Search

SUMMARY: Based on both forced oscillation and ultrasonic pulse transmission methods, we investigated solid pore infill influences on rock elastic moduli in a broad frequency range $[ {1 - 3000,\,\,{{10}^6}} ]$ Hz for different differential pressures. For a Berea sandstone sample, filled sequentially by solid (${22\,\,^{\rm{o}}}{\rm{C}}$), quasi-solid (${26\,\,^{\rm{o}}}{\rm{C}}$) and liquid (${34\,\,^{\rm{o}}}{\rm{C}}$) octadecane, a frequency-dependence was found for the Poisson's ratio, Young's modulus and bulk modulus, nevertheless, these elastic parameters were strongly suppressed by increasing pressures. Experimental measurements showed that shear wave velocity and modulus of solid-octadecane-filled samples are significantly larger than those of the dry and liquid-octadecane-filled ones, implying the potential stiffening effects related to solid infill in compliant pores. A three porosity structure model, which describes the solid stiffening effects related to equant, compliant and the intermediate pores with aspect ratios larger than those of compliant pores but much less than those of stiff pores, was used to compare against the experimentally measured elastic properties for octadecane pore infill, together with several other fluid/solid substitution theories. The agreement between experimental measurements and theoretical predictions is reasonably good for the sandstone tested, providing that the three porosity model can be applied for pressure- and frequency-dependent elastic moduli estimations for a viscoelastic pore-infill-saturated sandstone. Evaluating the combined squirt flow mechanism responsible for the observed moduli dispersion and attenuation is of great importance to reduce potential errors in seismic AVO inversion and 4-D seismic monitoring of gas-hydrate or bitumen-saturated reservoir, especially for reservoir rocks with complex microstructures and heterogeneous pore types. [ABSTRACT FROM AUTHOR]

Multiferroic nanocomposite films composed of P(VDF-TrFE) copolymer and CoFe2O4 (CFO) nanoparticles have been prepared by a modified polymeric processing. Structural characterizations reveal that CFO nanoparticles with 80–100 nm diameters are well distributed in the P(VDF-TrFE) matrix. The crystalline and microstructure of P(VDF-TrFE) are strongly dependent on the volume fraction of CFO nanoparticles, which are further analyzed by Raman spectra. Consequently, the ferroelectric and magnetoelectric responses are strongly influenced by the concentration of CFO nanoparticles. A significant magnetoelectric coupling effect of around 40 mV/cm Oe is obtained from the nanocomposites. A relatively simple model has been adopted to calculate the magnetoelectric coefficient, which is also in agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Pure ZnO and aluminum doped ZnO films (ZAO) were prepared by sol-gel method and the effect of Al doping on the microstructure and electrical properties of the films was investigated. The results showed that the transformation from granular to columnar structure could be observed in pure ZnO films with the increase in heating time while in aluminum doped films little structural changes occurred even after a prolonged heating time. Additionally, measurements of electrical properties showed that both microstructural evolution and doping could significantly improve the conductivity of the films, which could be assigned to an increase both in Hall mobility and carrier concentration. The relationship between microstructure and the electrical properties of the films was discussed, and various scattering mechanisms were proposed for sol-gel derived ZnO and ZAO films as a function of the carrier concentration. [ABSTRACT FROM AUTHOR]

The microstructure, magnetic, and optical properties of Mn-doped ZnO films have been examined. It has been found that Mn doping could improve the growth of ZnO (002) orientation without Mn oxide formation. All the films are ferromagnetic with a Curie temperature of above 350 K. The ferromagnetism comes from the ferromagnetic interaction activated by oxygen vacancies between the Mn ions that replace Zn ions, but not from Mn oxide impurities. At an atomic fraction of 2.2% Mn, the average moment per Mn ion reaches a maximum of 0.55μB. With the further increase of Mn atomic fraction, the average moment per Mn ion decreases because the antiferromagnetic energy is lower than the ferromagnetic one due to the reduced distance between the adjacent Mn ions. Meanwhile, the optical band gap value increases from 3.120 to 3.162 eV with the increase of Mn atomic fraction from 0% to 7.5%. [ABSTRACT FROM AUTHOR]

Nd-Fe-B permanent magnets with a small amount of CuZn5 powders doping were prepared by conventional sintered method. The effects of CuZn5 contents on magnetic properties and microstructure, electrochemical corrosion resistance of sintered Nd-Fe-B magnets were systematically studied. The results show that the magnetic properties of magnets do not have a significant variation by CuZn5 powders doping; the coercivity of magnets rises gradually, while the remanence of the magnets decreases a little with increasing of the CuZn5 amount. The CuZn5 doped magnets have more positive corrosion potential, Ecorr, and much lower corrosion current density, icorr, than the magnets without CuZn5 doping, indicating CuZn5 doping could improve the corrosion resistance. Both Zn and Cu enrich mainly into the Nd-rich phase, fully improve the wettability between the Nd-rich phase and the Nd2Fe14B phase, and repair the defects of the main phase, so the coercivity of magnets doped with CuZn5 powders rises. Such microstructure modification effectively restrains the aggressive inter-granular corrosion. As a result, the CuZn5 doped magnet possesses excellent corrosion resistance in NaCl electrolyte. [ABSTRACT FROM AUTHOR]

Intermetallic matrix composite coatings reinforced by TiC, TiB2, and Ti3AlC2 were fabricated by laser cladding the mixed power Ti, Al, and B4C on the Ti-6Al-4V alloy. X-ray diffraction, scanning electron microscope, and energy dispersive spectroscopy were chosen to investigate the structures and morphologies of the coatings. Results showed that the coatings mainly consisted of the reinforcements of TiC, TiB2, and Ti3AlC2 and the matrix of Ti3Al, TiAl, TiAl3, and α-Ti. The hardness and wear-resisting property of the prepared specimens of Ti-45Al-10B4C and Ti-45Al-20B4C were studied contrastively. It was found that the coating was metallurgical bonded to the Ti-6Al-4V substrate. The micro-hardness and dry sliding wear-resisting properties of the specimen of Ti-45Al-20B4C were enhanced further. And the micro-hardness of Ti-45Al-20B4C was from 900 HV0.2 to 1225 HV0.2. The wear-resisting property of Ti-45Al-20B4C was four times as large as that of the Ti-6Al-4V alloys. [ABSTRACT FROM AUTHOR]

Ferritic/martensitic (F/M) steels with high strength and excellent ductility are important candidate materials for the life extension of the current nuclear reactors and the design of next generation nuclear reactors. Recent studies show that equal channel angular extrusion (ECAE) was able to improve mechanical strength of ferritic T91 steels moderately. Here, we examine several strategies to further enhance the mechanical strength of T91 while maintaining its ductility. Certain thermo-mechanical treatment (TMT) processes enabled by combinations of ECAE, water quench, and tempering may lead to “ductile martensite” with exceptionally high strength in T91 steel. The evolution of microstructures and mechanical properties of T91 steel were investigated in detail, and transition carbides were identified in water quenched T91 steel. This study provides guidelines for tailoring the microstructure and mechanical properties of T91 steel via ECAE enabled TMT for an improved combination of strength and ductility. [ABSTRACT FROM AUTHOR]

This paper proposes a new method to investigate the effect of specimen size on fatigue life of metallic materials in high-cycle fatigue and very-high-cycle fatigue regimes in the light of statistical analysis. The performance of large specimen is correlated with that of small specimen via control volume (a high stress domain where potential fatigue crack initiation sites are located). The simulation results are in good agreement with a series of experimental data in high-cycle fatigue and very-high-cycle fatigue regimes from literature. The method is helpful for a quantitative estimation of fatigue life of large specimens from the experimental data of small specimens. [ABSTRACT FROM AUTHOR]

Nickel superalloys with cubic L1 2 structured γ′ (Ni 3 (Al, Ti)) precipitates exhibit high strength at high temperatures and excellent corrosion resistance when exposed to water. Unlike prior studies on irradiation damage of other Ni-based superalloys, our study on Rene N4 involves much larger γ′ precipitates, ∼450 nm in size, a size regime where the irradiation-induced disordering and dissolution kinetics and the corresponding mechanical property evolution are unknown. We report that under heavy ion irradiation at room temperature, the submicron-sized γ′ precipitates were fully disordered at ∼0.3 dpa and only later partially dissolved after 75 dpa irradiation. Nanoindentation experiments indicate that the mechanical properties of the alloy change significantly, with a dramatic decrease in hardness, with irradiation dose. Three contributions to the change in hardness were examined: defect clusters, disordering and dissolution. The generation of defect clusters in the matrix and precipitates slightly increased the indentation hardness, while disordering of the submicron-sized γ′ precipitates resulted in a dramatic decrease in the total hardness, which decreased further during the early stages of the intermixing between γ′ precipitates and matrix (<18 dpa). Controlling the long-range-ordering and chemical intermixing can be used to tailor the mechanical properties of Ni-based superalloys under irradiation. [ABSTRACT FROM AUTHOR]

In the present study, the amorphous Cr-Mo alloy was synthesised by mechanical alloying of immiscible Cr and Mo elements (Cr-35at.%Mo powders) at a temperature of ∼260 K under Ar atmosphere. The X-ray diffraction and transmission electron microscopy analysis showed that there was a transition between the Cr(Mo) solid solution and amorphous Cr-Mo phase during mechanical alloying. With increasing milling time, the initially formed Cr(Mo) solid solution transformed to the amorphous Cr-Mo alloy, which then transformed to Cr(Mo) solid solution once more. The underlying reason for this transition is likely the metastable nature of these two phase, i.e., solid solution and amorphous alloy. [ABSTRACT FROM AUTHOR]

Highlights: [•] The first successful severe plastic deformation of 12Cr ODS steels. [•] Significantly refined and homogeneous microstructure in ODS steels. [•] Shear stress induced drastic variation of geometry of Y2O3 nanoparticles. [•] Strengthening arising primarily from grain refinement. [ABSTRACT FROM AUTHOR]

We report on the microstructure and mechanical properties of T91 alloy subjected to different thermomechanical treatments (TMTs). Equal channel angular extrusion (ECAE) was performed at 23, 300, 625, and 700 °C. Mechanical strength of T91 alloy is enhanced after cold-ECAE at the expense of ductility. In comparison, the hot-ECAE process leads to less pronounced hardening but retention of ductility and work hardening ability. Microstructure analyses reveal that cold-ECAE has significantly reduced the average grain size, while hot-ECAE is more effective to refine and uniformly redistribute carbide nanoprecipitates. Post-ECAE annealing (500 °C/10 h) leads to reprecipitation of large carbide particles in cold-ECAE processed alloy, whereas the hot-ECAEed specimens retain smaller nanoscale carbide precipitates and uniform microstructure. A mechanism is proposed to explain the influence of TMT on the evolution of precipitates. Strengthening of T91 alloy is discussed through a modified model that considers the effects of dislocation density, grain size, and precipitation hardening. [ABSTRACT FROM AUTHOR]

Microstructure and mechanical properties of an AZ61 Mg alloy during cyclic closed die forging (CCDF) were studied. The mechanisms of grain refinement are discussed. The results show that the average grain size decreased with increasing number of CCDF passes; After 6 CCDF passes, the initial grain size of 152 μm decreased to about 16·5 μm, and the billet had a uniform microstructure. The grain refinement occurs mainly by continuous dynamic recrystallisation. With increasing numbers of CCDF passes, both the tensile strength and the elongation to failure of the alloy are significantly enhanced. [ABSTRACT FROM AUTHOR]

For the alloy to be shaped in the semisolid state, it must have an appreciable melting range; before thixoforming, the microstructures must consist of solid metal spheroids in a liquid matrix. Equal channel angular extrusion (ECAE) was used as a process to predeform as cast AZ80 magnesium alloy before partial remelting. The results show that fine and equiaxed grains are obtained due to dynamic recrystallisation during ECAE. Following partial remelting in each case, the microstructure consisted of globular solid grains with liquid film along the grain boundaries. During partial remelting, solid grain sizes at 560°C were smaller than those at 550°C. Moreover, the degree of spheroidisation at 560°C was greater than that at 550°C. Good mechanical properties are obtained for the thixoformed AZ80 alloy prepared by six-pass ECAE with a yield strength of 210 MPa, an ultimate tensile strength of 320 MPa and an elongation to fracture of 9·2%. The results also show that the process, ECAE plus partial remelting, can produce fine and spheroidal solid grains surrounded by liquid film, which are suitable for thixoforming. [ABSTRACT FROM AUTHOR]

Significant microstructural damage, in the form of defect clusters, typically occurs in metals subjected to heavy ion irradiation. High angle grain boundaries (GBs) have long been postulated as sinks for defect clusters, like dislocation loops. Here, we provide direct evidence, via in situ Kr ion irradiation within a transmission electron microscope, that high angle GBs in nanocrystalline (NC) Ni, with an average grain size of ~55 nm, can effectively absorb irradiation-induced dislocation loops and segments. These high angle GBs significantly reduce the density and size of irradiation-induced defect clusters in NC Ni compared to their bulk counterparts, and thus NC Ni achieves significant enhancement of irradiation tolerance. [ABSTRACT FROM AUTHOR]

A dual-resonator microstructure design is proposed for acoustic metamaterials to achieve broadband effective mass negativity. We demonstrate the advantage of acoustic wave attenuation over a wider frequency spectrum as compared to the narrow band gap of a single-resonator design. We explicitly confirm the effect of negative effective mass density by analysis of wave propagation using finite element simulations. Examples of practical application like vibration isolation and blast wave mitigation are presented and discussed. [ABSTRACT FROM AUTHOR]

Abstract: Equal channel angular pressing was used to refine the microstructure of a Fe–14Cr–16Ni (wt.%) alloy. The as-processed alloy had predominantly equiaxed austenite fine grains with an average grain size of 0.4μm and a low fraction of deformation induced martensite. Ex situ isothermal annealing experiments showed the fine microstructure was thermally stable up to 673K, and abnormal grain growth occurred at ∼873K. In situ annealing studies in a transmission electron microscope revealed the coarsening of grains. Analysis of grain growth kinetics from 873 to 1073K yielded average activation energy of grain growth to be ∼207kJ/mol. The grain growth mechanisms and annealing induced evolution of mechanical properties were discussed. [Copyright &y& Elsevier]

Abstract: The evolutions of microstructure and mechanical properties of Fe–14Cr–16Ni (wt.%) alloy subjected to Helium ion irradiations were investigated. Equal channel angular pressing (ECAP) process was used to significantly reduce the average grain size from 700μm to 400nm. At a peak fluence level of 5.5 displacement per atom (dpa), helium bubbles, 0.5–2nm in diameter, were observed in both coarse-grained (CG) and ultrafine grained (UFG) alloy. The density of He bubbles, dislocation loops, as well as radiation hardening were reduced in the UFG Fe–Cr–Ni alloy comparing to those in its CG counterpart. The results imply that radiation tolerance in bulk metals can be effectively enhanced by refinement of microstructures. [Copyright &y& Elsevier]

A two-dimensional (2D) lattice model with anisotropic resonant microstructures is found to provide an anisotropic band gap structure. A 2D continuum with anisotropic effective mass density is introduced to represent this lattice system. Two methods are proposed to derive the equivalent continuum. In the first method, the effective mass density of the equivalent continuum is obtained by matching the dispersion relations for harmonic waves propagating in the principal directions. The second approach employs an approximate estimation of the effective mass density by volume-averaging an effective mass that represents the resonant microstructure. For both equivalent continuum models, the effective mass density is frequency-dependent and may become negative in certain frequency ranges. Subsequently, the effective mass density of the equivalent continuum assumes the form of a second-order tensor. Thus, it suffices to determine the effective mass density tensor with respect to the principle directions. It is shown numerically that the local-resonance effect is accurately described by the equivalent continuum model. In addition, the effect of anisotropic mass density on wave propagation is numerically illustrated and discussed. [ABSTRACT FROM AUTHOR]

In this study, we investigated dispersion curves and the band gap structure of a multiresonator mass-in-mass lattice system. The unit cell of the lattice system consists of three separate masses connected by linear springs. It was demonstrated that the band gaps can be shifted by varying the spring constant and the magnitude of the internal masses. By using the conventional monatomic (single mass) lattice model as an equivalent system, the effective mass was found to become negative for frequencies in the band gaps. An attempt was made to represent the two-resonator mass-in-mass lattice with a microstructure continuum model. It was found that the microstructure continuum model can capture the dispersive behavior and band gap structure of the original two-resonator mass-in-mass system. [ABSTRACT FROM AUTHOR]

Magnesium matrix composites reinforced with SiO2 coated carbon fibers have been investigated, with an emphasis given on the relation between the material strength and interfacial microstructure. The composites were studied as a function of aluminium (Al) content that is varied between 0 and 9 wt%. The obtained results indicate that the reactivity at the C/Mg–Al interface of the composite can be controlled by varying the Al content. The low Al content in C/Mg–1Al has been completely dissolved in the matrix with no segregation even after solidification, leading to the best mechanical performance. If the Al content is increased to ≥3 wt% (composites such as C/AZ31 and C/AZ91), the SiO2 coatings are fully depleted due to an extensive formation of carbides at the interface. The precipitates are further identified as Al2MgC2 phase that is similar to binary carbide Al4C3. SiO2 coating on the fiber layer prior to fabrication of composite is found to be a promising way to suppress the carbide formation and enable the use of Mg–Al matrix with appropriate Al content. [ABSTRACT FROM AUTHOR]

The use of molecular dynamics (MD) to model and analyze the properties of nanostructured materials is very heavy on computing time. In this paper, the framework of continuum theory is extended so that it can capture the properties which are connected to the microstructure or nanostructure, but still maintain its simplicity and efficiency. The key step in this approach is the establishment of a relationship between the local kinematics and the global continuum variables. The developed model is capable of accounting for local deformation of micro/nanostructures. Propagations of harmonic waves of different wavelengths in layered media and lattice systems are considered and the resulting dispersion curves are used to evaluate the accuracy of the continuum model. The model is also employed to study wave reflection and transmission at the boundary of two media with different micro/nanostructures. [ABSTRACT FROM AUTHOR]

Iron aluminide (Fe³A1) composites reinforced with ~3 wt% of carbon nanotube (CNT) were fabricated by hot press consolidation. Ambient-temperature mechanical properties of the iron aluminide-CNT composites were determined. The hardness, compressive yield strength, and bending strength hardness of composites were higher by 63%, 1%, and 5%, respectively. Microscopic examination of the composite showed the added CNTs still keep their tubular structure. The preliminary results on the processing and improvement in mechanical properties of CNT-reinforced iron aluminide matrix composites are being reported here for the first time. [ABSTRACT FROM AUTHOR]

The objective of this paper is to extend the framework of the continuum theory so that it can capture the properties that are embedded in the microstructure or nanostructure and still keep its simplicity and efficiency. The model thus developed is capable of accounting for local deformation of microstructures in solids especially their micro- (local) inertia effect. The essence underlying this approach is the introduction of a set of bridging functions that relate the local deformation of microstructures to the macrokinematic variables. Once the solution of the macroscopically homogeneous continuum is obtained, the solutions in the microstructures are obtained through the use of these bridging functions. Propagation of waves of different wavelengths is considered and the dispersion curve is used to evaluate the accuracy of the model. The model is also employed to study wave reflection and transmission at the boundary of two media with microstructures of very different scales. [ABSTRACT FROM AUTHOR]

Abstract: We present in this paper the development of a high-resolution projection micro-stereolithography (PμSL) process by using the Digital Micromirror Device (DMD™, Texas Instruments) as a dynamic mask. This unique technology provides a parallel fabrication of complex three-dimensional (3D) microstructures used for micro electro-mechanical systems (MEMS). Based on the understanding of underlying mechanisms, a process model has been developed with all critical parameters obtained from the experimental measurement. By coupling the experimental measurement and the process model, the photon-induced curing behavior of the resin has been quantitatively studied. The role of UV doping has been thereafter justified, as it can effectively reduce the curing depth without compromising the chemical property of the resin. The fabrication of complex 3D microstructures, such as matrix, and micro-spring array, with the smallest feature of 0.6μm, has been demonstrated. [Copyright &y& Elsevier]

Grain growth dependence of microstructure in La[sub 2/3]Ba[sub 1/3]MnO[sub 3+δ] oxides has been studied in detail. The result shows that the crystals grew along three vertical axes with a concentric terrace pattern in the sample sintered at 1673K while the oxides sintered at 1573K grew with a lateral growth manner. However, the concentric terrace growth pattern resulted in twin microstructure in the cooling processing and the lateral growth manner produced non-twin microstructure in the oxides at ambient, respectively. It was found that the oxide with twin microstructure has a much higher saturation magnetization than the non-twin oxide. This may be due to the easier alignment of the domains in the twin-grained oxide through the rearrangement of dislocations in twin-boundaries. [ABSTRACT FROM AUTHOR]

In this letter, an elastic metamaterial which exhibits simultaneously negative effective mass density and bulk modulus is presented with a single unit structure made of solid materials. The double-negative properties are achieved through a chiral microstructure that is capable of producing simultaneous translational and rotational resonances. The negative effective mass density and effective bulk modulus are numerically determined and confirmed by the analysis of wave propagation. The left-handed wave propagation property of this metamaterial is demonstrated by the negative refraction of acoustic waves. [ABSTRACT FROM AUTHOR]

The application of nanophononic heterogeneous materials requires efficient and accurate modeling and analysis tools. For nanostructured materials, the use of atomistic simulation may be a potential solution. However, it is well known that this approach is beset with prohibitive computing time and an astronomical amount of data generated. In this letter, a microstructure continuum theory is employed to describe wave propagation in these materials. The key step in this approach is the establishment of a relationship between the local kinematics and the global continuum variables so that the characteristics of the nanostructure are captured. Propagation of longitudinal harmonic waves in nanophononic media is considered and the resulting dispersion curves are used to evaluate the accuracy of the microstructure continuum model. [ABSTRACT FROM AUTHOR]

Based on the synthesis of a sufficient amount of AlN nanowires (AlN-NWs), AlN-NWs/Al composites with homogenously distributed AlN-NWs were fabricated. Microstructural observations reveal that the interface between AlN-NWs and Al matrix is clean and bonded well, and no interfacial reaction product was formed at the nanowire-matrix boundary. Mechanical properties including yield and tensile strength of the composites were improved with AlN-NWs volume fraction changing from 5 to 15 vol%, and the maximum yield and tensile strengths of the composite were about 6 and 5 times, respectively, as high as those of Al matrix. Meanwhile, AlN-NWs effectively decreased the coefficient of thermal expansion (CTE) of the composites, and the CTE of 15 vol% composite was about one half that of Al matrix. The results obtained suggest that AlN nanowire is a promising reinforcement for optimizing the mechanical and thermal properties of metal matrix composites. [ABSTRACT FROM AUTHOR]

NiCoCrAlYSiB coatings were deposited on the Co-based superalloy K40 by arc ion plating (AIP). The oxidation behavior of the bare alloy and of the coated specimens was tested in static air for 200 h at 1000 °C and 100 h at 1050 °C. The results showed that the oxidation rate of the system was greatly reduced by the addition of the NiCoCrAlYSiB coatings. Thin and adherent á-A12O3 scales that formed on the coated specimens protected the substrates from further oxidation attack while non-protective oxide scales, mainly of Cr2O3 and CoCr2O4, appeared on bare K40 alloy. Element profiles on metallographic cross sections indicated that apparent interdiffusion occurred between the coatings and the substrates. The interdiffusion behavior and the resulting microstructure were investigated. As compared to aluminide coatings, NiCoCrAiYSiB coatings have less influence on the substrate microstructure. [ABSTRACT FROM AUTHOR]

This paper proposes a new model for semi-active Tuned Liquid Column Damper (sTLCD) where the sTLCD is connected to the primary structure using an adaptive spring. Short time Fourier transformation (STFT) based control algorithms (feedforward and feedback) are developed to control the stiffness of the spring such that the sTLCD is tuned in real-time when the dominant excitation frequency varies or damage occurs to the primary structure. The effectiveness of the proposed sTLCD and the associated control algorithms is examined numerically under random excitations including stationary and non-stationary excitations. Root Mean Square (RMS) response is computed in three cases: with no TLCD, with a passive Tuned Liquid Column Damper (pTLCD) and with the sTLCD. Results indicate that the developed control algorithms are effective in tuning the frequency of the sTLCD in real-time. As a result, the sTLCD provides more robust reduction than the pTLCD because the pTLCD becomes off-tuned and loses its effectiveness when the properties of the excitations or the primary structure vary. [ABSTRACT FROM AUTHOR]

Abstract: Nanostructured Cu/Fe multilayers on Si (110) and Si (100) substrates were prepared by magnetron sputtering, with individual layer thicknesses h varying from 0.75 to 200nm. The growth orientation relationships between Cu and Fe at the interfaces were determined to be of the Kurdjumov–Sachs and Nishiyama–Wasserman type. Nanoscale columnar grains in Fe, with an average grain size of 11–23nm, played a dominant role in the strengthening mechanism when h ⩾50nm. At smaller h the hardness of Cu/Fe multilayers with (100) texture approached a peak value, followed by softening due to the formation of fully coherent interfaces. However, abundant twins were observed in Cu/Fe films with (111) texture when h =0.75nm, which led to the retention of high hardness in the multilayers. [Copyright &y& Elsevier]

WB 2 /Cr multilayer films with different modulation ratios (λ = 1, 3, 5, 7, 12, and 20) were deposited by a combination of direct-current and pulse direct-current magnetron sputtering, and the number of bilayers was fixed at ten. The effect of the modulation ratio on the microstructure, mechanical and tribological properties of the multilayer films was investigated in detail. X-ray diffraction demonstrates that a preferred orientation of WB 2 (101) and Cr (110) exists, and WB 2 (101) dominates the film's growth with increasing of modulation ratio. The TEM results show that the multilayer films consist of nanograins dispersed in an amorphous matrix in WB 2 layers and polycrystalline grains in Cr layers. The hardness increases with the increasing modulation ratio, and the maximum hardness (31.1 GPa) is obtained at λ = 20. The indentation toughness presents an opposite changing trend, and the maximum indentation toughness (1.264 MPa m1/2) is obtained in S1 at λ = 1 which conforms to the rule of mixture due to the relatively thick bilayer thickness (Λ = 160–192 nm). The wear mechanism is investigated, and the results suggest that the multilayer film with λ = 7 possesses the best wear resistance (2.06 × 10−7 mm3/Nm), benefiting from the balance of hardness and indentation toughness. [ABSTRACT FROM AUTHOR]

• An method of electroplating, AIP and diffusion treatment was proposed to prepare ReCr co-doped β-NiAl coating. • ReCr co-doped β-NiAl coating was mainly consisted of β-NiAl, wherein plentiful ReCr-rich phases formed. • ReCr-rich precipitates were α-Cr phase, wherein some Re solubilized in α-Cr phase. To prepare ReCr co-doped β-NiAl coating, an innovative method that electroplating NiRe combined with arc ion plating (AIP) Cr, AIP Al and followed by diffusion treatment was proposed. ReCr co-doped β-NiAl coating contained an outer β-NiAl layer with fine dispersive ReCr-rich precipitates, an inner β-NiAl layer with fine dispersive W-rich precipitates and bottom interdiffusion zone (IDZ). And ReCr-rich phases were mainly distributed in the interior of coating grain. The TEM results proved that ReCr-rich precipitates were α-Cr phase as main phase, wherein some Re solubilized in α-Cr phase and it did not change the phase structure of α-Cr. [ABSTRACT FROM AUTHOR]

• The combustion reaction zone was composed of the oxide zone, melting zone and heat-affected zone. • The enrichment of elements at the melting zone/heat-affected zone interface influenced the interface propagation rate. • Broadening the liquid oxide zone was beneficial to improve the flame retardant properties. The combustion behavior and mechanism of TC25 alloy were investigated by titanium fire melt liquid droplet tests. Moreover, the microstructure and element distribution after combustion were analyzed. Results showed that the combustion reaction zone was composed of the oxide zone, melting zone and heat affected zone. The enrichment of alloying elements, such as Si, Zr, Mo, Sn and W at the melting zone/heat affected zone interface played a pivotal role in regulating the interface propagation rate. The diffusion of Al element was the rate-determining step in the initial stable combustion stage, whereas the diffusion of O element became the rate-determining step in the subsequent combustion stage. [ABSTRACT FROM AUTHOR]

Abstract A MoSi 2 coating was prepared on Nb-10Hf-1Ti alloys by a two-step process. The first step was arc ion plating (AIP) of the Mo layer, and the second step was halide-activated pack cementation (HAPC) of Si. The coating is composed of an outer layer of MoSi 2 and an inner bond layer. After oxidation testing at 1200 °C for 100 h in a static air atmosphere, the mass gain of the coated specimen was 0.64 mg/cm2. The good oxidation resistance of the MoSi 2 coating is attributed to the protective SiO 2 scale generated by the oxidation process. [ABSTRACT FROM AUTHOR]

• NiPt-Hf layer provided Ni element required to form the coating. • There was no TCP phase precipitation in DAZ for PtHf co-doped γʹ coating. • The thickness of DAZ in PtHf co-doped γʹ+β coating was about 18 μm. • The proportion of β-NiAl in coating increased with the increase of Al layer thickness. Two PtHf co-doped Ni-Al coatings were fabricated by the following steps: first, NiHf layer and Pt layer were electroplated on the substrate, then vacuum annealed at 800 ℃ for 5 h; Second, Al layer was deposited via arc ion plating (AIP); Finally, vacuum annealing was proceeded at 1050 ℃ for 2 h. The Al contents in PtHf co-doped γʹ coating and PtHf co-doped γʹ+β coating were about 24 at.% and 42 at.%, respectively. In addition, no topologically close-packed (TCP) phases were precipitated in the diffusion affected zone (DAZ) in the PtHf co-doped γʹ coating, while many TCP phases were precipitated in the DAZ in the PtHf co-doped γʹ+β coating. The interdiffusion coefficient of Al gradually decreased with the reduction of Al content and the increase of Pt content in coating, consequently suppressing the precipitation of TCP phases. [ABSTRACT FROM AUTHOR]

The study is mainly to optimize the process parameters (sputtering pressure and sputtering power) of the AlB 2 -type WB 2 films deposited by DC magnetron sputtering by comparing their microstructure, elemental composition, and tribo-mechanical properties. As the argon pressure (P Ar ) increases (0.3–1.0 Pa), the particle density increases first and then decreases, with a corresponding decrease for particle energy. Under this condition, both the deposition rate and the B/W atomic ratio of the WB 2 films increase first and then decrease under the competition effect between the sputtering and scattering process, the film orientation changes from (0 0 1) to (1 0 1), the microstructure changes from dense fine-fiber to porous column coupled with the stress evolution from compressive stress to increased tensile stress. Consequently, films deposited at P Ar > 0.5 Pa have the poor hardness and wear-resistance. As the sputtering power increases (150–310 W), both the particle density and particle energy increase. Thus, the deposition rate increases greatly, the B/W atomic ratio declines slightly due to the resputtering process, the film structure becomes dense but rough by the particle bombardment causing the stress change from tensile stress to enhanced compressive stress, and the film orientation changes from the well-crystallized (0 0 1) to poor-crystallized (1 0 1). In conclusion, films with (0 0 1) orientation, high B/W atomic ratio, dense structure and proper compressive stress, which can be deposited at P Ar = 0.5 Pa and sputtering current 0.5 A (corresponding to target power about 150 W), show the excellent tribo-mechanical properties with high hardness about 39.4 GPa and low wear rate of 2.2 × 10 −7 mm 3 /mN. [ABSTRACT FROM AUTHOR]

• The filler matrix/cBN abrasive coating was prepared using vacuum brazing. • The interfacial products TiN/TiB 2 /TiB were formed on the surface of cBN. • The filler matrix consisted of Ti 2 Ni, eutectic (Ti,Zr) 2 (Ni,Cu) and eutectoid. In order to maintain tight tolerance of aero-engine and reduce the risk of titanium fire, a filler matrix/cBN abrasive coating for blade tip of titanium alloy was prepared using vacuum brazing. The results revealed that the interfacial reaction products TiN/TiB 2 /TiB with interatomic bonding were formed between cBN particles and the filler matrix. Moreover, the filler matrix was composed of Ti 2 Ni, (Ti,Zr) 2 (Ni,Cu) and a small amount of lamellar eutectoid. The detailed analysis on the microstructure may provide novel insights into improving the wear resistance and burning resistance of the abrasive coating. [ABSTRACT FROM AUTHOR]

AISI 316 L austenitic stainless steels (316 L SS) were nitrided to enhance their mechanical property and corrosion resistance by a high efficiency low-pressure arc plasma nitriding process at low temperature (~ 400 °C). Arc currents ranging from 55 A to 95 A were applied to generate the arc plasma. The effect of arc current on the microstructure, mechanical property of the nitrided layers was investigated by using XRD, SEM, TEM, Vickers microhardness tester and ball-on-disk tribometer, respectively. The corrosion resistance was also evaluated by potentiodynamic polarization in 3.5% NaCl solution. The results showed that the nitrided layers consisted primarily of the expanded austenite (γ N ) phase with a trace of a mixture of CrN and Fe 3 N. The thickness of nitrided layer could reach 15 μm in 1 h at 400 °C in virtue of the high-density and high-energy nitrogen plasma generated from this process, which showed an extremely fast nitriding kinetics. Due to the solution strengthening of the nitrogen super-saturation γ N -phase formed on the surfaces of the samples, the surface microhardness and the wear resistance of the nitrided 316 L SS was significantly improved. The worn surfaces revealed that worn behavior of the low current (below 85 A) nitrided samples was remarkably dominated by micro-abrasion and spalling holes, while the 95 A sample was worn in a mode featured by cracks and spalling blocks. Besides, because chromium nitride precipitation was eliminated, the nitrided samples still showed excellent corrosion resistance, which was comparable to untreated 316 L SS. [ABSTRACT FROM AUTHOR]

The study is mainly to develop a new type of hard nanocomposite films based on the AlB 2 -type WB 2 (h-WB 2 ) system by studying the influence of carbon contents on the microstructures, mechanical and tribological properties, and thermal stability of the WBC films. By increasing the C 2 H 2 partial pressure (P C2H2 ), carbon atoms present in forms of solid solution h-WB x C y and amorphous carbide a-WC, a-WB x C y , a-C:H (polymeric carbon) successively. Consequently, two- or three-phase nanocomposite films with microstructures comprising of nanocrystalline grains embedded in an amorphous matrix have been developed. Films with the h-WB x C y /a-WC and h-WB x C y /a-WC/a-C:H (or h-WB x C y /a-WB x C y /a-WC/a-C:H) nanocomposite structure deposited at P C2H2 ≤ 0.01 Pa (14.9–26.4 at.% C) exhibit highest hardness about 45 GPa and lowest wear rate about 10 − 8 mm 3 /mN. And the transformation temperature of the h-WB 2 phase has been enhanced greatly from 700 to 1000 °C by slight C-doping due to the formation of the strong interfaces between the nanocrystalline and amorphous phase in the films deposited at P C2H2 = 0.008 Pa. Moreover, proper C content (less than 26.4 at.%) can refine the film structure and reduce the oxygen impurity content and thereby improve the film properties. The residual stress of the films changes from tensile to compressive stress with the introduction of carbon, and the value of compressive stress is closely related to the film structures. [ABSTRACT FROM AUTHOR]

Alternating multilayer diamond-like carbon (DLC) films [(Cr, N)-DLC/DLC] with different sp 3 contents in DLC layer have been prepared on YG8 (WC-Co) substrates by FCVA combined with DCVA technique. The structure was investigated by scanning electron microscopy and transmission electron microscopy. Chemical bonding was studied by Raman spectroscopy and X-ray photoelectron spectroscopy. Mechanical and tribological properties including residual stress, hardness, adhesion strength and wear resistance were evaluated by film stress tester, nanoindenter, scratch tester, ball-on-disk tribometer and surface profiler. The results showed that (Cr, N)-DLC layer had the composite structure of amorphous phase as base interspersed with a small amount of nano-crystals. The co-doping of Cr and N into DLC reduced the film's residual stress from − 1.62 GPa to − 0.99 GPa. For monolayer DLC, both the sp 3 content and residual stress decreased as the substrate's bias voltage increased in the range of − 100 V to − 600 V. And the decrease of sp 3 content contributed to an increase of the (Cr, N)-DLC/DLC films' toughness. In addition, the multilayer films presented good adhesion strength on YG8 substrates. The wear rates of all multilayer films belonged to the order of magnitude of 10 − 7 mm 3 /Nm. Prime novelty statement Multilayer films consisting of DLC and DLC co-doped with metal and nonmetal atoms [(Cr, N)-DLC/DLC multilayer films] have been prepared by FCVA combined with DCVA technique and investigated systematically. The composite structure of the (Cr, N)-DLC layer is based on amorphous phase and contains a small number of nano-crystalline compounds of chromium. [ABSTRACT FROM AUTHOR]

Highlights: [•] Microstructures of two Co modified NiAl coatings have been studied. [•] The addition of Co improves the corrosion resistance in sulfate salts at 700°C. [•] For the sulfide and its eutectic of Co are more stable than those of Ni. [•] In chloride salts coating with medium Co content has best corrosion resistance. [ABSTRACT FROM AUTHOR]

In this study, AlB2-type WB2 films are deposited on YG8 (WC–Co) substrates by DC magnetron sputtering at different substrate bias voltages and temperatures. Their effects on the film microstructure, elemental composition, mechanical and tribological properties are investigated systematically by various analysis methods, including X-ray diffraction (XRD), electron probe X-ray microanalyzer (EPMA), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), nano-indentation, ball-on-disk tribometer and micro scratch tester. The as-deposited films show an under-stoichiometric composition with rich tungsten concentration and have an obvious columnar structure. With the substrate bias voltage increasing (from 0V to −150V), the orientation of the films changes from (0 0 1) to (1 0 1). And films obtained at −50V show superior mechanical and tribological properties. By increasing the substrate temperature to 500°C, the maximum hardness about 40.5GPa and the best adhesive strength of 60N are detected. The films with the fine-grain amorphous structure, produced at 300°C and −50V, exhibit the minimum friction coefficient of 0.28. And the minimum wear rate of 2.3×10−7 mm3/mN is obtained for the films deposited at −50V and 400°C. The properties described above are attributed to the variations of microstructure and morphologies in the films. Furthermore, the wear track and debris are also discussed by virtue of FESEM/EDS to explore the self-lubricating behavior of the AlB2-type WB2 film. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogenated nanocrystalline silicon (nc-Si:H) films were prepared using diluted tetrachlorosilane (SiCl4) with various hydrogen flow rates (Hf) by plasma enhanced chemical vapor deposition (PECVD) at a constant substrate temperature (Ts) as low as 120°C. Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), infrared spectra (IR) and spectroscopic ellipsometry (SE) were employed to investigate the microstructure and hydrogen bonding of the nc-Si:H films. Our results showed that the microstructure and hydrogen content of the films could be effectively tailored by the hydrogen flow rates, and a distinct transition from amorphous to nanocrystalline phase was observed with an increase of Hf. At an optimal preparation condition, a deposition rate was as high as 3.7nm/min and the crystallinity reached up to 64.1%. In addition, the effect of hydrogen on the low-temperature growth of nc-Si:H film was proposed in relation to the surface reaction of radicals and the hydrogen diffusion in the surface growing region. [Copyright &y& Elsevier]

Abstract: CrN coatings have been grown by arc ion plating (AIP) onto Ti6Al4V alloy substrate at various nitrogen pressures (). The goals of this investigation are to study the influence of nitrogen pressure content on the composition, structure and mechanical properties of AIP CrN coatings, as well as their tribological properties. With an increase of , the main phases in the coatings changed from CrN+Cr2N+Cr to CrN, and the texture of CrN was transformed from CrN (111)-oriented to (220)-oriented. Furthermore, the multi-layers including a metal Cr layer, a Cr2N layer and a CrN layer were observed by cross-sectional TEM (XTEM), besides an “unbalanced” state transition layer at the interface of CrN/substrate which was analyzed by nucleation thermodynamics subsequently. An increase in nitrogen pressure also resulted in a change of micro-hardness due to the variation in composition and structure. Finally, the tribological properties of the Ti6Al4V substrate and the CrN/Ti6Al4V coating system have also been explored, which shows that CrN coatings can act as good wear resistance layer for Ti6Al4V substrate. [Copyright &y& Elsevier]