Critical Grain Research Articles

An inverse Hall-Petch relationship during room-temperature compression of commercially pure magnesium

The effect of grain size and strain rate on the room-temperature compression of pure magnesium was investigated. Samples with equiaxed grains and grain size ranging over 1.4–88 µm were obtained by extrusion at different temperatures. The extruded samples were compressed at strain rate between 1 × 10−2 s−1 and 1 × 10−6 s−1. In microstructures with grain size greater than 15 µm, the deformation mechanism was dominated by twinning; while in those with grain size smaller than 8 µm, the dominant deformation mechanism was dislocation slip. In addition, significant grain-boundary sliding was observed with decreasing grain size and strain rate. The Hall-Petch relationship broke down with mean grain size smaller than a critical grain size, which increased with decreased strain rate. Further, the deformation mode (compression or tension) had a negligibly small effect on the critical grain size for changes in the dominant deformation mechanisms and the Hall-Petch breakdown. The changes in deformation mechanisms with grain size were understood in terms of the strain-rate sensitivity exponent m. When the grain size decreased from 88 µm to 1.4 µm, m increased to approximately 0.3 from 0.01. The increase in m with grain refinement was consistent with enhanced grain-boundary sliding, in addition to dislocation slip and the suppression of deformation twinning. It thereby reduced the asymmetry of the tension-compression yield strength.

Designing hetero-structured ultra-strong and ductile Zr-2.5Nb alloys: Utilizing the grain size-dependent martensite transformation during quenching

• A heterogeneous structured Zr-2.5Nb alloys were fabricated successfully utilizing the grain size-dependent martensite transformation. • The present Zr-2.5Nb alloys manifest the highest yield strength (∼710 MPa), together with a high ultimate tensile strength (∼844 MPa) and good ductility (∼17.1%). • A model based on the grain-size-dependent critical resolved shear stress for dislocation slip and twinning has been proposed to explain the α' martensite substructures transition at a critical grain size d c = 3.3 μm. To further improve the service performance of Zr-2.5Nb alloy worked as pressure tubes in pressurized heavy water reactors, more investigation about the microstructure and thermomechanical processing route of Zr-2.5Nb alloy need to be conducted. In this work, a hetero-structured Zr-2.5Nb alloy was prepared by applying a novel technique. Microstructure analysis reveals that the alloy exhibits a grain size-dependent martensite substructure transition during post-rolling quenching. The hetero-structure consists of equiaxed primary α grains and the lamellae groups containing both parallel α' dislocation martensite and α' twin martensite. Compared with the previously reported Zr-Nb alloys, the present Zr-2.5Nb alloys manifest the highest yield strength (∼710 MPa), together with a high ultimate tensile strength (∼844 MPa) and good ductility (∼17.1%). The enhanced mechanical properties are found to arise from the properly controlled fraction/size of the two types of martensite, which not only significantly strengthens the alloy but also contributes to a stronger strain hardening. A model based on the grain-size-dependent critical resolved shear stress for dislocation slip and twinning has been proposed to explain the α' martensite substructures transition at a critical grain size d c = 3.3 μm. Below this size, the critical resolved shear stress (CRSS) for twinning is higher than that for the <c + a> slip. Thus, the α' dislocation martensite is more favorable to form. Otherwise, the α' twin martensite would exhibit a high activity. The present work indicates that making use of the grain size-dependent martensite transformation to tailor the hetero-structure in Zr alloys is an effective strategy to overcome the strength–ductility trade-off in the material.

Riego deficitario en maíz y soja

In regions with temperate and humid climate such as Uruguay, supplementary irrigation stabilizes and increases crop yields. Irrigation on demand generates higher water consumption, which affects production system sustainability due to inefficient use of resources. In order to determine environmentally and economically more sustainable irrigation strategies, three maximum irrigation depths were evaluated in field experiment, (T2) 3 mm d-1, (T3) 6 mm d-1, (T4) 9 mm d-1 and (T1) control without irrigation, on corn and soybean production. Performance differences were observed in both crops at different water deficit levels. When precipitation (PP) was higher than average, its poor temporary distribution generated water deficit at specific times, affecting yield. T1 and T2 did not cover the crop evapotranspiration (ETc) during the critical period and grain filling, which lowered yields. T3 and T4 gave higher yields and in the three years average they were significantly different. T3 did not always cover the ETc, but the soil reserve and PP contributed to cover it, saving irrigation water. The AquaCrop model was calibrated for maize and different irrigation strategies were evaluated. The calibrated model simulated well yield, biomass and soil moisture in the irrigated treatments. In T1, the model underestimated the yield. The soil allowed for further root exploration. At 0.90 m depth, the model simulated well the yield in T1, mainly in the dry year. The model predicts the yield with a good adjustment at different irrigation and PP situations if the stress coefficients are adjusted and the crop is properly parameterized. Finally, T1, three maximum irrigation depths (3, 6 and 8 mm net) and three irrigation management (depleting 10 mm, depleting 50 % of readily available water (RAW) and depleting 100 % of RAW) were evaluated in maize with AquaCrop. The productive variables, irrigation requirement, energy demand and partial income analysis were analyzed, considering a maize crop irrigated by central pivot. It is concluded that 5 mm net gives returns and income similar to 8 mm net, without considering investment costs. Regarding management, depleting 100 % of the RAW has higher water productivity, but it is risky in dry years; however, it is feasible to vary the strategy depending on the climatic perspectives of each year.

A crystal plasticity based approach to establish role of grain size and crystallographic texture in the Tension–Compression yield asymmetry and strain hardening behavior of a Magnesium–Silver–Rare Earth alloy

Existence of tension – compression yield asymmetry is a serious limitation to the load bearing capablities of Magnesium alloys in a number of light weight structural applications. The present work is aimed at nullifying the tension to compression asymmetry problem and strain hardening anomalies in a Magnesium – Silver – Rare Earth alloy by engineering different levels of microstructural conditions via friction stir processing and post process annealing. The existence and extent of yield asymmetry ratio in the range of microstructural conditions was experimentally obtained through quasistatic tensile and compression tests. The yield asymmetry problem was profoundly present in specimens of coarse grained microstructures when compared to their fine grained and ultra fine grained counterparts. The impact of the microstructure and associated mechanisms of plasticity on the macroscopic strain hardening behavior was established by Kock – Mecking's analysis. Crystal plasticity simulations using Viscoplastic Self Consistency approach revealed the consequential role of extension twinning mechanism for the existence of yield asymmetry and anomalies in strain hardening behavior. This was especially dominant with coarsening of grain size. Electron Microscopy and characterization were conducted thoroughly in partially deformed specimens to confirm the predictions of the above simulations. The role of crystallographic texture for inducing the polarity to Tension – Compression yield asymmetry was corroborated. A critical grain size in Magnesium – Silver – Rare earth alloy was hereby established which could nullify influences of extension twinning in yield asymmetry ratio.

Application of critical path analysis to streaming potential coupling coefficient in porous media

Streaming potential is a passive hydrogeophysical method that can be used to monitor water flow in porous media. However, a quantitative use of this method requires a good understanding of the streaming potential generation in water saturated porous media. In this work, we used the Critical Path Analysis (CPA) method to propose a new model to estimate the streaming potential coupling coefficient (SPCC) in porous media. By comparing the proposed model with 109 experimental data points for both unconsolidated samples such as uniform glass bead and sand packs and consolidated samples such as sandstones, carbonates and with 36 simulated data points, we demonstrated that the CPA is applicable to model the SPCC for porous media with both narrow and broad pore size distributions. Additionally, from the obtained result for the uniform grain packings, we found the rc–d relationship between the critical pore radius rc and grain diameter d that was validated by using 70 experimental data points available in literature. The obtained rc–d relationship may be helpful for applications of CPA-based models for uniform grain packings. We believe that the CPA-based model is an useful alternative approach for modeling the streaming potential coupling coefficient in porous media along with two other models available in literature.

Grain Size Tailoring to Control Strain Hardening and Improve the Mechanical Properties of a CoCrFeNiMn High-Entropy Alloy

An equiatomic CoCrFeNiMn high-entropy alloy was processed by severe plastic deformation followed by post-deformation annealing over a range of temperatures and times leading to a wide range of grain sizes from ~ 0.05 to ~ 70 μm. The results demonstrate there is a sharp evolution in grain size and hardness after annealing above 800 °C due to coarsening facilitated by the dissolution of precipitates together with a high rate of diffusion at high temperatures. Grain growth behavior revealed an incremental low value grain growth exponent with increasing annealing temperature together with a high value activation energy for grain growth of ~ 440 kJ mol−1. A critical grain size of ~ 2 µm is proposed in which deformation-induced twinning is suppressed during plastic deformation. Nevertheless, slip and deformation-induced twinning are deformation mechanisms occurring in samples with grain sizes above this critical value. A model is presented for engineering the grain size by controlling the annealing parameters in the fine grain size range to benefit from the advantages of deformation-induced twining in the CoCrFeNiMn alloy.

Overcoming strength-ductility trade-off in high-entropy alloys by tuning chemical short-range order and grain size

The chemical short-range order (CSRO) and grain size affect the strength and ductility of high-entropy alloys (HEAs). However, their superposition effect has not yet been studied, limiting further improvement in performance. In this work, we examined the synergistic effect of the CSRO and grain size on the tensile properties of CoCrFeMnNi at room temperature by conducting atomic simulations, because performing an experimental investigation on the formation and movement of dislocations is difficult. The results showed that the preferable locations of the various elements were different. Cr and Mn were preferentially distributed on the grain boundary, Co and Fe were enriched inside the grain, and Ni accumulated in the transition zone from the grain boundary to the intragranular region. In addition, increasing the CSRO appropriately can optimize the density and distribution of dislocations, simultaneously enhancing the strength and ductility of HEAs. Furthermore, an inverse Hall-Petch relation was observed in the system without the CSRO. The simulation computation revealed that the critical grain size that induces the inverse Hall-Petch relation is approximately 13.1 nm. However, the presence of the CSRO eliminates the inverse Hall-Petch relation.

Atomic insights into effects of temperature and grain diameter on the micro-deformation mechanism, mechanical properties and sluggish diffusion of nanocrystalline high-entropy alloys

In this work, the effects of temperature and grain diameter on the micro- deformation mechanism, tensile properties, and sluggish diffusion of nanocrystalline Al0.1CoCrFeNi HEAs during uniaxial tension have been studied by molecular dynamics (MD) simulations. The Hall-Petch (H-P) relation and inverse Hall-Petch relation still exist in nanocrystalline HEAs. At the case of grain diameter over a critical size (e.g., DG>14.77 nm for 300 K), the deformation mechanism of HEAs is that the accumulation of dislocations at grain boundaries leads to the increase of HEAs strength, which conforms the H-P relation. At the case of grain diameter below a critical size (e.g., DG<14.77 nm for 300 K), the migration of grain boundaries, amorphization of atoms as well as the rotation and merging of grains becomes the main deformation mechanism of HEAs, which weaken the strength of HEAs and conform the reverse H-P relation. The increase of temperature has a negative influence on the mechanical properties including Young’s modulus, yield strength and flow stress of HEAs. The critical grain size that undergoes the H-P and reverse H-P relation transformation increases with the increase of temperature. An increase in grain boundary thickness and the appearance of a large number of discrete amorphous atoms in the grains can be observed at high temperatures. The shear strain of atoms at grain boundaries is larger than that of atoms in other regions, and high temperature promotes the increase of atomic shear strains in HEA, especially at grain boundaries. The lengths of all types of dislocation lines and dislocation densities tend to decrease with increasing temperature, and Shockley dislocations always dominate all other dislocations at 300–1200 K. The MSD results show that nanocrystalline HEA have good stability at 300–1200 K, and small-grained HEAs have higher MSD value and diffusion coefficient than those of large-grained HEAs at 1200 K. Moreover, at higher temperature (2500 K), the MSD values of HEAs with DG= 7.4–23.45 nm all increases significantly, and the time-dependent curves basically overlap, indicating that the influence of grain boundaries on atomic diffusion can be ignored.

Unravelling the Size‐Dependent Mechanical Properties of Nanocrystalline Face‐Centered‐Cubic Metals: From the Dislocation Point of View

The grain size dependence of strain rate sensitivity, apparent activation volume, and yield stress of nanocrystalline (NC) face‐centered‐cubic metals (FCC) are modeled based on the bow‐out model of single dislocation. It is found that the grain size limitation on the dislocation length gives rise to the grain size effects on the mechanical properties. The model gives predictions that when temperature is at or below room temperature and the strain rate is in the quasistatic range, dislocation‐mediated mechanisms play a dominant role in the plastic deformations of FCC NC metals even for the grain size of several nanometers, which is consistent with known experimental and simulation results. Based on the model, abnormal mechanical phenomena of nanostructured metals, such as the appearance of the inverse Hall–Petch relationship, the existence of the critical grain size, and its strain rate dependence, are well predicted and interpreted.

Effect of high-molecular-weight glutenin subunit Dy10 on wheat dough properties and end-use quality

High-molecular-weight glutenin subunits (HMW-GSs) are the most critical grain storage proteins that determine the unique processing qualities of wheat. Although it is a part of the superior HMW-GS pair (Dx5+Dy10), the contribution of the Dy10 subunit to wheat processing quality remains unclear. In this study, we elucidated the effect of Dy10 on wheat processing quality by generating and analyzing a deletion mutant (with the Dy10-null allele), and by elucidating the changes to wheat flour following the incorporation of purified Dy10. The Dy10-null allele was transcribed normally, but the Dy10 subunit was lacking. These findings implied that the Dy10-null allele reduced the glutenin:gliadin ratio and negatively affected dough strength (i.e., Zeleny sedimentation value, gluten index, and dough development and stability times) and the bread-making quality; however, it positively affected the biscuit-making quality. The incorporation of various amounts of purified Dy10 into wheat flour had a detrimental effect on biscuit-making quality. The results of this study demonstrate that the Dy10 subunit is essential for maintaining wheat dough strength. Furthermore, the Dy10-null allele may be exploited by soft wheat breeding programs.

Anomalous weakened annealing-induced hardening in extremely fine nanograined NiFe alloys

Annealing-induced hardening effect was studied in electro-deposited nanocrystalline Ni and NiFe thin films. Nanoindentation testing showed obvious hardening effect for all grain sizes in experiment, which were precisely controlled by adding Fe solutes. Contrast to the general trend in which the hardening effect monotonically increases with decreasing grain size, it enhanced firstly, peaking at a critical grain size (~ 16 nm) and then lowered. Based on the apparent inverse H-P trend and unusual enhancement of strain rate sensitivity after annealing, we attributed the weakened annealing-induced hardening phenomena, despite of the strongest grain boundary pinning effect resulted from the highest Fe solutes (up to 50 at%), mainly to the more pronounced grain-boundary mediated plasticity in extremely fine nanograins. This work contribute directly to understanding the distinct effect of alloying on mechanical properties of nanocrystalline metals.

Production of single-domain powders of europium iron garnet using supercritical fluid technology

• Controlled size powders of Eu 3 Fe 5 O 12 were obtained using SAS method; • Thermal decomposition stages of the obtained garnet precursors were considered; • Critical grain size for the transition to the single-domain state is 33 nm. In this work, nanosized precursors of the Eu 3 Fe 5 O 12 complex oxide – europium iron garnet – were prepared for the first time by the method of a supercritical antisolvent precipitation. It was shown that changing the synthesis parameters, namely, pressure, temperature, concentration of the initial solution and nozzle diameter, made it possible to obtain particles of controlled size from 20 to 80 nm. The obtained samples were characterized by a complex of physicochemical methods of analysis: IR spectroscopy, XRD, TG/DSC analysis, TEM. The main magnetic characteristics were obtained from powders annealed at 800 °C on a vibration magnetometer. The dependence of the magnetic characteristics on the grain size was established. The critical size of the transition to the single-domain state is 33 nm. The features of the garnet crystalline phase formation for samples with the smallest grain size and extended surface were revealed.

Electrodeposition of nanocrystalline Ni-Mo alloys in pyrophosphate baths

Nanocrystalline Ni-Mo alloy coatings with excellent brightness, high hardness, and corrosion resistance were prepared. Nanocrystalline Ni-Mo alloy coating with a Mo content of 14.94 at% was electrodeposited on the copper foil substrate under the optimized conditions with the current efficiency of 51.64%. The electrodeposition behavior of Ni-Mo alloy coatings was studied by cathodic polarization curve and chronopotentiometry. Chronopotentiometry showed that the nucleation rate of Ni-Mo alloys can be accelerated with the increase of current density. Meanwhile, the cathodic polarization curves show that the additives can effectively inhibit the electrodeposition of Ni-Mo alloys. The (2 0 0) and (2 2 0) diffraction peaks of Ni gradually disappeared and the grain size gradually decreased with the increase of Mo content in the alloy coating according to XRD and TEM analysis. Scanning electron microscope (SEM) and confocal microscope observation results show that the coating becomes smoother and denser with the increase of Mo content when Mo content was lower than 14.94 at%, after which the density of the coating saw a decline due to the intensified hydrogen evolution reaction. The microhardness results of the alloy coating show that the microhardness of the alloy coating is related to the solid solution strengthening, texture evolution, and plastic deformation of the alloy. Meanwhile, the alloy coating has a Hall-Petch relationship and inverse Hall-Petch relationship, and the critical grain size is 5.5 nm. The corrosion resistance of Ni-Mo alloy coating is better than that of pure Ni coating, and the corrosion resistance is optimal when the Mo content is about 15 at%. In addition, in the plating solution containing additives, the deposited Ni-Mo alloy coating is smoother and denser, and the hardness and corrosion resistance of the alloy coating is also greatly improved.

Atomistic simulations of plasticity heterogeneity in gradient nano-grained FCC metals

Gradient nano-grained (GNG) metals are an emerging class of heterogeneous structured materials with extraordinary mechanistic performances and unnatural plasticity mechanisms, which are unachievable in traditional homogeneous nanocrystalline metals. Here, the metal-type dependence of plasticity heterogeneity in three different GNG structured face-centered cubic metals (Cu, Al, and Ni) was studied by large-scale molecular dynamic simulation, from the plasticity perspectives of dislocation, deformation twinning, and grain boundary. The dislocation and deformation twinning-based plasticity show clear metal-type dependence in GNG structure of different selected metals. For grain boundary activities, GNG Cu, Al, and Ni are equivalent in the overall grain boundary sliding and micro-cracking process, but GNG Ni shows markedly higher grain boundary-free volume and stress due to the grain size gradient-induced twinning process. We find that GNG Al shows the weakest plasticity-induced strengthening due to its weak strain hardening and ununiform plasticity distribution, while GNG Ni exhibits prominent plasticity-induced strengthening because of the obvious extra strain hardening process. Besides, we further discuss the reasonable gradient grain size design of GNG structure, considering the critical grain size of the Hall-Petch and inverse Hall-Petch relationship, which will demonstrate a more rational plasticity heterogeneity and internal atomic stress distribution.

Critical scale grain size for optimal lifetime of TBCs

• The critical scale grain size d c of ∼2.5 μm is identified for optimal TBC lifetime. • When d < d c , the rapid growth of the scale causes delamination failure of TBCs. • When d > d c , the growth stress causes vertical cracking and early failure of TBCs. Thermal barrier coatings (TBCs) suffer from spalling failure resulting from the rapid growth of thermally grown oxides (TGO) on the metallic bond coat. In this study, to achieve the optimal lifetime of TBCs, a lifetime phase diagram was constructed for the entire service of TBCs. Herein, both the thermal mismatch stress during thermal cycling and the TGO growth stress during thermal exposure were considered. First, thickening behavior of the Al 2 O 3 scale related to grain size was investigated. Second, transverse delamination failure due to the thermal mismatch stress was analyzed. Third, vertical cracking failure related to early scale growth was explored. Finally, a critical scale grain size of ∼2.5 μm was identified for achieving the optimal lifetime of TBCs. It was experimentally proved that vertical cracking of the Al 2 O 3 scale occurred during early oxidation as the scale grain size was larger than ∼4 μm after pre-oxidation. The proposed lifetime phase diagram and critical scale grain size effect serve as novel criteria for the design of next-generation durable TBCs.

Determination of the degree of recrystallization of a microalloyed HSLA steel by using metallographic methods

Abstract On the one hand, this work aims at describing the grain elongation of compressed samples of a microalloyed high-strength steel using appropriate parameters. On the other hand, the degree of recrystallization is to be determined based on the samples’ grain elongation. For this purpose, single-hit compression tests were performed with varying test parameter settings using a deformation dilatometer to generate samples characterized by various degrees of recrystallization. Three parameters were chosen to describe the grain elongation. It was found that the parameter defining the ratio length/ width of the original grain provides the highest sensitivity regarding changes in the grain elongation. Aiming at determining the degree of recrystallization, a critical grain elongation threshold value was determined below which it is assumed that a grain is recrystallized. The results show that choosing the right threshold value allows an automated determination of the degree of recrystallization of a microalloyed high-strength steel in the light microscope.

The critical grain size for optimal strength–ductility synergy in CrCoNi medium entropy alloy

In metals with homogeneous microstructure, whether there is a critical grain size, and exactly at which, that enables the optimal strength-ductility synergy alongside the trade-off relation? Here, this issue is investigated in the recrystallized CrCoNi medium entropy alloys across a wide grain size range of 0.23-108 μm. Results reveal that there is indeed a critical grain size of ∼2 μm at which the product of yield strength (∼800 MPa) and uniform elongation (>30%) reaches the maximum, i.e., achieving the optimal strength-ductility synergy. Physics behind this critical grain size are explored by microstructure examination: (i) reduced grain size renders short dislocation slip path for high strength; (ii) low initial dislocation density and dense grain/twin boundaries enables effective accumulation of defects for consistent work hardening during plastic deformation.

Hydrogen trapping and desorption affected by ferrite grain boundary types in shielded metal and flux-cored arc weldments with Ni addition

Hydrogen trapping behavior and diffusion induced by the microstructure of shielded metal and flux-cored arc weldments (SMAW and FCAW) were characterized using a combination of high-resolution microstructural characterization methods, hydrogen trap site studies, and a modeling technique. H trapping by HAGBs that was found by TDS was confirmed by NanoSIMS with a cryogenic stage. Cellular automaton modeling results showed that in grain sizes smaller than a critical grain size, the hydrogen diffusion coefficient decreases with decreasing grain size, indicating that H trapping dominates short-circuit diffusion mechanism along high-angle grain boundaries (HAGBs). These results firstly show that smaller grain size and high HAGB density in the FCAW specimen results in a lower H diffusion coefficient and higher density of relatively strong HAGB traps, and a lower total desorbed hydrogen content in the FCAW specimen. Also, it was suggested that the fraction of acicular ferrite grains can define the HAGB content in the alloy, and can be a determinant factor in the behavior of weldments in H-containing media.

Molecular dynamics studies of grain boundary mobility and anisotropy in BCC γ-uranium

Grain morphologies such as grain size and aspect ratio in uranium-based metallic fuels are important microstructural features that can impact various fuel performance properties such as fission-gas-induced swelling, thermal transport, high burnup structure formation, and radiation resistance. Accurate prediction of the fuel grain morphologies requires knowledge of critical grain growth parameters such as grain boundary (GB) mobility and anisotropy. In this work, molecular dynamics (MD) simulations were performed to study the GB mobility and its anisotropy in pure body-centered-cubic (BCC) γ uranium. Nine GBs with different combinations of misorientation angles (20°, 30°, 45°) and rotation axes (<100>, <110>, <111>), as well as an additional <111> 38.2° GB were studied using three interatomic potentials. It is found that the GB mobility anisotropy has complex trends, depending on both rotation axis and misorientation. However, in general the <110> rotation axis has the fastest GB mobility at the same misorientation. The results of this work can be used as not only a baseline for future studies of GB mobility in uranium-based alloys such as uranium-molybdenum (U-Mo) fuels, but also input for mesoscale modeling of grain growth in uranium-based alloys.

Examination of critical grain size of isotropic nanocrystalline iron through molecular dynamics analysis

ABSTRACT The critical grain size for isotropic nanocrystalline pure iron was investigated utilizing Molecular Dynamics (MD). First, number of grains required for isotropic behaviour was determined utilizing statistically significant grain counts – alleviating challenges faced in simulation of nanocrystalline materials. The current investigation provides a thorough guideline for simulating isotropic nanocrystalline materials. Second, an investigation into the effect of strain rate was performed to demonstrate its effect on mechanical properties of pure, isotropic nanocrystalline iron. Next, the critical grain size of pure nanocrystalline iron was investigated, indicating the change from Hall-Petch to inverse Hall-Petch. It was shown that MD of an isotropic pure nanocrystalline iron structure possessed a clearly defined critical grain size through examination of flow stress and maximum stress. It was shown that neither elastic modulus nor Poisson’s ratio were viable indicators for a critical grain size, instead, both tended towards their macroscale equivalent. Alternatively, yield stress may be viable, but was not recommended due to varying definitions for what exactly constitutes the yield point. Lastly, an investigation into the microstructure was performed near the critical grain size and at the extremes of grain sizes investigated. This highlighted the microstructural behaviour within both Hall-Petch and inverse Hall-Petch regimes throughout straining.