High Temperature Deformation Behavior Research Articles

High temperature deformation behaviour and recrystallization mechanism of TiC/Ti6Al4V gradient material fabricated by laser directed energy deposition

Metal-ceramic gradient materials are of considerable interest due to their unique capability to integrate the ductility of metals with the mechanical strength and high-temperature resistance of ceramics, thereby reducing the risk of cracking induced by thermal stress. In this article, TiC/Ti6Al4V gradient materials were prepared through the laser directed energy deposition (LDED) process. Subsequently, high-temperature compression tests were performed at various temperatures to investigate the deformation behaviour and recrystallization mechanism of the gradient materials. The Zener-Holomon constitutive equation was then used to calculate the gradient material at 750–900 °C and 0.001–0.1 s−1 to obtain a deformation activation energy of 362.36 KJ·mol−1. The EBSD was used to analyze the microstructural evolution of the gradient material. The results indicate a significant reduction in the average grain size of the specimens after high-temperature compression, and a more random crystal orientation due to the occurrence of dynamic recrystallisation (DRX). The primary softening mechanism of TiC/Ti6Al4V gradient materials is discontinuous dynamic recrystallisation, with TiC primarily affecting the nucleation of discontinuous dynamic recrystallisation (DDRX) and the subsequent grain growth. The nucleation becomes easier with increasing TiC content. However, the TiC hinders the migration of grain boundaries, resulting in a smaller DDRX grain size. After high-temperature compression, the main slip system of the crystal is converted from Pri to Bas. Pyr is difficult to activate due to its high critical resolved shear stress.

Exploring high-temperature deformation and damage behaviour in high-performance ferritic (HiperFerSCR) steel with Laves phase particles

The mechanical behaviour at high temperatures and the corresponding microstructural characteristics of a newly developed high-performance ferritic, salt-corrosion-resistant (HiperFerSCR) steel containing Laves phase particles were studied to investigate the active deformation mechanisms and the evolution of damage. A series of tensile tests were conducted at both room temperature and elevated temperatures (550, 600, and 650 °C), along with detailed microstructural analyses using scanning electron microscopy and electron backscatter diffraction. The tensile flow characteristics of HiperFerSCR at room temperature exhibit significant strain hardening, which is due to the Laves phase particles that encourage planar slip, demonstrated by the formation of numerous slip bands and low-angle grain boundaries. The intersections of these slip bands with grain boundaries appear to be the initiation sites for cracks, which then propagate intergranularly as well as within grain interiors along the slip bands. At high temperatures, the flow characteristics show strain softening, which is attributed to a dynamic recovery (DRV) mechanism, evident in the formation of subgrain boundaries decorated with Laves phase particles. During high-temperature deformation, damage initiates in the particle-free zone (PFZ), which expands at higher temperatures, leading to strain localisation, void formation along the grains, and eventually, grain boundary decohesion.

High-temperature tensile properties and deformation behavior of a multi-phase FeNiCrAlTi alloy

Single-phase multi-principal elements alloys (MPEAs) within the elevated temperature experience particularly severe strength loss, and even a distinct ductile-to-brittle transition. Herein, we report on a non-equiatomic, multi-phase FeNiCrAlTi MPEA which possesses remarkable combinations of mechanical properties across a wide range of temperatures from 400 °C to 800 °C, especially its specific yield strength possesses nearly 100 MPa/g∙cm−3 at 600 °C. The excellent mechanical behavior benefits from the synergistic effect of the special phase structure and precipitation strengthening by the ordered Ni (Al, Ti) B2 nanoparticles. The transformation of deformation mode at 600 °C should be considered the dominant of the resistance to intermediate or high-temperature embrittlement. This work provides a new methodology for regulating mechanical properties of superior alloys that involve high-temperature conditions.

Investigation on effect of high-efficiency solid solution and hot stamping process on microstructure evolution and mechanical properties of high-strength aluminum alloy

Aluminum alloy has become an important lightweight material in the automotive industry due to its excellent performance. The development of hot stamping technology has effectively promoted the application of high-strength aluminum alloys in auto parts. However, aluminum alloy hot stamping requires a long time for solid solution and aging heat treatment, which hinders its mass production application in the existing mature hot stamping production line. Therefore, this paper studies the effect of a high-efficiency solid solution and hot stamping process on the microstructure and mechanical property strengthening mechanism of high-strength aluminum alloy. The contact heating and hot stamping experiment device was designed. It was found that the temperature rise rate of the sheet during the contact heating process could reach 44.51 °C/s. The experiment results show that contact heating treatment with a solution temperature of 480 °C and a solution time of 20s can achieve the high-efficient solution treatment of the sheet metal. The high-temperature deformation behavior of 7075-T6 at different temperatures (300-450 °C) and different strain rates (0.01∼1/s) under the condition of high-efficiency solid solution rapid heating was studied.

Interplay between high-temperature creep deformation behavior and nanoscale precipitate evolution in a newly designed Fe–Ni-based superalloy

In an endeavor to achieve the critical goals of carbon neutrality, an explorative study was conducted to scrutinize the precipitate evolution and high-temperature creep behavior of an innovative and cost-effective Fe–Ni-based superalloy that was meticulously engineered for the next-generation ultra-supercritical (USC) power plants. The creep experiments conducted at temperatures and stresses of 650 °C/280 MPa (17,179 h), 675 °C/250 MPa (10,271 h), and 700 °C/250 MPa (2378 h), coupled with proficient data fitting were employed to accurately assess the long-term service performance of the superalloy under real-world operational environments. Though it can withstand theoretically an intense stress of 130 MPa at 700 °C for approximately 30 years as calculated by the Larson-Miller equation, its performance was not without a degree of perceived vulnerability. This was primarily traced to the conspicuous coarsening behavior of the precipitate-free zones (PFZs)/discontinuous coarsening zones (DCZs) formed in the grain boundaries (GBs) on a longer time scale. It had a significant diminishing impact on the overall strength of the GBs, resulting in a recorded creep life that was considerably shorter than initially projected. Moreover, a synergistic mechanism between PFZs/DCZs with TiC carbides was advanced to interpret the intergranular fracturing dynamic, which was postulated due to the evidence gathered from electron backscatter diffraction (EBSD), highlighting that the banded distribution of TiC carbides circumambient to GBs engendered considerable stress aggregation. Conversely, the plentiful supply of coincidence site lattice (CSL) boundaries disrupted the continuous network structure of random high-angle grain boundaries (HAGBs), thereby creating an effective barricade against the proliferation of cracks. These empirical findings paved the way for the proposition of an enhanced blueprint and the industrial utilization of such.

Analysis of Hot Tensile Fracture and Flow Behaviors of Inconel 625 Superalloy.

In this work, Inconel 625 alloy is explored regarding high-temperature tensile deformation and fracture behaviors at a strain rate of 0.005-0.01 s-1 under a deformation temperature ranging from 700-800 °C. The subsequent analysis focuses on the impact of deformation parameters on flow and fracture characteristics. The fractured surface reveals that ductile fracture is dominated by the nucleation, growth, and coalescence of microvoids as the primary failure mechanisms. The elevated deformation temperature and reduced strain rate stimulate the level of dynamically recrystallized (DRX) structures, resulting in intergranular fractures. The Arrhenius model and the particle swarm optimization-artificial neural network (PSO-ANN) model are developed to predict the hot tensile behavior of the superalloy. It indicates that the PSO-ANN model exhibits a correlation coefficient (R) as high as 0.9967, surpassing the corresponding coefficient of 0.9344 for the Arrhenius model. Furthermore, the relative absolute error of 9.13% (Arrhenius) and 1.85% (PSO-ANN model) are recorded. The developed PSO-ANN model accurately characterizes the flow features of the Inconel 625 superalloy with high precision and reliability.

A phenomenological constitutive model of Novel Rheo Gravity Die Cast Al-15Mg2Si-4.5Si-0.01Sr-0.015B composite

The present study discusses the high temperature deformation behaviour as well as phenomenological constitutive model development of the novel Rheo gravity die cast (RGDC) Al-15Mg2Si-4.5Si-0.01 Sr-0.015B composite. Within the scope of the study, uniaxial isothermal compression tests are performed on the RGDC Al-15Mg2Si-4.5Si-0.01 Sr-0.015B composite, covering a range of strain rates from 10−3 to 10 s−1 and deformation temperatures spanning from 250 °C to 450 °C. Analysis using X-ray Diffraction (XRD), Energy dispersive spectroscopy (EDS) and Electron Probe Micro Analyzer (EPMA) revealed the presence of distinct phases within the material, including primary Al, Mg2Si, and elemental Si. The study employed three different constitutive models i.e., the Johnson-Cook (JC), modified Johnson-Cook (mJC), and sine hyperbolic Arrhenius (shA) types, to predict the flow stress of the material as a function of strain, strain rate, and deformation temperature. The results indicated that the sine hyperbolic Arrhenius type model and the modified Johnson Cook model effectively accounted the coupling effect of strain, strain rate, and deformation temperature, which affect the flow stress. Statistical analysis, specifically Pearson coefficient correlation (R), average absolute relative error (AARE) and standard deviations, established a reasonable agreement between the predicted flow stress values and the experimental flow stress data. Furthermore, it is observed that the sine hyperbolic Arrhenius type model exhibited superior accuracy compared to the modified Johnson Cook model, particularly at higher strain levels.

An Investigation into Microstructure Evolution and High-temperature Deformation Behavior during the Instability of In-service Welding

It is of great significance to reveal deformation behavior coupling with both the high-temperature effect and microstructure for the in-service welding instability zone. In the present paper, microstructure evolution and high-temperature deformation behavior at the representative temperatures 900 °C and 1100 °C inside the in-service welding instability zone were investigated based on the in-situ high-temperature laser scanning confocal microscope (LSCM). The results indicated that a sufficient condition of carbide precipitation is to hold it at 900 °C for a certain time. However, the phenomenon of carbide precipitation failed to be presented during continuous heating to 1150 °C. Although the slip and twining deformation occurred inside austenite grain, the fracture mechanism gave priority to intergranular cracking, which could be ascribed to the carbides with higher hardness and the grain boundary weakening caused by the temperature effect.

High-temperature deformation behaviour and processing map of near eutectic Al–Co–Cr–Fe–Ni alloy

The high-temperature deformation behaviour of near-eutectic high entropy alloy was studied at 800–1100 °C and 0.01–10 s−1. The microstructure of the as-cast alloy depicted a proeutectic L12 phase and epitaxially grown eutectic colonies of lamellar L12 and B2. Deformation temperature and strain rate played vital roles in defining the precipitation and deformation behaviour of the alloy. The lower-temperature deformed samples were characterized by extensive deformation twinning and strain accumulation. In contrast, high-temperature deformation led to uniform deformation with dynamic recrystallization, recovery, B2 lamellar fragmentation and B2 precipitation. The microstructure of the deformed samples corresponded well with the processing maps developed via dynamic materials model. The processing zones for the alloy were identified to be 800–950 °C and 10−2 – 10−1.25 s−1 as well as 925–1100 °C and 10−2 – 10−0.5 s−1. The critical material flow parameters displayed a complex relationship with temperature, strain rate and strain. In the studied temperature and strain rate regime, the critical strain rate was determined to be 0.1s−1. At strain rates above and below this value, the critical strain for recrystallization was higher. Within the studied temperature and strain rate regime, the near eutectic alloy displayed superior compressive strength and wider thermos-mechanical processing region than its eutectic counterpart.

Hot processing map and high temperature deformation behaviour of TB17 Ti alloy

The thermal compression experiments of TB17 titanium alloy under different thermal deformation process parameters were carried out using a thermal simulation compressor. The high-temperature plastic flow behaviour of the alloy was studied. It was found that with the decrease of the deforming temperature and the increase of the strain rate, the flow stress increased, and the discontinuous yield phenomenon occurred in hot deformation. The larger the strain rate, the more obvious the discontinuous yield phenomenon. The thermal activation energy Q decreased with the increase of strain, and the average value of activation energy Q is 209.54 KJ / mol. The constitutive equation of high-temperature plastic flow of TB17 titanium alloy was established. The predicted values of this equation are in good agreement with the experimental values. The average error is 3.987 %, and the correlation coefficient is 0.9972, which has high accuracy. Based on the Prasad criterion, the hot processing map of TB17 titanium alloy was constructed. It was found that the flow instability zone was mainly concentrated in the high strain rate region. The flow instability zone was determined to be 795 °C ~ 895 °C, 0.046s-1 ~ 1s-1, and the stable deformation zone was mainly located in the region with high temperature and low strain rate. The optimum processing parameter range is 860 °C ~ 895 °C, 0.001 s-1 ~ 0.025 s-1.

Microstructure evolution of high-temperature deformation behavior of nickel based alloys for advanced ultra-supercritical applications

The microstructure evolution of nickel based alloy used in advanced ultra-supercritical power plants was studied in the strain range of 0.22–0.91 at 1000–1100 °C/0.01 s−1 by using the electron backscattered diffraction technique. The interaction of the dislocation with the Σ3 twin boundary causes the Σ3 twin boundary to deviate from its specific misorientation. The Σ3 twin boundary is stripped of its signature by the interaction between the dislocation and the Σ3 within the deformed grain. In the process of recrystallization, the Σ3 twin boundaries are affected by both recrystallization fraction and the size of recrystallization grain. Three recrystallization mechanisms, including DDRX, CDRX and TDRX, play their role in the deformation of the alloy. Leading to the recrystallized grains with high misorientation, CDRX tends to grow and promote twin nucleation, and the mechanism of CDRX becomes less significant with the increase of deformation temperature. Due to deformation, the orientation of the grain shifts to <101> direction. At 1000 °C and 1050 °C, the recrystallization texture inherits the deformation texture due to the effect of CDRX and the slow diffusion of the recrystallization process, which causes the recrystallization texture to show a sharp <101> fiber texture. At 1100 °C, the enhancement of the DDRX mechanism and the high diffusivity of the recrystallization process lead to the randomization of the texture, and the oriented growth of recrystallized grains at 1100 °C/0.91 enhances the <001> texture. In addition, both recrystallization and twinning are contributory to the randomization of texture.

Studying the effects of Nb on high-temperature deformation in TiAl alloys using atomistic simulations

Intermetallic γ(TiAl)-based alloys find their application as high-temperature materials for aero engine and automotive components. Microstructure optimization and microalloying play key roles in optimizing these alloys. Several pioneering experimental works showed improved mechanical properties of γ(TiAl)-based alloys containing Niobium (Nb). Despite Nb being a key alloying element, its contribution remains debated, if not least understood, due to the TiAl microstructure's complexity with hierarchical interfaces. This work examines the effects of Nb on the high-temperature deformation behavior of TiAl alloys using atomistic simulations. These revealed that Nb alloying retarded the stress-induced phase transformation of γ → α2, favoring a refined microstructure with the dislocation sources from microstructure boundaries and interfaces at high temperature and improving thus the ductility. Our microstructure-informed atomistic models reveal a comprehensive picture of the underlying nanomechanical events.

Investigation on microstructural and microhardness evolution of GH4698 superalloy under transiently varying strain rates

The high-temperature deformation behavior of GH4698 superalloy was explored via isothermal compressive tests under transiently varying strain rates. The impacts of loading types and deformation temperature on flow stress, microstructural evolution, and microhardness were explored, and the underlying nucleation mechanisms for dynamic recrystallization (DRX) were elucidated. Experimental results indicated that the flow stress decreased when the strain rate decreased transiently. Specifically, under loading type I (interrupted strain = 0.11), the flow stress was higher than that under loading type II (interrupted strain = 0.36). Moreover, the flow stress decreased with increase in deformation temperature. When the initial interrupted strain was high, a high degree of DRX was observed in the deformed microstructure. The DRX fraction of types I and II are 48 % and 61 %, respectively. Higher deformation temperatures accelerated the growth of DRX grains, and at a deformation temperature of 1100 °C, DRX fraction reaches 87 %. The microhardness of the DRX grains was higher than that of the deformed grains. At higher deformation temperatures, the γ′ phase dissolved, and the DRX grains grew, resulting in smaller microhardness of the DRX grains than that at lower deformation temperatures. However, microhardness was not sensitive to the loading type (i.e., the value of interrupted strain). Furthermore, discontinuous dynamic recrystallization (DDRX), activated by the initial bulging of grain boundaries, served as the fundamental mechanism for DRX nucleation. Similarly, continuous dynamic recrystallization (CDRX), characterized by the formation of subgrains through dislocation cell structures within individual grains, as well as the γ′ phase and twin boundaries, also played crucial roles in the nucleation of DRX during transiently variation states conditions.

High Temperature Deformation Behavior and Microstructure Evolution of Harmonic Structure Composites with WC-Co and High Speed Steel

The high-temperature deformation behavior and microstructural changes of harmonic structure composites with WC-Co alloys and high-speed steel (HSS) were investigated in detail. A harmonic structure composite was fabricated by consolidating the mechanically milled powder having WC-Co and HSS powder. The harmonic structure composite demonstrates the microstructure composed of network area (WC-Co) and dispersed area (HSS). The harmonic structure composite shows a sufficient compressive strength in the compression tests at 773 K, but the compression strength decreases at temperatures of above 873 K. The 0.2% proof stress at high temperature almost unchanged even if the network area fraction changed. Furthermore, the network area plays an important role in the high temperature deformation of harmonic structure composites. These results suggest that the formation of voids for WC-Co boundary sliding and poor sintering is an important factor in stress reduction in the high-temperature compression of harmonic structure composites.

High temperature deformation behaviour of as-cast Al0.4Co0.9Cr1.2Fe0.9Ni1.2(Si, Ti, C, B)0.375 complex concentrated alloy during tensile and compression tests

High temperature deformation behaviour of as-cast Al0.4Co0.9Cr1.2Fe0.9Ni1.2(Si, Ti, C, B)0.375 complex concentrated alloy during tensile and compression tests

Study of high-temperature deformation behavior and thermal processing diagram of cast TA15 titanium alloy

Study of high-temperature deformation behavior and thermal processing diagram of cast TA15 titanium alloy

The effect of solutionizing heat treatment on ductility loss and damage evolution in AA7075 aluminum sheet deformed at 450°C

The high-temperature deformation behavior of AA7075 sheet was investigated using hot tensile testing. The specimens were solutionized at 475 °C for 15 min prior to cooling to a deformation temperature between 300 and 450 °C. AA7075 exhibited a progressive rise in ductility with increasing deformation temperature until a sudden drop in ductility was observed at 450 °C. The loss of ductility is attributed to localized melting at the grain boundaries during the solutionizing step. Increasing the holding time at 450 °C prior to the onset of deformation resulted in the gradual restoration of the ductility of the material as a result of isothermal solidification. Samples which are directly heated to 450 °C, without solutionizing at 475 °C, did not experience any loss of ductility. The elongation of non-solutionized sample was always greater than that of the solutionized one when deformation is carried out at 450 °C. This is attributed to the different distribution of particles on the grain-boundaries within the two materials. Trace analysis revealed that intergranular crack propagation proceeds preferentially on higher-indexed random grain boundary planes such as (533), (420), and (531).

Artificial Neural Network-Based Critical Conditions for the Dynamic Recrystallization of Medium Carbon Steel and Application

This study presents a novel and thorough approach to comprehending and simulating the DRX process while hot compressing steel. To achieve this goal, we studied the high-temperature deformation behavior of a medium-carbon steel through hot compression testing on a Gleeble-3800 thermomechanical simulator over a broad range of strains, strain rates, and temperatures. We also employed an artificial neural network (ANN) to model the thermo-visco-plastic behavior with a flow law. The precision of quantifying the DRX volume fraction is dependent on critical conditions, which are essential for both analytical model evaluation and numerical implementation in finite element software. This study proposes a second ANN, serving as a universal approximator, to fit the data required for DRX critical condition calculations, whereas the Johnson–Mehl–Avrami–Kohnogorov (JMAK) model served as an analytical tool to estimate the DRX volume fraction, which underwent validation through experimental measurements. A numerical implementation of the JMAK model was conducted in ABAQUS software and compared against experimental data by means of microstructure analysis. The comparison revealed a strong correlation between the simulation and experiment. The study investigated the impact of temperature, strain, and strain rate on DRX evolution. The findings showed that DRX increases with rising temperature and strain but decreases with increasing strain rate.

Tensile properties of Ti6.5Al2Zr1Mo1V titanium alloy fabricated via electron beam selective melting at high temperature

Here, near α titanium alloy TA15 (Ti-6.5Al–2Zr–1Mo–1V) samples were fabricated by electron beam selective melting (EBSM) and their high-temperature tensile deformation behaviors were studied at 773K–1023K. The results show that the tensile strength decreases gradually with the deformation temperature while the yield ratio increases as temperature increases from 773K to 923K, and then decreases gradually with further increasing the temperature. The deformation mechanism of EBSM-built TA15 samples at elevated temperatures can be ascribed to work hardening caused by the increase of dislocation density, and softening caused by the recovery and recrystallization. The studied TA15 alloy exhibits obvious work hardening behaviors at both 773K and 823K, dynamic recovery occurs during tensile deformation at 873K, and dynamic recrystallization plays a dominant role at 923K–1023K. The EBSM-built TA15 samples have excellent mechanical properties at medium temperatures, and the present results are helpful for the industrial applications of EBSM-built titanium alloy components in the aerospace fields.

Constitutive description of work hardening and dynamic softening behavior under variable deformation states

By carrying out hot compression experiments for 316 L austenitic stainless steel under dynamic changes in deformation conditions, the work hardening and softening behaviors are systematically analyzed during the temperature and strain rate changing process. The response pattern of stresses to changes in temperature and strain rate during deformation is related to material properties and deformation conditions. Zener Hollomon parameters can unify the influence. The stress response pattern changes as the value of Z increases or decreases. Further a computational procedure of materials constitutive relationship suitable for the deformation process under dynamic changes in deformation conditions is proposed. The calculation procedure is based on the phenomenal model. Compared with physical-based model, the procedure shows the same accuracy for the prediction of stress and degree of recrystallization and a simple establishment process. The calculation procedure is embedded into DEFORM software. The high-temperature deformation behavior is numerically simulated under dynamic changes in deformation conditions. The dynamic changes in deformation conditions affect the center deformation resistance during the deformation process, affecting the competitive coordination of material deformation resistance and indenter-sample interfacial friction and ultimately affecting the deformation distribution. 4)The microstructure evolution during dynamic variation states is revealed by EBSD characterization. The deformation conditions variation results in the hardening and softening mechanism changing. Especially, at 1000 ℃ the strain rate changing from 0.01 s−1 to 0.001 s−1 results in the recrystallization mechanism changing from CDRX to DDRX to CDRX.