High Temperature Compression Tests Research Articles

High-temperature deformation followed in situ by X-ray microtomography: a methodology to track features under large strain.

Metallic materials processing such as rolling, extrusion or forging often involves high-temperature deformation. Usually under such conditions the samples are characterized post mortem, under pseudo in situ conditions with interrupted tests, or in situ with a limited strain rate. A full in situ 3D characterization, directly during high-temperature deformation with a prescribed strain-rate scheme, requires a dedicated sample environment and a dedicated image-analysis workflow. A specific sample environment has been developed to enable highly controlled (temperature and strain rate) high-temperature deformation mechanical testing to be conducted while performing in situ tomography on a synchrotron beamline. A dedicated digital volume correlation algorithm is used to estimate the strain field and track pores while the material endures large deformations. The algorithm is particularly suitable for materials with few internal features when the deformation steps between two images are large. An example of an application is provided: a high-temperature compression test on a porous aluminium alloy with individual pore tracking with a specific strain-rate scheme representative of rolling conditions.

Flow Behavior and Constitutive Model of a β-γ TiAl-Based Alloy Under Hot Deformation

The flow behavior of a TNM alloy was evaluated in the high-temperature compression tests. The constitutive models for the flow curves and dynamic recrystallization were constructed to predict stress-strain and microstructure variations. The flow behavior of a Ti-43Al-4Nb-1Mo-0.2B alloy was studied by employing hot compression tests within a temperature range of 1000–1200°C and strain rates of 0.001–0.1 s-1. The flow stress of the alloy was gradually going down with temperature and strain rate decrease, and dynamic recrystallization was the main softening mechanism. The peak shape evolution indicated that recrystallization occurred preferentially at high temperatures and low strain rates. The constitutive model for the flow behavior of the alloy was constructed with the fifth-order polynomial fitting method. Additionally, simulation of the volume fraction and grain sizes in recrystallization was effected. All the models demonstrated a good fit with the experimental results.

Flow Stress Modeling using the Material Constitutive Model of Modified Zerilli-Armstrong

The high temperature compression tests of 2Cr13 martensitic stainless steel under the deformation conditions at the temperatures between 1000°C and 1150°C with strain rates between 0.01s−1 and 10s−1 were carried out by using the Gleeble simulator. A new material constitutive model of modified Zerilli-Armstrong to predict 2Cr13 martensitic stainless steel flow stress behavior was developed.

Influence of intra-granular void distribution on the grain sub-structure of UO2 pellets after high temperature compression tests

The aim of this work is to study the role of intra-granular voids on the macroscopic behavior and the microstructure of uranium dioxide (UO2) for different strain conditions in the high temperature dislocational creep regime.Two batches (B1 and B2) of stoichiometric UO2 pellets were fabricated by adapted powder metallurgy processes to obtain very close mean grain size and porosity but different fractions of intra-granular voids: they were 2.5 times more numerous in the second batch. The pellets were then compressed at 1773 K mostly in the dislocational regime for different strain levels and strain rates. Large Electron BackScattered Diffraction (EBSD) maps were acquired to quantify the sub-boundaries fraction in each deformed sample (with reliable detection of disorientation lines down to 0.25°). Accurate-Electron Contrast Channeling Image (Accurate-ECCI) experiments were also performed to evidence the arrangement of dislocations in the sub-boundaries and highlight their interaction with intra-granular voids. The fractions of sub-boundaries and their disorientation increased in both batches with increasing strain levels and strain rates. This confirms that during creep, UO2 is subject to a dynamic recovery mechanism. Interestingly, for similar deformation conditions, the pellets from batch B2 crept slower than those from batch B1. They also had a higher fraction of sub-boundaries which were more tortuous and located essentially close to the grain boundaries where the voids clustered. This suggests an influence of intra-granular voids on the creep rate, probably due to a void pinning effect of dislocation sub-boundaries. This effect should be taken into account to optimize the microstructure and mechanical properties of UO2 nuclear fuel, in order to improve its behavior under irradiation.

Effect of SiC particles on hot deformation behavior of closed-cell Al/SiCp composite foams

Aluminum foams are one of the best energy absorber materials for various impact protection applications; such as lightweight structural panels, packing materials, and energy-absorbing devices. In the present study, the hot deformation behavior of closed-cell Al/SiCp composite foams was investigated at different contents of SiC particles (3, 6, and 10 vol%) and at various temperatures (100, 200, 300, and 400 °C). High-temperature uniaxial compression tests with constant 0.1 s−1 strain rate were carried out to get the fundamental stress–strain profiles. The results showed that the yield strength, plateau stress, and energy absorption of composite foams increase with increase in the SiC content and decrease with increase in the deformation temperature. Mechanical properties and electron microscope photographs demonstrated that increase in the SiC particle contents, as microstructural obstacles, resulted in cell’s walls reinforcement against the early failure especially at the higher temperatures.

Direct Energy Deposition of TiAl for Hybrid Manufacturing and Repair of Turbine Blades.

While repair is mainly used to restore the original part geometry and properties, hybrid manufacturing aims to exploit the benefits of each respective manufacturing process regarding either processing itself or resulting part characteristics. Especially with the current implementation of additive manufacturing in the production of TiAl, turbine blades for both hybrid manufacturing and repair new opportunities are enabled. One main issue is the compatibility of the two or more material types involved, which either differ regarding composition or microstructure or both. In this study, a TNMTM-alloy (Ti-Nb-Mo) was manufactured by different processes (casting, forging, laser additive manufacturing) and identically heat-treated at 1290 °C. Chemical compositions, especially aluminum and oxygen contents, were measured, and the resulting microstructures were analyzed with Scanning Electron Microscopy (SEM) and High-energy X-ray diffraction (HEXRD). The properties were determined by hardness measurements and high-temperature compression tests. The comparison led to an overall assessment of the theoretical compatibility. Experiments to combine several processes were performed to evaluate the practical feasibility. Despite obvious differences in the final phase distribution caused by deviations in the chemical composition, the measured properties of the samples did not differ significantly. The feasibility of combining direct energy deposition (DED) with either casting or laser powder bed fusion (LPBF) was demonstrated by the successful build of the dense, crack-free hybrid material.

Impact of high temperature on the compression behavior of carbon-bonded alumina filters with functionalized coatings

Carbon-bonded alumina is currently applied in metal casting processes due to its excellent thermomechanical performance. Used as ceramic foam filters in steel casting, the surface composition of such material is essential for trapping primary and secondary inclusions in liquid steel, where functionalized coatings are proven to enhance the filtration efficiency considerably. In this paper, compression tests on uncoated and coated Al2O3–C foam filters are performed at high temperatures under argon atmosphere. The macrostructure of the prepared filters before the high temperature compression tests and the microstructure afterwards are examined by computer tomography and scanning electron microscopy, respectively. High temperature compression strength of the studied filters generally exceeds cold crushing strength values thanks to plastification processes. The applied coatings have positive impact on the filter strength. The observed high scatter of the compression strength can be attributed to the inhomogeneity of strut thickness, distribution of the oxide and non-oxide materials within the struts as well as coating thickness.

Development of multi-physics numerical simulation model to investigate thermo-mechanical fatigue crack propagation in an autofrettaged gun barrel

In this research, a detailed multi-physics study has been carried out by numerically simulating a solid fractured gun barrel for 20 thermo-mechanical cycles. The numerical model is based on thermal effects, mechanical stress fields and fatigue crack mechanics. Elastic-plastic material data of modified AISI 4340 at temperatures ranging from 25 to 1200 °C and at strain rates of 4, 16, 32 and 48 s−1 was acquired from high-temperature compression tests. This was used as material property data in the simulation model. The boundary conditions applied are kept similar to the working gun barrel during continuous firing. A methodology has been provided to define thermo-mechanically active surface-to-surface type interface between the crack faces for a better approximation of stresses at the crack tip. Comparison of results from non-autofrettaged and autofrettaged simulation models provide useful information about the evolution of strains and stresses in the barrel at different points under combined thermo-mechanical loading cycles in both cases. The effect of thermal fatigue under already induced compressive yield due to autofrettage and the progressive degradation of the accumulated stresses due to thermo-mechanical cyclic loads on the internal surface of the gun barrel (mimicking the continuous firing scenario) has been analyzed. Comparison between energy release rate at tips of varying crack lengths due to cyclic thermo-mechanical loading in the non-autofrettaged and autofrettaged gun has been carried out.

The effect of Ni-doping on the microstructure, hot deformation behavior, and processing map of as-cast Al–Si piston alloy

Al–Si alloy is widely utilized in automobile pistons and cylinders due to good castability, high strength-to-weight ratio, excellent thermal conductivity, good resistance to corrosion/oxidation, and acceptable wear resistance. To increase the efficiency of engine motor, it is imperative to modify and engineer the microstructure of Al–Si alloy to enhance the high-temperature behavior. For this reason, in the current study, different concentration of Ni (0.8% and 2%) was doped into Al–Si alloy during casting to generate various Ni-rich intermetallic compounds within the alloy matrix. AlNiCu, AlCu, AlFeSi, and Mg2Si were found to be the main intermetallic compounds precipitated within the dendritic and interdendritic regions, which could enhance the thermal stability and high-temperature performance. High-temperature compression test at high temperatures ranging from 400 to 550 °C and at different strain rates ranging from 10−3 to 1 s−1 was carried out to develop high-temperature processing map and optimize the hot workability parameters of Ni-doped Al–Si alloy. The maximum power dissipation efficiency (η) was observed within the temperature range of 450–500 °C and strain rate of 0.05–0.08 s−1 (lower strain rate) for Al–Si–0.8%Ni alloy and within the temperature range of 450–500 °C and strain rate of 0.3–1 s−1 (medium to high strain rate) for Al–Si–2%Ni alloy. Dynamic recrystallization was found to be the primary softening mechanism at high temperatures (T > 450 °C).

Theoretical predication of dislocation-included high-temperature deformation mechanism maps for GH4742 alloy

ABSTRACT Based on high-temperature compression tests and focusing on the mechanical behaviour characteristics and microstructure evolution laws during high-temperature compression, laws relating to the strain-rate sensitivity index m and the activation energy of deformation Q-value at varying strain rates and deformation temperatures are clarified. Deformation mechanism maps involving dislocation quantity are plotted. Dislocation evolution laws and deformation mechanisms of the grain size with Burgers vector compensation, and the flow stress with modulus compensation during high-temperature deformation are predicted using the deformation mechanism maps.

A dislocation density-based model and processing maps of Ti-55511 alloy with bimodal microstructures during hot compression in α+β region

Hot compression features of Ti-55511 alloy are investigated by high-temperature compression tests in α+β region. It is found that the flow stress and softening mechanisms are obviously influenced by deformation conditions. The true stress decreases with the reduced strain rate or the raised temperature. The spheroidization of α phase and dynamic recrystallization (DRX) of β phase easily occur at low temperatures such as 973, 1003 and 1033 K, while the dynamic recovery (DRV) of β phase mainly occurs at high temperatures such as 1063 K because of the transformation from α phase to β phase at relatively high temperatures A dislocation density-based constitutive model, which is associated with DRV, work hardening mechanisms and the spheroidization of α phases, is established and validated to describe flow behavior. The correlation coefficient (R) and average absolute relative error (AARE) of the established model are 0.9924 and 6.8%, respectively. 3D power dissipation efficiency maps and processing maps are established to determine the appropriate processing window, i.e., too low temperatures (lower than 973 K) or too high strain rates (higher than 1 s−1) easily induce flow instability. Therefore, the medium temperature (1003–1063 K) and the low strain rate (0.001–0.1 s−1) are applicable for thermal compression of the studied titanium alloy.

Role of the Secondary Phase \u03b7 During High-Temperature Compression of ATI 718Plus\xae

High-temperature compression tests were performed on a Ni-base superalloy with a multi-phase microstructure. Particular attention was given on the influence of the η phase on recrystallization of ATI 718Plus®. The compression tests were performed at two temperatures over a variety of strains and strain rates. Meta-dynamic recrystallization was studied by exposing the samples to a set dwell time at the test temperature after deformation. Electron backscatter diffraction (EBSD) was used to investigate the microstructures after the tests. Secondary electron imaging (SEI) and scanning transmission electron microscopy (STEM) were utilized in order to investigate the deformation behavior of η and obtaining a detailed understanding of the recrystallization mechanism. The secondary η phase was found to increase the recrystallized fraction compared to η free tests. However, clusters of thin lamellar η inhibited recrystallization. The flow curve softening was distinctly stronger in the microstructure containing precipitates. It could be shown by SE images that this was due to the breakage and realignment of η. In addition, η was also found to accommodate the stresses by a remarkable deformation without breaking up. This was considered to be due to the composite nature of the precipitate as well as the ongoing recrystallization in the surrounding matrix.

Microstructure and high temperature mechanical properties of wire arc additively deposited Stellite 6 alloy

In this work, wire arc additive deposition of Stellite 6 alloy was carried out using cold metal transfer (CMT) process and the microstructural features, microhardness, and high temperature mechanical properties were studied. The as-deposited multi-layer wall was free of any defects. High temperature compression test samples were extracted parallel to the build direction, and the tensile samples were prepared along parallel and perpendicular orientation to the build direction. The hot compression test data was used to predict the flow behavior of the additively deposited alloy using an Arrhenius type equation at a strain of 0.6. The flow behavior of the additively deposited Stellite 6 alloy was similar to the conventional Co-based alloys in spite of the layer-by-layer macrostructure and microstructural variations. Microstructure, hardness, and phase analysis studies were carried out for the deformed samples after hot compression. The high temperature tensile properties were found to be anisotropic and location-specific, which were correlated with the columnar dendritic microstructure, alignment of the layer interfaces and variation in the secondary dendrite arm spacing due to repeated thermal cycles and difference in the cooling rate.

Superior Temperature-Dependent Mechanical Properties and Deformation Behavior of Equiatomic CoCrFeMnNi High-Entropy Alloy Additively Manufactured by Selective Laser Melting

The microstructure, temperature-dependent mechanical properties and deformation behaviors of equiatomic CoCrFeMnNi high-entropy alloy (HEA) additively manufactured by selective laser melting (SLM) were investigated. SLM-built HEA had a face-centered cubic (FCC) single-phase random solid solution. In addition, SLM-built HEA was composed of epitaxial growth grains, dislocation network and nano-sized oxides. Room- and high-temperature compression tests confirmed that SLM-built HEA has outstanding mechanical properties in all temperature ranges compared to equiatomic CoCrFeMnNi HEAs reported up to the present. The excellent mechanical properties of SLM-built HEA were achieved with fine grains, high dislocation density and fine precipitates at low temperatures (25 °C to 600 °C), and by high dislocation density and fine precipitates at high temperatures (700 °C or higher). On the other hand, the deformation microstructure showed that slip and deformation twins are the main deformation mechanisms from 25 °C to 600 °C, and slip and partial recrystallization are the main deformation mechanisms above 700 °C. Based on the above findings, this study also discusses correlations among the microstructure, superior mechanical properties and deformation mechanisms of SLM-built equiatomic CoCrFeMnNi HEA.

Laboratory Evaluation on the Performance Degradation of Styrene-Butadiene-Styrene-Modified Asphalt Mixture Reinforced with Basalt Fiber under Freeze-Thaw Cycles.

This paper aims at the freeze–thaw (F-T) cycles resistance of styrene-butadiene-styrene (SBS) modified asphalt mixture reinforced with basalt fiber in order to explore the performance evaluation and prediction of asphalt mixtures at seasonal frozen regions. Asphalt was firstly modified by the common SBS and then SBS-modified stone mastic asphalt (SMA) specimens with basalt fiber were prepared by using Superpave gyratory compaction (SGC) method. Next, asphalt mixture specimens processed by 0–21 F-T cycles were adopted for the high-temperature compression test, low-temperature splitting test and indirect tensile stiffness modulus test. Meanwhile, a three-dimensional model of F-T damage evolution of the mixtures was also established based on the reliability and damage theory. The test results showed that the loss rates of mechanical strength increased rapidly, and then gradually flattened; however, these indications changed significantly after 15–18 F-T cycles. In addition, the exponential function could reflect the variation trend of the mechanical performances with F-T cycles to a certain degree. The damage evolution and prediction model based on the reliability and damage theory can be established to analyze the internal degradation law better.

Fracture Damage Properties of SBS-Modified Asphalt Mixtures Reinforced with Basalt Fiber after Freeze-Thaw Cycles Using the Acoustic Emission Approach

This paper focuses on the fracture damage characteristics of styrene-butadiene-styrene (SBS)-modified SMA-13 specimens with basalt fiber under various freeze-thaw (F-T) cycles. SBS-modified stone mastic asphalt (SMA)-13 specimens with basalt fiber were prepared, first, using the superpave gyratory compaction method. Then, asphalt mixture specimens processed with 0–21 F-T cycles were adopted for the high-temperature compression and low-temperature splitting tests. Meanwhile, the acoustic emission (AE) test was conducted to evaluate the fracture characteristics of the asphalt mixture during loading. The results showed that the AE parameters could effectively reflect the damage fracture characteristics of the asphalt mixture specimen during the high-temperature compression and low-temperature splitting processes. The fracture damage of the asphalt mixture specimens during compression or splitting are classified into three stages based on the variation of the AE signals, i.e., when the load level is below 0.1~0.2 during the first stage and the load level is 0.1–0.9 or 0.2–0.8 during the second stage. The AE signal amplitude and count show clear correlations with the compression and splitting load levels. Meanwhile, the AE signal clarifies the formation, development, and failure of internal damage for the asphalt mixture specimens during the compression and splitting processes. The intensity (value and density) of the AE signal parameters of asphalt mixture decreases with increasing F-T cycles. It is evident that the F-T cycle has a significant adverse effect on the mechanical strength of asphalt mixture, which makes asphalt mixtures more likely to cause early failure.

A Mechanism for the Evolution of Hot Compression Cracking in Inconel 625 Alloy Ingot With Respect to Grain Growth

Hot compression cracking of as‐cast Inconel 625 alloy is investigated utilizing high temperature and high strain rate compression tests. The formation mechanism of the hot crack is systematically investigated based on grain growth and crystal slipping. Scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) analysis are used to characterize the crack morphology and microstructure. SEM results showed that the hot cracking during hot compression of Inconel 625 alloy is determined to be quasi‐cleavage fracture. The formation of carbide (NbC) plays a key role in the formation and propagation of the hot crack. The various slip systems activation strongly contributes to the overall growth of the dynamic recrystallization (DRX) grains. In addition, subgranular boundary formation within the grown grains is attribution to various slip systems activation in different local regions. The initiation and propagation of the hot compression cracks in Inconel 625 alloy depend on the development of the subgranular boundary within the grown grain.

Numerical simulation and experimental research on hot extrusion of 5B70 aluminum alloy complex end frame part

5B70 aluminium alloy is strengthened by Sc and Zr. It has higher strength and plasticity than common aluminum alloy. Meanwhile, 5B70 aluminum alloy which is widely used as a structural material also presents some advantages, such as corrosion resistance, excellent formability, and weldability. In this study, the high-temperature deformation behavior of 5B70 aluminum alloy and the hot extrusion process of the complex end frame part were studied, and the deformation property of 5B70 aluminum alloy at elevated temperature was analyzed by the high-temperature compression test. The numerical simulation of hot extrusion of complex end frame part was carried out. Moreover, the optimal hot extrusion parameters of 5B70 aluminum alloy were obtained, and the hot extrusion property and microstructure evolution of 5B70 aluminum alloy were investigated.

Effect of post-heat treatment on the thermophysical and compressive mechanical properties of Cu-Ni-Sn alloy manufactured by selective laser melting

This study investigated the effect of heat treatment on the microstructure, room- and high-temperature mechanical properties, and thermal properties of selective laser melted Cu-Ni-Sn alloy. Initial microstructural observation confirmed that the as-fabricated sample was composed of Cu, Cu6Sn5, Cu3P and undissolved Ni phases, and then the heat-treated sample was composed of CuNi solid solution, (Cu, Ni)3Sn and (Cu, Ni)3P. Room- and high-temperature compression tests (25 °C ~ 500 °C) were performed, and the yield strengths at room temperature measured 230.4 MPa and 346.0 MPa for as-fabricated and heat-treated materials, which indicates an approximately 50% increase in strength after heat treatment. Furthermore, as temperature increased, a phenomenon where the yield strength inverts occurred for both materials, and the cause of such a phenomenon was identified to be due to the difference in strengthening mechanisms. Thermal diffusivity is lower in heat-treated sample at all temperatures, but on the other hand, thermal conductivity interestingly is higher in heat-treated sample than as-fabricated sample (As-fabricated sample: 30.7–44.0 W/m∙K, heat-treated sample: 32.8–49.6 W/m∙K). The reason for this is identified to be due to microstructure evolution and defect control after heat treatment. Correlations between initial microstructures and mechanical- and thermophysical-properties were also discussed based on these findings.

Microstructure and High Temperature Mechanical Properties of Wire Arc Additively Deposited Stellite 6 Alloy

In this work, wire arc additive deposition of Stellite 6 alloy was carried out using the cold metal transfer (CMT) process and the microstructural features, microhardness, and high temperature mechanical properties were studied. The as-deposited multi-layer wall was free of any defects. High temperature compression test samples were extracted parallel to the build direction, and the tensile samples were prepared along parallel and perpendicular orientation to the build direction. The hot compression test data was used to predict the flow behavior of the additively deposited alloy using an Arrhenius type equation at a strain of 0.6. The flow behavior of the additively deposited Stellite 6 alloy was similar to the conventional Co-based alloys in spite of the layer-by-layer macrostructure and microstructural variations. Microstructure, hardness, and phase analysis studies were carried out for the deformed samples after hot compression. The high temperature tensile properties were found to be anisotropic and location-specific, which were correlated with the columnar dendritic microstructure, alignment of the layer interfaces and variation in the secondary dendrite arm spacing due to repeated thermal cycles and difference in the cooling rate.