Order-disorder Transformation Research Articles

Grain boundary strengthening in ZrB2 by segregation of W: Atomistic simulations with deep learning potential

Interaction between grain boundaries and impurities usually leads to significant altering of material properties. Understanding the composition-structure-property relationship of grain boundaries is a key avenue for tailoring and designing high performance materials. In this work, we studied segregation of W into ZrB2 grain boundaries by a hybrid method combining Monte Carlo (MC) and molecular dynamics (MD), and examined the effects of segregation on grain boundary strengths by MD tensile testing with a fitted machine learning potential. It is found that W prefers grain boundary sites with local compression strains due to its smaller size compared to Zr. Rich segregation patterns (including monolayer, off-center bilayer, and other complex patterns); segregation induced grain boundary structure reconstruction; and order-disorder like segregation pattern transformation are discovered. Strong segregation tendency of W into ZrB2 grain boundaries and significant improvements on grain boundary strengths are certified, which guarantees outstanding high temperature performance of ZrB2-based UHTCs.

Interpretation of Fe-rich part of Fe–Al phase diagram from magnetic properties of A2-, B2-, and DO3-phases

Iron-rich Fe–Al binary phase diagram in the composition range of 23–26 at% Al shows a complex structure partly due to magnetic properties of the disordered A2-phase, the ordered B2-phase and the ordered DO 3 -phase. In this study, the disorder-order transformations between the constituent phases have been investigated through magnetization measurements of Fe- x Al alloys ( x = 22.0, 24.0, 24.3, 24.7, 26.5 at%). It is found that spontaneous magnetization of the B2-phase is larger than that of the DO 3 -phase and smaller than that of the A2-phase. The former relation disagree with previous reports but was further confirmed as the decrease of the B2-DO 3 transformation temperature under magnetic field (−1.58 K/T). It is also found that the Curie temperature of the B2-phase (836 K for Fe-24.7 at%Al alloy) coincides with that of the A2-phase; furthermore, these temperatures agree with the phase boundary between B2-region and (A2+B2)-region. • Temperature dependence of spontaneous magnetization was evaluated for the A2-, B2- and DO3-phases of Fe24.7at%Al alloy, and found that the value decreases in this order at any temperature. • Magnetic field dependence of B2-DO3 transformation temperature was evaluated for several Fe-Al alloys, and confirmed that it decreases as magnetic field increases. • Critical behavior for the magnetic transition was analyzed for several Fe-Al alloys and revealed that Curie temperature of the B2-phase almost coincides with that of the A2-phase.

Ultrahigh hardness and biocompatibility of high-entropy alloy TiAlFeCoNi processed by high-pressure torsion.

Despite significant studies on mechanical properties of high-entropy alloys (HEAs), there have been limited attempts to examine the biocompatibility of these alloys. In this study, a lattice-softened high-entropy alloy TiAlFeCoNi with ultrahigh hardness (examined by Vickers method), low elastic modulus (examined by nanoindentation) and superior activity for cell proliferation/viability/cytotoxicity (examined by MTT assay) was developed by employing imperial data and thermodynamic calculations. The designated alloy after casting was processed further by high-pressure torsion (HPT) to improve its hardness via the introduction of nanograins, dislocations and order-disorder transformation. The TiAlFeCoNi alloy with the L21-BCC crystal structure exhibited 170-580% higher hardness and 260-1020% better cellular metabolic activity compared to titanium and Ti-6Al-7Nb biomaterials, suggesting the high potential of HEAs for future biomedical applications.

Deformation behavior of annealed Cu64Zr36 metallic glass via molecular dynamics simulations

In the present work, we investigate the isothermal annealing process of Cu64Zr36 metallic glass (MG) by means of molecular dynamics (MD) simulations, and characterize the compression properties under different temperatures and compressive rates. The pair distribution functions, the bond-orientational order, and the cluster-type index method are modeled and analyzed to characterize changes in the structure. Results of the modeling and analysis reveal that the MgZn2-type Laves, MgCu2-type Laves and five-fold local symmetry structures can be formed during the isothermal holding at 950 K. Study on the compression properties shows that at a fixed strain rate, the yield strength and yield drop all increase with decreasing temperature. At a fixed temperature, however, the increase of the strain rate leads to a noticeable increase in the yield strength at 600 K, but has little effect on yield strength at 10 K. Moreover, the modeling and analysis of the structure at a temperature of 10 K and strain-rate of 5 × 107 s−1 demonstrate that the order-disorder transformation initiates the shear band.

Controlling crystallographic ordering in Mo–Cr–Ti–Al high entropy alloys to enhance ductility

Refractory high entropy alloys (RHEAs) from the Mo–Cr–Ti–Al system exhibit promising strength at elevated temperatures. However, at room temperature they possess a B2-ordered crystal structure and, therefore, exhibit reduced ductility. Guided by thermodynamic calculations, the Al concentration was systematically reduced in MoCrTi-xAl (x = 25, 15, 10, 5, 3 at%) in order to achieve a disordered, solid solution with A2-type crystal structure even at room temperature. The alloys were manufactured by arc melting followed by a homogenization treatment. To evaluate the chemical homogeneity, backscatter electron (BSE) imaging and energy dispersive X-ray spectroscopy (EDS) were performed. Dynamic differential scanning calorimetry (DSC) and selected area diffraction utilizing transmission electron microscopy (TEM-SAD) were performed for the: (i) detection of the characteristic heat signatures of the disorder-order transformations and (ii) determination of the ordering state at room temperature of the synthesized alloys, respectively. In case of MoCrTi–3Al, a single-phase A2 crystal structure without indications of a disorder-order transformation was obtained. Compression tests at temperatures ranging from room temperature up to 800 °C reveal a significant improvement of plastic deformability at room temperature as compared to the formerly investigated equiatomic MoCrTiAl with its B2 crystal structure.

Disorder-order and order-order phase transformations in Ta5C4 phases predicted using the evolutionary algorithm and symmetry analysis.

A search for stable ordered phases in the nonstoichiometric cubic tantalum carbide TaC0.8 has been performed by use of the evolutionary algorithm and symmetry analysis. Four stable Ta5C4 superstructures with tetragonal, monoclinic, orthorhombic, and triclinic symmetry have been predicted for the first time. The DOS values of these Ta5C4 superstructures and stoichiometric TaC1.00 carbide have been calculated. All the tantalum carbide superstructures and stoichiometric TaC1.00 carbide have metal conductivity. The disorder-order phase transition channels TaCy → Ta5C4 associated with the formation of the considered model superstructures include superstructural vectors of non-Lifshitz stars {k1}, {k2}, and {k4}. The distribution functions of carbon atoms over the sites of the tetragonal, monoclinic, orthorhombic, and triclinic Ta5C4 superstructures have been calculated. For the first time, the physically permissible sequence of disorder-order and order-order phase transitions is established for the detected phases of the Ta5C4 family. Based on the formation enthalpy and the cohesion energy magnitudes, the triclinic Ta5C4 superstructure is the most favorable among all Ta5C4 phases predicted. The composition of the predicted Ta5C4 superstructures corresponds to TaC0.80 which possesses the highest melting temperature and hardness.

An indication of spin-transition accompanied by an order-disorder structural transformation in [Ni(phpyNO)2(NCS)2] (phpyNO = tert-butyl 5-phenyl-2-pyridyl nitroxide).

Reaction of nickel(ii) thiocyanate and tert-butyl 5-phenyl-2-pyridyl nitroxide (phpyNO) afforded a 2p–3d–2p heterospin triad [Ni(phpyNO)2(NCS)2]. The compound crystallizes in the orthorhombic Pbcn space group. The whole molecule is crystallographically independent. The torsion angles around Ni–O–N–C2py are 26.8(4) and 27.3(4)° at 400 K, indicating appreciable orbital overlaps of the radical π* and nickel(ii) 3dx2−y2/3dz2 orbitals. In a low-temperature region, the torsion was enhanced, and the space group changed to monoclinic P21/c with a doubled asymmetric unit volume. The χmT value was practically null below ca. 140 K and, on heating to 400 K, gradually increased and reached 1.30 cm3 K mol−1. A van't Hoff analysis suggests a spin transition at T1/2 = 530(20) K. Density functional theory calculation reproduced ground Stotal = 0 with singlet-triplet gaps of 910 and 1263 K for the 140 K structure, and the gap was reduced to 297 K at 400 K. Consequently, the present compound can be considered as an incomplete spin-crossover material, as a result of T1/2 located above the experimental temperature window.

Exploring a lead-free organic-inorganic semiconducting hybrid with above-room-temperature dielectric phase transition.

Recently, organic–inorganic hybrid lead halide perovskites have attracted great attention for optoelectronic applications, such as light-emitting diodes, photovoltaics and optoelectronics. Meanwhile, the flexible organic components of these compounds give rise to a large variety of important functions, such as dielectric phase transitions. However, those containing Pb are harmful to the environment in vast quantities. Herein, a lead-free organic–inorganic hybrid, (C6H14N)2BiCl5 (CHA; C6H14N+ is cyclohexylaminium), has been successfully developed. As expected, CHA exhibits an above-room-temperature solid phase transition at 325 K (Tc), which was confirmed by the differential scanning calorimetry measurement and variable temperature single crystal X-ray diffraction analyses. Further analyses indicate the phase transition is mainly governed by the order–disorder transformation of organic cyclohexylaminium cations. Interestingly, during the process of phase transition, the dielectric constant (ε′) of CHA shows an obvious step-like anomaly, which displays a low dielectric constant state below Tc and a high dielectric constant state above Tc. Furthermore, variable temperature conductivity combined with theoretical calculations demonstrate the notable semiconducting feature of CHA. It is believed that our work will provide useful strategies for exploring lead-free organic–inorganic semiconducting hybrid materials with above room temperature dielectric phase transitions.

Two bilayer organic-inorganic hybrid perovskite compounds exhibiting reversible phase transition and dielectric anomalies

Ruddlesden-Popper two-dimensional (2D) organic-inorganic hybrid perovskites have been explored for multiple applications, benefitting from their structural tunability, superior stability and congenital quantum-well effects. Herein, two bilayer hybrid perovskite-type compounds with the general formula [A2Bn-1PbnI3n+1] (n is the number of layer) [(C5H8NS)2(MA)Pb2I7] (1) and [(C5H8NS)2(FA)Pb2I7] (2) (C5H8NS: 2-thiophenemethylamine, MA: methylamine, FA: formamidine) are reported. The differential scanning calorimetry (DSC) measurements revealed both compounds 1 and 2 exhibit reversible phase transitions above the room temperature, accompanied by dielectric anomalies near the Curie temperature (Tc). The variable-temperature X-ray single-crystal diffraction disclosed the phase transitions derive from the order-disorder transformation of organic cations 2-thiophenemethylamine, methylamine and formamidine. Furthermore, compounds 1 and 2 exhibited strong emission peaks at about 600 ​nm when under an excitation wavelength of 475 ​nm.

Experimental study of phase equilibria on Co–Fe-rich side of Co–Al–Fe system

Despite various studies on Co–Al–Fe ternary system, its phase equilibria are still in doubt. Phase equilibria, magnetic transition and bcc_A2/bcc_B2 order–disorder transformation at the Co–Fe-rich side of the Co–Al–Fe alloys were carefully investigated by means of electron probe microanalysis (EPMA), X-ray diffraction (XRD) and differential scanning calorimetry. The equilibrium phases and their compositions were determined by 18 alloy samples annealed at 900, 1000, 1100 and 1200 °C for 528, 336, 168 and 96 h, respectively, followed by quenching. However, by adopting the above traditional method, bcc_A2 and fcc_A1 phases are difficult to be distinguished through XRD analysis at room temperature due to the martensitic transformation of fcc_A1 phase during quenching. For this reason, high-temperature in situ XRD technique was utilized to correctly establish the phase relationships among bcc_A2, bcc_B2 and fcc_A1 phases. The phase transformation between bcc_A2 and B2 phases was determined to be second order instead of first order at temperatures higher than 900 °C. The equilibrium phases and compositions were further confirmed by fabricating 16 diffusion couples together with EPMA. Meanwhile, using three-dimensional differential scanning calorimetry method, bcc_A2/B2 and ferro-/paramagnetic transitions were determined with high accuracy.

Effect of stoichiometry on the evolution of thermally annealed long-range ordering in Ni–Cr alloys

Ni-based alloys, such as alloys 690 and 625, are widely used in the nuclear industry as structural components, because of their desirable mechanical properties and resistance to stress corrosion cracking. However, in some high chromium alloys, a disorder-order phase transformation near 33 at% Cr, is known to decrease ductility and fracture toughness. In this study, the ordering transformation is investigated in Ni–Cr binary model alloys to better understand the effects of composition. Model alloys with different stoichiometries (Ni/Cr = 1.8, 2.0, 2.2, 2.4) were isothermally aged up to 10,000 h at three temperatures (373 °C, 418 °C, and 475 °C) and characterized by transmission electron microscopy (TEM), microhardness, and synchrotron-based X-ray diffraction (XRD). TEM results show the evolution of the Ni2Cr (MoPt2-type) ordered precipitates between 3000 h and 10,000 h with corresponding size of ∼10–20 nm. Microhardness testing results show that off-stoichiometry (Ni/Cr ≠ 2.0) alloys exhibit a smaller change with ordering compared to the stoichiometric (Ni/Cr = 2.0) alloy at all temperatures. XRD quantifies ordering induced lattice contraction in the matrix structure and the size of the ordered precipitates. No BCC Cr was detected by XRD or TEM during characterization in the range of 29.83–35.66 at% Cr after 10,000 h of aging, confirming that all of the hardening can be attributed to the development of Ni2Cr in alloys ranging from Ni/Cr of 1.8 to Ni/Cr of 2.4.

Magnetic penetration depth in the κ-(BEDT-TTF)2Cu[N(CN)2]Br organic superconductor

Abstract This paper systematically studied the magnetic penetration depth λ//(T) and superfluid density as a function of the cooling rate through the order–disorder transformation near 80 K for both the hydrogenated (κ-H8-Br) and deuterated (κ-D8-Br) κ-(BEDT-TTF)2Cu[N(CN)2]Br organic superconductors. The magnetic penetration depth has been determined from the results of the dc magnetization measurements. The penetration depth was calculated near the critical temperature TC, our results show that the cooling of the samples at different rates through the order-disorder transformation near 80 K has a dramatic effect on the penetration depth, superfluid density and superconducting transition temperature TC.

Composition-driven anionic disorder-order transformations triggered single-Eu2+-converted high-color-rendering white-light phosphors

Single-component, single-activator-converted high-color-rendering index (CRI) white-light phosphors have sparked much interest for phosphor-converted white light-emitting diodes. However, manipulating the distribution and locations of single activators to target desired sites in a given host lattice is still a challenge. Herein, we report the remote regulation of the distribution of Eu2+ ions by engineering and controlling the structural ordering in Sr3(Ce1−xLax)(PO4)3:0.05Eu2+ (SCLP:Eu2+) compound, which are designed by using two-color phosphors with different anionic structural ordering, viz., Sr3Ce(PO4)3:Eu2+ (yellow) with disordered state of PO4 tetrahedra, and Sr3La(PO4)3:Eu2+ (blue) with ordered state of PO4 tetrahedra. The successive substitution of Ce by La triggers a pronounced disorder-to-order structural transformation of PO4 tetrahedra within SCLP:Eu2+ compounds and guides remotely the distribution of Eu2+ activators, which is demonstrated by a detailed analysis of synchrotron X-ray diffraction refinement, electron paramagnetic resonance spectra, electron spin-echo envelope modulation spectra, Raman spectra, nuclear magnetic resonance spectra and micro-cathodoluminescence spectrum. Benefitting from the controllable structural ordering transformation, as-prepared samples form a unique disorder-order crystal structure, exhibiting controllable microstructure acting on Eu2+ ions, tunable-color emissions including a high CRI (Ra = 90) white-light, increased structural rigidity and thermal stability. These interesting findings in the local structure-dependent luminescence properties demonstrate that structural ordering engineering may be an effective approach to regulate the migration of Eu2+ activators and improve the thermal stability of phosphors.

Crystallographic ordering in a series of Al-containing refractory high entropy alloys Ta–Nb–Mo–Cr–Ti–Al

High entropy alloys based on the Ta–Nb–Mo–Cr–Ti–Al system are expected to possess high creep and oxidation resistance as well as outstanding specific mechanical properties due to presumed high melting points and low densities. However, we recently reported that arc-melted and subsequently homogenized alloys within this system exhibit a lack of ductility up to 600 °C [H. Chen et al. in Metall. Mater. Trans. A 49 (2018) 772–781 and J. Alloys Cmpd. 661 (2016) 206–215]. Thermodynamic calculations suggest the formation of a B2-type ordered phase below the homogenization temperature. In the present article, we provide results of a detailed microstructural characterization of a series of Ta–Nb–Mo–Cr–Ti–Al derivatives and evaluate if B2-type ordering could be the origin for the observed lack of ductility. Backscatter electron (BSE) imaging, energy dispersive X-ray spectroscopy (EDX) and atom probe tomography (APT) were used to verify uniform elemental distribution after homogenization. X-ray diffraction (XRD) patterns indicate both, A2 or B2-type crystal structure, whereas transmission electron microscopy (TEM) diffraction experiments unambiguously confirm B2-type order in the as-homogenized state of all investigated alloys. In MoCrTiAl, planar defects that show antiphase boundary contrast with a {100}-type habit plane were detected by TEM dark field (DF) imaging. They are wetted by a Cr-enriched and Ti-depleted layer as confirmed by scanning transmission electron microscopy (STEM)-EDX line scans as well as APT analyses. The planar defects arise from a disorder-order solid-state phase transformation during cooling, as indicated by differential scanning calorimetry (DSC).

Effect of La addition on high-temperature order-disorder phase transformation in Fe − 18Ga alloy

The microstructure, internal friction (IF) behavior spectra, heat flow curves, and mechanical strength of Fe-18Ga-xLa (x = 0.05, 0.1, 0.2, 0.5, and 1.0 at.%) alloys were systematically analyzed in this investigation. In the IF spectra, a relaxation IF peak (Labeled as P1) and a peak related to order-disorder phase transition (Labeled as Ptr) are observed in the temperature range of 400 °C–690 °C. It is found trace La doping has a significant effect on the Ptr peak. With the increase of the La-doped content, the peak of Ptr gradually shifts to a lower temperature and the net peak height decreases. Combining with phase diagram, DSC, Grazing Incidence X-ray diffraction (GI-XRD) spectra and SEM, the mechanisms of the reduction of both the critical temperature and the strength of Ptr peak for the Fe-18Ga-xLa alloy are ascribed to the precipitation of LaGa2 phase, which reduces the Ga content gradually in the matrix. Further, the mechanism is verified in Fe-18.1Ga alloy and Fe-19.3Ga alloy. In addition, the trace La doping can significantly improve the mechanical strength of the Fe − 18Ga alloy.

Investigation on thermo-physical and mechanical properties of Dy3(Ta1-xNbx)O7 ceramics with order-disorder transition

Abstract Rare earth tantalate and niobate have attracted much attention due to their excellent thermo-physical properties and are considered as potential thermal barrier coating (TBC) materials. The bulk specimens of Dy3(Ta1-xNbx)O7 (x = 0, 1/6, 2/6, 3/6, 4/6, 5/6, and 6/6) ceramics are synthesized by high-temperature solid-state reaction in this work, and the results of the phase structure identification show that the Dy3(Ta1-xNbx)O7 ceramics vary from ordered weberite structure to disordered defect fluorite structure with the increase of component parameters x. Interestingly, the thermo-physical properties and mechanical properties of Dy3(Ta1-xNbx)O7 ceramics are closely related to the order-disorder transformation process. Furthermore, the Dy3(Ta1-xNbx)O7 ceramics possess low thermal conductivity and high thermal expansion coefficients, which suggests that Dy3(Ta1-xNbx)O7 ceramics can be candidates as TBC materials.

Probing the temperature effects in the radiation stability of Nd2Zr2O7 pyrochlore under swift ion irradiation

The pyrochlore structure is of particular interest to the nuclear industry due to its potential for nuclear waste immobilization and as a host material for inert matrix fuels. Herein, the experimental results of the temperature and ion fluence dependence on the disordered ion tracks produced by the electronic excitation in the pyrochlore compound Nd2Zr2O7 are presented. The samples were exposed to extreme conditions of ion irradiation with 100 MeV 107Ag9+ ions at ion fluences ranging from 3 × 1011 ions/cm2 to 2 × 1013 ions/cm2 at temperatures of 300 K and 1000 K. The in-situ X-ray diffraction along with micro-Raman spectroscopic analysis on Nd2Zr2O7 samples irradiated at 300 K displays order-disorder phase transformation which is consistent with earlier reports. The direct-impact model is used to calculate the amorphous fraction which exists due to massive deposition of electronic-energy in a localized region, and the estimated value of track radius is 2.98 ± 0.56 nm. Furthermore, theoretical thermal spike simulations are performed to estimate the track radius (∼4.2 nm) which provides strong support for experimental results. To simulate the response of Nd2Zr2O7 under nuclear reactor environment, irradiation carried out at an elevated temperature that exhibits significant radiation tolerance. Its substantiality is revealed from comparative temperature dependent irradiation studies where a slow rate of amorphization is found at the elevated temperature because of the competition between defect production and thermal healing mechanism. Thus, obtained results strongly endorse the appositeness of Nd2Zr2O7 as inert matrix material for the fabrication of futuristic nuclear fuel.

Two‐Step Structure Phase Transition, Dielectric Anomalies, and Thermochromic Luminescence Behavior in a Direct Band Gap 2D Corrugated Layer Lead Chloride Hybrid of [(CH3)4N]4Pb3Cl10

A direct band gap 2D corrugated layer lead chloride hybrid, [(CH3 )4 N]4 Pb3 Cl10 (1), shows analogous topology to the {Mg3 F10 4- }∞ layer in Cs4 Mg3 F10 , and with the (CH3 )4 N+ cations locating in the inorganic layer voids and between the interlayers. Two reversible structural phase transitions occur in 1 at 225/210 K and 328/325 K upon heating/cooling, respectively. On going from the low- to intermediate-temperature phase, the space group changes from P21 /c to Cmca, and the crystallographic axis perpendicular to the layers is doubled with the order-disorder transformation of (CH3 )4 N+ cations between the interlayers. The intermediate- and high-temperature phases are isomorphic with similar cell parameters and packing structure; their main difference concerns the disorder degree of the (CH3 )4 N+ cations between the interlayers. The two-step structural phase transitions lead to dielectric anomalies around the corresponding Tc . Interestingly, 1 shows multiband emission, originating from the recombination of exciton and emission of defects. Moreover, 1 exhibits divergent thermochromic luminescent features around the Tc on the intermediate to low temperature transition.

Order—Disorder transformation and its effect on the properties of (Lanthanide)2Zr1.5Hf0.5O7 functional nanoceramics

Order disorder transformations and its effect on the structural, optical and ionic transport properties of the cubic pyrochlore – defect fluorite structures are the prime focus of this study. Nanoceramics of Ln2Zr1.5Hf0.5O7 (Ln = Pr, Nd, Sm, Gd, Dy and Er) are prepared through the modified combustion technique. X – ray diffraction analysis and electron microscopic studies show the cubic nano crystallite nature of the materials. Vibrational studies reveal the pyrochlore–fluorite phase transformation in the series. Highly dense bulk ceramics are prepared from the nano particles at relatively low temperatures. The gradual replacement of Ln3+ ions in Ln2Zr1.5Hf0.5O7 changes the pyrochlores (Ln = Pr-Sm) to defect fluorite (Ln = Er) through the weakly ordered defect fluorites (Ln = Gd and Dy). Impedance spectroscopic analysis carried on the bulk ceramics shows the influence of phase transformation on the oxide ion conduction of bulk materials. The peak oxide ion conduction is observed for the Ln = Dy ceramic, which is at the pyrochlore fluorite phase boundary.

Phase transformation and structure evolution of a Ti-45Al-7.5Nb alloy processed by high-pressure torsion

Intermetallic γ-based titanium aluminides of Ti-45Al-7.5Nb have been subjected to high-pressure torsion (HPT) processing. Significant grain refinement has been achieved from ∼10 μm to ∼30 nm, leading to the improvement in both physical and mechanical properties. Complementary studies correlated the microstructure, phase transformation behavior and the enhancement of mechanical properties. Neutron and X-ray diffraction revealed that an ongoing order-disorder transformation occurs by HPT processing, resulting in large heterogeneous behavior between the surface-near and the median layers of the disk. While the γ-phase almost disappeared underneath the surface region, such order/disorder phase transformation consistently decreases towards the middle-thickness section of the samples. A low bulk texture index is consistent with grain rolling and swirling rather than slip deformation. Vickers micro-hardness indentation confirms the improvement of hardness from 308 Hv to 605 Hv. For the first time, the present work demonstrates heterogeneity in structural transformation, such as displacive transformation and order/disorder transformation, which can be compared to earlier reported inhomogeneity in mechanical properties and microstructure within bulk nanostructured materials that were processed by HPT.