  
Recrystallization Process ◽  
Density Of Dislocations ◽  
Niobium Microalloyed Steel ◽  
Rolling Temperatures ◽  
Final Rolling ◽  
Lüders Bands

In this paper, thermomechanical processing of niobium microalloyed steel was performed with the purpose of determining the interaction between niobium precipitates and dislocations, as well as determining the influence of the temperature of final deformation on the degree of precipitation and dislocation density. Two variants of thermomechanical processing with different final rolling temperatures were carried out. Samples were studied using electrochemical isolation with an atomic absorption spectrometer, transmission electron microscopy, X-ray diffraction analysis, and universal tensile testing with a thermographic camera. The results show that the increase in the density of dislocations before the onset of intense precipitation is insignificant because the recrystallization process takes place simultaneously. It increases with the onset of strain-induced precipitation. In this paper, it is shown that niobium precipitates determine the density of dislocations. The appearance of Lüders bands was noticed as a consequence of the interaction between niobium precipitates and dislocations during the subsequent cold deformation. In both variants of the industrial process performed on the cold deformed strip, Lüders bands appeared.

scholarly journals Strengthening Mechanisms of Magnesium-Lithium Based Alloys and Composites

2016 ◽  
Vol 2016 ◽  
pp. 1-11 ◽  
Author(s):  
C. O. Muga ◽  
Z. W. Zhang
Keyword(s):  
Thermal Treatment ◽  
Dislocation Density ◽  
Thermomechanical Processing ◽  
Precipitation Strengthening ◽  
Strengthening Mechanisms ◽  
Engineering Applications ◽  
The Past ◽  
Treatment Processes ◽  
Solution Strengthening ◽  
Suitable Processing

Mg-Li based alloys are widely applied in various engineering applications. The strength of these alloys is modified and enhanced by different strengthening mechanisms. The strengthening mechanisms of these alloys and their composites have been extensively studied during the past decades. Important mechanisms applied to strengthening the alloys include precipitation strengthening, solution strengthening, grain and subgrain strengthening, and dislocation density strengthening. Precipitation and solution strengthening mechanisms are strongly dependent on composition of the alloys and thermal treatment processes, whereas grain and subgrain and dislocation density strengthening mechanisms majorly depend on thermomechanical processing. In this paper, recent studies on conventional processes for the strengthening of Mg-Li based alloys are summarized as they are critical during the alloys design and processing. Main strengthening mechanisms are objectively reviewed, focusing on their advantages and drawbacks. These can contribute to enhancing, initiating, and improving future researches for alloys design and suitable processing selection.

scholarly journals Deformed and stressed states of materials at the rolling of three layer stacks, dislocation structure of inner layer – nickel foil

2021 ◽  
Vol 66 (3) ◽  
pp. 270-279
Author(s):  
L. I. Hurski
Keyword(s):  
Dislocation Density ◽  
Shear Deformation ◽  
Dislocation Structure ◽  
Three Dimensional ◽  
Nickel Foil ◽  
Dislocation Network ◽  
Uniform Compression ◽  
Degree Of Deformation ◽  
Density Of Dislocations

The deformed and stressed states during rolling of a three-layer stack from various materials with a nickel foil inner layer are considered. The technique of determining the density of dislocations is described. The data about the influence of deformation conditions on the distribution and density of dislocations during rolling of nickel foil in various stacks are presented, including the registration or determination of the dislocation structure of nickel foil before deformation and at various degrees of deformation. It is shown that the mechanical scheme of deformation of the inner layer of the stack, namely, the deformation of the nickel foil by non-uniform compression with shear, has a decisive influence on the development of the dislocation structure and properties. It is established that the dislocation density is determined not only by the degree of deformation, but also by a scheme of the deformed and stressed state of matter, and for the case of shear deformation with increasing degree of deformation the dislocation density increases more rapidly than in the case of tensile strain or compression without shear; the result of shear deformation is a significant refinement of the structure of materials: with increasing degree of plastic deformation of the material a three-dimensional cellular network of dislocation is formed, wherein the borders of cells are formed by tangles of dislocations. With increasing degree of deformation, the density of dislocations at the cell boundaries increases, and the size of the cells decreases; in this case, the areas inside the cells of the dislocation network are always free of dislocations. The obtained results allow recommending the schemes with shear deformation for new promising processes of production of materials with unique properties.

Stored Energy of Plastic and Elastic Origin and Recrystallization

2008 ◽  
Vol 571-572 ◽  
pp. 143-148
Author(s):  
Krzysztof Wierzbanowski ◽  
Andrzej Baczmanski ◽  
Jacek Tarasiuk ◽  
Paul Lipiński ◽  
Alain Lodini
Keyword(s):  
Residual Stress ◽  
Plastic Deformation ◽  
Dislocation Density ◽  
Stress Field ◽  
Driving Force ◽  
Recrystallization Process ◽  
Stored Energy ◽  
Residual Stress Field ◽  
Orientation Distributions ◽  
Deformation Models

Stored energy is generally considered as a main driving force of recrystallization process. After plastic deformation a high dislocation density and residual stress field remain in a material. Both quantities are at the origin of the stored energy and we call them as the “plastic” and “elastic” parts of this energy. Their orientation distributions can be determined using diffraction and deformation models. Both components of the stored energy are studied in the present work. Their distributions and characteristics are studied for f.c.c. and b.c.c. materials.

scholarly journals Microstructural characterization of NiTi shape memory alloy produced by rotary hot forging

2017 ◽  
Vol 32 (S1) ◽  
pp. S201-S206
Author(s):  
P. Rodrigues ◽  
F. M. Braz Fernandes ◽  
A. S. Paula ◽  
J. P. Oliveira ◽  
S. B. Ribeiro ◽  
...  
Keyword(s):  
Shape Memory ◽  
Thermomechanical Processing ◽  
Niti Alloy ◽  
Cold Deformation ◽  
Hot Forging ◽  
Microstructural Characterization ◽  
Niti Shape Memory Alloy ◽  
Scanning Calorimetry ◽  
Rotary Forging

The thermomechanical processing of NiTi shape memory alloys usually involves several steps of hot and/or cold deformation. The present work presents the structural characterization of a Ni-rich NiTi alloy bar, produced by vacuum-induced melting and thermomechanical processing in laboratory scale, aiming at massive production in the future. This study focused on the first step of hot working at 800 °C during rotary forging. Microstructural characterization was performed using differential scanning calorimetry, high- and low-temperature X-ray diffraction (XRD) using a laboratory source and synchrotron XRD. Thus, it was possible to obtain the phase transformation characteristics of the material: the transformation temperatures and the transformation sequence. Proposed thermomechanical processing is intended for production of bars and wires that will be subsequently drawn to get thin wires, for different applications, including orthodontic arch wires.

Characterization of Dislocations in GaN Thin Film and GaN/AlN Multilayer

2012 ◽  
Vol 725 ◽  
pp. 75-78
Author(s):  
Noriko Ohmori ◽  
Tomonori Uchimaru ◽  
Hiroyuki Fujimori ◽  
Jun Komiyama ◽  
Yoshihisa Abe ◽  
...  
Keyword(s):  
Thin Film ◽  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Dislocation Density ◽  
Buffer Layer ◽  
Direction Parallel ◽  
Density Of Dislocations ◽  
Transmission Electron ◽  
Sudden Decrease

The dislocations in GaN thin film with GaN/AlN multilayer (ML) as the buffer layer were evaluated using transmission electron microscopy. A high density of dislocations parallel to the GaN/ML interface and a sudden decrease in the dislocation density at the GaN/ML interface were found. Dislocation propagation in the direction parallel to the GaN/ML interface by turning horizontally on the GaN/ML interface is considered to be effective in decreasing the dislocation density at the top layer of GaN.

Stored Energy and Recrystallization Process

2007 ◽  
Vol 539-543 ◽  
pp. 3335-3340 ◽  
Author(s):  
Andrzej Baczmanski ◽  
Krzysztof Wierzbanowski ◽  
Abdelilah Benmarouane ◽  
Alain Lodini ◽  
Paul Lipiński ◽  
...  
Keyword(s):  
Dislocation Density ◽  
Residual Stresses ◽  
Elastic Energy ◽  
Crucial Role ◽  
Driving Force ◽  
Recrystallization Process ◽  
Stored Energy ◽  
Grain Interaction ◽  
Deformation Models

Stored energy plays a crucial role in recrystallization process. One can distinguish two contributions to this energy. The first one is the elastic energy, connected with residual stresses, i.e., with grain-grain interaction. Another part of the stored energy is due to dislocation density, which is mainly localized inside grains. The latter one is considered as a main driving force of recrystallization. However, the stored energy connected with residual stresses can also have some influence on this process. Both types of energy can be determined experimentally and predicted by deformation models. Taking into account both types of the stored energy, some features of recrystallization textures can be explained.

Microstructure and Mechanical Properties of Nanostructured Intermetallic Alloy Based on Ti2AlNb

2008 ◽  
Vol 584-586 ◽  
pp. 153-158
Author(s):  
M.R. Shagiev ◽  
G.A. Salishchev
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Room Temperature ◽  
Thermomechanical Processing ◽  
Nanocrystalline Structure ◽  
Nanostructured Material ◽  
Intermetallic Alloy ◽  
Superplastic Behavior ◽  
Average Grain Size ◽  
Rolling Temperatures

Homogeneous nanocrystalline structure with the average grain size of about 300 nm was produced in Ti2AlNb-based intermetallic alloy by a thermomechanical processing which included multistep isothermal forging at temperatures below the β-transus and intermediate annealings. Nanostructured material possessed excellent mechanical properties. At room temperature, elongations up to 25% were obtained and the ultimate strength reached 1400 MPa. The alloy exhibited superplastic behavior in the temperature range of 850-1000°C. The maximum elongation of 930% and steady state flow stress σ50 of about 125 MPa were obtained at 900°C and strain rate of 4.2×10-3 s-1. The rolling temperatures of nanostructured alloy were defined from analysis of its mechanical behavior at a typical rolling strain rate of about 10-1 s-1 and intermetallic sheets with improved mechanical properties were produced.

scholarly journals Influence of Niobium on the Beginning of the Plastic Flow of Material during Cold Deformation

2013 ◽  
Vol 2013 ◽  
pp. 1-5 ◽  
Author(s):  
Stoja Rešković ◽  
Ivan Jandrlić
Keyword(s):  
Plastic Flow ◽  
Deformation Zone ◽  
Microalloyed Steel ◽  
Cold Deformation ◽  
Low Carbon Steel ◽  
Low Carbon ◽  
Thermoelastic Effect ◽  
Niobium Microalloyed Steel ◽  
Thermographic Measurement ◽  
Lüders Band

Investigations were conducted on low-carbon steel and the steel with same chemical composition with addition of microalloying element niobium. While tensile testing was carried out, the thermographic measurement was tacking place simultaneously. A specific behavior of niobium microalloyed steel was noticed. Test results have shown that, in the elastic deformation region, thermoelastic effect occurs, which is more pronounced in niobium microalloyed steel. Start of plastic flow in steel which is not microalloyed with niobium begins later in comparison to the microalloyed steel, and it is conducted so that, at the point of maximum stress, deformation zone is formed within which stresses grow. In steel microalloyed with niobium after proportionality limit, comes the occurrence of the localized increase in temperature and the occurrence of Lüders band, which propagate along the sample forming a deformation zone.

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