Role Of Grain Size Research Articles

Thermomechanical response and crack evolution of sandstone at elevated temperatures

Understanding the thermomechanical response of rock at high temperatures is crucial for various energy applications such as underground coal gasification and geothermal systems. The study investigated the effects of temperature, mineral composition, and grain size on crack initiation (CI) and crack damage (CD) thresholds in Jodhpur sandstones using uniaxial compressive strength with acoustic emission, Brazilian tensile strength, and thermogravimetric analysis subjected to elevated temperatures. The study revealed distinct patterns in crack initiation stress threshold ratios (CISTR) and crack damage stress threshold ratios (CDSTR) influenced by mineral composition and grain size under temperature treatments. Ferruginous quartz arenite exhibited an inverse relationship between quartz content and crack initiation/damage stress thresholds, while siliceous quartz arenite and subarkose showed a positive correlation. The established variation is attributed to the differing grain boundary strengths among the minerals. Comparative analysis of crack thresholds with the minerals, excluding quartz and feldspar, revealed complex relationships with clay and other minerals. Finer-grained sandstones showed direct proportionality in CI and CISTR with clay content, while coarser sandstones exhibited an inverse relationship. Additionally, the study highlighted differential trends in toughness parameters and CISTR, emphasizing the role of grain size and heat-treatment conditions in governing stress thresholds. Significant chemical changes, including quartz phase shifts and kaolinite/muscovite dehydroxylation, occurred in sandstones at 500–600°C. The presence of kaolinite/hematite in ferruginous quartz arenite caused the increased mass loss in pure O2 due to kaolinite breakdown, while siliceous quartz arenite exhibited a greater mass loss in standard conditions. The findings suggest that quartz content does not consistently enhance rock strength under heat treatment, particularly in the presence of significant clay minerals, leading to an inverse quartz-rock strength relationship in ferruginous quartz arenites. The study provides valuable insights into the thermomechanical behavior of sandstones, which is crucial for assessing rock stability and durability in energy applications.

Role of grain size and anisotropy of neighboring grains in hydrogen‐assisted intergranular fatigue crack initiation in austenitic stainless steel

AbstractThis study explores the impact of microstructural features on fatigue crack initiation in poly‐crystalline materials, emphasizing hydrogen‐induced complexities. Grain anisotropy, misorientations, grain size variations, and elastic–plastic inhomogeneities concentrate stress at grain boundaries, making them susceptible to crack initiation during fatigue loading. The presence of hydrogen compounds this process, due to complications of characterization of local hydrogen content and activating embrittling mechanisms. Building upon a model for nickel, this research investigates 316L austenitic stainless steel specimens with varying grain sizes, both uncharged and hydrogen‐charged. In situ low‐cycle fatigue loading experiments establish correlations between fatigue crack initiation and microstructural features. The study reveals specific combinations of features crucial in the initiation process, undergoing alterations in the presence of hydrogen. A proposed qualitative model links microstructural features with accumulated plastic shear strain during fatigue and prevalent hydrogen embrittlement mechanisms like hydrogen‐enhanced local plasticity and hydrogen‐enhanced decohesion.

Role of grain size in the evolution of stress-induced martensite and the tensile deformation behavior of Ti-7333 alloy

The evolution of martensite and the tensile deformation behavior of Ti-7333 alloy with different β grain size was studied. It is found that the β grain size (45–260 μm) significantly affects the triggering stress of stress-induced α″ martensite (SIMα″), and then affects the distribution and morphology of α″ martensite. At the initial stage of deformation, the larger β grain can inhibit the stress-induced secondary α″ martensitic transformation and the formation of α″ twinning. While under the same strain, the stress-induced martensite and martensite twinning can be activated simultaneously in the alloy with the smaller β grain, including {111}α″ type Ⅰ twinning, {130}<310>α″ compound twinning, <211>α″ type Ⅱ twinning, {021}<512>α″ type Ⅱ twinning, which can effectively accommodate localized strains and improve the work hardening rate of Ti-7333 alloy. When the β grain size varies in the range of 45–84 μm, there is a higher work hardening plateau in the deformation stage II of Ti-7333 alloy. The yield strength and β grain size are in accordance with the Hall-Petch relation. As the grain size increases to 128 even to 260 μm, the work hardening rate continues to decrease and the yield strength inversely increases. It is demonstrated that the triggering stress for SIMα″ exhibits U-shaped fluctuations as β grain size increases, and the inflection point of Ti-7333 alloy is between 84 μm and 260 μm.

Transport and retention of nanobubbles in saturated porous media: Overlooked role of grain size and shape

Nanobubbles (NBs) are widely used in groundwater pollution treatment due to their unique properties such as small size and high gas mass transfer rate. Therefore, the transport behavior of NBs in the groundwater environment has attracted more attention. Due to the diversity and complexity of aquifer media in the natural environment, grain sands with different sizes and shapes are ubiquitous. Thus, consideration of grain size and shape in porous media is crucial to predict and evaluate the transport and fate of NBs in soil and groundwater systems. This work investigated the stability of NBs in pure water. The transport behavior and mechanism of NBs under different grain sizes and shapes were demonstrated by the column experiment, microscopic observation, and numerical simulation. The results showed that NBs had excellent stability, remaining in solution for more than 10 days. The retention of NBs in coarse, medium and fine sands was 23.5 %, 43.8 % and 50.8 %, respectively. The retention in sphere sands, oval sands and irregular sands was 22.9 %, 24.0 % and 43.8 %, respectively. The smaller grain size and roundness limited the NBs transport in the saturated porous media, which was mainly due to the complexity of the flow channel and the narrowing of the pore throat of fine sands and angular shape of irregular sand that would hinder the NBs transport. This was proved by the Derjaguin − Landau − Verwey − Overbeek (DLVO) theory and ultra − depth − of − field microscope. The BTCs of NBs were fitted by the one − site deposition model (only attachment) and two − site deposition model (attachment and straining), and it was found that two − site deposition model showed a better fit. The straining rate (kstr) was greater than the attachment rate (katt) in different grain sizes and shapes media, indicating that the retention mechanism of NBs in porous media was a synergistic mechanism dominated by pore straining and supplemented by electrostatic attraction.

Influence of grain size on electromechanical properties of (Ba,Ca)(Zr,Ti)O3: A multiscale analysis using spark plasma sintering and aerosol deposition

The piezoelectric and ferroelectric properties of aerosol deposited (AD) thick ceramic films are significantly reduced in comparison to bulk materials, which is assumed to be largely related to the nanometer-sized grains (∼0.01 μm) observed in the resulting microstructures. This work, therefore, focuses on understanding the role of grain size in electromechanical properties within the range of AD films based on Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT). In a comprehensive compilation of the piezoelectric constant (d33) of samples from various studies the grain size dependency of the d33 was shown for the lead-free ferroelectrics BCZT, BaTiO3, and (K,Na)NbO3. In this, it can be seen that no BCZT sample with a grain size below 0.4 μm was analyzed regarding their d33 before, thereby leaving a gap to the grain size of AD films. In this study, the grain size of ceramic bulk samples was varied using spark plasma and conventional sintering (0.1 μm – 11 μm) and their properties compared to those of AD films. To enable the fabrication of bulk samples in the same range as AD films, a hydrothermal powder with an average particle size of 0.075 μm was synthesized. A continuous increase of the permittivity, the polarization, and the piezoelectric coefficient was observed through grain size increase. These results suggest that the grain size of AD films needs to be enhanced to improve their properties. Importantly, the insights of this multiscale analysis on the grain size can help to tailor also the properties of other BCZT films and bulk samples.

The role of grain size in achieving excellent properties in structural materials

Advanced structural materials are expected to display significantly improved mechanical properties and this may be achieved, at least in part, by refining the grain size to the submicrometer or the nanocrystalline range. This report provides a detailed summary of the role of grain size in the mechanical properties of metals. The effect of grain size on the high temperature behavior and the development of superplasticity is illustrated using deformation mechanism maps and the development of exceptional strength through grain refinement hardening at low temperatures is also discussed. It is shown that the deformation mechanism of grain boundary sliding, as developed theoretically, can be used to effectively predict both the high and low temperature behavior of metals having different grain sizes. This analysis explains the increase in strain rate sensitivity in ultrafine-grained metals with low and moderate melting points and the ability to increase both the strength and ductility of these materials to thereby overcome the strength-ductility paradox. The recent development of hybrid materials is also reviewed and it is demonstrated that, although these hybrids have received only limited attention to date, they provide a potential for making significant advances in the production of new structural materials.

The Role of Grain Size in the Mechanical Properties of Metals

It is now well established that the grain size is the fundamental microstructural feature of all polycrystalline materials. In practice, a very wide range of grain sizes will be needed in order to fully evaluate the effect of grain size on the mechanical properties of metals. For many years this was a significant limitation because it was not possible to use conventional thermomechanical processing to produce materials with submicrometer or nanometer grain sizes. Recently, this problem has been addressed by developing alternative processing techniques based on the application of severe plastic deformation. This overview demonstrates that, although the flow stress increases with decreasing grain size at low temperatures and decreases with decreasing grain size at high temperatures, this clear dichotomy in behavior may be adequately explained by using a single theoretical flow mechanism based on the occurrence of grain boundary sliding.

Proton irradiation, tribological and corrosion characteristics of Fe-Ni based ODS alloys

In the current study, Fe–42% Ni–2% Y2O3–2%Ti (2Ti) and Fe–42% Ni–2% Y2O3–2%Ti-2%Al (2AlTi) (All in wt%) invar-based alloys were investigated thoroughly under extreme environmental conditions including wear resistance, proton irradiation characteristic, and corrosion behavior. Both the compositions were developed by mechanical alloying (MA) followed by spark plasma sintering (SPS). The phase evolution characteristics and microstructural features of sintered samples were investigated through x-ray diffraction (XRD), and electron backscatter diffraction (EBSD) and TEM analysis. The influence of proton irradiation damage on micrographic features as well as on hardness values of the sintered samples was studied in detail to understand the roles of grain size and complex dispersoids on irradiation damage. Grain boundary seems to play as radiation sinks, whereas regions of dispersoids are found to remain unaffected by proton irradiation. A detailed tribological study was conducted on the sintered samples at 20, 300, and 500 °C to understand the effect of temperature, and correlation between the microstructural constituents and wear mechanisms. Analysis of wear data revealed that material loss is gradually reduced with increase in temperature, especially in the 2AlTi sample, due to fast evolution of Al-containing glossy oxide layer providing a better lubricating film to prevent from further wear. Wear mechanism is gradually changed from adhesive to abrasive wear with increase in temperature due to the development of finer glossy protecting oxide debris. In contrast to the wear behaviour, potentiodynamic polarization test analysis of the sintered samples (conducted in an electrolyte of 3.5% NaCl) revealed that the Al-containing alloy showed rigorous degradation (huge pitting) due to the presence of coarser Al-rich Y-Al-O dispersoids in fine grained matrix.

Grain-size variability in debris flows of different runout lengths, Wenchuan, China

Debris-flow grain-size distributions (GSDs) control runout length and mobility. Wide, bimodal GSDs and those containing a higher proportion of silt and clay have been shown experimentally to increase runout length. However, the relationship between grain size and mobility has not been well established in field conditions. Here, we compared the grain-size characteristics of two debris flows with considerably different runout lengths (1.5 km vs. 8 km) to understand the role of grain size in governing runout. The two debris flows were triggered in the same rainfall event from coseismic landslide debris generated in the 2008 Wenchuan earthquake in catchments with similar lithology and topography. We compared the deposited GSDs and their spatial patterns using our rare, three-dimensional GSD datasets. Surprisingly, the proportions of each size fraction deposited by the two flows were statistically indistinguishable. The spatial pattern of grain size differed between the two flows, with evidence of inverse grading only preserved in the smaller deposit. From these observations, we can infer that the GSDs of both flows were determined by the coseismic landslide source material, and that there was little difference in the GSDs of material entrained as the flows bulked. The contrasting spatial distributions of grains indicated that different internal processes were dominant within the two flows. These findings demonstrate that where GSDs are dominated by coarse grains and are governed by similar source conditions, grain size plays a lesser role relative to sediment supply and hydrology in controlling the runout length of large catastrophic post-earthquake debris flows.

Addressing the strength-ductility trade-off in a thermomechanical-processed high entropy alloy

High entropy alloys (HEAs) have garnered significant attention due to their exceptional mechanical behavior. However, the influence of secondary phases and dislocation substructures has yet to be thoroughly investigated. This study focuses on the incorporation of the decomposed η-phase within a face-centered cubic (FCC) microstructure at different recrystallization levels, aiming to achieve adequate ductility while maintaining strength at gigapascal levels. Various characterization techniques were employed to analyze the microstructure of both homogenized and annealed+aged conditions. Implementing a sub-micron grain size distribution and introducing a favorable dislocation substructure significantly enhanced the mechanical properties of yield strength, ultimate tensile strength, and ductility, reaching up to 1291 MPa, 1450 MPa, and 17.5%, respectively. The results highlight the influential role of grain size in facilitating the generation of geometrically necessary dislocations during plastic deformation.

Dependence of coercivity, relative permeability and magnetic losses on oscillating magnetic field frequencies and maximum polarisation for NGO and HGO steels

This study investigated two types of electrical steels: high permeability grain oriented (HGO) 3.25 wt%Si and 0.25 mm thick and two non-grain oriented (NGO) grades 2 wt%Si and 0.50 mm and 0.54 mm thick The dependence of the frequency of the external magnetic field H and maximum polarisation Jmax on the different magnetic losses (hysteresis, classical and excess), coercivity, relative permeability were investigated over a wide frequency range of 3-2000 Hz (10 and 100 Hz increments for low and high frequencies, respectively), and Jmax range of 0.1–1.5 T (0.1 T increment). With this large data set it was observed that the relative permeability as a function of Jmax exhibited a maximum at approximately 1.1 T (HGO) and 0.8 T (NGOs), and the coercivity was dependent on the frequency up to 2000 Hz. Further, the remanence increased up to frequencies of 250 Hz and then became constant. All these distinct dependencies with f and Jmax show the key role of grain size, morphology and crystallographic and magnetic texture on magnetic properties. Furthermore, a scenario showing the component losses that dominated under certain frequency and Jmax ranges was established; we found that the hysteresis loss was dominant for the NGO at frequencies up to 100 Hz and Jmax up to 1 T, whereas the excess loss was the smallest of all in the entire range studied. Above this 1 T field, the classical loss was the most expressive. Regarding HGO, another scenario was observed; the excess loss was the highest of all up to 500 Hz with Jmax up to 0.4 T, and the classical loss dominated above 400 Hz. This clearly shows that different scales in the magnetisation process relate different physical mechanisms (the wall pinning domain and magnetic domain), which regulate the loss components. Thus, our contribution shows the processes and/or parameters that must be considered to tune a certain magnetisation scale to obtain the best material efficiency and thus the best possible performance of a device.

Electrochemical performance of heat-treated beta titanium alloy in artificial saliva: Key role of grain size

The corrosion response of heat-treated Beta C titanium alloy in three distinct electrolytes at different temperatures was examined. All the recrystallized specimens with the random orientation of the grains showed similar corrosion behavior in fluoride-free electrolytes, whereas, in the case of fluoridated saliva a state transition occurred. Larger grain-sized specimens (900 ⁰C treated) with lower in-grain misorientation ensured higher corrosion resistance. XPS investigation confirmed that stable TiO2 passive film played a key role in preventing corrosion. Optimum combination of grain size and grain boundary energy developed for 900 ⁰C specimens is appropriate for usage in fluoride-treated dental works.

The role of grain size in active galactic nuclei torus dust models

Context. Active galactic nuclei (AGN) are surrounded by dust within the central parsecs. The dusty circumnuclear structures, referred to as the torus, are mainly heated by radiation from the AGN and emitted at infrared wavelengths, producing the emergent dust continuum and silicate features. Fits to the infrared spectra from the nuclear regions of AGN can place constraints on the dust properties, distribution, and geometry by comparison with models. However, none of the currently available models fully describe the observations of AGN currently available. Aims. Among the aspects least explored, here we focus on the role of dust grain size. We offer the community a new spectral energy distribution (SED) library which is based on the two-phase torus model developed before with the inclusion of the grain size as a model parameter, parameterized by the maximum grain size Psize or equivalently the mass-weighted average grain size ⟨P⟩. Methods. We created 691 200 SEDs using the SKIRT code, where the maximum grain size can vary within the range Psize = 0.01 − 10.0 μm (⟨P⟩ = 0.007 − 3.41 μm). We fit this new library and several existing libraries to a sample of 68 nearby and luminous AGN with Spitzer/IRS spectra dominated by AGN-heated dust. Results. We find that the GoMar23 model can adequately reproduce up to ∼85–88% of the spectra. The dust grain size parameter significantly improves the final fit in up to 90% of these spectra. Statistical tests indicate that the grain size is the third most important parameter in the fitting procedure (after the size and half opening angle of the torus). The requirement of a foreground extinction by our model is lower compared to purely clumpy models. We find that ∼41% of our sample requires that the maximum dust grain size is as large as Psize ∼ 10 μm (⟨P⟩∼3.41 μm). Nonetheless, we also remark that disk+wind and clumpy torus models are still required to reproduce the spectra of a nonnegligible fraction of objects, suggesting the need for several dust geometries to explain the infrared continuum of AGN. Conclusions. This work provides tentative evidence for dust grain growth in the proximity of the AGN.

Grain‐Size Effects During Semi‐Brittle Flow of Calcite Rocks

AbstractWe study the role of grain size in the rheological behavior of calcite aggregates in the semi‐brittle regime. We conduct compressive triaxial deformation tests on three rocks, Solnhofen limestone, Carrara marble and Wombeyan marble, with grain sizes of 5–10, 200, and 2 mm, respectively, at pressures in the range 200–800 MPa and temperatures in the range 20–400°C. At all conditions, both strength and hardening rate increase with decreasing grain size. Flow stress scales with the inverse of grain size to a power between 1/3 and 2/3. For a given pressure and temperature, the typical strength of Solnhofen limestone (grain size 5–10 μm), is greater than that of Wombeyan marble, (grain size of around 2 mm), by about 200–300 MPa (i.e., around a factor of 2). Hardening rate decreases linearly with the logarithm of grain size. In situ ultrasonic monitoring reveals that P‐wave speed tends to decrease with increasing strain, and that this decrease is more marked at room temperature than at 200 and 400°C. The decrease in wave speed is consistent with microcracking, which is more prevalent at low temperature and low pressure. Microstructural observations reveal high twin densities in all deformed samples. Twin density increases with stress, consistent with previous datasets. Spatial distributions of intragranular misorientation indicate that twins are sometimes obstacles to dislocation motion, but this effect is not ubiquitous. Computed slip‐transfer statistics indicate that twins are typically weaker barriers to dislocation glide than grain boundaries, so that their effect on dislocation accumulation and hardening rates is likely smaller than the effect of grain size.

Role of grain size and shape on undrained monotonic shear, liquefaction, and post-liquefaction behaviour of granular ensembles

This paper presents a fundamental study to explore the independent effects of grain size and shape on the pre-liquefaction, liquefaction, and post-liquefaction shearing behaviour of granular ensembles through a series of multi-stage constant volume simple shear tests. Three different granular materials (glass ballotini, river sand, and manufactured sand) of three different sizes (fine, medium, and coarse) with distinct shape descriptors were chosen for the study. Shape parameters of the granular materials, including roundness, sphericity, regularity, and angularity, and their grain level kinematic behaviour were determined from the microscopic images using image analysis algorithms. Experiments were carried out on reconstituted specimens prepared at different relative densities of 15, 30, and 45%, and the results were interpreted in the light of the critical state framework. Undrained monotonic shear tests showed that ensembles with similar grain shapes exhibit a unique critical state line (CSL) and also exhibit a unique phase transformation line (PTL), irrespective of the grain size. However, ensembles with different grain shapes exhibited different CSLs and different PTLs. Irrespective of grain shape, an increase in grain size increased the liquefaction resistance because of an increase in the tendency for dilation. Irrespective of grain size, an increase in particle angularity and irregularity increased the liquefaction resistance due to an increase in the interlocking tendency at grain contacts. Grain size and shape significantly affected the post-liquefaction shear strength of the granular ensembles. The post-liquefaction initial and secondary shear moduli were found to be highly dependent on the grain size and shape.

Technical note: colab_zirc_dims: a Google Colab-compatible toolset for automated and semi-automated measurement of mineral grains in laser ablation–inductively coupled plasma–mass spectrometry images using deep learning models

Abstract. Collecting grain measurements for large detrital zircon age datasets is a time-consuming task, but a growing number of studies suggest such data are essential to understanding the complex roles of grain size and morphology in grain transport and as indicators for grain provenance. We developed the colab_zirc_dims Python package to automate deep-learning-based segmentation and measurement of mineral grains from scaled images captured during laser ablation at facilities that use Chromium targeting software. The colab_zirc_dims package is implemented in a collection of highly interactive Jupyter notebooks that can be run either on a local computer or installation-free via Google Colab. These notebooks also provide additional functionalities for dataset preparation and for semi-automated grain segmentation and measurement using a simple graphical user interface. Our automated grain measurement algorithm approaches human measurement accuracy when applied to a manually measured n=5004 detrital zircon dataset. Errors and uncertainty related to variable grain exposure necessitate semi-automated measurement for production of publication-quality measurements, but we estimate that our semi-automated grain segmentation workflow will enable users to collect grain measurement datasets for large (n≥5000) applicable image datasets in under a day of work. We hope that the colab_zirc_dims toolset allows more researchers to augment their detrital geochronology datasets with grain measurements.

Role of Grain Size and Recrystallization Texture in the Corrosion Behavior of Pure Iron in Acidic Medium

This work investigates the role of grain size and recrystallization texture in the corrosion behavior of pure iron in 0.1 M sulfuric acid solution. Annealing heat treatment was applied to obtain samples with different average grain sizes (26, 53 and 87 µm). Optical microscopy, X-ray diffraction and electron backscatter diffraction techniques were used to characterize the microstructure. The EBSD data analysis showed ferrite phase with no inclusions and very low geometrically necessary dislocation density, indicating strain-free grains constituting all samples. The crystallographic texture analysis of the samples revealed that the 26 µm grain size sample had a high volume fraction of {111} oriented grains parallel to the sample surface, while other samples exhibited nearly random crystallographic texture. The electrochemical results from potentiodynamic polarization and electrochemical impedance spectroscopy showed a decrease in corrosion resistance from 87 µm to 53 µm grain size sample and then an increase for the 26 µm grain size sample. This increase was attributed to the dominant effect of recrystallization texture on the corrosion behavior of the sample. The cathodic hydrogen evolution reaction kinetics was found to play a decisive role in the corrosion behavior of iron.

Relationship between Grain Size and Sample Thickness on the Creep-Rupture Performance of Thin Metallic Sheets of INCONEL Alloy 740H

A study was conducted on INCONEL® alloy 740H® to examine the role of grain size and sheet thickness on the alloy’s creep-rupture behavior. Three different starting sheet thicknesses were utilized and multiple heat-treatment conditions anticipated for compact heat exchanger (CHX) manufacturing were applied to produce a range of grain sizes. Creep-rupture testing was conducted at 750 °C for times up to about 6000 h and the results were compared to wrought databases. The data show that both creep strength and ductility were important factors in the overall creep performance of the sheets. Reductions in performance were observed due either to accelerated creep when grain size was fine or loss of rupture ductility when grain sizes approached the sheet thickness. Some combinations of heat-treatment and thickness were able to produce typical expected wrought creep properties. Historically a ‘rule-of-thumb’ requirement for creep testing suggests 3-5 grains per sample minimum dimension to ensure homogeneous behavior. This research shows that to ensure representative wrought creep performance (i.e. no effect of sample size), the sample minimum cross-section should be 10 times the average ASTM grain size. Statistical analysis of the microstructures suggests the population of larger grains as a controlling feature in creep failure.

Physical insights into the grain size effect on the electrical properties of nanocrystalline La2Zr2O7 pyrochlores

The role of grain size on the electrical properties of nanocrystalline La2Zr2O7 (LZO) ceramics prepared by chemical co-precipitation is reported. Grain size from 10 to 70 nm was obtained. The XRD and Raman scattering showed a pyrochlore structure of La2Zr2O7. Morphology and chemical analysis were done by SEM and XPS, respectively. Electrical conductivity studies using impedance spectroscopy resolved the conductivity borne to grain and grain boundary with a non-Debye nature of conduction. The activation energy (Ea) for electrical conduction through grain was almost the same for all the grain sizes and equal to 1.20 ± 0.03 eV. However, the Ea of the grain boundary had decreased from 1.17 eV to 0.78 eV with an increase in grain size, and the conduction is due to oxygen ion migration. The conduction mechanism was governed by the non-overlapping small polaron tunneling model. Additionally, ion-ion correlation in conduction is increased with increasing grain size.

Grain Growth upon Annealing and Its Influence on Biodegradation Rate for Pure Iron.

Biodegradable pure iron has gained significant interest as a biomedical material. For biodegradable implant applications, the biodegradation behavior of pure iron is important. In this work, the influence of ferrite grain size on the biodegradation rate for pure iron was studied by means of heat treatment that was annealed below the austenized temperature using as-forged pure iron. Grains were coarsened and a spectrum of ferrite grain sizes was gained by changing the annealed temperature. Biodegradation behavior was studied through weight loss tests, electrochemical measurements and microscopic analyses. Hardness (HV) and biodegradation rate (Pi or Pw) were linearly ferrite grain size-dependent: HV=58.9+383.2d-12, and Pi=-0.023+0.425d-12 or Pw=0.056+0.631d-12. The mechanism by which the role of grain size on biodegradation rate was attributed to the ferrite grain boundary traits.