Thermomechanical Processing Parameters Research Articles

Microstructure evolution and dynamic recrystallization mechanism of tantalum-tungsten alloys under hot compression

Ta-W alloys exhibit outstanding comprehensive properties at high temperatures, allowing them to have great application prospects in the high-temperature field. High-temperature compression tests (1573~1873 K) were conducted to evaluate the high-temperature mechanical properties of Ta-12W alloy, and the strain-compensated Arrhenius-Type model and hot processing map were developed to predict the optimal processing window. The electron backscatter diffraction, Transmission electron microscope, and DEFORM-3D software were performed to investigate the microstructure evolution and distributions of strain. The results demonstrated that the flow stress of Ta-12W alloy presented apparent negative temperature sensitivity and positive strain rate sensitivity. Based on the thermal processing diagrams and EBSD analysis, the results show that the low deformation temperature and high strain rate introduce stress concentration and deformation instability in the Ta-12W alloy. The optimized processing temperature and strain rate are at 1800 ~1873 K/0.001 s-1~0.05 s-1, and the microstructure at 1873 K/0.001 s-1 is more uniform and exhibits a low residual stress level. As the temperature increases, dynamic recovery and dynamic recrystallization cause significant softening effects, and continuous dynamic recrystallization dominates the high-temperature deformation behavior. Moreover, multiple continuous dynamic recrystallizations occur simultaneously, including sub-grain nucleation inside large grains, sub-grain nucleation at grain boundaries, and grain fragmentation accompanied by grain rotation. This study revealed the mechanisms of microstructural evolution during hot deformation of Ta-12W alloy, providing important guidance for optimizing the thermomechanical processing parameters.

On the Relationship between Thermomechanical Processing Parameters and Recrystallization Texture in AA1100 Aluminum Alloy

In this study, 48 hot-rolling processing conditions were designed to investigate the influences of thermomechanical processing parameters on the recrystallization behavior and texture development. The hot-rolling experiments were conducted using the thermomechanical simulator Gleeble 3800 at temperatures of 275, 300, and 350 °C with strain rates of 5 and 90 s−1 up to 60 and 85% reduction. The microstructure and texture analysis were measured by using the EBSD technique on a large area. Experimental results show that the Cube component maintains a volume fraction between 10% and 20%, below the 40% recrystallization fraction, but the volume fraction of Cube significantly increases between 20% and 50% above the 40% recrystallization fraction. However, the fractions of Rotated Cube (RC) and Goss components remain below 10%.

Recent development of grain oriented electrical steel in Shougang steel

Shougang Steel has been pursuing the development of low iron loss and high permeability grain oriented electrical steels for more than a decade. Grain oriented electrical steel requires a very strong Goss {110}〈001〉 texture and as such a comprehensive control of thermo-mechanical processing parameters is required to achieve a strict control of texture. In this paper the key metallurgical problems associated with manufacture of grain oriented electrical steel are discussed, including the factors that affect both primary recrystallization and secondary recrystallization leading to the development of a strongly textured final sheet. The metallurgical factors affecting magnetostriction of electrical steels are also analyzed, and a technological approach for domain refinement, and its effect on magnetic properties, is described. Examples of magnetic properties under non-sinusoidal magnetization conditions are also reported and analyzed. As a result of continuous research and development efforts the high permeability low iron loss grain oriented electrical steel of thin gauge products of 0.2 mm/0.18 mm thickness have recently been developed to meet the requirements of the new China national standard of energy efficiency grades for power transformers.

Understanding the hot deformation behavior of Mo[sbnd]42Re alloy: Insights from strain rate sensitivity, microstructure, and misorientation

Mo42Re alloy, as a high-temperature structural and functional material, has broad application prospects in the nuclear industry. In this study, the hot deformation behavior of Mo42Re alloy was systematically investigated using hot compression tests and electron backscatter diffraction (EBSD) techniques in the temperature range of 1200–1500 °C and strain rate range of 0.001–1 s−1. The results showed that the flow stress of Mo42Re alloy exhibited a strong dependence on temperature and strain rate. The strain rate sensitivity index (m-value) was high under the conditions of 1350–1450 °C and 0.001 s−1. With increasing deformation temperature and decreasing strain rate, dynamic recrystallization (DRX) was significantly promoted, and the recrystallized volume fraction increased from 2.79% at 1200 °C/1 s−1 to 20.3% at 1500 °C/0.001 s−1. Meanwhile, the occurrence of and DRX effectively reduced the grain reference orientation deviation (GROD) gradients and kernel average misorientation (KAM) levels within the grains. This study revealed the mechanisms of microstructural evolution during hot deformation of Mo42Re alloy, providing important guidance for optimizing its thermomechanical processing parameters.

A novel approach to predict the effect of chemical composition and thermo-mechanical processing parameters on Cu–Ni–Si alloys using a hybrid deep learning and ensemble learning model

The study presents a novel hybrid deep learning and ensemble learning (DL-EL) model to predict the effects of chemical composition and thermo-mechanical processing on the properties of Cu–Ni–Si alloys. The model integrates various input parameters like chemical composition and thermo-mechanical processing parameters and aims to predict key output properties such as mechanical properties and electrical conductivity. This study addresses gaps in existing research by providing a comprehensive model for Cu–Ni–Si alloys and integrating thermo-mechanical processing parameters with chemical composition in the predictive model. The research demonstrates the model's superior predictive performance, with near-perfect R2 values on both training and test sets. The hybrid DL-EL model was compared with three other machine learning models and its efficacy was assessed using R2 value, offering new insights into the performance of these alloys. A feature importance analysis was conducted to identify the most influential features of the model. This work contributes to the material science field by providing insights into optimizing alloy composition and processing, leveraging machine learning to enhance material design.© 2017 Elsevier Inc. All rights reserved.

STUDY OF THE EFFECTIVENESS OF THE INFLUENCE OF PLASTICIZERS AND FUNCTIONAL ADDITIVES IN THE RECEIVING OF THERMOPLASTIC STARCH ON ITS FILM-FORMING AND DESTRUCTIVE PROPERTIES

A literature review on the production of thermoplastic starch (TPS) with various plasticizing additives as a component of biodegradable polymer compositions was conducted. Plasticizing additives with different functional groups, due to which starch modification occurs, were analyzed. In order to expand the spectrum of functional additives for the formation of TPS, the introduction of acids with different amounts of carboxyl groups: citric, oxalic, oleic, stearic was studied. The technological parameters of thermomechanical processing of starch compositions and the quantitative composition of the components are determined. Physical and mechanical tests of strength and elasticity of film samples of TPS compositions and compatible with synthetic polymer were carried out. In order to obtain the structural characteristics of TPS and TPS films with polyethylene, studies were carried out by IR-Fourier spectroscopy and mass spectrometry. Studies of the effect of UV irradiation on the degradability of TPS compositions after exposure in a climate chamber for 90 days were conducted. It was found that the loss of strength and elasticity of TPS and TPS+PE film samples is (82–90)%, elasticity (60–70)%, depending on plasticizing and structure-forming additives and their amounts.

Modelling the spatial evolution of excess vacancies and its influence on age hardening behaviors in multicomponent aluminium alloys

Excess vacancies play crucial roles in the precipitation of age-hardening precipitates in aluminium alloys, but their spatial evolution across grains during heat treatments is less known. In this work, a numerical model is developed to predict the spatial evolution of non-equilibrium excess vacancies during cooling from solution treatment and during ageing heat treatments of multicomponent aluminium alloys. A finite volume scheme is applied to derive the spatial distribution of vacancy site fraction across grains by solving the diffusion equations of vacancies under the influence of solute elements. Binding energies between solute atoms and vacancies predicted by first-principles calculations has been used to handle the trapping of excess vacancies by solute atoms and atom clusters. The annihilation rates of excess vacancies at grain boundaries and at dislocation jogs have been derived based on a rigorous description of the annihilation mechanisms of vacancies. The evolution of the density of dislocation jogs due to vacancy annihilation has been taken into account. The model is successfully applied to interpret the age hardening behaviors of experimental alloys subjected to different thermomechanical processing conditions. This model will help to reach a deeper understanding of the roles of excess vacancies in precipitation kinetics and therefore is important to further optimize thermomechanical processing parameters and alloy composition to improve the macroscopic mechanical properties of age hardening aluminium alloys.

Investigation of microstructure and texture as related to primary recrystallization of grain-oriented silicon steel

Grain-oriented silicon steel requires a very strong Goss {110}<001> texture and as such a comprehensive control of thermo-mechanical processing parameters is required to achieve a strict control of texture. In particular the cold rolling and decarburization annealing process parameters have a determining effect on the grain size, the grain size distribution and the crystal texture distribution. In this study, the effect of cold rolling reduction on texture distribution in cold-rolled sheet has been analyzed. Secondary recrystallization of grain-oriented silicon steel is also highly dependent on the microstructure and texture after primary recrystallization. The influence of annealing temperature and carbides on the primary recrystallization process has also been investigated by measurements of grain growth and texture following primary recrystallization. By optimizing the microstructure and the texture of primary recrystallization of grain-oriented silicon steel, it is shown that a grain-oriented silicon steel exhibiting high magnetic induction low iron loss has been developed at Shougang Steel.

Tailoring the microstructure and mechanical properties of (CrMnFeCoNi)100-xCx high-entropy alloys: Machine learning, experimental validation, and mathematical modeling

As a common thermomechanical treatment route, “cold rolling and annealing” is widely used for the processing and grain refinement of interstitial-containing high-entropy alloys (HEAs). The interrelationship between the parameters of this process, the content of interstitial elements, and their interactions are outstanding challenges and areas of open discussion. Accordingly, the data-driven machine learning approach is a favorable choice for tuning the microstructure and mechanical properties, which needs to be systematically investigated. In the present work, these subjects were addressed in terms of correlating the thermomechanical processing parameters and chemical composition with the recrystallization and grain growth behaviors, grain size, carbide precipitation, and the resulting tensile yield stress for the model (CrMnFeCoNi)100-xCx HEAs. For this purpose, machine learning models based on adaptive neuro-fuzzy inference system (ANFIS), backpropagation artificial neural network (BP-ANN), and support network machine (SVM), as well as mathematical relationships and equations for the contribution of each strengthening mechanism were proposed and verified by extensive experimental work, which shed light on the design and prediction of the microstructure and properties of HEAs.

Microstructure and microchemistry changes at U-10Mo fuel/AA6061 cladding interfaces with varying hot isostatic pressing conditions

Monolithic uranium - 10 wt.% molybdenum (U-10Mo) is a promising high-assay low-enriched uranium fuel system for nuclear reactors used in research, medical isotope production, and remote power applications. During manufacturing, an aluminum alloy (AA6061) cladding is bonded to the U-10Mo fuel plate via hot isostatic pressing, during which diffusion and fuel/cladding chemical interaction occurs at plate edges. The microstructure and microchemistry changes that occur at fuel/cladding interfaces are important to understand as a function of process parameters to develop a reliable fuel fabrication process and to meet the desired specifications. Here, microstructural and microchemical changes are studied using complementary electron microscopy and atom probe tomography for two manufactured fuel plates with varied hot isostatic pressing (HIP) parameters. Results highlight that modifying thermomechanical processing parameters significantly changes the interaction layer thickness between U-10Mo and AA6061 by an order of magnitude. In addition, the distribution and concentration of elements (i.e., Al, Si, Mg) from cladding to fuel are investigated.

Synergistic effect of different testing environments on the hydrogen-induced mechanical degradation to establish the role of microstructural features on the failure of X70 pipeline steel

Hydrogen-induced mechanical degradation was evaluated in different environmental conditions on two X70 pipeline steels having the same composition but different thermomechanical processing parameters, and a further correlation between microstructural features and hydrogen embrittlement (HE) susceptibility was established. HE susceptibility was determined by performing the Slow Strain Rate Tensile Test (SSRT) in air, ex-situ hydrogen-charged, in corrosive media, in-situ hydrogen-charged and Charpy impact tests before and after hydrogen charging in a wide range of temperatures.The SSRT results indicated that the synergistic action of stress and hydrogen in in-situ charged sample leads to maximum HE susceptibility in both X70 steels. Charpy results demonstrated that ductile-to-brittle transition temperature (DBTT) increases after hydrogen charging. The texture analysis revealed that X70-2 with a higher volume fraction ratio of Ƴ-fiber/{100}<011> demonstrated improved HE resistance, whereas X70-1 with higher fractions of {113}<110> and {100} || ND demonstrated a higher DBTT than before and after hydrogen charged X70-2.

Deformation induced precipitation in CuCrZr composites

In this study, we enhanced both hardness and electrical conductivity in solution-treated Cu-0.66Cr-0.05Zr (at%) wires. After cold deformation, hardness increased by ∼100%, and electrical conductivity increased by 24%. We further demonstrated that post-deformation aging increased hardness by another 27%–38% and electrical conductivity by up to an additional 80%. In previous research on composite conductors, hardness increase by deformation was usually accompanied by a decrease in electrical conductivity. But we were able to increase both simultaneously by controlling thermo-mechanical process parameters to engineer precipitate size and density. We attributed our simultaneous enhancement of hardness and conductivity to the generation of deformation-induced, disc-shaped, and semi-coherent precipitates with thicknesses less than a nanometer. Aging-induced precipitates remained only a couple of nanometers thick, but their Cr content (1.2–8.4 at%) was relatively greater than that of deformation-induced precipitates. We subjected solution-treated materials to either aging followed by deformation or deformation followed by aging. Our results were the same regardless of order.

Use of miniaturized tensile specimens to evaluate the ductility and formability of dual phased steels for Rapid Alloy Prototyping

This work aims to investigate feasibility of using non-standard miniaturized tensile specimens (MTS) to characterize total elongation and formability behaviour of dual phase steels: to establish the scaling rules for MTS to predict a range of mechanical properties of steels obtained through rapid alloy prototyping (RAP) in the laboratory. Accurate measurement of these properties using miniature specimens allows the formability behaviour of materials produced using RAP, a process which can produce lab scale samples of < 100 grams. This allows the effects of multiple compositions and thermomechanical processing parameters on formability to be evaluated. For this study, the ability of miniature tensile specimens to characterize ductility, forming limits and r-values has been compared to properties measured using standard sized tensile specimens for the dual phase steels, DP600 and DP800. 5 different tensile specimens were investigated, with gauge lengths varying from 80 mm to 5 mm and samples were taken at different orientations to the rolling direction. Total elongation was evaluated against slimness ratio for each tensile sample using the Bertelle–Oliver method and good correlations were obtained, despite specimen thicknesses being below the critical value, and the tensile strength of DP800 exceeding the limit stated for the method. Forming limit curves (FLC) were predicted using the Keeler–Brazier method, based on tensile data obtained using the standard and non-standard tensile specimens These curves compared favourably to experimentally obtained FLCs, however the curve predicted using the miniaturized tensile specimen over-predicted the major strain. The anisotropy of the rolled sheet steels was characterized from r-values obtained from tensile tests performed at different orientations to the rolling direction. Values obtained from the miniature tensile test were comparable to those obtained from standard tests within the range of scatter. The results obtained through this study provide confidence in using the miniature tensile specimens to predict the formability of heterogeneous alloys such as DP steels, manufactured using the RAP process.

The Differences in Microstructure, Microtexture, and Tensile Anisotropy of Ti80 Heavy Plate Across the Thickness

Herein, the differences in microstructure, microtexture, and tensile behavior of the Ti80 heavy plate across the thickness are investigated. The Ti80 heavy plate consists of equiaxed α and transformed β grains with high degrees of recrystallization microstructures. Significant differences are observed in the main texture components between the central and surface zones. The inhomogeneous distribution of hot compression and shear leads to different deformation textures during processing. Due to temperature distribution, the combination of the variant selection mechanism and α–β phase interaction is responsible for the evolution of surface texture, while only the former plays a major role in the center. Final fracture areas of tensile samples show ductile fracture characteristics. The anisotropy behaviors in planar tensile of the Ti80 heavy plate at room temperature are evaluated. They are related to the difficulty of activating prismatic slip and basal slip , which are determined by the crystallographic texture of the material. This work helps to explore reasonable thermomechanical processing parameters and establish rolling schedules to weaken the mechanical heterogeneity across the thickness of near‐α‐titanium alloy heavy plates.

Phase field simulation of microstructure evolution and process optimization during homogenization of additively manufactured Inconel 718 alloy

An in-depth and integral understanding of the microstructural evolution during thermomechanical process (TMP) is of great significance to optimize the manufactural process for high-quality components via additive manufacturing. The solidified microstructure model of Inconel 718 alloy fabricated via laser powder bed fusion (L-PBF) is established by multiphase field model firstly. Furthermore, the microstructural evolution during homogenization process is simulated and optimized in this study. Phase field simulation results show that the concentration gradient of Nb along the radius of the cellular substructure decreases from the initial 1.217 wt% to 0.001 wt%, and 67% area fraction of the Laves phase dissolves at the homogenization time of 0.5 h, which have achieved the homogenization purpose. The experimental results show that the average grain size decreases from 9.4 μm to 5.9 μm at the homogenization time from 1.5 h (the standard AMS 5383) to 0.5 h, which resulted in the increase of yield strength and tensile strength of the aged alloy by 14% and 6%, respectively. This research can provide guidance and reference for the microstructural control as well as the TMP parameters design of the additive manufactured alloys.

Hot Deformation Behavior of 4130 High-Strength Steel.

Hot deformation behavior of 4130 steel and optimization of its processing parameters are presented in this paper. Compression tests were performed at temperatures ranging from 800 to 1200 °C and at the strain rates in the range from 0.01 to 100 s-1. A comprehensive analysis of the material behavior at different temperature and strain-rate ranges was performed taking into account various criteria of stability and instability of the material flow under various thermomechanical conditions. The flow-stress curves obtained during compression tests, as well as the processing maps elaborated on the basis of various flow-stability criteria, are discussed. Processing parameters developed according to the Prasad's and Murty's criteria are recommended for designing the technology of forging of the investigated steel. Such parameters ensure the homogeneity and stability of the material flow in a forged part, what was confirmed by successful forging of 4130 steel in industrial conditions. The processing map developed according to Gegel's approach, as compared to the processing maps obtained in accordance with the Prasad's and Murty's criteria, should be treated as general support for determining the thermomechanical processing parameters.

Nucleation of recrystallization in magnesium alloy grains of varied orientation and the impacts on texture evolution

Selection of appropriate thermomechanical processing parameters is crucial for control of the crystallographic texture and grain size distribution in wrought magnesium alloys, which in turn dictate their mechanical properties. In this work, the recrystallization behavior of binary Mg-Zn alloys are examined after warm rolling as a function of alloy content and heat treatment temperature. The Avrami exponent increased with increasing heat treatment temperature up to the MgZn solvus, while the strength of the recrystallization texture decreased. Neither the Avrami exponent nor the qualitative trends in texture evolution were sensitive to the Zn alloying content in the examined range. EBSD and transmission electron microscopy observations revealed that the changes in texture and recrystallization kinetics could be attributed to differences in the nucleation behavior of basal and off-basal orientations.

Multi-stage hot deformation and dynamic recrystallization behavior of low-cost Ti–Al–V–Fe alloy via electron beam cold hearth melting

To explore the optimal thermomechanical processing parameters (TMP) of Ti–Al–V–Fe alloys with direct rolling potential after electron beam cold hearth melting (EBCHM) and the grain refinement mechanism during thermal deformation, the multi-pass hot deformation and dynamic recrystallization (DRX) behavior of Ti–4Al–2.5V–1.5Fe alloy ingot produced via EBCHM were investigated in this paper. The multi-pass compression tests were conducted on a Gleeble-3500 thermal simulation experimental machine with deformation temperatures of 850–1000 °C and strain rates of 0.01–1 s−1. The results showed that the flow stress and the microstructure of the alloy were both sensitive to the deformation temperature and strain rate. The as-cast Ti–4Al–2.5V–1.5Fe alloy had the highest fraction of DRX and the smallest average grain size at the deformation temperature of 950 °C and the strain rate of 0.01 s−1 suggest that the DRX mechanism had a significant grain refinement effect. The softening mechanism at higher deformation temperature or lower strain rate was dominated by dynamic recrystallization (DRX). In the continuous dynamic recrystallization (CDRX) mechanism, sub-grain boundaries transformed LAGBs into HAGBs by continuously absorbing dislocations, which was more evident at low deformation temperatures compared to discontinuous dynamic recrystallization (DDRX). In this paper, the original coarse cast titanium alloy grains were refined to smaller sizes through multi-pass thermal deformation, the synergistic regulation laws of thermal deformation behavior and microstructure evolution under different deformation conditions, and the corresponding DRX behavior were elucidated, providing scientific guidance for the direct rolling of cast titanium alloys.

Precipitate number density determination in microalloyed steels by complementary atom probe tomography and matrix dissolution

Particle number densities are a crucial parameter in the microstructure engineering of microalloyed steels. We introduce a new method to determine nanoscale precipitate number densities of macroscopic samples that is based on the matrix dissolution technique (MDT) and combine it with atom probe tomography (APT). APT counts precipitates in microscopic samples of niobium and niobium-titanium microalloyed steels. The new method uses MDT combined with analytical ultracentrifugation (AUC) of extracted precipitates, inductively coupled plasma–optical emission spectrometry, and APT. We compare the precipitate number density ranges from APT of 137.81 to 193.56 × 1021 m−3 for the niobium steel and 104.90 to 129.62 × 1021 m−3 for the niobium-titanium steel to the values from MDT of 2.08 × 1021 m−3 and 2.48 × 1021 m−3. We find that systematic errors due to undesired particle loss during extraction and statistical uncertainties due to the small APT volumes explain the differences. The size ranges of precipitates that can be detected via APT and AUC are investigated by comparison of the obtained precipitate size distributions with transmission electron microscopy analyses of carbon extraction replicas. The methods provide overlapping resulting ranges. MDT probes very large numbers of small particles but is limited by errors due to particle etching, while APT can detect particles with diameters below 10 nm but is limited by small-number statistics. The combination of APT and MDT provides comprehensive data which allows for an improved understanding of the interrelation between thermo-mechanical controlled processing parameters, precipitate number densities, and resulting mechanical-technological material properties.Graphical abstract

Investigation of Thermomechanical Processing of Nb Microalloyed Steel Produced by Powder Metallurgy

One of the most important properties of microalloyed steels is the different microstructures which are obtained by changing the thermomechanical processing parameters and steel composition. The control of microstructure such as grain size, precipitates, dislocation structure and inclusions are highly effective to determine the mechanical properties of microalloyed steels. The strengthening of mechanical properties can be done by thermomechanical processesing due to increase of nucleation sides via maximizing the austenite boundary and density of the deformation band. In this study, the unalloyed steel and microalloyed steel containing 0.15% Nb were produced by powder metallurgy and hot deformed to reduce the thickness by 40% and 75%. EDX analyzes, density, hardness and grain size measurements were also performed on specimens. According to the SEM microstructure results, the grain size gradually decreased with respect to the deformation rate in both steels. It was observed that small grains occurred due to a complete recrystallization process at 75% deformation rate which were supported by grain size analysis. The density and hardness values increased by the increase in deformation rate. While the density and hardness of microalloy steel under sintered conditions was 89.46% and 75 Hv, respectively, 75% deformed condition was 98.51 % and 231 Hv.