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Among various processing methods for growing perovskite thin layers, dual-source vacuum deposition was once regarded as the most economical and high throughput method. However, co-evaporation of MAI and PbI2 often leads to an inevitable PbI2 interfacial layer formed by the initial growth of evaporation resulting in a compromised efficiency of vacuum deposited MAPbI3 solar cell. Here, two modified growth methods based on vacuum co-evaporation, namely solution-vacuum hybrid method (SVHM) and soaking-assistant fully-vacuum method (SAFVM), are developed to grow a completely converted MAPbI3 perovskite layer at the interface prior to the co-evaporation of MAPbI3 perovskite layer. Upon these two methods, the unwanted PbI2 layer can be removed from the interface resulting in much improved power conversion efficiency up to 14.35%. Our result shows that, while unwanted interfacial PbI2 layer is the main cause of low performing co-evaporated perovskite solar cell devices, by removing the PbI2 interfacial layer we can unlock the full potential of vacuum-based perovskite solar cells to industrial mass production.

Oxidation behaviours and the interactions between friction and oxidation of Ni-based composites with in-situ carbides reinforcement were investigated at 800℃. Oxidation kinetics obey parabolic and parabolic-linear law. Oxide layers present hierarchy with three sublayers. I and II sublayers contain NiO, TiO2 and NiTiO3 etc.; III sublayer is O embrittled alloy layer. The pores in oxide layer result to transformation of oxidation kinetics from parabolic law to linear law. The worn oxide layers show the similar three-layered structure, comparable composition and faster thickening. Ultra-high flash temperature on worn surface induced by friction accounts for the formation and development of oxide layer.

This study aims to enhance the physical and mechanical properties of brick-concrete recycled aggregate (BCRA) using pozzolan slurry combined with sodium silicate and silicon-based additives. To investigate the modification mechanism, the particle shape characteristics, pore structure, and microstructure of BCRA were studied before and after the compound modification treatment. The research results showed that the apparent density of BCRA after compound modification treatment can be increased by 2.6%, and the water absorption and crushing index can be reduced by 42.4% and 28.5%, respectively. Specifically, the modification treatment of pozzolan slurry combined with sodium silicate has advantages in improving the apparent density and mechanical strength of BCRA, while the modification treatment of pozzolan slurry combined with silicon-based additives is more effective in reducing the water absorption of BCRA. Macro, meso, and microstructure changes were observed in the treated BCRA, where surface homogeneity, low porosity, and increased compactability were observed. The dynamic water absorption characteristics were also tested to evaluate the hydrophilic and hydrophobic behaviors of the untreated and treated BCRAs. Finally, a compound modification mechanism model for the BCRA was established.

The MAB phases are ternary, atomically laminated compounds that crystallize with orthorhombic structures and consist of transition metal (M) boride sublattices interleaved with single or double layers of Al. To date, the magnetic properties of ferromagnetic Fe2AlB2 have been well-studied experimentally, but those of most end member MAB phases with other transition metals remain poorly understood. Herein, predominantly single-phase Cr3AlB4 and Cr2AlB2 powders, with minor amounts of CrB impurities, were synthesized by heating mixtures of chromium monoboride (CrB), aluminum (Al), and boron or CrB and Al under flowing Ar. These reactants were found to substantially suppress the formation of undesired phases in the Cr-Al-B system. The magnetic properties of Cr3AlB4, Cr2AlB2 and CrB powders were characterized. All compounds exhibit paramagnetic behavior down to 4 K, with susceptibilities that are quite weakly temperature dependent at higher temperatures and a Curie-Weiss-like component prominent at low temperatures. Magnetization isotherms of the three compounds, showed approximately linear behavior above 5 kOe and no saturation of the magnetic moment up to 40 kOe, which is consistent with paramagnetism. The magnitude of the magnetic moments showed little variation with composition, on a per Cr atom basis. While the exact nature of the Curie-Weiss component is not entirely clear, we tentatively attribute it to dilute extrinsic impurities.

To explore the deterioration process and improvement mechanism concrete blended with supplementary cementitious materials (fly ash, slag, and silica fume) in frozen areas, the SCM content, w/b ratio, curing age, freeze-thaw (F-T) cycle, and salt-frost (S-F) cycle were varied to systematically evaluate the chloride permeability resistance and S-F resistance. Pore structures, hydration degree, phase composition and interfacial transition zone (ITZ) between aggregate and matrix of investigated mixtures were characterized by mercury intrusion porosimetry (MIP), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and SEM-EDS, respectively. The S-F resistance of blended concrete is greater than that of control mixture without SCMs. The crystallization pressure is dominated by larger saturation with higher salt concentration at the early stage of S-F cycles, and greatly affected by the actual volume expansion of salt solutions at its later stage. SCMs can compensates the structure deterioration under S-F and F-T conditions, where quaternary blends shows an optimal refinement for the pore structures. It is found that the total pore volume, average pore size, and porosity are highly correlated with the chloride permeability resistance of concrete by grey degree analysis. The SCMs blends can improve cement hydration degree by pozzolanic and hydraulic reactions at the later curing age. With the S-F cycles, the internal stresses could cause pore nucleation and crack propagation, while SCMs can effectively control the ITZ width and mitigate the structural deterioration of concrete.

A fiber laser assisted the preparation of a nitride layer on the Ti6Al4V surface in a pure nitrogen atmosphere. Through SEM, XRD, and XPS analyses, the nitride layer is found to be mainly composed of dendritic TiN phase and an interdendritic α′-Ti phase. Not only the true crystal structure of the two main phases (TiN and α′-Ti) were directly characterized using TEM, but also the mechanical properties were tested by micro-indentation and nano-indentation methods for the first time.It is found that the nano-hardness of the TiN phase is 2609 HV, and the elastic modulus is 208 GPa. During the TiN dendritic fracture process, the primary dendrites undergo near ductile fracture along the growth direction of the secondary dendrites, and microcracks, bifurcations, deflection, etc. occur to form a crack-toughening mechanism. The nano-hardness of α′-Ti is 632 HV, and the elastic modulus is 142.8 GPa. The entanglement of two sets of parallel dislocations in α′-Ti crystals forms subgrain boundaries, which exert a positive influence on work hardening and fine-grain strengthening.

Fiber reinforced concrete (FRC) has been widely used due to its perfect mechanical performance, but inclusion of fibers has a decisive influence on the fresh properties. Workability as a short-term property is expected to affect long-term properties of concrete. In this paper, the definition of workability, rheological models of FRC, measurement methods of workability and rheological properties, as well as the measure techniques of the fiber orientation and distribution were discussed in detail. This paper presents a complete and updated literature review on the effects of fiber, various constituent, mixing and temperature on the fresh and rheological characteristics. It also reveals the relationship between workability, rheological properties and mechanical performance of FRC. Most importantly, the paper discusses plausible strategies to control rheological properties of FRC, which makes workability and mechanical performance of FRC simpler and more predictable.

This study explored a novel method for inhibiting the effects of acid rain erosion and fatigue loading in concrete by incorporating super absorbent polymers (SAP). Three different dosages and four particle sizes of SAP were considered to evaluate the erosion resistance to a simulated acid rain solution (pH = 3.0) for eight test cycles. The mass loss, compressive strength, flexural strength, and erosion depth as well as the results of X-ray diffraction (XRD) and the mercury intrusion porosimetry (MIP) testing were employed to explore the erosion behavior and mechanism of the internally cured concrete with SAPs. The results show that the coupled effects of acid rain and fatigue loading has a remarkable influence on the performance degradation of concrete. The erosion of concrete by acid rain was delayed and weakened with the addition of SAP, particularly when 0.10% SAP was added with a particle size of 100–120 mesh. Moreover, the SAP promoted hydration, which lessened the deterioration caused by pore deformation and improved the internal pore structure.

The NiCrAlY-Mo-Ag composite was fabricated by vacuum hot-pressing sintering. The friction and wear behaviour of the composite were investigated from room temperature to 900 °C. Furthermore, the wear mechanism was studied over this wide range of temperatures. At the same time, the compressive properties of the composite were researched. The composition and microstructure of the composite were analyzed by X-ray diffraction (XRD) and scanning election microscopy (SEM). At 700 °C and 900 °C, the tribo-chemical reaction occurred on the worn surface and formed a high-temperature tribo-layer based on NiO and silver molybdates, which could effectively reduce the friction coefficient and wear rate of the composite. The existence of broken particles and the pullout of hard phase particles were seen on the fracture surface of the composite, which were determined by the interfacial bonding strength.

The conventional and nanostructured NiCrAlY-Mo-Ag composite coatings were prepared by atmospheric plasma spraying so as to make the hot parts achieve and maintain excellent tribological properties at elevated temperature of up to 900 °C. The microstructure, mechanical and tribological properties of these two composite coatings were investigated and compared. The X-ray diffraction (XRD), micro-Raman, scanning election microscopy (SEM) and transmission electron microscopy (TEM) were used to analyze the composition and microstructure of the composite coatings. Results show that the nanostructured composite coating presented higher microhardness and adhesive strength than conventional composite coating. Meanwhile, the nanostructured composite coating had less defects, lower porosity, more compact microstructure and smaller grains as compared to the corresponding conventional coating which was useful to improve the performance of the composite coating. The nanostructured composite coating possessed better tribological properties as compared with the conventional composite coating. The sliding process could promote the tribo-chemical reaction between silver, nickel and molybdenum to form silver molybdates and nickel molybdates lubricating films on the worn surface at high temperature. The silver molybdates and nickel molybdates could also enhance tribological properties of composite coatings at high temperature.

The NiAl-Mo-Ag and NiAl-Cr2O3-Mo-Ag composite coatings were fabricated by atmospheric plasma spraying with the substrate material of Inconel 718. The effect of heat treatment on the microstructure, adhesive strength, microhardness and tribological properties of NiAl-Cr2O3-Mo-Ag composite coating was investigated. The heat treatment temperatures were chosen as 400, 500 and 600 °C. The composition and microstructure of composite coatings were analyzed by X-ray diffraction (XRD), scanning election microscopy (SEM) and transmission electron microscopy (TEM). The results show that the addition of Cr2O3 could effectively reduce the wear rate of NiAl-Mo-Ag composite coating. The adhesive strength, microhardness and tribological properties of NiAl-Cr2O3-Mo-Ag composite coating were improved by heat treatment. After 500 °C heat treatment, the microstructure of composite coating became more homogeneous and the coating had the highest adhesive strength, microhardness and the best tribological properties. The sliding process could promote the silver, nickel and molybdenum occur tribo-chemical reaction to form silver molybdates and nickel molybdates lubricating films which were responsible for the good tribological properties of composite coatings at elevated temperatures.

The VN/Ag composite films with various silver content were prepared by PLD technique, and the microstructures, mechanical and tribological properties at elevated temperature to 900 °C of films were investigated, respectively. The results show that the films were composed of the fcc VN and Ag nano-crystalline grains. With the increase of silver content from 8.2 to 56.1 at.%, the grain size increased and the surface morphology deteriorated gradually, the hardness and elastic modulus of the films decreased from 18.6 GPa, 226.3 GPa–8.1 GPa, 126.6 GPa, respectively. Only appropriate silver addition could improve the lubricity of the VN/Ag films. The film with 16.6 at.% Ag were found to be optimized for lubrication from RT to 900 °C. At low temperatures, the lubricant property of the film relied on the metal silver heavily. At elevated temperatures, a series of Magneli phase (vanadium oxides) and the layered structure silver vanadates (such as Ag3VO4, AgVO3) formed by tribochemical reactions in the contact area played a critical role in improving lubrication properties. A synergy of the lubricating Ag at low temperatures and the new lubrication phases generated at high temperatures could be responsible to the excellent lubricity of the VN/Ag films in wide temperature range.

The temperature dependence of initial transient current-voltage (I-V) characteristic of planar perovskite solar cell by one-step solution process is investigated. An S-shaped I-V characteristic emerges in response to low temperature and the photovoltaic parameters drop dramatically. This is mainly attributed to the increasing amount of negative charges accumulating in the TiO 2 /CH 3 NH 3 PbI 3 interface region and the reduced built-in field separating the photo-generated carriers in the absorber layer. The influence of negative charge accumulation can be represented by two extra diodes that are in series with a conventional solar cell circuit model at low temperature whereas it acts as a resistor with low resistivity above room temperature. These findings help to understand the charge transport mechanism in perovskite solar cells.

Brick waste is a major part of the solid waste generated by construction and demolition activities around the world, and its disposal consumes land and pollutes the environment. At the same time, cement is the main raw material in cement-based materials. Cement production consumes resources and produces greenhouse gases, so is also not environmentally friendly. In this context, grinding brick waste into recycled brick powder (RBP) and using it instead of cement to produce sustainable construction materials is considered a feasible method. Therefore, based on the existing research, this paper reviews the fresh, mechanical, shrinkage, durability and microstructural properties of cement-based materials when RBP partially replaces Portland cement. The literature shows that RBP is rich in SiO2, Al2O3, Fe2O3 and has pozzolanic activity. The workability, mechanical and durability properties of cement-based materials can be improved to a certain extent by adding an appropriate amount of RBP (5%-15%). It is therefore considered a potential raw material for replacing Portland cement in cement-based materials. The utilization of RBP not only saves a large amount of land occupied by piled brick waste but also reduces the dependence of the concrete industry on Portland cement. It can guarantee the sustainability of construction materials and promote prosperity worldwide.

Mechanical, tribological performance, and high temperature oxidation behaviour of Ni- and NiCrAlY-based composite coatings with the addition of TiO2/ZnO were investigated. NiCrAlY-based composite coating presents a higher microhardness value than that of the Ni-based composite coatings. The tribological performance of composite coatings is improved by incorporating TiO2/ZnO. In particular, the NiCrAlY- based composite coatings present the lowest friction coefficient (0.24) and wear rate (7.3 × 10−6 mm3 N−1 m−1) at 800 °C. The results of high-temperature oxidation experiments show that the ZnO within the coating diffuses gradually to the surface with the extension of holding time at 800 and 1000 °C. The diffusion behaviour at 800 °C can be inhibited by the substitution of the metal matrix from Ni to NiCrAlY, while it was accelerated as temperature rising up to 1000 °C and have no difference in Ni- and NiCrAlY-based composite coatings.

NiAl composites with AgNbO3 (NABO1, NiAl–20 wt%AgNbO3) and Ag/Nb2O5 (NABO2, NiAl–8.68 wt%Ag–10.7 wt% Nb2O5) were fabricated by vacuum-hot-pressing sintering. Their tribological performances were evaluated in the range of 25–800 °C. The regeneration mechanisms of AgNbO3 for the composites with different additions methods during a high-temperature friction process were simultaneously investigated. During sintering, the decomposition of AgNbO3 to Ag/NbC phases was aggregately distributed in NABO1, while Ag/Nb2O5 phases in NABO2 formed Ag and NbC phases that were distributed in a monomorphic state. The regeneration mechanism of AgNbO3 relies on Ag/NbC phases distribution in the composites. Particularly, during the high-temperature friction process, Ag/NbC phases in the aggregate state regenerate AgNbO3 more easily than that in the monomorphic state.

In order to avoid the impurity phase, such as Ag 3 SbS 3 and Sb 2 S 3 among AgSbS 2 particles and simplify the complicated steps in synthesizing AgSbS 2 via conventional methods, the cubic AgSbS 2 silk-like nanoflowers with well-defined crystalline structure were synthesized by the one-step, facile and practical solvothermal chemical process. The results show that the as-prepared stoichiometric AgSbS 2 nanoflowers with the diameter of 1 µm are comprised of silk-like ultrathin nanoflakes. Moreover, the possible formation mechanism of AgSbS 2 silk-like nanoflowers with PSS (poly (sodium-p-styrenesul-fonate)) is studied. Furthermore, the AgSbS 2 nanoflowers exhibit a broad absorption and high value of incident photon to current conversion efficiency (IPCE) in visible light range, indicating that it is a promising photovoltaic absorption material.

The uniform and compact n-type TiO 2 window layers were prepared by RF sputtering using a TiO 2 ceramic target. A high open circuit voltage of about 1.03 V with the efficiency of 13.23% can be obtained as compared to 0.92 V of solution based TiO 2 . Nearly 100% coverage of perovskite film on sputtered TiO 2 can be observed in the scanning electron microscopy images, obviously higher than 92% coverage on solution-based TiO 2 . The full coverage of perovskite and the proper band alignment between sputtered TiO 2 and spiro-OMeTAD are two reasons responsible for the high open circuit voltage. The effects of annealing, growth temperature, sputtering target and thickness on performance of solar cell are also discussed.

To solve the existing problems occurring in the field of digital fabric appearance analysis, such as information loss, visual expression difficulty and low accuracy, a novel three-dimensional (3-D) surface reconstruction method based on the multi-view stereo (MVS) technology was proposed for the appearance evaluation of complex fabrics in this paper. Initially, the fabric images were captured by the self-developed multiple image acquisition system. Subsequently, the dense point cloud of fabric surface could be obtained by the operations of feature point detection and matching, camera intrinsic and extrinsic parameter calculation, image pre-processing, sparse point cloud generation, patch expansion and patch filtering. For the sake of acquiring the high accuracy and great completeness of dense point cloud, planar patches with different scales were used to fit the fabric surface, the normalized cross correlation (NCC) algorithm was adopted to improve the accuracy of photo-consistency measurement, and besides, a derivative-free particle swarm optimization (PSO) method was applied to obtain the optimal patches. Our experimental results show that the fabric surface model could be reconstructed by this method accurately, which can be used to characterize the surface texture and 3D weaving profile of woven fabrics. The reconstructed 3D fabric surface model with high precision can be used not only for three-dimensional illustration or rendering but also for structural analysis, quality evaluation of fabric appearance and etc., it provides a useful solution for artificial intelligence production in the textile industry.

The rapid development of the concrete industry consumes many natural resources and has many negative impacts on the environment. Large numbers of research attempts are focused on finding alternatives to cement and sand for use in concrete mixes to improve the sustainability of concrete. Wollastonite microfibers comprise a calcium metasilicate minerals with a wide range of sources and can be used as cement substitutes in cementitious composites, which has attracted worldwide attention in recent years. This paper presents the state-of-the-art research on the properties of cementitious composites containing wollastonite microfibers as partial cement replacement from the following aspects: setting time, workability, mechanical properties, shrinkage, durability, microstructural properties, environmental and economic analysis, and future prospects. The literature review confirms the feasibility of using wollastonite microfiber as a partial substitute for cement in cementitious composites, but this research still needs to be further studied and discussed.

Herein we report on the phases and microstructures obtained when Ni and commercial Ti2AlC powder mixtures - with Ti2AlC molar fractions of 0.1, 0.5 and 0.64 – are hot pressed (HPed) at 1050 °C for 2 h at a stress of 36 MPa in a vacuum hot press and then further annealed either at 1200 °C for 16 h or at 1350 °C for 16 h under the protection of high purity argon, Ar. After HPing, the 0.1 Ti2AlC composite sample was comprised of a Ni-based solid-solution with some dissolved Ti, fine TiCx particles and γ′ precipitates (Ni3(Al,Ti)). Heat treating at 1200 °C for 16 h did not change the phase content. However, after annealing at 1350 °C for 16 h, the TiCx phase substantially coarsened and become the major phase. HPing of the 0.5 Ti2AlC mixture, resulted in the formation of sub-stoichiometric TiCx, NiAl, Ti3NiAl2C, Ni2AlTi, and a small amount of Ti3AlC2. After annealing at 1200 °C for 16 h, the Ti3AlC2 phase disappeared. After the 1350 °C anneal, the Ni2AlTi phase was no longer detected and the microstructure was comprised of coarsened TiCx particles dispersed in a Ti-solutioned NiAl matrix with a small fraction of Ti3NiAl2C. Lastly, after HPing, the 0.64 Ti2AlC mixture, the phases present were TiCx, Ti3NiAl2C, NiAl, small amounts of Ti3AlC2 and traces of unreacted Ti2AlC. After annealing at 1200 or 1350 °C for 16 h, the Ti3AlC2 and Ti2AlC phases disappear, and a new ternary Al-rich aluminide, Ti6Al16Ni7 phase emerges. The final microstructure was thus comprised mostly of Ti6Al16Ni7 and TiCx. The reactions resulting in these compositions are developed.

Spectral characterization can be used for the color calibration of the fabric image to eliminate the influence of the imaging equipment and illumination environment, so as to obtain the actual yarn color information of the fabric image and improve the accuracy of fabric color analysis and rendering. However, existing algorithms based on spectral reflectance reconstruction were not ideal to minimize the obvious c between the reconstructed and its actual color. Compared with the index of spectral reflectance reconstruction accuracy, the chromaticity error is a direct index of image color quality evaluation by human vision. Therefore, to eliminate the influence of imaging equipment and illumination environment on the fabric image color occurring during the fabric image acquisition, a novel color calibration method based on spectral reflectance reconstruction was proposed for fabric image analysis in this paper, which focused on the optimal selection of representative colors and defined a new spectral reconstruction error evaluation function E = α E r m s e + β E C A . Experimental results show that the proposed method in this paper is superior to the existing methods in color reconstruction accuracy and visual quality.

The optoelectrical properties of semiconductor devices are strongly related to the film morphology. Here, we found that, for CsPbBr3 thin films prepared by spray coating, the addition of polymethyl methacrylate (PMMA) can completely eliminate voids and greatly reduce the surface roughness of the as-deposited films. As a consequence, the optoelectronic properties of the photodetectors fabricated as a simple vertical structure of Au/CsPbBr3(PMMA)/ITO can be improved. With the addition of PMMA, the dark current of the photodetector is reduced at least four times, and the photodetector exhibits a favourable optical response. With the illumination ranging from 400 to 510 nm, the calculated responsivity varies from 3.70 to 5.20 A/W. A good response speed with a rise time of 6.6 ms and a decay time of 11.3 ms can be achieved. Moreover, unlike the inorganic-organic hybrid perovskite detectors, this inorganic perovskite photodetector without encapsulation shows a favourable stability with a decay of 20% after 40 days under ambient air at 20% humidity.

NiAl–NbC–Ag composites were successfully prepared by vacuum-hot-pressing sintering with directly addition of AgNbO3 powders, where AgNbO3 were synthesized using a solid state reaction method. The tribological behaviors of composites were evaluated from 25 °C to 800 °C. The consequences reveal AgNbO3 are completely decomposed during sintering process and in-situ formed NiAl–NbC–Ag composites, which hold excellent high temperature tribologicial properties. At mid-low temperature, NAB20 (NiAl-20 wt%AgNbO3) has a relative lower friction coefficient compared to NiAl, which was attributed to the existence of Ag. While the lowered friction coefficients at 600 °C and 800 °C were attributed to the lubricating glaze layers formed by tribo-chemical reaction on the worn surfaces, which were consisted of typical layered structure Ag2Nb4O11, perovskite AgNbO3 with a highly flexible crystal structure and AgNb3O8.

The effect of Al 2 O 3 content on the mechanical and tribological properties of Ni–Cr alloy was investigated from room temperature to 1000 °C. The results indicated that NiCr–40 wt% Al 2 O 3 composite exhibited good wear resistance and its compressive strength remained 540 MPa even at 1000 °C. The values obtained for flexural strength and fracture toughness at room temperature were 771 MPa, 15.2 MPa m 1/2 , respectively. Between 800 °C and 1000 °C, the adhesive and plastic oxide layer on the worn surface of the composite was claimed to be responsible for low friction coefficient and wear rate.

The influences of cobalt (Co) on creep rupture lives and dislocation structures in nickel base superalloys with and without rhenium (Re) are investigated. The creep rupture test conditions were high temperature low stress (1100 °C/150 MPa), intermediate temperature and stress (982 °C, 1010 °C) and low temperature high stress (850 °C/586 MPa). The results show that increasing Co content could enhance the creep rupture lives at low and intermediate temperature, and does not degrade the creep rupture lives of alloys at high temperature. In Re-containing alloys, at high temperature low stress (1100 °C/150 MPa), the effects of Co on the dislocation structures are negligible, while at low temperature high stress (850 °C/586 MPa), stacking faults are generated in alloy with 12% Co, and in alloy with 3% Co and free of Co, gamma prime particles are sheared by dislocation pairs. In Re-free alloys, at intermediate temperature and stress (1010 °C/248 MPa), large quantities of stacking faults appear in alloy without Co, while in alloy having 12% Co, gamma prime particles are sheared by dislocation pairs coupled by anti-phase boundary (APB). The gamma prime sheared by stacking faults or by dislocation pairs coupled by APB depends on the competition of stacking faults energy and APB energy which is affected by temperature and the interaction of Re and Co.

Silver vanadate (AgVO3) nanowires were synthesized by hydrothermal method and self-lubricating NiAl/Mo-AgVO3 composites were fabricated by powder metallurgy technique. The composition and microstructure of NiAl/Mo-based composites were characterized and the tribological properties were investigated from room temperature to 900 degrees C. The results showed that NiAl/Mo-based composites were consisted of nanocrystalline B2 ordered NiAl matrix, Al2O3, Mo2C, metallic Ag and vanadium oxide phase. The appearance of metallic Ag and vanadium oxide phase can be attributed to the decomposition of AgVO3 during sintering. Wear testing results confirmed that NiAl/Mo-based composites have excellent tribological properties over a wide temperature range. For example, the friction coefficient and wear rate of NiAl/Mo-based composites containing AgVO3 were significantly lower than the composites containing only metallic Mo or AgVO3 lubricant when the temperature is above 300 degrees C, which can be attributed to the synergistic lubricating action of metallic Mo and AgVO3 lubricants. Furthermore, Raman results indicated that the composition on the worn surface of NiAl-based composites was self-adjusted after wear testing at different temperatures. For example, Ag3VO4 and Fe3O4 lubricants were responsible for the improvement of tribological properties at 500 degrees C, AgVO3, Ag3VO4 and molybdate for 700 degrees C, and AgVO3 and molybdate for 900 degrees C of NiAl-based composites with the addition of metallic Mo and AgVO3. (C) 2014 Elsevier Inc. All rights reserved.

The tribological properties of NiCr–40 wt%Al 2 O 3 (NC40A) cermet-based self-lubricating composites containing 10 wt%–30 wt% SrSO 4 against alumina ball were investigated at elevated temperatures. The results indicated that the friction coefficients and wear rates were significantly reduced by adding different amounts of SrSO 4 above 200 °C. NC40A–10SrSO 4 composite exhibited satisfactory tribological properties above 200 °C due to the formation of synergistic lubricating films SrAl 4 O 7 and NiCr 2 O 4 on the contact surface, while low friction coefficient and wear rate of NC40A–30SrSO 4 composite at 400 °C were attributed to the synergistic lubricating effect of Sr 4 Al 2 O 7 , SrAl 2 O 4 and NiCr 2 O 4 .

NiAl-based nanocomposites reinforced by in situ Mo 2 C ceramic precipitates were successfully fabricated by mechanical alloying and hot-pressing sintering. The microstructure and mechanical properties of NiAl-based nanocomposites reinforced by in situ Mo 2 C ceramic precipitates were investigated. The results showed that the nanostructured powder particles with the average size below 30 nm were successfully obtained by mechanical alloying. After sintering, the composites were constituted of B2-ordered NiAl and in situ Mo 2 C ceramic precipitates, and the crystallite size of NiAl phase was below 200 nm and Mo 2 C ceramic precipitates were evenly dispersed in the NiAl-matrix. Mo 2 C precipitates were formed by the solid-state reaction of C and metallic Mo element during the hot-pressing sintering process. The relative density, hardness and compressive strength of high-density nanostructured NiAl materials increased with increasing Mo content, which can be attributed to the second phase hardening effect of Mo 2 C ceramic particulates and fine grain strengthening of nanocrystalline NiAl phase. The wear test results showed that the friction coefficient of NiAl–Mo 2 C nanocomposites at 700 °C (0.35) was significantly lower than that of NiAl alloy (0.48). The improvement of high temperature tribological properties could be attributed to the formation of molybdenum trioxide tribofilm and the second phase hardening effect of Mo 2 C ceramic particulates.

Nanocrystalline NiAl materials were fabricated using mechanical alloying and hot-pressing sintering technique. The crystal structural and microstructure of milled powders during mechanical alloying, and the microstructure and mechanical properties of bulk NiAl intermetallic were characterized. The results show that B2 ordered nanocrystalline NiAl powders were successfully synthesized by solid-state diffusion via the gradual exothermic reaction mechanism during mechanical alloying. Scanning electron microscope image confirmed that the powder particles were flat and flake shape in the early stage of milling, but changed to a spherical shape with the crystallite size about 30 nm after the milling. After sintering, the crystal structure of nanocrystalline NiAl intermetallic was assigned to B2 order NiAl phase with the average crystallite size about 100 nm. The nanocrystalline NiAl intermetallic exhibited prominent room temperature compressive properties, such as the true ultimate compressive strength and the fracture strain were 2143 MPa and 32.2%, respectively. The appearances of vein-like patterns on the fracture surface of NiAl intermetallic materials indicated that the fracture mechanism could be characterized as ductile fracture. It can be concluded that higher sintering density and nanocrystalline of NiAl intermetallic were benefited for the improvement of mechanical properties.

The tribological properties of NiCr-40 wt% Al 2 O 3 (NC40A) cermet-based composites containing SrSO 4 and other lubricant (graphite, MoS 2 and Ag) against alumina ball were evaluated to identify their self-lubrication mechanisms from room temperature to 800 °C. The composites demonstrated distinct improvements in effectively reducing friction and wear, as compared to NC40A cermet. The best results were observed for NC40A–10SrSO 4 –10Ag composite, which exhibited satisfactory reproducibility of friction coefficient over a wide temperature range (200–800 °C) through high temperature cyclic friction tests due to the formation of synergistic lubricating films SrAl 4 O 7 , NiCr 2 O 4 and Ag on the contact surface.

Tribological properties of Ni-based composites containing silver and molybdenum disulfide were studied from room temperature to 700 °C. The composites were prepared by powder metallurgy technique and the phase composition and microstructure were addressed according to the characterization by SEM and XRD. The results show that the composites were composed of Ni, Cr2O3, Ag and CrxSy phases after sintering. The best tribological properties were obtained when the silver and molybdenum disulfide contents were 20 wt% and 8.5 wt%, respectively. The tribo-chemical reaction occurred between Ag and Mo oxide during the rubbing process, which led to the formation of silver molybdate lubricating film. The improved tribological properties were attributed to the formation of silver molybdate lubricating tribolayers.