Amorphous-nanocrystalline Structure Research Articles

Atomic scale formation mechanism of the Amorphous-Nanocrystalline biphase structure in TiSiN Coating: Phase field crystal simulation and experimental characterization

TiSiN nanocomposite coatings have exceptional strength, toughness, and corrosion resistance due to their unique biphase amorphous/nanocrystalline structure with tiny TiN grains embedded in an amorphous Si3N4 phase. However, the unclear formation process makes microstructural control challenging. In this study the phase field crystal method has been employed to analyze the microstructure evolution in TiSiN coatings, uncovering a four-step formation mechanism for the amorphous-nanocrystalline structure. The initial stage results in appearance of concentration heterogeneities and the development of the triangular-like short-range order (Stage I). This stage is followed by the nucleation of nanocrystals in Ti-rich zones and the transformation of triangular short-range to the long-range order with a square symmetry (Stage II). Then, during coarsening stage, Ti-rich polycrystalline nanocrystals are formed (Stage Ⅲ) followed by the vacancy migration from the polycrystalline nanocrystals to amorphous phase and formation of monocrystalline Ti nanocrystals embedded in amorphous phase (Stage Ⅳ). The simulation results are compared qualitatively with aberration-corrected High-Resolution Scanning Transmission Electron Microscopy and High-Resolution Transmission Electron Microscopy images from our study.

Tailoring the amorphous-nanocrystalline structures of TiNbZrNx films towards improving the anti-corrosion and mechanical properties by controlling nitrogen flow ratio

Multi-principal element alloy (MPEA) films demonstrate superior corrosion resistance and tribological properties, which have substantial potential for applications in marine engineering equipment. In this study, the TiNbZrNx MPEA nitride films were successfully deposited on 316 L austenitic stainless steel by direct current (DC) magnetron sputtering at various nitrogen flow ratio (RN2). The phase, composition, microstructure, corrosion and mechanical behaviors were investigated in detail. The results showed that the phase transitioned from amorphous to amorphous/nanocrystalline as RN2 increased. The TiNbZrNx films deposited at RN2 = 0.15–0.4 exhibited better corrosion performance in the electrochemical and salt spray tests. The RN2 = 0.4 film presented the optimal corrosion resistance, with the lowest self-corrosion current density (0.249 μA/cm2) and the largest passivation zone (from OCP to >1.2 VSCE). The amorphous/nanocrystalline film deposited at RN2 = 0.2 showed a remarkable nanohardness of 7.03 GPa and adhesion strength of 18.86 N. The strengthening effect can be attributed to the interstitial dissolution of nitrogen atoms among the metal atoms. The formation of nitride nanocrystalline phases and the existence of interfaces can effectively improve the plastic deformation ability of amorphous alloy films. This work provides theoretical guidance for the development of MPEA nitride films with tunable properties for key moving parts in marine equipment.

Orientation dependence of the nanocrystallization and magnetic behavior during annealing of the FINEMET alloy

The microscopic strain evolution and microstructural of FeCuNbSiB amorphous alloy samples were studied under both free and tensile stress annealing conditions using in-situ synchrotron X-ray diffraction (XRD) and transmission electron microscopy (TEM). An amorphous-nanocrystalline structure was developed in both samples after annealing at 813 K, as the microstrains increased and decreased along the parallel and perpendicular stress directions respectively. The applied stress during annealing imposed limitations on the size of nanocrystals along the tensile and perpendicular stress directions, resulting in smaller sizes compared to those obtained under free annealing conditions, due to the reduction in Gibbs free energy by the applied stress and the subsequent enhancement of nucleation rates. The nanocrystalline size perpendicular to the stress direction was slightly larger than that along the parallel stress direction because the suppression of atomic diffusion perpendicular to the stress direction during crystallization could be favorable for local atomic rearrangement.

In-situ construction of amorphous–crystalline NiCo bimetallic oxyhydroxide for low-temperature supercapacitor device

As rechargeable energy storage device, supercapacitor (SC) cell is facing a new challenge for low-temperature application since the low-temperature environment seriously suppresses the reaction kinetics of the electrode materials. In this work, NiCo bimetallic oxyhydroxides (NixCoyOOH, Ni/Co = x/y) composed of amorphous-crystal structure were in-situ synthesized using electrodeposition, which are capable of operating at temperatures as low as − 4 °C, totally different from the pure Ni or Co oxyhydroxides counterparts. The microstructures of the NixCoyOOH were characterized by XRD, SEM, TEM, and XPS, finding an obviously transit from microparticles (NiOOH) and porous arrays (CoOOH) to flower-like nanospheres and a complicated amorphous-nanocrystalline structure. Electrochemical tests show that the Ni2Co1OOH cathode presents a super-high specific capacitance of 3720 and 2311F g−1 at low and high charging current densities of 1 and 20 A/g at 23 ℃ in aqueous electrolyte, respectively. The assembled device of Ni2Co1OOH//activated carbon (AC) delivers a high energy density of 22.8 Wh kg−1 at 7466 W kg−1 in polyvinyl alcohol (PVA)-KOH hydrogel at 0 ℃, and offers anexceptionalstability of 92.5 % of capacity after 8000 cycles at 10 A/g and 0 ℃. To evaluate the serviceability of the as-prepared electrode materials, the devices in parallel and series connections encapsulated by 3D printing exhibits a stable discharging performance at 0 °C, demonstrating a potential application in cold environment. Heteroatomic intercalating promotes the co-adsorption of hydroxyls on the double active sites of the Ni and Co, resulting in an improved supercapacitance.

Features of Tribooxidation of the High-Entropy Coating (AlCrZrTiTa)N during Dry High-Speed Cutting

The high-entropy PVD coating (AlCrZrTiTa)N, characterized by its high hardness (50–60 GPa), elastic modulus above 300 MPa, and high heat resistance up to 1300 °C, is used for coating cutting tools operating under extreme metalworking conditions. The nanostructured monolayer 3 μm PVD coating was deposited on cutting plates in the hybrid arc deposition PVD coater. The coating had an amorphous nanocrystalline microstructure with a grain size of about 10–50 nm. The samples of SS 304 steel were investigated during dry high-speed (600 m/min) cutting. Raman spectroscopy was used to study the formation of tribooxides on the tool surface at the running-in stage of the cutting. After 130 m of cutting, Cr2O3 oxide appears on the wear surface while other elements are bound with N atoms. When the cutting length is increased to up to 260 m, oxide Al2O3 · ZrO2 (mullite) and amorphous oxides TaO2 and CrO2 are formed. The method EELFS made it possible to determine the amorphous nanocrystalline structure of triboceramics based on CrO2 and Al2O3 · ZrO2. The nearest atomic surrounding of Cr-Cr, O-O, and Cr-O and their subsequent comparison with the available literature data allow us to calculate the equilibrium lattice constants of the CrO2 unit cell, which are equal to (a, b) = 4.3754 Å and c = 0.5927. The triboceramic films on the base of non-equilibrium mullite Al2O3·ZrO2 have an amorphous structure. In the first coordination sphere, the interatomic distances of Zr-O and Al-O were 1.79 and 1.89 Å. An accelerated adaptive reaction to extreme external stimuli, at the very beginning of the running-in stage, is established. The tribological adaptability of the high-entropy ultra-fine amorphous nanocrystalline coating under extremely loaded dry high-speed cutting is based on non-equilibrium phenomena: the partial oxidation of fragments of the nitride and dynamic formation of protective tribooxides, which have a good thermal barrier and frictional properties. These factors interact synergistically and determine the life of the cutting tool.

Boosting electro-Fenton performance by constructing a large-scale 3D-architected amorphous–nanocrystalline structure

Metallic glasses (MGs) catalysts have shown promise in Fenton-like reactions for environmental remediation. However, the challenge of balancing catalytic activity and recyclability has hindered their practical application. Here, we present a novel approach to fabricate a three-dimensional (3D) amorphous-nanocrystalline catalyst on Cu-foam using thermal spraying, which shows excellent catalytic activity-recyclability synergy. This method enables large-scale production of a 3D porous MG composite (referred to as 3DP MGC) without the need of post-treatment. The architected 3DP MGC exhibits exceptional electro-Fenton activity, surpassing the performance of most Fe-based catalysts reported to date, with a kinetic rate constant 1.4 times higher than that of the amorphous FeSiB MG ribbon. Furthermore, the 3DP MGC catalyst demonstrates excellent reusability, maintaining efficiency for over 60 cycles without decay. The excellent catalytic activity of the 3D-architected MGC is attributed to the galvanic coupling between the MG and α-Fe phases with a low grain boundary effect and accelerated electronic transfer kinetics, facilitating the generation of multiple reactive oxygen species. Additionally, the catalyst benefits from a sustainably active surface enriched with Fe(II) species, resulting in ultrahigh reusability. Finally, we demonstrate the exceptional environmental tolerance of the architected 3DP MGC catalyst, showcasing its high efficiency in degrading real oilfield wastewater and suggesting its potential for the 3D engineering of MG materials in catalytic applications.

Compositionally graded multi-principal-element alloy coating with hybrid amorphous-nanocrystalline structure by directional electrical explosion

Electrical explosion, characterized by ultra-fast atomization and quenching (dT/dt ∼1010–1012 K/s) of the sample, is a unique approach for the one-step synthesis of nanoparticles or coatings. A dense μm-thick alloy coating made of AlCuTiMoWSn was manufactured via the pulsed-discharge-driven intertwined wire explosion in μs-timescale. The explosion products were guided by a nozzle, forming a thermal plasma jet spray (km/s) towards the substrate. The condensation and stacking of those elements on Si wafer appeared graded element distribution, on account of the discrepancy in electrical explosion dynamics of various metals and the jet-wall interaction effects. High-speed photography along with electro-physical diagnostics was applied to characterize the dynamics of the synthesizing process. Scanning electron microscopy and energy dispersive spectrometer were used to capture the microstructural and compositional features of the coating from the top/sectional views. The results indicate the discordance in electrical explosion causes various element abundance and phase states at different depths of the coating. Specifically, Sn is the first to explode and spray toward the Si wafer, then Al/Cu, and finally Ti/Mo/W. Morphology and x-ray diffraction results confirm the co-existence of nanocrystalline and amorphous phase for the alloy coating. In addition, the quenching, nucleation, and condensation are deeply associated with fluid dynamics such as turbulent mixing, near-wall vortex, etc. Also, the influence of nozzle configuration was discussed. This ingenious path could favor fabricating materials suited to applications demanding variable mechanical/electrical functions.

Magnetization and microhardness of iron–chromium alloy films electrodeposited from an aqueous solution containing N, N-dimethylformamide

Iron-chromium (Fe–Cr) alloy films were electrochemically synthesized from an aqueous solution containing N,N-dimethylformamide (DMF). The chromium content of the alloy films increased up to ca. 32 at%, with an increase in the cathodic overpotential during the electrodeposition. Based on the XRD profiles and electron diffraction patterns, it was revealed that the electrodeposited Fe–Cr alloy films have an amorphous nanocrystalline structure. The crystal grain size of the alloys decreased due to an alloying effect of Cr atoms as well as an increase in the nucleation site density of the alloys that were electrodeposited, accompanying a significant overpotential from the stable complex ions. The saturation magnetization of the electrodeposited Fe–Cr alloy films decreased with an increase in the chromium content. On the contrary, the microhardness increased due to the synergistic contribution of solid solution strengthening and crystal grain refinement. The microhardness of the electrodeposited Fe–Cr alloy films reached up to 422.0 kgf/mm2 (HV0.05) and greatly exceeded that of the solidified Fe–Cr alloy ingots.

Cathodic arc-PVD Zr-B-Si-C-Ti-(N) coatings

Arc-PVD coatings Zr-B-Si-C-Ti-N and Zr-B-Si-C-Ti were obtained using combined evaporated ZrB2-SiC-Ti cathodes in a residual atmosphere of N2 and Ar. Their structure and composition were investigated. The Zr-B-Si-C-Ti-N coating has a predominantly amorphous structure, formed mainly on the basis of nitride, carbide, boride phases and complex compounds Zr, Si, Ti. The Zr-B-Si-C-Ti coating is characterized by an amorphous-nanocrystalline structure. The amorphous component of this coating is formed mainly by phases based on Zr and Si. The nanocrystalline structure is formed by a complex carbide (Zr, Ti) C.

Unexpected thermal stability of dual-phase amorphous-nanocrystalline Al0.74Mo0.26 alloy film prepared by annealing-induced crystallization

Dual-phase amorphous-nanocrystalline Al0.74Mo0.26 alloy film was fabricated by annealing-induced crystallization (AIC) in precursor of amorphous Al0.74Mo0.26 alloy film at 550 °C. The precipitated Al3Mo nano-grains with average size of ~5 nm was uniformly dispersed in Al-Mo amorphous matrix. Additionally, the dual-phase amorphous-nanocrystalline structure of the film was maintained even when the annealing process was performed above the crystallization temperature. The unexpected thermal stability of the dual-phase amorphous-nanocrystalline Al0.74Mo0.26 alloy film resulted from effect of diffusion field impingement. Ham model was employed to quantitatively describe the kinetic stabilization mechanism of the film. Furthermore, the prepared film benefited from the combined effect of amorphous and nanocrystalline phase, which exhibited outstanding mechanical properties with elastic modulus and hardness as high as 240 and 17 GPa, respectively. Also, the film had extraordinary corrosion resistance with very positive corrosion potential, low corrosion current and stable passive state.

Transition from Crystal to Metallic Glass and Micromechanical Property Change of Fe-B-Si Alloy During Rapid Solidification

The effects of high undercooling and a large cooling rate can be achieved by the use of a containerless drop tube technique, which is conducive to rapid solidification and formation of a metastable phase. Here, the rapid solidification of Fe78Si13B9 (S1) and Fe78Si9B13 (S2) alloys was completed under microgravity condition. Based on theoretical calculations, a maximum undercooling of 433 K (0.29 TL) and 412 K (0.28 TL) was obtained, respectively. The microstructure evolution and the formation of an amorphous-nanocrystalline structure for the two alloys were compared and analyzed. The results show that S2 alloy has better amorphous forming ability and higher hardness. During the solidification of S1 alloy, the primary phase α-Fe grows by the manner of dendrites, and the secondary dendrite arm spacing decreases exponentially with increased undercooling. An amorphous-nanocrystalline structure is developed when the undercooling is increased up to 388 K; S2 alloy forms an amorphous-nanocrystalline structure at an undercooling of 275 K and is completely amorphized after exceeding an undercooling of 402 K. In addition, the hardness and elastic modulus are acquired by nanoindentation technology under different degrees of undercooling. The phase constitution, morphology, distribution, and grain refinement of the alloys have important effects on the micromechanical properties of these alloys.

Formation of Zr-contained Amorphous Alloy Films by Magnetron Co-sputtering

In order to explore the application of magnetron co-sputtering in fabricating the amorphous alloy, Zr-contained amorphous films were prepared by this technique and investigated by scanning electron microscope, energy disperse spectroscopy and X-ray diffraction. The results show that the co-sputtered films are in fully amorphous state or with amorphous-nanocrystalline structure. The XRD patterns of the Zr-Cu and Zr-Ni amorphous films exhibit a double-peak phenomenon. There is a shift of diffusive peak with changing the sputtering current which is possibly attributed to the change of Zr-Ni and Zr-Cu intermetallic like short range orders. In addition, Zr-Cu-Ni ternary co-sputtered films have a sharper peak at high angle. The sputtering yield of element during co-sputtering ranks as Cu>Ni>Zr, which can be ascribed to the contribution of melting and boiling temperature, atomic size and electrical conductivity of elements.

Specific Features of the Atomic Structure of the Ti50Ni25Cu25 Alloy Amorphized during Rapid Quenching from a Melt

This paper presents results of the structural study of the Ti50Ni25Cu25 alloy formed under rapid quenching from a melt. The studies were performed using neutron and X-ray diffraction and transmission and scanning electron microscopy. It has been revealed that this alloy has an amorphous nanocrystalline structure, which contains В2, L21, and L12 ensembles of nanocrystals with sizes to several nanometers in an amorphous matrix alongside with microspherolites, which have sustained the thermoelastic В2–В19 martensitic transition. It has also been shown for the first time that topological and compositional short-range atomic order is formed in the amorphous matrix of the Ti50N25Cu25 alloy in the form of localized nanodomains by the same three types of superstructures (В2, L21, L12).

Solid state amorphization in the Ni-Nb-Y system by mechanical alloying

Amorphous and heterogeneous amorphous Ni-based alloys have shown promise as electrocatalytic materials for various reactions. The Ni-Nb-Y system is of particular interest due to the immiscibility of Nb and Y that facilitates a heterogeneous amorphous-amorphous or amorphous-nanocrystalline structure. Amorphous alloys in the Ni-Nb-Y system have been previously limited to those produced through rapid solidification processing. In this study, a high energy ball milling process was successfully used for the first time to mechanically alloy novel amorphous-based Ni-Nb-Y alloys. A thermodynamic model of the Ni-Nb-Y alloy system was developed to guide the ternary alloy design while X-ray diffraction and transmission electron microscopy characterized the microstructure of the Ni-Nb-Y alloys. The targeting of high melting NiY and NiNb intermetallic compounds facilitated the amorphization process. A novel amorphous Ni79.2Nb12.5Y8.3 alloy was produced after 6 h of cryogenic ball milling. Partial crystallization of the amorphous structure was observed upon prolonged milling with the formation of a secondary nanocrystalline Ni5Y phase in an amorphous matrix. The alloying design strategy shows promise in analogous alloy systems where immiscibility exists among the alloy constituents.

Synthesis and characterization of sol-gel derived non-stoichiometric aluminum phosphate coating

The aim of this study was to synthesize a non-stoichiometric aluminum phosphate coating with high thermal stability. The aluminum phosphate precursor solution, in the presence of polyvinylpyrrolidone (PVP) as a crack-limiting agent was prepared by a sol–gel process and then applied on AISI 304 stainless steel substrate using the dip coating technique. Phase composition analysis of the coating material was performed by X-ray diffraction (XRD). The surface and cross sectional morphology of the coating after annealing at 500 °C for 15 min were observed using scanning electron microscopy (SEM). Topography and roughness of coated surface were investigated by atomic force microscopy (AFM). The amorphous-nanocrystalline structure and distribution of nanocrystals in the amorphous matrix were studied by transition electron microscopy (TEM). Thermal analysis and study of amorphous to crystalline transformation were investigated by thermal-gravimetric and differential scanning calorimetry (TG-DSC). Molecular spectroscopy of the synthesized powder was studied by Raman spectroscopy. According to SEM and AFM images a smooth, uniform, continuous and crack-free coating with 6.7 nm surface roughness was achieved. XRD analysis showed that the amorphous structure of the coating remained almost unchanged after annealing at 500 °C for 15 min. Conversely, an amorphous-nanocrystalline structure was obtained after air annealing at 1100 °C for 1 h. Also, oxide peaks number and intensity after oxidation at 1100 °C for 10 h were remarkably less in the coated sample than the bare one indicating the surface protection of aluminum phosphate coating against oxidation. The presence of graphitic and amorphous carbon (ID:IG = 0.97) in the coating structure was confirmed by Raman spectroscopy. TEM observations also confirmed the amorphous structure of the coating after annealing at 500 °C for 15 min and the partial transformation into a mixed amorphous-nanocrystalline structure after annealing at 1100 °C for 1 h. Accordingly, the thermal analysis of the coating material showed that the onset temperature of the amorphous to crystalline transformation was around 1050 °C, a value higher compared to previous reports (below 1000 °C) for the same material.

Evaluating oxidation behavior of amorphous aluminum phosphate coating

The aim of this study was to investigate the oxidation properties of amorphous aluminum phosphate coating. Aluminum phosphate precursor solution was prepared by a sol–gel process and then applied on AISI 304 stainless steel using dip coating technique. To evaluate the oxidation behavior, samples were placed in an electrical furnace upto 1100 °C for 100 h in air with weight measurements performed at regular ten-hour intervals. Phase composition analysis of the coatings before and after cyclic oxidation process were performed by X-ray diffractometer (XRD). The surface and cross-sectional morphology of the coatings were observed using scanning electron microscopy (SEM) analysis equipped with energy dispersive spectroscopy of characteristic X-rays (EDS). The amorphous-nanocrystalline structure and distribution of nanocrystals in the amorphous matrix were studied by transition electron microscopy (TEM). According to SEM images a uniform, continuous and crack-free coating was achieved. XRD analysis as well as TEM observations showed that the amorphous structure of coating remained unchanged after annealing at 500 °C for 15 min however; an amorphous-nanocrystalline structure was obtained after annealing at 1100 °C for 1 h. Weight change measurements after 100 h oxidation test revealed that the trace of weight gain against oxidation time for both coated and un-coated substrates were parabola in nature and the range of the weight change of the bare substrate was about 30 times greater than that of observed for the aluminum phosphate coating. In general, the results showed that the synthesized amorphous aluminum phosphate is capable of surface protecting of metals/alloys against degradation at harsh environments.

Structure of Fe–Nb–Cu–Si–B Nanocrystalline Alloy Strip Produced by Melt Spinning

Recently, amorphous and nanocrystalline magnetically soft iron alloys have been used to create protective materials that are effective in a broad range of magnetic and electromagnetic fields. These alloys are obtained in strip form by superfast quenching of a plane melt jet on a rapidly spinning cooled disk. In the production of amorphous strip, metal melted in a high-frequency inductor is supplied through a cut on the surface of the cooling disk. The surface layers of the congealing strip in contact with the cooled disk are cooled more rapidly than higher layers in no contact with the disk. As a result, residual compressive stress may be formed on the contact side of the strip, while tensile stress may be formed on the free side. This may lead to anisotropic structure and properties over the strip thickness. In the present work, the structure is investigated by transmission microscopy (planar geometry and cross-sectional geometry) over the thickness of AMAG-200 Fe–Nb–Cu–Si–B alloy strip obtained by spinning. A relation is established between AMAG-200 Fe–Nb–Cu–Si–B alloy strip produced in controlled crystallization and the structure of the amorphous strip obtained by superfast quenching of melt at rates up to 106 K/s. That explains the structural anisotropy over the strip thickness. Heat treatment at 530°C forms excellent magnetic characteristics and decreases the work of destruction on account of the formation of optimal amorphous–nanocrystalline structure in terms of the bulk content and size of the crystallites. A scanning electron microscope is used to study the destruction of strip associated with the structure formed in the strip on superfast quenching from melt and after heat treatment at 530°C. In the state supplied, the surface fracture of the strip on sudden decrease in grain size is ductile; after heat treatment, it is consistently brittle.

Lamp processing- and heat treatment-induced structural transformations of an amorphous Al85Ni10La5 alloy: Hardness and local plasticity

We have studied the structural transformations and deformation behavior of an amorphous Al85Ni10La5 alloy during nanoindentation and uniaxial tension tests and assessed the influence of crystalline phases resulting from lamp processing and heat treatment. Our results confirm the high effectiveness of lamp processing: at identical phase compositions, the lamp processing time is shorter by more than two orders of magnitude. The microplasticity of the amorphous alloy has been shown to manifest itself in both nanoindentation and uniaxial tension tests. The high proportion of local plasticity in the work of indentation has been accounted for in terms of possible intercluster sliding. The observed lamp processing- and heat treatmentinduced changes in the hardness of the alloy reflect changes in its phase composition and the percentages of the amorphous and crystalline phases, which does not rule out a cluster mechanism of local deformation or its deceleration by nanocrystalline phases in the amorphous–nanocrystalline structure.

Formation of Ti-Ta-based surface alloy on TiNi SMA substrate from thin films by pulsed electron-beam melting

TiNi shape memory alloys (SMAs) are unique metallic biomaterials due to combination of superelastisity and high corrosion resistance. Important factors limiting biomedical applications of TiNi SMAs are a danger of toxic Ni release into the adjacent tissues, as well as insufficient level of X-ray visibility. In this paper, the method for fabrication of protective Ni-free surface alloy of thickness ∼1 μm of near Ti70Ta30 composition on TiNi SMA substrate has been successfully realized. The method is based on multiple alternation of magnetron co-deposition of Ti70Ta30 thin (50 nm) films and their liquid-phase mixing with the TiNi substrate by microsecond low-energy, high current electron beam (≤15 keV, ∼2 J/cm2) using setup RITM-SP (Microsplav, Russia). It was found by AES, XRD, SEM/EDS and HRTEM/EDS examinations, that Ti-Ta surface alloy has an increased X-ray visibility and gradient multiphase amorphous-nanocrystalline structure containing nanopores.

Structure and mechanical properties of Ag–Cu films prepared by vacuum codeposition of Au and Cu

We have studied in detail the structure formation process in Ag–Cu films in the course of vacuum deposition of the metals, followed by thermal annealing, and compared the hardness values of nanocrystalline Ag, Cu, and Ag–Cu films. Under equivalent deposition conditions, the hardness of the Ag–Cu films produced by codeposition of the metals exceeds that of the Ag and Cu films. The high hardness of the mixedphase Ag–Cu films is due to their amorphous–nanocrystalline structure. We have determined the limiting grain size above which plastic deformation follows a dislocation mechanism.