High Temperature Deformation Mechanisms Research Articles

車載用電子部品に用いられるSn-Cu 系はんだ合金の高温変形挙動に関する研究

車載用電子部品に用いられるSn-Cu 系はんだ合金の高温変形挙動に関する研究

High-temperature deformation mechanism of γ-TiAl-based alloy with ultrafine grains

ABSTRACTEquiaxed ultrafine duplex alloys γ-TiAl and α2-Ti3Al are prepared by high-energy milling and hot pressing sintering. Microstructures presenting in the mixed and sintered powders are studied by scanning electron microscopy. Structural characteristics are investigated by high-resolution electron microscopy before and after compression at 1100–1200°C. The data reveal grain sizes of 300–500 and ∼100 nm for sintered γ-TiAl and α2-Ti3Al alloys, respectively. High deformation temperatures and low strain rates lead to low peak flow stress, and at such conditions the α2/γ and α2/α2 interfaces are prone to forming dislocation structure. The studies also reveal the presence of large-angle grain boundaries for the and (0002)α2/(0002)α2 interfaces.

Microstructural analysis and calcite piezometry on hydrothermal veins: Insights into the deformation history of the Cocos Plate at Site U1414 (IODP Expedition 344).

In this study we present microstructural data from hydrothermal veins in the sedimentary cover and the igneous basement recovered from Hole U1414A, Integrated Ocean Drilling Program (IODP) Expedition 344 (Costa Rica Seismogenesis Project), to constrain deformation mechanism operating in the subducting Cocos Plate. Cathodoluminescence studies, mechanical e‐twin piezometry and electron backscatter diffraction (EBSD) analyses of carbonate veins were used to give insights into the deformation conditions and to help to understand the tectonic deformation history of the Cocos Plate offshore Costa Rica. Analyses of microstructures in the sedimentary rocks and in the basalt of the igneous basement reveal brittle deformation, as well as crystal‐plastic deformation of the host rock and the vein material. Cathodoluminescence images showed that in the basalt fluid flow and related precipitation occurred over several episodes. The differential stresses, obtained from two different piezometers using the same parameter (twin density), indicate various mean differential stresses of 49 ± 11 and 69 ± 30 MPa and EBSD mapping of calcite veins reveals low‐angle subgrain boundaries. Deformation temperatures are restricted to the range from 170°C to 220°C, due to the characteristics of the existing twins and the lack of high‐temperature intracrystalline deformation mechanisms (>220°C). The obtained results suggest that deformation occurred over a period associated with changes of ambient temperatures, occurrence of fluids and hydrofracturing, induced differential stresses due to the bending of the plate at the trench, and related seismic activity.

High temperature deformation in fine grained high entropy alloys

There is considerable interest currently in developing and understanding microstructural evolution, stability and deformation in the new class of highly concentrated, multi-principal element solid solution high entropy alloys. This overview provides a brief description of potential high temperature deformation mechanisms in such fine grained alloys, discusses the significance of diffusion, and compares the available experimental results with appropriate theoretical models. It is shown that diffusion is not substantially slower in such alloys, and that superplastic deformation follows the standard model established for conventional polycrystals. The data also suggest that deformation at higher stresses occurs by dislocation glide creep, followed by a power-law breakdown regime. It is necessary to exercise caution in interpreting spherical nanoindentation creep data, although some data on a nanocrystalline HEA suggest that deformation at room temperature occurs by Coble diffusion creep. Based on the available data and understanding, a deformation mechanism map is developed highlighting the dominance over different regimes of grain size and stress of Coble diffusion creep, superplastic flow, dislocation creep and power-law breakdown.

Effect of Strut Thickness on Room and High Temperature Compressive Properties of Block-Type Ni-Cr-Al Powder Porous Metals

AbstractThis study investigated the effect of strut thickness on the room and high temperature compressive properties of block-type Ni-Cr-Al powder porous metals with ~3000 μm pore size manufactured using a new powder process. Two block-type Ni-Cr-Al porous metals with different strut thicknesses were manufactured. The strut thicknesses of two block foams were 340 μm (A) and 383 μm (B), respectively. Room temperature, 500°C, 650°C and 800°C compressive tests were performed. The compressive results identified typical elastic, plateau and densification regions of foam material in all temperature conditions. Regardless of the strut thickness, compressive strength (maximum peak stress) decreased as deformation temperature increased. In all deformation temperature ranges, the compressive strength measured higher in the porous metal with greater strut thickness (B). The high temperature deformation behavior of powder porous metal was confirmed to be affected by the structural factor and microstructural factor of the porous metal. With the findings described above, this study also discussed the high temperature deformation mechanism of the Ni-Cr-Al metal foam based on fracture surfaces after the high temperature compressions.

High Temperature Deformation Mechanisms in a DLD Nickel Superalloy.

The realisation of employing Additive Layer Manufacturing (ALM) technologies to produce components in the aerospace industry is significantly increasing. This can be attributed to their ability to offer the near-net shape fabrication of fully dense components with a high potential for geometrical optimisation, all of which contribute to subsequent reductions in material wastage and component weight. However, the influence of this manufacturing route on the properties of aerospace alloys must first be fully understood before being actively applied in-service. Specimens from the nickel superalloy C263 have been manufactured using Powder Bed Direct Laser Deposition (PB-DLD), each with unique post-processing conditions. These variables include two build orientations, vertical and horizontal, and two different heat treatments. The effects of build orientation and post-process heat treatments on the materials’ mechanical properties have been assessed with the Small Punch Tensile (SPT) test technique, a practical test method given the limited availability of PB-DLD consolidated material. SPT testing was also conducted on a cast C263 variant to compare with PB-DLD derivatives. At both room and elevated temperature conditions, differences in mechanical performances arose between each material variant. This was found to be instigated by microstructural variations exposed through microscopic and Energy Dispersive X-ray Spectroscopy (EDS) analysis. SPT results were also compared with available uniaxial tensile data in terms of SPT peak and yield load against uniaxial ultimate tensile and yield strength.

High Temperature Deformation Mechanism in Hierarchical and Single Precipitate Strengthened Ferritic Alloys by In Situ Neutron Diffraction Studies

The ferritic Fe-Cr-Ni-Al-Ti alloys strengthened by hierarchical-Ni2TiAl/NiAl or single-Ni2TiAl precipitates have been developed and received great attentions due to their superior creep resistance, as compared to conventional ferritic steels. Although the significant improvement of the creep resistance is achieved in the hierarchical-precipitate-strengthened ferritic alloy, the in-depth understanding of its high-temperature deformation mechanisms is essential to further optimize the microstructure and mechanical properties, and advance the development of the creep resistant materials. In the present study, in-situ neutron diffraction has been used to investigate the evolution of elastic strain of constitutive phases and their interactions, such as load-transfer/load-relaxation behavior between the precipitate and matrix, during tensile deformation and stress relaxation at 973 K, which provide the key features in understanding the governing deformation mechanisms. Crystal-plasticity finite-element simulations were employed to qualitatively compare the experimental evolution of the elastic strain during tensile deformation at 973 K. It was found that the coherent elastic strain field in the matrix, created by the lattice misfit between the matrix and precipitate phases for the hierarchical-precipitate-strengthened ferritic alloy, is effective in reducing the diffusional relaxation along the interface between the precipitate and matrix phases, which leads to the strong load-transfer capability from the matrix to precipitate.

High temperature deformation mechanisms in the 14% Cr ODS alloy

The stress relaxation behavior of the ODM401 ODS steel is tested at the temperature range 400–800°C in order to investigate the deformation mechanisms. The repeated relaxation tests are performed on the tensile specimens within the plastic strain range 10−4–10−1. The deformation mechanisms are analyzed in terms of an activation volume, dislocation density and velocity, a thermal stress component and a strain rate hardening. The deformation is driven by the dislocation glide and climb. Dispersed particle-dislocation interactions is a dominant effect at temperatures 400–600°C. Short-range interactions between dislocations and a lattice are most significant at 600°C. The non-conservative motion of dislocations becomes active at temperatures above 600°C. The majority of the mobile dislocations is not trapped and is able to move freely in the microstructure.

High-temperature deformation and fracture mechanisms of an advanced heat resistant Fe-Cr-Ni alloy

In this work creep-strain test ranging from 180 to 240MPa at 973K, 998K, and 1023K were conducted to investigate the high temperature deformation and fracture mechanisms for Sanicro 25 alloy. The relationship between minimum creep rate and applied stress followed Norton's law. Apparent stress exponent values of 8, 6.5, and 5 were obtained at 973K, 998K, and 1073K, respectively, with an apparent creep activation energy value of 437.3–606.1kJ/mole illustrating that the rate-controlled creep occur in Sanicro 25 during creep. The threshold stresses were 129.5, 111.5, and 82.0MPa at 973K, 998K, and 1023K, respectively. The true creep activation energy and the true stress exponent were found to be 271.6kJ/mole and 3, respectively. The presence of nanoscale MX and Cu precipitates were observed and theoretical calculations of threshold stresses confirmed that shearing of the nano-Cu precipitates occurred at 973K, while the dislocations climbed up MX precipitates at 973–1023K. The apparent stress exponent obtained for creep rupture shows that similar mechanisms operate in creep deformation and rupture behavior for Sanicro 25. A damage tolerance factor of ~5 in the alloy indicates that the microstructural degradation such as coarsening of precipitate and subgrain structure is the dominant creep damaging mechanism in the alloy.

Probing Plasticity Mechanisms in Low Melting Temperature Metallic Nanostructures Using Synchrotron X-Ray Microdiffraction

A nondestructive ex situ Synchrotron Laue X-ray Microdiffraction (µSLXRD) technique is used to investigate the plasticity mechanisms in the metallic nanostructures and their evolution at high homologous temperatures through analyzing low melting temperature metals such as tin. Without the use of expensive high temperature equipment, the current approach of studying plasticity mechanisms at high temperature is enabled by the low melting behaviors of the samples allowing them to provide insights on high temperature deformation mechanisms, such as thermally activated dislocation climbs. Nanopillars with a diameter near 1µm were deformed by uniaxial compression to strains of in excess of 20% at a strain rate of approximately 0.001s-1. Defect density evolution in the nanopillars was evaluated by synchrotron Laue X-ray microdiffraction (µSLXRD) before and after deformation (ex situ). It was found from the Laue peak broadening measurements that there was no significant change in the dislocation density of the same pillar before and after such an extent of deformation. These findings were being compared to similar experimental results of indium and gold nanopillars (from our previous reports). They were found to be in stark contrast to our previous results with indium (although both are low melting temperature metals) where the synchrotron Laue X-ray microdiffraction showed significant peak broadening – before vs. after the uniaxial compression to a similar amount of deformation. It appears high temperature plasticity mechanism in tin nanostructures involves significant lattice diffusion behavior, as opposed to simple displactive behavior (through dislocation movements) that has been proposed in recent studies of tin nanostructures.

微結晶粒セラミック材料における低温高速超塑性の可能性

For attaining high-strain-rate superplasticity (HSRS) in ceramic materials, prerequisites are described on the basis of existing knowledge about high-temperature plastic deformation and intergranular cavitation mechanisms. The knowledge suggests that a combination of grain-size refinement to 100-200 nm or smaller and enhanced diffusion caused by doping may highly enhance stress-relaxation around triple junctions and may lead to HSRS at temperatures lower than 1250-1300°C in structural ceramics. From this point of view, recent studies are reviewed and discussed on ceramic superplasticity at strain rates higher than 1 × 10−2 s−1. Attention is also placed on the fabrication of materials with nanosized grains and the resultant superplastic properties.

Microstructure and high temperature mechanical properties of powder metallurgical Ti-45Al-7Nb-0.3W alloy sheets

The microstructure, high temperature mechanical properties and deformation mechanism of powder metallurgical (PM) Ti-45Al-7Nb-0.3W (at.%) alloy sheets were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The tensile test results showed excellent high temperature mechanical properties with a yield stress (YS) of 670MPa and an ultimate tensile stress (UTS) of 874MPa at 700°C and displayed an anomalous strengthening effect, which could be explained by the pinning mechanism of dislocation locks. In addition, the brittle-ductile transition temperature (BDTT) was found at between 800°C and 850°C. When deformed below BDTT, high density of dislocations and mechanical twins were observed in the microstructures. However, with increasing deformation temperature above BDTT, kinking of α2/γ lamellar colonies and dynamic recrystallization also occurred. It was noteworthy that the as-rolled sheets displayed superplastic behaviors at 950°C with initial strain rates of 1×10−4s−1 and 5×10−5s−1. At the same time, severe dynamic recrystallization took place and the grain boundary sliding was improved by β phase, which resulted in an elongation of 243% at the strain rate of 5×10−5s−1.

Superplasticity of beryllium

Beryllium is a metal having unique physicomechanical properties, including a record specific rigidity, but it undergoes cold and red brittleness. As a result of long-term investigations, we were the first to manufacture high-purity fine-grained beryllium, which has the room-temperature plasticity that is higher than that of commercial-purity powdered beryllium by an order of magnitude and exhibits superplastic flow at elevated temperatures. In this review, we summarize the results of the long-term study of the superplastic flow of beryllium and the mechanisms of high-temperature deformation.

High Temperature Deformation Behavior of P92 Steel

The ferritic-martensitic steels are superior steels based on the potential properties that they possess; especially, the elevated temperature properties. Among these ferritic-martensitic steels, Cr–Mo–W steel is a candidate structural material for high temperature applications such as future advanced reactors and aerospace applications. The hot deformation behavior of P92 steel was carried out at elevated temperatures between 600 and 700 °C and different strain rates of 10−5–10−3 s−1. Thereafter, the hot deformation behavior was analyzed, taking into account the peak stress values for each condition. As a result, the activation energy of P92 steel and the stress exponent were obtained to be 6.7 and 628 kJ/mol, respectively. The activation energy assessed the high-temperature deformation mechanism for this class of steels. Even though, the obtained activation energy was much higher than that of iron self-diffusion, it came in good agreement with the reported values in literature. Subsequently, the relevant hot deformation constitutive equation and the relationship between peak stresses and deformation rate at elevated temperature were developed.

High temperature deformation mechanism of 15CrODS ferritic steels at cold-rolled and recrystallized conditions

The ODS ferritic steels realize potentially higher operating temperature due to structural stability by the dispersed nano-size oxide particles. The deformation process and mechanism of 15CrODS ferritic steels were investigated at 1073 K and 1173 K for the cold-rolled and recrystallized conditions. Tensile and creep tests were conducted at the stress in parallel (LD) and perpendicular (TD) directions to the grain boundaries. Strain rate varied from 10−1 to 10−9 s−1. For the LD specimens, deformation in the cold rolled and recrystallized conditions is reinforced by finely dispersed oxide particles. The dominant deformation process for the recrystallized TD specimen is controlled through the grain boundary sliding and stress accommodation via diffusional creep at temperature of 1173 K and lower strain rate less than 10−4 s−1. The grain boundary sliding couldn't be rate-controlling process at 1073 K for the as-cold rolled TD specimen, where a dynamic recovery of the dislocation produced by cold-rolling is related to the deformation process.

Climb Enabled Discrete Dislocation Plasticity of Superalloys

Ni-based superalloys comprising of elastic particles embedded in a single crystal elastic-plastic matrix are usually subject to loading at elevated service temperatures. In order to enhance the understanding of high temperature deformation mechanisms a two dimensional discrete dislocation plasticity framework wherein the dislocations movement that incorporates both glide and climb is formulated. The climbing dislocations are modelled as point sources/sinks of vacancies and the vacancy diffusion boundary value problem is solved by superposition of the vacancy concentration fields of the point sources/sinks in an infinite medium and a complementary non-singular solution that enforces the relevant boundary conditions. The vacancy concentration field along with the Peach-Kohler force provides the climb rate of the dislocations.

High temperature deformation mechanisms and constitutive modeling for Al/SiCp/45 metal matrix composites undergoing laser-assisted machining

The material removal mechanism in LAM of Al/SiCp composite. In the present study, material removal mechanisms were inferred from the analysis of the chip and chip root morphology at different cutting conditions, and the shear zone stress was determined by using three dimensional machining theory with a new approach to determining shear angles for saw-tooth chips formed in LAM of Al/SiCp composite. Based on the deformation mechanisms associated with LAM, a constitutive equation which predicted the shear zone stress was proposed, and the effects of operating conditions on the shear zone stress were determined from a systematic experimental study. A comparison of the constitutive equation predictions with the experimental results showed a smaller than the estimated uncertainty (15%) in the stress calculation.

High temperature deformation mechanisms in pure magnesium studied by nanoindentation

The effect of temperature on the main deformation mechanisms of pure magnesium (Mg) was investigated using nanoindentation combined with atomic force microscopy, electron backscatter diffraction and finite element crystal plasticity simulations. While twinning is clearly apparent near the indents performed at room temperature, almost no twinning activity was detected at 300 °C. The analysis of the residual imprints confirms that the decrease of the twin activity with temperature is compensated by a profuse activation of the prismatic slip systems.

Effect of Ta additions on microstructure and mechanical properties of a single-crystal Co–Al–W-base alloy

Microstructures and mechanical properties of Co–9.5Al–5W–16Ni–6Cr–xTa (at% where x=0, 1.8, 2.8, named as 0Ta, 1.8Ta and 2.8Ta) alloys are investigated. Microstructures of heat-treated samples are composed of γ and cubical γ′ precipitates. The γ′ solvus temperature increases obviously with Ta additions. The yield strength as well as creep strength is improved with the addition of Ta. Ta additions affect the high-temperature tensile deformation mechanism. The γ′ phase of the three alloys is rafted along the tensile axis direction during creep tests at 900°C. The creep strength of 2.8Ta alloy is approaching the level of a first-generation Ni-base single-crystal superalloy.

Deformation mechanisms in a precipitation-strengthened ferritic superalloy revealed by in situ neutron diffraction studies at elevated temperatures

The ferritic superalloy Fe–10Ni–6.5Al–10Cr–3.4Mo strengthened by ordered (Ni,Fe)Al B2-type precipitates is a candidate material for ultra-supercritical steam turbine applications above 923K. Despite earlier success in improving its room-temperature ductility, the creep resistance of this material at high temperatures needs to be further improved, which requires a fundamental understanding of the high-temperature deformation mechanisms at the scales of individual phases and grains. In situ neutron diffraction has been utilized to investigate the lattice strain evolution and the microscopic load-sharing mechanisms during tensile deformation of this ferritic superalloy at elevated temperatures. Finite-element simulations based on the crystal plasticity theory are employed and compared with the experimental results, both qualitatively and quantitatively. Based on these interphase and intergranular load-partitioning studies, it is found that the deformation mechanisms change from dislocation slip to those related to dislocation climb, diffusional flow and possibly grain boundary sliding, below and above 873K, respectively. Insights into microstructural design for enhancing creep resistance are also discussed.