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Drought poses a severe threat to terrestrial ecosystems' carbon sequestration function, which in turn affects regional sustainable development. Understanding its impact on carbon source/sink dynamics is crucial for addressing extreme climate change challenges. This study, based on the Carnegie-Ames-Stanford approach (CASA) model and soil heterotrophic respiration equation, the Net Ecosystem Productivity (NEP) of the middle reaches of the Yellow River Basin (MRYRB) from 2001 to 2019 were estimated and utilized to characterize the vegetation carbon source/sink. Additionally, four factors, namely, average surface temperature (AST), root-zone soil moisture (RM), drought frequency (DF), and drought intensity (DI), were selected and a multiscale geographically weighted regression (MGWR) model was applied to assess the dominant factors influencing vegetation carbon source/sink dynamics at the spatial scale. The results indicated that: (1) MRYRB vegetation acted as a carbon sink, showing an increasing trend. Carbon sink was primarily located in Shaanxi's central region, while carbon source was primarily located in Inner Mongolia and Shaanxi's northern part. (2) Both the extent and severity of drought in the MRYRB showed a mitigating trend, presenting a spatial distribution of high-intensity low-frequency and low-intensity high-frequency. (3) AST, RM, DF, and DI had larger effects on carbon source than carbon sink. AST dominated mainly in northern Shanxi and Shaanxi, RM in central Shaanxi and Gansu, while DI and DF were concentrated in central Shaanxi and northern Shanxi. [ABSTRACT FROM AUTHOR]

Precise and timely prediction of crop yields is crucial for food security and the development of agricultural policies. However, crop yield is influenced by multiple factors within complex growth environments. Previous research has paid relatively little attention to the interference of environmental factors and drought on the growth of winter wheat. Therefore, there is an urgent need for more effective methods to explore the inherent relationship between these factors and crop yield, making precise yield prediction increasingly important. This study was based on four type of indicators including meteorological, crop growth status, environmental, and drought index, from October 2003 to June 2019 in Henan Province as the basic data for predicting winter wheat yield. Using the sparrow search algorithm combined with random forest (SSA-RF) under different input indicators, accuracy of winter wheat yield estimation was calculated. The estimation accuracy of SSA-RF was compared with partial least squares regression (PLSR), extreme gradient boosting (XG-Boost), and random forest (RF) models. Finally, the determined optimal yield estimation method was used to predict winter wheat yield in three typical years. Following are the findings: 1) the SSA-RF demonstrates superior performance in estimating winter wheat yield compared to other algorithms. The best yield estimation method is achieved by four types indicators' composition with SSA-RF) (R2 = 0.805, RRMSE = 9.9%. 2) Crops growth status and environmental indicators play significant roles in wheat yield estimation, accounting for 46% and 22% of the yield importance among all indicators, respectively. 3) Selecting indicators from October to April of the following year yielded the highest accuracy in winter wheat yield estimation, with an R2 of 0.826 and an RAISE of 9.0%. Yield estimates can be completed two months before the winter wheat harvest in June. 4) The predicted performance will be slightly affected by severe drought. Compared with severe drought year (2011) (R2 = 0.680) and normal year (2017) (R2 = 0.790), the SSA-RF model has higher prediction accuracy for wet year (2018) (R2 = 0.820). This study could provide an innovative approach for remote sensing estimation of winter wheat yield, yield. [ABSTRACT FROM AUTHOR]

Drought is one of the most destructive natural disasters in China and can cause serious environmental and socio-economic impacts. Based on monthly precipitation and temperature data from 571 meteorological stations, the Standardized Precipitation Evapotranspiration Index (SPEI) was calculated on a 12-month scale (SPEI-12) from 1985 to 2018 in mainland China, and it was compared with the records of the Bulletin of Flood and Drought Disasters in China to verify its drought monitoring accuracy. Then, run theory was used to explore in depth the spatiotemporal distribution of drought characteristics and trends in various climatic sub-regions. The results showed that: (1) the comparison with the Bulletin of Flood and Drought Disasters in China indicated that the results of SPEI-12 monitoring drought had high accuracy and could identify drought events in mainland China. (2) About 70% of the regions in mainland China experienced droughts more than 50 times, and about 43% of the regions had drought durations of between 100 and 110 months. Nearly 11% of the regions had drought severities of more than 130, which were mainly located in the Northwest Desert (NWC), the southern part of Northeast China (NEC), and the western part of North China (NC). (3) In the past 34 years, the droughts in the Northwest Desert (NWC), the western part of Inner Mongolia (IM), and the Qinghai-Tibet Plateau (TP) showed an aridity trend, while the droughts in South China (SC) and eastern Central and South China (CSC) presented a mitigation tendency. (4) Specifically, the droughts in South China (SC) were more influenced by precipitation, while those in the Northwest Desert (NWC) and Northeast China (NEC) were influenced by temperature and potential evapotranspiration, and the evolution of drought in North China (NC) and the Qinghai-Tibet Plateau (TP) was mainly influenced by soil moisture. The study could provide scientific guidance and a reference for drought response and sustainable development in China. [ABSTRACT FROM AUTHOR]

The superior tribological properties of bearings with low friction appear to be actualized by not a single lubrication, but the adaptive multi-mode co-lubrication in which the interface can adjust according to the friction conditions. This study attempts to reveal the friction adaptive mechanism of textures under grease lubrication. The single-stage linear groove surfaces (SLGSs) and the multi-stage bionic texture surfaces (MBTSs) were respectively designed, and MXenes lithium composite grease (MLCG) with MXenes as an additive was prepared. Compared with the non-textured surface, the friction coefficient of MBTS-1.5 is reduced by 67.6%, and the wear rate is reduced by 45.4%. The friction contact area presents an adaptive multi-mode lubrication trend from oil to grease-solid synergistic lubrication. [Display omitted] • MBTSs can help to improve the flow characteristics of grease. • MXenes and thickener could achieve the synergistic self-repairing effect. • MXenes can form a beneficial friction layer at the friction interface. • Multi-mode lubrication system has excellent adaptability and reliability. [ABSTRACT FROM AUTHOR]

Workpiece will face corrosive problems during its application after the manufacturing process. As the common final process, grinding can generate special metamorphic layer on the surface of workpiece and change the initial corrosion resistance of workpiece. In order to study the corrosion resistance of workpiece after grinding process, the paper carries on combining experiment of grinding and electrochemical corrosion. The characteristic of corrosion resistance of grinding is revealed based on the association of grinding mechanism and electrochemical theory. The corrosion potential of workpiece after grinding is higher than matrix, which shows the grinding surface is difficult to begin to corrode. Electrochemical impedance spectroscopy (EIS) shows the grinding surface has large phase angle, impedance and capacitance characteristic because the metamorphic layer of grinding has good obstructive ability. They reveal that grinding improves the surface corrosion resistance of workpiece. Then the mechanism of the corrosion resistance of grinding is revealed. The special grain boundary formed in grinding with much C element, large clusters and complex shape prolongs the corrosion channel, which reduces the corrosive speed. While, the sensitive hardening structure generated in grinding hardening with much free energy is easy to form the corrosion cell, which will accelerate the corrosion. [ABSTRACT FROM AUTHOR]

Ovarian cancer is one of the most common cancers in women and is often diagnosed as advanced stage because of the subtle symptoms of early ovarian cancer. To identify the somatic alterations and new biomarkers for the diagnosis and targeted therapy of Chinese ovarian cancer patients, a total of 65 Chinese ovarian cancer patients were enrolled for detection of genomic alterations. The most commonly mutated genes in ovarian cancers were TP53 (86.15%, 56/65), NF1 (13.85%, 9/65), NOTCH3 (10.77%, 7/65), and TERT (10.77%, 7/65). Statistical analysis showed that TP53 and LRP1B mutations were associated with the age of patients, KRAS, TP53, and PTEN mutations were significantly associated with tumor differentiation, and MED12, LRP2, PIK3R2, CCNE1, and LRP1B mutations were significantly associated with high tumor mutational burden. The mutation frequencies of LRP2 and NTRK3 in metastatic ovarian cancers were higher than those in primary tumors, but the difference was not significant (P = 0.072, for both). Molecular characteristics of three patients responding to olapanib supported that BRCA mutation and HRD related mutations is the target of olaparib in platinum sensitive patients. In conclusion we identified the somatic alterations and suggested a group of potential biomarkers for Chinese ovarian cancer patients. Our study provided a basis for further exploration of diagnosis and molecular targeted therapy for Chinese ovarian cancer patients. [ABSTRACT FROM AUTHOR]

This paper investigates the evolution of a Richtmyer–Meshkov (RM)-like instability on the internal surface of particle rings impinged by divergent blast waves. Despite the signature spike–bubble instability structure analogous to the hydrodynamic RM instability, the growth of the perturbation amplitude in granular media undergoes an exponential phase followed by a linear phase, markedly differing from the hydrodynamic RM instability and indicating a fundamentally different mechanism. The granular RM-like instability arises from the incipient transverse granular flows induced by hydrodynamic effects upon the shock interaction. Substantial perturbation growth is initiated by the ensuing rarefaction dilation when the hydrodynamic effects are small. It is found that the interplay between the localized transverse and radial granular flows sustains the persistent perturbation growth and drives the corresponding morphological changes in the instability pattern. [ABSTRACT FROM AUTHOR]

The workpiece surface obtains the fine machining during the grinding as well as the impacting effect of grinding wheel, which causes the changing of its hardness. In order to predict the hardness of structural steel workpiece after grinding, the paper established an approximate hardness model of workpiece after grinding by establishing a calculating method for the cooling condition, the model of grinding strain, and the correlation between the equivalent strain and hardness. The hardness value and distribution of hardness field of grinding were predicted by the method with accuracy relatively. The variation and influencing mechanism of hardness along with grinding parameters were studied. And dynamic hardness field of the model revealed the dynamic recovery and recrystallization during grinding. A grinding experiment verified the accuracy of the model approximately. [ABSTRACT FROM AUTHOR]

[Display omitted] • A drought risk assessment framework was constructed using the random forest algorithm. • The drought vulnerability dimension was enriched by considering the impact of ecosystem resilience. • The spatial distribution pattern of drought risk under the influence of ecosystem resilience was assessed. Drought caused by global warming has a profound impact on the stability of terrestrial ecosystems and agricultural production. As one of the key indicators to measure the response of ecosystems to climate change, the spatial difference of ecosystem resilience will also affect the accuracy of regional drought risk assessment. In this study, the 12-month standardized precipitation evapotranspiration index (SPEI-12) was used to identify drought characteristics and combined with meteorological elements to characterize drought hazard. Drought vulnerability was characterized using crop and environmental sensitivity, disaster prevention, and mitigation capacity. Specifically, ecosystem resilience was also considered in assessing vulnerability. And drought exposure was investigated by considering crop sown area and population density. Based on this, a drought risk assessment framework was constructed using the random forest algorithm and applied to the Huang-Huai-Hai (HHH) Plain, China. The results showed that: (1) approximately 66.34 % of the HHH Plain had a drought hazard level above moderate; among them, southern Hebei, northern Anhui, northern Henan, and scattered small areas in Shandong were extreme high hazard areas. (2) The northeast Anhui, central and southern Shandong, and northeast Jiangsu were extreme high drought vulnerability areas, accounting for 10.34% of the total area. (3) The drought risk in the HHH Plain was low in the south and north, and high in the center. Among these, the drought risk in the border regions of Shandong and Anhui, the northeast part of Jiangsu, as well as central Henan were extreme high, accounting for 11.23%. (4) The drought risk assessment framework constructed by considering ecosystem resilience was more suitable for HHH Plain. This study result could provide scientific reference for managing water resources and preventing drought. [ABSTRACT FROM AUTHOR]

The effects of functionally gradient structure of graphene nanoplatelets (GNPs) reinforced Ni 3 Al metal matrix composites (GNMMCs) prepared by laser melting deposition on the tribological performance, as well as friction-induced vibration and noise are investigated. Results show that GNMMCs with GNPs gradient structure can improve the tribological performance and weaken the intensity of high frequency vibration and noise under the variable loadings, which are affected by the synergy effects of lubricant and gradient structure. High level of GNPs content in contact interface layer allows an easier GNPs deposition and promote the formation of smooth surface. GNMMCs with gradient hardness change has the abilities of absorbing heavy loads and resisting the deformation of contact interface. Hence, friction-induced vibration and noise is reduced. Image 1 • The gradient Ni 3 Al self-lubricating composites (GNMMCs) is prepared. • Friction and wear behavior is tested under two kinds of loading conditions. • The sources of friction-induced vibration and noise are investigated. • The inherent correlation between noise signals and worn states is discussed. [ABSTRACT FROM AUTHOR]

In order to meet more rigorous tribological requirements for aerospace and automobile applications, there is a need to improve the wear and frictional performance of Ni 3 Al-based metal matrix composites. This investigation sought to improve performance by designing gradient-type Ni 3 Al metal matrix, self-lubricating composites (GNMMCs), in which each layer contained a different content of graphene nanoplatelets (GNPs). Dry sliding tests of a novel material are conducted as a basic assessment for the reference of the specific applications. Rotating sliding tests of GNMMCs against Si 3 N 4 balls were performed under different loading conditions to compare with Ni 3 Al metal matrix without graphene nanoplatelets (NA) and with homogeneous graphene nanoplatelets (NMCs). The results show that the friction coefficients and wear loss of GNMMCs under different loading conditions are lower than those of NA and NMCs. It is attributed to the facts that together, GNPs and oxides on the worn surface can form a tribo-layer with excellent anti-friction and wear performance, and GNPs accumulations in the worn subsurface can further enhance the strength of the tribo-layer to resist deformation. Additionally, the deposited layers with a gradient GNP content of GNMMCs present a grain gradient structure transiting from the fine grains to coarse grains, which is characteristic of a gradient hardness change. When GNMMCs with high strain accommodating ability are compressed under heavy loading, plastic deformation propagates from coarse grains to fine grains progressively to accommodate the stresses, and that process effectively maintains the wear resistance of tribo-layer. Image 1 • The gradient Ni 3 Al self-lubricating composites (GNMMCs) is designed. • The microstructure and mechanical properties of GNMMCs are investigated. • Wear tests of GNMMCs are performed under different loading conditions. • Wear resistance and strengthening mechanism of GNMMCs are discussed. [ABSTRACT FROM AUTHOR]

Abstract The potential tribological properties of load-adaptive M50-based self-lubricating composites under various loads were investigated. Pure M50 and M50 composite containing 10 wt%(50Sn40Ag10Cu) (MSAC) samples were prepared by spark plasma sintering. Besides, samples M50 and MSAC, which were all surface-scattered with C60 microparticles, were defined as M-C and MSAC-C, respectively, and the tribological tests of M50, MSAC, M-C, and MSAC-C sliding against Si 3 N 4 ball from 2 to 18N at 0.2 m/s-350 °C were performed. Results show that MSAC-C exhibits the excellent friction and wear performance within the range of loads. Analysis indicates that this phenomenon is mainly due to the formation of a composite lubricating film rich in soft metal lubricant Sn-Ag-Cu and C60 microparticles. Graphical abstract Image 1 Highlights • Sn-Ag-Cu provides excellent lubricating properties within the low loads from 2 to 12N. • C60 provides excellent lubricating properties within the high loads from 12 to 18N. • (Sn-Ag-Cu)-C60 has the merit of load-adaptive action to produce good lubrication. • Compounds of Fe 2 O 3 , CuO produced friction process can enhance lubrication capacities. [ABSTRACT FROM AUTHOR]

Dry tribological tests of M50 matrix composites containing 0, 2.5, 5.0, and 7.5 wt% Ag are undertaken at 0.2 m/second 15 N from 25°C to 450°C against Si3N4 ceramic balls. The results indicate that the tribological performance is strongly dependent on the content of solid lubricant Ag. M50 matrix composites containing 5.0 wt% Ag exhibits the great tribological performance with the low friction coefficients of 0.23 to 0.43 and less wear rates of 1.89 to 3.52 × 10−6 mm3 N−1 m−1 from 25°C to 450°C, which is attributed to the formation of thick lubricating film on the worn surface. Furthermore, the migration model of solid lubricant Ag in M50 matrix composites is established to predict the thickness of formed lubricating film. [ABSTRACT FROM AUTHOR]

M50 steel is the main material used in aircraft bearings, and its friction performance will directly affect the reliability and service life of the whole bearing. Hence, this paper focuses on the tribological behavior and self-healing function of as-prepared M50 steel-based self-lubricating material covered with surface micropores filled with Sn-Ag-Cu (MMSAC). Friction results show that MMSAC exhibits the distinguished tribological behavior. Analysis indicates that this is mainly due to the lubricating film formed on the worn surface and the self-healing behavior on the worn surface of MMSAC. Sn-Ag-Cu in micropores can precipitate onto the friction surface to form the lubricating film, while the volume expansion caused by the oxidation of Sn and Cu plays an important role in filling cracks. [ABSTRACT FROM AUTHOR]

Purpose This paper aims to predict and evaluate the wear rate of TiAl-2 Wt.% MoO3 tabular crystals (TMCs) using the Newton interpolation methods.Design/methodology/approach The friction and wear behaviors of TMC were examined using pin-on-disc apparatus at different times, namely, 1,200, 2,400, 3,600, 4,800 and 6,000 s. The wear rates of five different times as interpolation nodes were measured and calculated by electron probe microanalysis (EMPA) and field emission electron microscope (FESEM). Then, the prediction formula of wear rate was constructed using the Newton interpolation method. The accuracy of the prediction formula and the relationship with friction layer and worn surface are verified for evaluating the reliability of the prediction formula.Findings The prediction formula shows a similar variation trend of TMC as the experimental results, indicating that the prediction formula can forecast the wear rate and working condition of TMC. Moreover, the microstructures of friction layer and worn surface also have a strong impact on the prediction formulas.Originality/value The prediction formulas of the Newton interpolation polynomial can be adopted to predict working longevity in the mechanical components, which can guide the practical engineering application in industrial fields. [ABSTRACT FROM AUTHOR]

Abstract As the main steel used in aircraft bearings, tribological properties of M50 directly affect the performance of aero-engines. In this paper, the anti-friction and wear properties of friction surface of M50-10 wt%(50Sn40Ag10Cu) composites (MSACC-2) sliding against Si 3 N 4 ball from 25 to 450 °C were investigated. XRD, XPS, EPMA, FESEM, and EDS mapping were conducted to understand the major mechanism leading to the improvement in the sliding behavior of MSACC-2. Results show that the surface of MSACC-2 exhibits excellent anti-friction and wear performances from 25 to 450 °C. At 350 °C, MSACC-2 shows the best tribological performance (0.18–0.27, 1.5–2.2 × 10−6mm3N−1m−1). It is attributed to the formed lubricating structure on the friction surface which is composed of the upper surface lubricating layer and underneath load-bearing layer. The surface lubricating layer mainly contains massive added Sn-Ag-Cu, intermetallic compounds of Cu 6 Sn 5 and Ag 3 Sn produced during the preparation process, and FeSn, FeSn 2 and oxides formed in friction process. The load-bearing layer can support the surface lubricating layer to play an outstanding anti-friction and wear effect. Moreover, the martensitic phase transformation on surfaces caused by Sn-Ag-Cu and the action of cyclic stress of Si 3 N 4 balls makes MSACC-2 have more excellent wear resistance performance. Graphical abstract Image 1 Highlights • The surface of MSACC-2 exhibits excellent anti-friction and wear properties. • 50Sn40Ag10Cu is an ideal solid lubricant for M50 over a wide temperature range. • Lubricating structure on surface consists of lubricating layer and load-bearing layer. • Lubricating layer contains added Sn-Ag-Cu and Ag 3 Sn, FeSn 2 produced during friction. • Phase transformation on surface makes MSACC-2 exhibit the best wear resistance. [ABSTRACT FROM AUTHOR]

The sliding friction and wear behaviors of TiAl-multilayer graphene (MLG)-silver composites (TMSCs) sliding against Si 3 N 4 balls from 0.10 to 0.30  m/s were studied in this paper. The tribological test results showed that friction coefficient and wear rate of TMSCs decreased with the increasing of sliding speed from 0.10 to 0.30  m/s. TMSCs exhibited the lower fiction coefficient and the less wear rate at 0.30  m/s, which was attributed to the formation of intact tribo-film containing MLG and Ag on the worn surface. In the formed tribo-film, Ag worked as the solid lubricant to provide good lubricating effect, while MLG with high strength played the active role in enhancing the anti-rupture ability of tribo-film. It indicated that TMSCs obtained the excellent tribological performance due to the remarkable synergistic effect of MLG and Ag. Moreover, the friction heat increased with the increase of sliding speed, which made contributions to the formation of tribo-film. [ABSTRACT FROM AUTHOR]

Abstract: Since its domestication from wild rice thousands of years ago, rice has been cultivated largely through transplantation. During transplantation from the nursery to the paddy field, rice seedlings experience transplantation shock which affects their physiology and production. However, the mechanisms underlying transplantation shock and rice adaptation to this shock are largely unknown. Here, we isolated a transplant‐sensitive chloroplast‐deficient (tsc1) rice mutant that produces albino leaves after transplantation. Blocking light from reaching the juvenile leaves and leaf primordia caused chloroplast deficiencies in transplanted tsc1 seedlings. TSC1 encodes a noncanonical adenosine triphosphate‐binding cassette (ABC) transporter homologous to AtNAP14 and is of cyanobacterial origin. We demonstrate that TSC1 controls plastid development in rice under dark conditions, and functions independently of light signaling. However, light rescued the tsc1 mutant phenotype in a spectrum‐independent manner. TSC1 was upregulated following transplantation, and modulated the iron and copper levels, thereby regulating prolamellar body formation during the early P4 stage of leaf development. Therefore, TSC1 is indispensable for plastid development in the absence of light, and contributes to adaptation to transplantation shock. Our study provides insight into the regulation of plastid development and establishes a framework for improving recovery from transplantation shock in rice. [ABSTRACT FROM AUTHOR]

In order to study the tribological performance of Ni 3 Al matrix composites containing MoO 3 tabular crystals (Ni 3 Al-MTCs) under different sliding speed, the friction and wear behaviors of Ni 3 Al-MTCs sliding against Si 3 N 4 ball are tested using a constant load of 10 N at room temperature under 0.1–0.7 m/s. The effects of shear stress and different amount of friction heat on the wear mechanism of Ni 3 Al-MTCs under different sliding speed are studied. The results show that MoO 3 tabular crystals are beneficial to the formation of friction layer with the increase of sliding speed, resulting in the excellent tribological properties of Ni 3 Al-MTCs. At 10N-0.7 m/s, higher friction heat at higher speed produces rich oxides on worn surface, which is beneficial to the formation of smoother and larger coverage of lubricating film with good antifriction property. In addition, lower shear stress acting on worn surface at higher speed brings the more stable friction layer with excellent wear resistant property, if compared to other working conditions. The results could be used to guide the selection of suitable working conditions and study the wear mechanisms of Ni 3 Al-MTCs for having excellent tribological performance during sliding process. [ABSTRACT FROM AUTHOR]

M50 steel was widely applied to manufacture aircraft bearing whose service life was mainly determined by its tribological behavior. The primary purpose of this study was to investigate the tribological behavior of M50-5 wt%MoS 2 composites (MMC) sliding against Si 3 N 4 balls from 150 to 450 °C at 20N-0.2 m/s. The results showed that the excellent tribological performance of MMC was obtained for the lower friction coefficient of 0.17–0.62 and the less wear rate of 1.9–3.5 × 10 −6 mm 3 N −1 m −1 at 150–450 °C, which was attributed to the formed lubricating structure consisting of the lubricating film mainly containing massive MoS 2 and FeS, as well as underneath compacted layer. The enriched added MoS 2 and FeS generated during the sintering process in the lubricating film could provide good lubrication from 150 to 350 °C, while FeS for its excellent plastic flow capacity from 350 to 450 °C was well spread out on the friction surface to realize the lubricating role continuously, which made MMC maintain a long-lasting lubricating performance. The compacted layer played the role in supporting the lubricating film to prevent it from being damaged. [ABSTRACT FROM AUTHOR]

The objective of this paper was to study effect of competitive mechanism between O and Ag contents on the friction and wear behaviors of TiAl-10 wt%Ag. Based on the changes in the contents of O and Ag on wear scars, the tribological performance of TiAl-10 wt%Ag was analyzed sliding against silicon nitride balls at 25–900 °C. The testing results showed the excellent sliding friction and wear behavior of TiAl-10 wt%Ag was mainly attributed to the forming of lubricating film containing massive Ag at 450 °C. It was found that at 0–30 min, the friction coefficient and wear rate were rapidly lowered with the increasing of O and Ag contents. At 30–240 min, massive Ag was squeezed out of TiAl-10 wt%Ag to form lubricating film containing massive Ag, it decreased oxidation reaction rate and resulted in the increasing of Ag content and the decreasing of O content on wear scar. The sliding friction coefficients and wear rates of TiAl-10 wt%Ag were further lowered at 30–240 min. [ABSTRACT FROM AUTHOR]

The pre-stressed hardening grinding (PSHG) combines with the advantages of pre-stressed grinding and grinding hardening. In order to study the characteristic of PSHG, especially its residual stress within a hardened layer after PSHG, the PSHG experiment was carried on. Combining with theory and experiment results, the variation and its mechanism of residual stress were studied. The paper shows the PSHG can obtain a hardened layer with controllable residual stress after the process. The residual stress decreases with the increasing of feeding speed and grinding depth. When the grinding depth is small, the tensile residual stress decreases with the increasing of pre-stress. And when the grinding depth is large, the compressive residual stress decreases first and then increases with the increase of pre-stress because of the comprehensive effect of heat and phase transformation. Then, a finite element method (FEM) simulation was performed to study the variation of thermal stress in a hardened layer after PSHG process. Distribution and variation of thermal stress were obtained. In the end, according to the relationship between residual stress and thermal stress, the distribution and variation mechanisms of phase transformation stress were obtained and studied. They vary along with the level of phase transformation. The compressive phase transformation stress increases with the increasing of grinding depth. And due to the pre-stress's influence on the phase transformation, it decreases first and then increases with the increase of pre-stress. [ABSTRACT FROM AUTHOR]

A dislocation-density-based model is selected to investigate the mechanisms of the improvement in the mechanical and tribological performance of the tribo-layer during sliding friction. Ni 3 Al matrix composites are used for validating the analysis model. The experimental results show that the existing model can be successfully applied to predict the friction and mechanical performance of the tribo-layer which is formed during the sliding contact. The thermal effect caused by the frictional heat and crack propagation have been incorporated into the model. The grain growth and the thermal effect play an important role in the improvement of the wear resistance and decrease of friction. [ABSTRACT FROM AUTHOR]

The sliding wear of Ni3Al matrix composites with addition of 1.5 wt.% graphene nanoplates was studied through pin-on-disc wear testing. The spontaneous formation of a tribo-layer produced during sliding wear was found to result in a deviation from Archard scaling and an unexpected high wear resistance that was not based on hardness alone. The tribo-layer exhibited specific microstructural evolution with significant severe deformation and grain refinement after wear. In the grain refinement area, the accumulation of dislocations and an increase in misorientations were found to lead to strain hardening. For the plastic deformed area, reduction in the dislocation density inside the elongated ultrafine grains reduced strain hardening compared with the grain refinement area. It can be concluded that the deviation from Archard scaling occurred primarily as a result of the microstructural evolution of the tribo-layer, resulting in the specific performance of mechanical and tribological properties of Ni3Al matrix composites under cyclic sliding wear process. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

• A new drought index, i.e., the water storage deficit index was defined. • There is a large variation in the propagation time of drought in different regions. • The sensitivity of vegetation to drought is influenced by the type of vegetation. • There is a significant time lag effect of drought on vegetation. Due to climate change and human activities, drought has become one of the most complex natural disasters in the Huang-Huai-Hai River basin, China. The purpose of the current research is to analyze the response of vegetation to drought in the Huang-Huai-Hai River basin by calculating the lag time correlation coefficient between the enhanced vegetation index (EVI) and drought indices. First, the water storage deficit index (WSDI) calculated from the total water storage anomalies (TWSA) was used as the hydrological drought index. The meteorological drought index we used was the self-calibrating Palmer drought severity index (scPDSI) provided by the Climate Research Unit (CRU). Then, the relationship between hydrological and meteorological drought was obtained based on the wavelet coherent change. Finally, the response of different vegetation types to drought was analyzed based on the lag time correlation coefficient. The results showed that: the average time of hydrological drought lagged meteorological drought in the three first-level basins of the Huang-Huai-Hai River basin, respectively, was 50 days (Yellow River basin), 43 days (Huaihe River basin), and 35 days (Haihe River basin); the lag time correlation coefficient of the different time scales (1–12 months) can reflect the sensitivity of vegetation to drought in different vegetation types and regions. The forest was the least sensitive to drought in the Huang-Huai-Hai River basin, followed by cropland, while grassland was the most sensitive to drought. It was discovered that hydrological drought had a huge influence on vegetation rather than meteorological drought by comparing the maximum lag time correlation coefficients of EVI with drought indices (scPDSI and SPEI). This study stresses the importance of taking into account the effects of various types of drought on the vegetation in the Huang-Huai-Hai River basin. This will help us better understand how drought affects vegetation. [ABSTRACT FROM AUTHOR]

The textured surface is one of the hotspots in the field of tribology research on reducing friction and wear. By calculating and optimizing the micro-texture structure, researchers designed and prepared textures with excellent tribological properties on the mechanical part surfaces. In this work, the tribological performance of 42CrMo matrix composite textured surfaces (CTSs) with different textured densities under grease lubrication was studied. The CTS was composed of 42CrMo alloys and SnAgCu-MXenes-Ti 3 C 2 (SACM). The results showed that when the textured density ρ of CTS was 36%, the friction coefficient (0.090) and wear rate (5.4 × 10−9 mm3N−1m−1) of counterpart ball could be respectively reduced by 75.7% and 38.6% compared with those of counterpart ball against the untextured sample. CTS could enhance the stability of friction system. Mxenes-Ti 3 C 2 wrapped by SnAgCu could form the lubricating layer containing sub-micron rollers on the worn surface, effectively reducing the friction and wear of samples under grease conditions. [Display omitted] • The composite textured surfaces (CTSs) were designed and prepared. • MXenes wrapped by SnAgCu could form sub-micrometer rollers in wear scar. • CTS exerted tribological enhancement function under starvation. • CTS could produce excellent synergistic effect with grease. [ABSTRACT FROM AUTHOR]

The wear fatigue of slewing bearings at the contact areas of raceways (AISI 4140 steel (AS)) and rollers (AISI 52100 steel) seriously reduces the service life of equipment. AS-SnAgCu-TiC composites (AS-SACT) were prepared by filling multi-solid lubricants into surface biomimetic textures of AS to improve the wear resistance. Tribological properties were tested using a block-on-ring tribometer. The materials of block and ring were AS and AISI 52100 steel, respectively. Compared with that of AS, coefficient of friction of AS-SACT was decreased by 67.93%, and wear height was reduced by 42.19%. Wear triggered the diffusion of SnAgCu from the bionic textures to worn surface. The hard phase of nano-TiC was wrapped by a cluster of multi-layer lubricants to form spherical particles, which not only converted sliding to rolling contact, but also repaired pits and furrows on worn surface. Hence, AS-SACT with self-repairing behavior had excellent properties of antifriction and wear resistance. [Display omitted] •Tribological properties of AISI 4140 steel were improved by texture and SnAgCu–TiC. •Average COF of AS-SnAgCu-TiC was 67.93% lower than that of AS (AISI 4140 steel). •Wear defects were filled with solid lubricants to produce self-repairing behavior. •Spherical particles transformed the frictional mode from sliding to rolling. •Nano-TiC particles wrapped by SnAgCu can promote wear defects to be filled. [ABSTRACT FROM AUTHOR]

Inspired by shell surface structure, the surface textures were extracted by curve fitting method and the corresponding bionic wavy textures filled with SnAgCu-WS 2 composite solid lubricants were prepared on the surface of TC4. The coupling effect of bionic wavy textures and SnAgCu-WS 2 and the effect of variable reciprocating friction frequency on the tribological properties of TC4 were explored. The results show that bionic textures improve the precipitation efficiency of SnAgCu-WS 2 , and the sliding effect of WS 2 promotes the spreading and repairing of composite solid lubricants in the wear track, thus improving the formation quality of the lubricating film and its adaptability to the change of reciprocating frequency. [Display omitted] • Bionic textures with lubricants were used to improve tribological performance of TC4. • Bionic wavy textures improve the precipitation efficiency of SnAgCu-WS 2. • Sliding effect of WS 2 promotes spreading and repairing of lubricants in wear track. • Coupling effects improve adaptability to the change of reciprocating frequency. • The average friction coefficient of TWs-SACW02 is reduced to 0.219 at 20 N and 1 Hz. [ABSTRACT FROM AUTHOR]

Titanium-coated silicon carbide whiskers were prepared by vacuum slow vapor deposition process. W-20Cu composite powder was fabricated by spray drying and calcining-continuous reduction technology. The paper adopted hot-press sintering to prepare titanium-coated silicon carbide whiskers/W-20Cu composites. Effects of addition amount of titanium-coated silicon carbide whiskers on the phases, microstructures, and properties of the composites were investigated. Titanium-coated silicon carbide whiskers/W-20Cu composites with improved mechanical properties and thermal conductivities were fabricated by hot-press sintering at 1350℃ under a pressure of 30 MPa for 2 h in pure Ar atmosphere. The transverse rupture strength and thermal conductivity of the 0.6 wt% titanium-coated silicon carbide whiskers/W-20Cu composite when compared with W-20Cu-based alloy were enhanced by 22% and 26%, respectively. With reasonable addition amount of titanium-coated silicon carbide whiskers, the composites without graphite, tungsten carbide, and silicon phases were obtained. [ABSTRACT FROM AUTHOR]

The wear and friction behavior of materials depends on the structure of the surface layers that can develop during sliding contact. The evolving dynamic recrystallization process of the friction layer of Ni 3 Al matrix composites (NMCs) at different contact loads was characterized. A pin-on-disk contact geometry was used. Silicon nitride ceramic was chosen as the pin material because of its inertness. A wear-induced tribo-layer composed of a grain growth layer and a nanocrystalline (NC) structured layer was formed. The soft wear-induced (0.6 GPa) layer, supported by the harder NC structure layer (7.4 GPa), is proposed to be beneficial both to achieving a low friction coefficient and a high wear resistance for the NMCs. [ABSTRACT FROM AUTHOR]

Multilayer graphene (MLG) shows an attractive prospect for the demanding engineering applications. This paper reports the mechanical and tribological properties of MLG reinforced Ni 3 Al matrix composites (NMCs) under dry sliding at varying sliding speed. The hardness and elastic modulus of the NMCs are significantly influenced with MLG content. It is found that the hardness and elastic modulus of the NMCs are found to be increased by increasing MLG content up to 1.0 wt.%, while decreased when MLG content is above 1.0 wt.%. Tribological experiments suggest that MLG can dramatically improve the wear resistance and decrease the friction coefficient of the NMCs. Such marked improvement of wear resistance is attributed to the reinforcing mechanisms of MLG, such as crack deflection and pull-out, and reduction of friction coefficient is related to the formation of a tribofilm on the sliding contact surface. [ABSTRACT FROM AUTHOR]

The main objective of this work has been the characterization of wear behavior of the graphene nanoplates (GNPs) in Ni3Al matrix composites (NMC). The friction and wear behaviors of NMC with the addition of 1 wt.% GNPs against Si3N4 ball are tested under different loads using a constant speed of 0.2 m/s. Tribological test results have revealed that small amounts of GNPs are able to drastically improve the antifriction and antiwear properties of NMC. A possible explanation for these results is that, the GNPs not only provide an enhanced effect for NMC to produce better wear resistance, but also form a local protective layer on the contact surfaces to reduce the friction. The investigation shows that GNPs hold great potential applications as an effective solid lubricant for Ni3Al matrix composites and possibly other alloys. [ABSTRACT FROM AUTHOR]

In recent years, reducing friction and wear-related adverse impacts on efficiency and durability in moving mechanical systems has gained increased attention. Herein, the search continues for novel materials and lubricants that can potentially reduce friction and wear. As one of the emerging self-lubricating materials, the tribological potential of graphene has been researched deeply. This article was dedicated to explore the combined lubrication of multilayer graphene (MLG) and WS. The as-prepared sample of NiAl-1.5 wt% MLG-5 wt% WS (NB) exhibited excellent tribological properties. During the sliding process, a continuous lubricating film was formed to provide the low-strength junctions at the interface, reducing the friction coefficient and wear rate. Moreover, the MLG played the role of reinforcement particles and improved loading carrying ability. [ABSTRACT FROM AUTHOR]

More durable, low-friction self-lubricating materials in modern industry are greatly needed for tribological systems. The current paper presents the tribological performance of TiAl matrix self-lubricating composites (TSC) containing MoS, hexagonal BN and TiSiC designated as MhT against GCr15 steel counterface under several sliding speeds from 0.2 to 0.8 m s and applied loads from 6 to 12 N. The results suggested that MhT played an important role in decreasing friction coefficients and wear rates. The covering percentage of transfer layers on worn surfaces varied with the changing of sliding speeds and applied loads, hence resulting in the distinct friction and wear characteristics of TSC. TSC containing 10 wt% MhT exhibited the best excellent tribological performance at 10 N-0.8 m s, which could be due to the formation of the best compaction and largest coverage of transfer layer on the worn surfaces. [ABSTRACT FROM AUTHOR]

Research on the friction layer is needed to minimize friction- and wear-related mechanical failures in moving mechanical assemblies. Dry sliding tribological tests of NiAl matrix composites (NMCs) with 1.5 wt% graphene nanoplatelets (GNPs) sliding against different counterface balls are undertaken at the condition of 10 N-0.234 m s in this study. When sliding against GCr15 steel, a uniform and thick friction layer is formed, resulting in a lower friction coefficient (0.29-0.31) and wear rate (2.0-3.1 × 10mmNm). While sliding against AlO and SiN, the formation and stability of the friction layers are restricted in the severe wear regime, and the NMCs exhibit higher friction coefficients and wear rates. Therefore, various counterface balls have a great effect on the stability and thickness of the friction layer, thus affecting the tribology performance of NMCs. The result also shows that GNPs exhibit enrichment and self-organized microstructures in the friction layer. In addition, the friction layer is also found to be divided into two layers, protecting the subsurface from further damage and reducing shear. [ABSTRACT FROM AUTHOR]

Highlights: [•] Tribological properties of NATMs from RT to 800°C were tested. [•] Ti3SiC2–MoS2 brought about an improvement in tribological behavior of NATMs. [•] Synergetic effect of Ti3SiC2–MoS2 was key to tribological performance of NATMs. [•] NATM5 showed the best self-lubricating performance and tribological properties. [ABSTRACT FROM AUTHOR]

Highlights: [•] Tribological properties of NMSC from RT to 800°C were tested. [•] Tribological properties of NMSC strongly depended on the addition content of WAh. [•] WAh and TiC brought about an improvement in tribological properties of NMSC. [•] NE showed the excellent tribological properties from RT to 800°C. [ABSTRACT FROM AUTHOR]

Dry sliding tribological properties of TiAl matrix self-lubricating composites (TMSC) containing Ag, TiSiC, Ag and TiSiC were investigated from 25 to 800 °C under ball-on-disk test conditions against SiN counterface under the same conditions of 10 N-0.234 m/s. The results indicated that the tribological properties were strongly dependent on the lubricant additives. TMSC with the addition of Ag and TiSiC (TAT) exhibited the lower friction coefficients (0.32-0.43) and less wear rates (1.23-4.13 × 10 mm Nm) in the wide temperature range of 25-800 °C. The excellent tribological properties of TAT over the wide temperature range were attributed to the synergetic effect of Ag and TiSiC lubricants, silver diffusion forming a rich-silver smooth tribo-film on the frictional surface of TAT at low and moderate temperatures from 25 to 400 °C, while TiSiC oxidation reaction forming rich-oxide tribo-film on the worn surface of TAT at higher temperatures of 600 and 800 °C. [ABSTRACT FROM AUTHOR]

Abstract: An investigation was conducted on the possible beneficial synergistic effects of multiple additives in self-lubricating composites for use in high temperature friction and wear applications. The sliding friction and wear rates of NiAl based self-lubricating composites with different solid lubricant additions (PbO, Ti3SiC2–MoS2, Ti3SiC2–WS2) were obtained from room temperature to 800°C with a pin-on-disc configuration. Dry sliding wear tests against Si3N4 balls (the pin specimens) were run using a constant load of 10N and a constant speed of 0.2m/s. The results showed that the composites with Ti3SiC2–MoS2 exhibited excellent self-lubricating and anti-wear properties over a wide temperature range. MoS2 lubricated better at low temperatures, while Ti3SiC2 lubricated better at high temperatures. The Ti3SiC2–MoS2 binary lubricant presented the best synergetic lubricating effect of the three candidate compositions. [Copyright &y& Elsevier]

Abstract: Investigations in graphene of controlling friction and wear of Ni3Al matrix self-lubricating composites (NMSC) are needed for moving mechanical assemblies. The friction and wear behaviors of NMSC with graphene nanoplatelets (GNPs) against Si3N4 ball are tested using a constant load of 10N and a constant speed of 0.2m/s from room temperature (RT) to 600°C. Tribological test results have revealed that small amounts of GNPs in the NMSC are able to drastically reduce the friction coefficients and wear rates over the effective operating range (RT-400°C). A possible explanation for these results is that the refinement of grains accompanying the slippage of laminated sheets between GNPs could provide a source of the stress dissipation and form the GNP protective layer during sliding process, leading to the reduction of wear rates as well as the friction coefficients. It is concluded that GNPs hold great potential applications as an effective solid lubricant for moderate loads and stress, and can be easily used for the preparation of the self-lubricating composites in the future. [Copyright &y& Elsevier]

Abstract: This paper reports on preparation technique and tribological properties of multilayer graphene (MLG) reinforced TiAl matrix composites (GTMC). GTMC are successfully prepared by spark plasma sintering (SPS). Structural characterization of starting MLG and the sintered GTMC are performed using Raman spectroscopy and field emission scanning electron microscopy, which indicates that MLG homogeneously distributes in GTMC. Tribological studies suggest that MLG plays an important role in decreasing friction coefficients by a factor of 4 and wear by almost 4–9 times of magnitude. Such marked reductions are attributed to the fact that MLG easily shears and forms a conformal anti-wear protective layer on the sliding contact interfaces, thus drastically reduces the friction coefficients and wear rates of GTMC. MLG can actually act as an effective reinforcement and lubricant phase in GTMC. [Copyright &y& Elsevier]

Highlights: [•] Tribological properties of TMSC from RT to 600°C are tested. [•] ATBC brings about an improvement in tribological behavior of TMSC. [•] Synergetic effect of ATBC is key to tribological performance of TMSC. [•] TB shows the best self-lubricating performance and tribological properties. [ABSTRACT FROM AUTHOR]

Abstract: The SiCf/W–20Cu composites are prepared by spark plasma sintering (SPS) process at 1200°C for 10min under a pressure of 30MPa, using titanium nitride (TiN) coated SiC fibers (SiCf) and W–20Cu composite powders. Effects of amounts of the TiN coated SiCf on the phases, microstructure and properties of the composites are investigated. The results show that the transverse rupture strength of the 0.8wt.% TiN coated SiCf/W–20Cu composites is enhanced 50%, while an increase of 31% in the thermal conductivity is observed, if compared to the base W–20Cu alloy. When the amount of the TiN coated SiCf is less than 1.0wt.%, the SiCf/W–20Cu composites without silicon, ditungsten carbide and tungsten carbide, as well as graphite phases are obtained. The TiN coating can be effective to control the detrimental interfacial reaction between the SiCf and W–20Cu alloy based matrix. [Copyright &y& Elsevier]

Inspired by the ability of tree frog toes to regulate body fluids, this control mechanism is applied to the tooth surface of slewing bearing (AISI 4140 steel (AS)) by adopting the regular hexagonal microtexture. SnAgCu-TiC (SACT) lubricants are filled in the microtextures. Results of two-factor analysis of variance show that there is a significant interaction between the microtexture and lubricants. When the microtextures with 1000 µm side are filled with SnAgCu-4 wt% nano-TiC (AS-SACT410), coefficient of friction (COF) of sample is the lowest. Compared with AS (0.437), COF of AS-SACT410 is reduced to 0.085, decreased by 80.55%. Macroscopic anti-friction originates because SnAgCu wraps around nano-TiC to form tribofilms containing submicron rollers, achieving substantially reduced COF. [Display omitted] • Bionic texture with lubricants was used to improve the friction performance of AS. • The synergistic effect is confirmed by two-factor analysis of variance. • SnAgCu wraps nano-TiC particles to form tribofilms containing submicron rollers. • The sliding friction is converted to rolling friction by the submicron rollers. • Compared with AS (0.437), COF of AS-SACT410 is reduced to 0.085 under dry friction. [ABSTRACT FROM AUTHOR]

Abstract: Dry sliding tribological behavior of TiAl matrix self-lubricating composites (TMSCs) containing silver against Si3N4 was investigated from 25 to 800°C at the condition of 10N–0.234m/s. The results indicated that the friction coefficients increased with the increase in test temperature. Moreover, the friction coefficients of TMSC containing silver were lower than that of the base alloy at all the temperatures, which was attributed to the synergetic effect of Ag and Ti2AlC lubricants. TMSC containing 10wt% silver exhibited the best tribological properties over the wide temperature range. [Copyright &y& Elsevier]

Dry sliding tribological tests of Ni3Al matrix self-lubricating composites (NMSC) with addition of 15wt% Ti3SiC2 are undertaken against Si3N4, Al2O3, WC-6Co at 25–800°C. The results show that the tribological properties are strongly dependent on the counterface materials. NMSC against Si3N4 shows the lower friction coefficients (0.31–0.48) and wear rates (0.34–2.1×10−5 mm3 N−1 m−1) from 25 to 800°C, while there is no clear difference in tribological performance of NMSC against Al2O3 or WC-6Co. NMSC against Si3N4 may be the optimal design for the excellently tribological performance. [ABSTRACT FROM AUTHOR]

Abstract: The effect of sliding speed and load on the friction and wear behavior of NiAl–10wt%Ti3SiC2 composites (NAT) at room temperature was investigated through determination of friction coefficients and wear rates in different conditions and analysis of morphologies and compositions of wear debris and worn surfaces of both NAT and Si3N4 ball. The results showed that the friction coefficients decreased and wear rates increased with increase in load, whereas they both decreased with increase in sliding speed. The transition in the wear mode from mild to severe wear was strongly influenced by the sliding speed and load. [Copyright &y& Elsevier]

Abstract: The dry sliding friction and wear behavior of Ti3SiC2/(WC–10Co) composites (TWCs) against GCr15 steel pair at room temperature was investigated through the determination of friction coefficient and wear rate under different conditions and the analysis of the morphologies and compositions of wear debris, worn surfaces of TWC and GCr15 steel. The friction coefficients of TWC with 3wt.% WC–10Co were in the range of 0.40–0.48, and the wear rate varied from 0.6×10−4 mm3 (Nm)−1 to 1×10−4 mm3 (Nm)−1. At the load of 10N and sliding speed of 0.353m/s, the glazes were formed on the worn surfaces of TWC. The wear mechanisms were complicated, including micro-cutting and abrasive wear of TWC, oxidation wear of GCr15 steel, as well as adhesive wear caused by the glaze flaking. [Copyright &y& Elsevier]

Abstract: NiAl matrix self-lubricating composites (NMCs) with various contents of Ti3SiC2 were fabricated by in situ technique using spark plasma sintering. The effects of Ti3SiC2 content on tribological properties of NMC were investigated. The results showed that NMC were composed of the matrix phase of NiAl alloy, enhanced phase of TiC and lubricating phases of Ti3SiC2 and C. NMC with 10wt.% Ti3SiC2 exhibited low friction coefficient of 0.60 and wear rate of 5.45×10−5 mm3 (Nm)−1 at the condition of 10N–0.234m/s at room temperature. The optimum content of Ti3SiC2 was 10wt.%. The excellent tribological performance of NMC could be attributed to the balance between strength and lubricity, as well as synergetic effect of enhanced phase and lubricating phases. The wear mechanisms changed with the increasing of the doped content of Ti3SiC2. [Copyright &y& Elsevier]