Diffusion Creep Research Articles

High‐temperature deformation and consolidation of polycrystalline α‐SiC by spark plasma sintering

AbstractThe main objective of this investigation is the consolidation and flexural strength of alpha silicon carbide ceramics produced without additives by spark plasma sintering. Using the design of the experiment method, we optimized temperature and dwell to achieve fully dense silicon carbide bulks. The consolidation process of silicon carbide was analyzed similarly to the creep of bulk ceramics, and it was determined that the activation energy for the densification process was 596 ± 39 kJ/mol, while the stress exponent n was below 2. Bulk additive‐free silicon carbide ceramics gradually increased flexural strength as the temperature rose to 2000°C. The flexural strength at 2000°C was influenced by the loading rate, and under 2.5 mm/min, it reached a maximum of 2.08 GPa. To explain this phenomenon, a deformation mechanisms map was created, indicating that diffusion creep is the most probable mechanism for the strain sensitivity of SiC at 2000°C. Transmission electron microscopy indicated a substantial rise in twin density within the α‐SiC grains at 2000°C, indicating the activation of a previously unreported self‐reinforcing mechanism.

Superplastic behavior and deformation mechanisms of Al-Mg-based alloy processed by isothermal multidirectional forging

The evolutions of microstructure and superplastic deformation mechanisms for Al-Mg-based alloy with L12-nanoprecipitates and recrystallized 1.8 µm grains processed by multidirectional forging were studied. The alloy exhibiting excellent superplastic properties at 460 °C high strain rates of (1–6) × 10−2s−1. Due to a high fraction of high-angle grain boundaries and grain size stability, grain boundary sliding contributed ∼50 % to the total strain and it was accommodated by both dislocation slip/creep and diffusional creep mechanisms. The dislocation slip/creep contribution increased with increasing strain rate.

Microstructural evolution and deformation mechanisms of superplastic aluminium alloys: A review

Aluminium alloy is one of the earliest and most widely used superplastic materials. The objective of this work is to review the scientific advances in superplastic Al alloys. Particularly, the emphasis is placed on the microstructural evolution and deformation mechanisms of Al alloys during superplastic deformation. The evolution of grain structure, texture, secondary phase, and cavities during superplastic flow in typical superplastic Al alloys is discussed in detail. The quantitative evaluation of different deformation mechanisms based on the focus ion beam (FIB)-assisted surface study provides new insights into the superplasticity of Al alloys. The main features, such as grain boundary sliding, intragranular dislocation slip, and diffusion creep can be observed intuitively and analyzed quantitatively. This study provides some reference for the research of superplastic deformation mechanism and the development of superplastic Al alloys.

Interrogating an along-strike variation in the evolution and rheology of a large continental strike-slip fault zone

Along-strike variations in lithology, temperature, fluid activity, etc. can induce rheological changes in strike-slip faults that may be recorded by different fault rocks and fabrics. This article interrogates localized formation of granite-derived mylonite in a large strike-slip fault zone in which ultramylonite is the principle granite-derived fault rock to better understand this rock record of faulting. Microtextures show that rate-limiting deformation mechanisms in mylonite were dislocation creep in quartz and diffusion creep in very-fine-grained feldspar aggregates. Microtextures also show that mylonite formation is fully compatible with continuous viscous deformation whereas coeval ultramylonite along strike formed after whole-rock cataclasis at the brittle-viscous transition. Differential stresses determined from quartz aggregates in ultramylonites are 40–150% greater than stresses in mylonites. Hence, mylonites represent a local weak sector within this otherwise relatively strong fault zone. Mylonite formation is correlated with syndeformational chemical alteration as well as quartz microstructures and mineral assemblages indicating elevated deformation temperatures. Not all mylonite samples record significant chemical alteration. Therefore, mylonite formation likely records locally elevated temperatures. These results illustrate how a local shift in deformation conditions can affect the evolution and rheology of a large strike-slip fault zone, and how fault rocks record these processes.

Influence of martensite and grain size on the mechanical behavior of austenitic Fe–C–Mn–Ni–Al medium Mn steels with TWIP mechanism under uniaxial tension/compression and micromechanical creep

Medium Mn steels with induced plasticity mechanisms have effectively addressed the high-strength and ductility requirements for structural applications. However, there is still uncertainty about the impact of residual martensite on medium Mn steels with an austenitic matrix under uniaxial tension and compression. Furthermore, research on the influence of grain size through incomplete recrystallization in medium Mn alloys is scarce. In this context, our study focused on design and manufacturing a medium Mn Fe–C–Mn–Ni–Al alloy through controlled atmosphere casting incorporating martensite, aiming to analyze its effects under uniaxial stress conditions. Thermomechanical and annealing heat treatments were applied to control grain growth and nucleation of new grains, allowing us to explore how grain size affects the twinning process and mechanical reinforcement in the alloy. Microstructural characterization techniques, including optical and scanning electron microscopy, were employed to assess the mechanical response and damage mechanisms. Mechanical tests included tension, compression, and nanoindentation. The results indicated that residual martensite generates an accelerated damage mechanism under tension due to co-deformation at the interface with austenite, resulting in crack nucleation and rapid propagation through mode I fracture. Consequently, ductility in tension significantly decreases, while no apparent failure is observed during the compression deformation process. Furthermore, incomplete recrystallization was observed to enhance the creep response in both tension and compression. The strain hardening rate results revealed the activation of primary twinning in tension and both primary and secondary twinning in compression for annealed samples. Nanoindentation tests confirmed the presence of twinning and revealed that diffusion creep and grain boundary sliding are the predominant creep mechanisms.

Deformation and melt–rock interaction in the upper mantle: Insights from the layered structure of the Horoman peridotite, Japan

To obtain a better understanding of melt–rock interactions in the upper mantle, microstructural and petrological analyses were conducted on deformed mantle peridotites from the Horoman peridotite complex, Hokkaido, Japan. The Horoman peridotite complex is lithologically heterogeneous and contains various kinds of ultramafic and mafic rocks. We studied an outcrop of 3 × 70 m in size that contains layered spinel harzburgite, plagioclase lherzolite, and mafic rocks. The results indicate that reactive melts migrated preferentially along the foliation in the already deformed peridotite, and that these melt-rich zones became especially prone to further deformation. This inference is supported by (1) the parallelism of the boundaries of rock layers and foliation in the deformed peridotite, and the shape and crystallographic preferred orientations (SPOs and CPOs) of olivine in the peridotites; (2) the diffusive trends of magnesium and modal compositions of pargasite grains near the boundaries between peridotite and mafic layers; (3) variations in the NiO content of olivine crystals; (4) variations in olivine CPOs with orthorhombic (010)[100] slip system patterns and weak fiber-[010] patterns; and (5) the strong pargasite SPOs, the cuspate shapes of the pargasites, and the absence of intercrystallite deformation. The results, combined with previously reported P–T conditions for the Horoman peridotite complex, indicate that the deformed peridotites and mafic rocks with a layered structure represent temperatures of 1050–1150 °C and pressures of 0.7–1.5 GPa. Our results suggest that a decrease in pressure led to the transition from a melt-free to a melt-bearing system with a consequent change in the deformation mechanism, from dislocation creep in the melt-free system to diffusion creep in the melt-bearing system, with strain localization in the fine-grained melt-rich layers. The change in deformation mechanism is likely to have occurred in the uppermost mantle beneath a mid-ocean ridge, where strong rheological contrasts are controlled by spatial variations in the melt fraction.

Co–Ni–Al–W γ/γ′ superalloy with Cr and Ti additions fabricated via laser fusion of elemental powders

A Co-based superalloy (Co-0.20Ni-0.11Al-0.07W-0.04Cr-0.03Ti, mole fraction) was synthesized by laser powder-bed fusion of a blend of elemental powders. The as-built alloy shows a γ-FCC matrix where the high-melting Ti and Cr powders are fully dissolved, but the refractory W particles are only partially melted. Full dissolution of the W particles is achieved after homogenization at 1150 °C, resulting in a homogeneous, single-phase γ microstructure. Upon aging at 900 °C, a two-phase γ/γ′ microstructure forms, with a high-volume fraction of sub-micron γ′ precipitates with cuboidal shape. Compared to a control quaternary alloy without Cr and Ti fabricated by the same method, the present alloy has increased γ′ fraction and microhardness after aging for 300 h, maintaining a strong γ′ strengthening effect without forming γ′-depleted zone at grain boundaries. Micrometer-size γ′-precipitates at grain boundaries also shift the transition between diffusional and dislocation creep to lower stress levels, by inhibiting diffusional creep and grain-boundary sliding. However, overall creep resistance is lowered, consistent with a reduction of lattice mismatch due to Cr additions and rafting of γ′ precipitates. Furthermore, Cr and Ti additions improve oxidation resistance at 900 °C, due to the formation of a continuous Cr-, Ti- and Al-rich oxide layer.

Vacancy-mediated transport and segregation tendencies of solutes in fcc nickel under diffusional creep: A density functional theory study

Vacancy-mediated transport and segregation tendencies of solutes in fcc nickel under diffusional creep: A density functional theory study

Superplastic deformation behaviors of fine-grained Ti-15 V-3Cr-3Al-3Sn alloy prepared via ultra-low heat input friction stir processing

In this work, a fine-grained Ti-15 V-3Cr-3Al-3Sn alloy with 0.93 μm in average grain size and 75.6% of high-angle grain boundaries was achieved by ultra-low heat input friction stir processing (FSP). The superplastic behavior of the friction stir processed (FSPed) sample was investigated at the temperature of 600 °C–700 °C and strain rates range of 1 × 10−4 s−1-3 × 10−3 s−1. The FSPed sample exhibited the largest elongation of 1110% at 675 °C and 3 × 10−4 s−1. This elongation was the largest reported for the alloy to date. The main reasons could be drawn as follows: Firstly, the α phase precipitated during the heating process before superplastic deformation pinned the β grain boundaries in the subsequent superplastic deformation process. Secondly, the dynamic recrystallization occurred during superplastic deformation, which significantly refined the grains and kept the ratio of high-angle grain boundaries >80%. Thirdly, an obvious diffusional creep of the β grains was observed in the late superplastic deformation period, which coordinated the sliding of β grain boundaries. In summary, the superplastic deformation mechanism of the FSPed sample deformed at 675 °C and 3 × 10−4 s−1 was grain boundary sliding accompanied by dynamic recrystallization and diffusional creep.

Strain localization by diffusion creep of Bridgmanite-Ferropericlase mixture: Application of self-consistent method

In this study, we investigate the finite deformation of a polycrystalline mixture of bridgmanite (Br) and ferropericlase (Fp) by diffusion creep at the lower mantle-like temperature and pressure by using the self-consistent approach. We explore the influence of volume fraction of Fp, viscosity contrast, and strain dependence (effect of shape change) under both axial (coaxial deformation) and simple shear (non-coaxial deformation). Our present study shows: i) the strength (viscosity) contrast between Fp and Br increases with strain since the viscosity of Fp significantly decreases as Fp grain elongates, and (ii) deformation starts from nearly homogeneous strain to finally nearly homogeneous stress under simple shear whereas deformation behavior remains nearly homogeneous strain under axial deformation. A more substantial creep rate partitioning occurs in simple shear than in axial deformation. These results imply that strain localization via diffusion creep might occur in the lower mantle, particularly in regions where the simple shear is dominated (i.e., in the boundary layers (e.g., the D″ layer)).

Diffusion-Mediated Superelongation in Metal Nanorods.

We report insitu electron microscopy observation of the superelongation deformation of low-melting-point metal nanorods. Specifically, metal nanorods with diameters as small as 143nm can undergo uniform stretching by an extraordinary 786% at ∼0.87T_{m} without necking. Moreover, the corresponding fracture stress exhibits a pronounced size effect. By combining experimental observations with molecular dynamic simulations, a crystal-core-liquid-shell structure is revealed, based on which a constitutive model that incorporates diffusion creep mechanism and surface tension effect is developed to rationalize the findings. This study not only establishes a pioneering reference for comprehending the diffusion-dominated constitutive response of nanoscale materials but also has substantial implications for strategic design and processing of metals in high-temperature applications.

Deformation mechanisms and fluid conditions of mélange shear zones associated with seamount subduction

Lithologic heterogeneity and the presence of fluids have been linked to seamount subduction and collocated with slow earthquakes. However, the deformation mechanisms and fluid conditions associated with seamount subduction remain poorly understood. The exhumed Chichibu accretionary complex on Amami-Oshima Island preserves mélange shear zones composed of mudstone-dominated mélange and basalt–limestone mélange deformed under sub-greenschist facies metamorphism. The mudstone-dominated mélange contains sandstone, siliceous mudstone, and basalt lenses in an illitic matrix. The basalt–limestone mélange contains micritic limestone and basalt lenses in a chloritic matrix derived from the mixing of limestone and basalt at the foot of a seamount. The basalt–limestone mélange overlies the mudstone-dominated mélange, possibly representing a submarine landslide from the seamount onto trench-fill terrigenous sediments. The asymmetric S–C fabrics in both mélanges show top-to-SE shear consistent with megathrust-related shear. Quartz-filled shear and extension veins in the mudstone-dominated mélange indicate brittle failure at near-lithostatic fluid pressure and low differential stress. Microstructural observations show that deformation in the mudstone-dominated mélange was accommodated by dislocation creep of quartz and combined quartz pressure solution with frictional sliding of illite, whereas the basalt-limestone mélange was accommodated by frictional sliding of chlorite and dislocation creep of coarse-grained calcite, with possible pressure solution creep and diffusion creep of fine-grained calcite. The mélange shear zones formed in association with seamount subduction record temporal changes in deformation mechanisms, fluid pressure, and stress state during megathrust shear with brittle failure under elevated fluid pressure, potentially linking tremor generation near subducting seamounts.

Densification mechanisms during high-pressure sintering of nanocrystalline Gd2Zr2O7 ceramic

High-pressure sintering (HPS) is a promising technique for producing nanocrystalline ceramics with unique properties. However, the densification mechanisms of HPS for nanocrystalline ceramics at different sintering stages remain controversial. This study focuses on Gd2Zr2O7 (GZO) nanocrystalline ceramics, investigating their microstructure evolution and densification behavior under varying pressures, temperatures, and dwelling times. The HPS process involves distinct stages: cold compaction, hot compaction, and isothermal progression. During cold compaction, densification is driven by the breakdown of aggregates, particle rearrangement, and local plastic deformation, resulting in a relative density of 84.8 %. The intermediate stage achieves an increase to ∼93.7 % in relative density by grain boundary-mediated plastic deformation mechanism. The final isothermal stage, held at 500 °C/5 GPa, achieves nearly full density (∼99.2 %) through diffusion creep, eliminating microstructural defects. This comprehensive understanding of HPS densification mechanisms, exemplified by GZO ceramics, contributes to advancing nanocrystalline ceramic applications.

A thermodynamically consistent creep constitutive model considering damage mechanisms

This paper derives a physically-based creep-damage and life prediction model through the basic laws of thermodynamics. The model divides creep damage into two parts: one corresponding to high temperature and low stress, related to cavity nucleation and cavity growth, and the other corresponding to high stress, related to dislocation movement. The creep strain rate consists of two components: diffusion creep, which is assumed to occur in all stress ranges, and dislocation-related creep, which activates when the external stress exceeds a certain threshold. The proposed model characterizes damage by the degradation of creep free energy. It accurately describes creep behavior over a wide stress range, including the transition phenomena observed in creep strain rate curves and creep life curves. This provides a constitutive reference for simulating long-term creep damage and life based on short-term creep data.

Plastic deformation of dry fine-grained olivine aggregates under high pressures

Abstract This study investigates the effect of pressure on diffusion creep of dry San Carlos and synthetic (prepared by sol-gel method) olivine. We prepared dry (water content < 9 ppm wt) fine-grained (< 1 μm grain-size) olivine and deformed the samples (both San Carlos and solgel olivine in the same assembly) in the same sample assembly under high-pressure (P = 2.9–8.8 GPa) and modest temperatures (T = 980–1250 K) at a fixed strain-rate. Evolution of strength was studied using the radial X-ray diffraction from various diffraction planes. We found that San Carlos and sol-gel olivine show similar rheological behaviour (when normalized to the same grain-size). Stress estimated by the radial X-ray diffraction increases with time and initially shows similar values for all diffraction planes. In many cases, stress values start to depend on the diffraction planes in the later stage and time dependence becomes minor. The micro-structural observations show that grain-size increases during an experiment. The results are interpreted using a theory of radial X-ray diffraction and the theoretical models of diffusion and dislocation creep. We conclude that the initial stage of deformation is by diffusion creep, but deformation in the later stage is by dislocation creep. For dislocation creep, our results are in reasonable agreement with previous low temperature dislocation creep results after a correction of temperature effect. For diffusion creep, we obtain an activation volume of 7.0 ± 2.4 cm3/mol that is substantially smaller than the values reported on dislocation creep but agrees well with the results on grain-growth. By comparing the present results on dry olivine with the previous results on wet (water-saturated) olivine, we found that water enhances diffusion creep but only modestly in comparison to dislocation creep. The difference in the pressure and water content dependence between diffusion and dislocation creep has an important influence on the dominant deformation mechanisms of olivine in the upper mantle.

Effect of Compressive Stress on Copper Bonding Quality and Bonding Mechanisms in Advanced Packaging.

The thermal expansion behavior of Cu plays a critical role in the bonding mechanism of Cu/SiO2 hybrid joints. In this study, artificial voids, which were observed to evolve using a focused ion beam, were introduced at the bonded interfaces to investigate the influence of compressive stress on bonding quality and mechanisms at elevated temperatures of 250 °C and 300 °C. The evolution of interfacial voids serves as a key indicator for assessing bonding quality. We quantified the bonding fraction and void fraction to characterize the bonding interface and found a notable increase in the bonding fraction and a corresponding decrease in the void fraction with increasing compressive stress levels. This is primarily attributed to the Cu film exhibiting greater creep/elastic deformation under higher compressive stress conditions. Furthermore, these experimental findings are supported by the surface diffusion creep model. Therefore, our study confirms that compressive stress affects the Cu-Cu bonding interface, emphasizing the need to consider the depth of Cu joints during process design.

The influence of viscous slab rheology on numerical models of subduction

Abstract. Numerical models of subduction commonly use diffusion and dislocation creep laws from laboratory deformation experiments to determine the rheology of the lithosphere. The specific implementation of these laws varies from study to study, and the impacts of this variation on model behavior have not been thoroughly explored. We run simplified 2D numerical models of free subduction in SULEC, with viscoplastic slabs following (1) a diffusion creep law, (2) a dislocation creep law, and (3) both simultaneously, as well as several variations of model 3 with reduced resistance to bending. We compare the results of these models to a model with a constant-viscosity slab to determine the impact of the implementation of different lithospheric flow laws on subduction dynamics. In creep-governed models, higher subduction velocity causes a longer effective slab length, increasing slab pull and asthenospheric drag, which, in turn, affect subduction velocity. Numerical and analogue models implementing constant-viscosity slabs lack this feedback but still capture morphological patterns observed in more complex models. Dislocation creep is the primary deformation mechanism throughout the subducting lithosphere in our models. However, both diffusion creep and dislocation creep predict very high viscosities in the cold core of the slab. At the trench, the effective viscosity is lowered by plastic failure, rendering effective slab thickness the primary control on bending resistance and subduction velocity. However, at depth, plastic failure is not active, and the viscosity cap is reached in significant portions of the slab. The resulting high slab stiffness causes the subducting plate to curl under itself at the mantle transition zone, affecting patterns in subduction velocity, slab dip, and trench migration over time. Peierls creep and localized grain size reduction likely limit the stress and viscosity in the cores of real slabs. Numerical models implementing only power-law creep and neglecting Peierls creep are likely to overestimate the stiffness of subducting lithosphere, which may impact model results in a variety of respects.

Recent progress in the study of lattice-preferred orientation of olivine

Recent progress on the study of olivine LPO after (Karato et al., 2008) is reviewed with the emphasis on three issues: (i) LPO formed by the rotation of olivine crystals with anisotropic shape (euhedral crystals) in diffusion creep (Miyazaki et al., 2013), (ii) B-type LPO in the olivine + basaltic melt (Holtzman et al., 2003), and (iii) pressure change in the influence of LPO (Ohuchi and Irifune, 2013). Regarding the role of euhedral crystals, we show that euhedral olivine crystals occur in a mixture of forsterite and diopside (used by (Miyazaki et al., 2013)) but not in a mixture of olivine and enstatite. Consequently, the results by reported by (Miyazaki et al., 2013) are not applicable to the Earth’s upper mantle where olivine co-exists mostly with enstatite. Also we show that the LPO reported by (Miyazaki et al., 2013) is not consistent with the shape of olivine, and the observed LPO is likely due to dislocation glide (A-type fabric) under the conditions near the diffusion-dislocation creep regime boundary.Regarding the LPO of olivine with the presence of melt, (Qi et al., 2018)’s experimental study with the torsion geometry did not reproduce the B-type fabric reported by (Holtzman et al., 2003) indicating that the B-type fabric reported by (Holtzman et al., 2003) was indeed an artifact of the direct shear experiments. The weak LPO found by (Qi et al., 2018) (compared to that by (Zimmerman et al., 1999)) can be explained by the smaller grain size in their experiments. I conclude that a majority of the experimental results on olivine LPO at relatively low pressures (<2 GPa) can be understood based on the basics of deformation mechanism map and LPO caused by various slip systems in olivine. Regarding a claim by (Ohuchi and Irifune, 2013) that the A-type LPO (a-slip) dominates at high water content and c-slip dominates at low water content at pressures higher than ∼7 GPa, a compilation of experimental studies by (Masuti et al., 2019) and the observed LPO of the ultra-deep xenolith do not support their claim. However, experimental studies under these high-pressure conditions are limited and there remain large uncertainties regarding the LPO at high pressures (P>3 GPa).

A Common Diffusional Mechanism for Creep and Grain Growth in Polymineralic Rocks: Application to Lower Mantle Viscosity Estimates

AbstractIn a previous study (Okamoto &amp; Hiraga, 2022, https://doi.org/10.1029/2022jb024638), we concluded that diffusion creep and grain growth in polymineralic rocks proceed by a common diffusional mechanism. Here, we built on that finding and estimated lower mantle grain size and viscosity during a single mantle convection cycle dominated by diffusion creep. We approximated the lower mantle as a two‐phase material consisting of bridgmanite + ferropericlase and post‐perovskite + ferropericlase, depending on depth. We used previously reported self‐diffusivities for bridgmanite and post‐perovskite. We predict a bridgmanite grain‐size of tens to hundreds of microns shortly after the phase transition at ∼660 km depth. This size remains relatively constant until the mantle material enters the post‐perovskite zone, which is marked by significant grain growth up to ∼9 mm just prior to upwelling. This size is sufficient to prevent further grain growth until the mantle material reaches the top of the lower mantle. These grain sizes combined with the diffusivities yield viscosities that vary laterally and with depth. At a lateral temperature difference of up to 800 K in the lower mantle, fine‐grained cold downwelling mantle is almost as viscous as, or more likely to be softer than coarse‐grained hot upwelling mantle. The lateral viscosity variations cannot be more than 2 orders of magnitude, and we estimated viscosities of 1018–1020 Pa · s in the upper lower mantle, 5 × 1020–5 × 1022 Pa · s in the lower bridgmanite zone, and 1017–1019 Pa · s in the post‐perovskite zone, which compare well with the values estimated in previous geophysical modeling studies.

Near-strain-free anode architecture enabled by interfacial diffusion creep for initial-anode-free quasi-solid-state batteries

Anode-free (or lithium-metal-free) batteries with garnet-type solid-state electrolytes are considered a promising path in the development of safe and high-energy-density batteries. However, their practical implementation has been hindered by the internal strain that arises from the repeated plating and stripping of lithium metal at the interlayer between the solid electrolyte and negative electrode. Herein, we utilize the titanium nitrate nanotube architecture and a silver-carbon interlayer to mitigate the anisotropic stress caused by the recurring formation of lithium deposition layers during the cycling process. The mixed ionic-electronic conducting nature of the titanium nitrate nanotubes effectively accommodates the entry of reduced Li into its free volume space via interfacial diffusion creep, achieving near-strain-free operation with nearly tenfold volume suppressing capability compared to a conventional Cu anode counterpart during the lithiation process. Notably, the fabricated Li6.4La3Zr1.7Ta0.3O12 (LLZTO)-based initial-anode-free quasi-solid-state battery full cell, coupled with an ionic liquid catholyte infused high voltage LiNi0.33Co0.33Mn0.33O2-based cathode with an areal capacity of 3.2 mA cm−2, exhibits remarkable room temperature (25 °C) cyclability of over 600 cycles at 1 mA cm−2 with an average coulombic efficiency of 99.8%.