Preparation and Anti⁃arc Erosion Property of Ag Matrix Electrical Contact Material Reinforced by Novel Ti_(2)Cd

Due to their outstanding electrical contact properties,Cd-containing silver-matrix electrical contact materials can meet the requirements of high stability and long life for military defense and aerospace applications.In order to further reduce the Cd content under the premise of meeting the high-performance requirements,in this study,high-purity intermediate Ti_(2)Cd powder of MAX phase(Ti_(2)CdC)was synthesized with a pressureless technique and then applied to reinforce the Ag matrix.The Cd content of the as-prepared Ag/Ti_(2)Cd composites was actually reduced by 38.31%compared with conventional Ag/CdO material.Based on the systematic study of the effect of heat treatment temperature on the physical phase,morphology,interface and comprehensive physical properties of Ag/Ti_(2)Cd composites,the preferred samples(heat treated at 400°C for 1 h)showed high density(97.77%),low resistivity(2.34μΩ·cm),moderate hardness(90.8HV),high tensile strength(189.9 MPa),and exhibited good electrical contact performance after 40000 cycles of arc discharging under severe conditions(DC 28 V/20 A).The results of microscopic morphological evolution,phase change and elemental distribution of the electrical contact surface show that the combination of high stability of Ti_(2)Cd reinforcing phase,good interfacial bonding with Ag matrix and improved melt pool viscosity in the primary stage of arc erosion,results in low and stable contact resistance(average value 13.20 mΩ)and welding force(average value 0.6 N),low fluctuation of static force(2.2-2.5 N).The decomposition and absorption energy of Ti_(2)Cd and the arc extinguishing effect of Cd vapor are the main reasons for the stable arcing energy and arcing time of electric contacts in the late stage of arc erosion.

Excellent mechanical properties and resistance to cavitation erosion for an ultra-low carbon Cr Mn N stainless steel through quenching and partitioning treatment

The retained austenite content(RAC),the mechanical properties,and the resistance to cavitation erosion(CE)of the00Cr13Mn8Mo N steel after quenching and partitioning(Q&P)processing were investigated.The results show that the Q&P process affected the RAC,which reached the maximum value after partitioning at 400°C for 10 min.The tensile strength of the steel slightly decreased with increasing partitioning temperature and time.However,the elongation and product of strength and elongation first increased and then decreased.The sample partitioned at 400°C for 10 min exhibited the optimal property:a strength-ductility of 23.8 GPa?%.The resistance to CE for the 00Cr13Mn8Mo N steel treated by the Q&P process was improved due to work hardening,spalling,and cavitation-induced martensitic transformation of the retained austenite.

Soil erosion and soil properties in reclaimed forestland of loess hilly region

Based on data observed from 1989 to 1998 in the Ziwuling survey station, changes of soil erosion and soil physico-mechanical properties were studied after forestland reclamation. When the man-induced factors changed the eco-environment by reclaiming forestlands, the intensity of man-made soil erosion in reclaimed lands was 1,000 times more than that of natural erosion in forestlands. From the analysis of soil physical and mechanical properties, the clay content and physical clay content decreased 2.74% and 3.01% respectively, and the >0.25 mm water stable aggregate content decreased 58.7%, the soil unit weight increased and the soil shear strength decreased, all of which were easier to cause soil erosion. The results of the correlation analysis showed that the >0.25 mm water stable aggregate content was the greatest influencing factor on soil erosion, the partial correlated coefficient was 0.9728, and then were soil coarse grain and soil shear strength, the partial correlated coefficients being 0.8879 and 0.6020 respectively. The relationships between the >0.25 mm water stable aggregate content, the soil sheer strength and the soil erosion intensity were analyzed, which showed that the first and seventh years were the turning years of the soil erosion intensity after the forestland reclamation. The degenerative eroded soil and eco-environment formed the peculiar erosion environment, which aggravated the soil erosion rapidly.

Experimental investigation on the relevance of mechanical properties and porosity of sandstone after hydrochemical erosion

Under the effect of chemical etching,the macroscopic mechanical properties,mesoscopic structure,mineral content,and porosity of rocks undergo significant changes,which can lead to the geological disasters; thus,an understanding of changes in the microscopic and macroscopic structure of rocks after chemical etching is crucial.In this study,uniaxial mechanical tests and nuclear magnetic resonance(NMR) spectroscopy were carried out on sandstone samples that had been previously subjected to chemical erosion under different p H values.The aim was to study changes in properties and mechanical characteristics,including deformation and strength characteristics,of the rock,and microscopic pore variation characteristics,and to perform preliminary studies of the chemical corrosion mechanism.Results show that different chemical solutions have a significant influence on the uniaxial compressive strength,the axial strain corresponding to the peak axial stress,elastic modulus,etc.With the passage of time,porosity increases gradually with exposure to different chemical solutions,and exposure to chemical solutions results in large changes in the NMR T2 curve and T2 spectrum area.Sandstone exposed to different chemical solutions exhibits different corrosion mechanisms; the root cause is the change of mineral.

Mechanical properties and plasma erosion resistance of BN_p/Al_2O_3-SiO_2 composite ceramics

BNp/Al2O3-SiO2 system ceramic matrix composites with different volume fractions （10%-60%） of hexagonal BN particulates （BNp） were prepared by hot-press sintering technique. Phase components, microstructure, mechanical properties and plasma erosion resistance were also investigated. With the increase of h-BNp content, relative density and Vickers＇ hardness of the composite ceramics decrease, while the flexural strength, elastic modulus and fracture toughness increase and then decrease. The plasma erosion resistance linearly deteriorated with the increase of BNp content which is mainly determined by the density, crystal structure and atomic number of the elements.

Effect of Alternation of Aging and Seawater Erosion on Properties of Rubber Material Used in Lead Rubber Bearing

An artificially accelerated alternation of aging and seawater erosion test of rubber materials used in lead rubber bearing(LRB)was performed,mainly to study the time-varying laws of rubber materials mechanical properties.Time-varying laws of the Mooney–Rivlin and Neo-Hookean constitutive parameters of rubber materials under the alternation of aging and seawater erosion were also analyzed.Results indicate that the rubber material mechanical properties were significantly affected by alternation of aging and seawater erosion.Hardness and elongation stress increased exponentially with test time.And 120 days after the test,the hardness increased by 14%,the maximum percentage increase in stress of 124.76%occurred at 100%constant elongation and the minimum percentage increase in stress of 68.32%occurred at 300%constant elongation;Tensile strength and elongation at break decreased by 44.96%and 53.09%.Besides,constitutive parameters of Mooney–Rivlin and Neo-Hookean all changed greatly with test duration.Finally,time-varying laws of constitutive parameters were verified by comparing the simulated and experimental results of the lead rubber bearing’s stiffness.Research results are of great significance to the seismic performance research and life-cycle performance analysis of offshore traffic engineering such as cross-sea bridges and bridges in the marine environment.

Effects of collapsing gully erosion on soil qualities of farm fields in the hilly granitic region of South China

Collapsing gully erosion is a specific form of soil erosion types in the hilly granitic region of tropical and subtropical South China, and can result in extremely rapid water and soil loss. Knowledge of the soil physical and chemical properties of farmland influenced by collapsing gully erosion is important in understanding the development of soil quality. This study was conducted at the Wuli Watershed of the Tongcheng County, south of Hubei Province, China. The aim is to investigate soil physical and chemical properties of three soil layers （0-20, 20-40 and 40-60 cm） for two farmland types （paddy field and upland field） in three regions influenced by collapsing gully erosion. The three regions are described as follows： strongly influenced region （SIR）, weakly influenced region （WIR） and non-influenced region （NIR）. The results show that collapsing gully erosion significantly increased the soil gravel and sand content in paddy and upland fields, especially the surface soil in the SIR and WIR. In the 0-20 cm layer of the paddy field, the highest gravel content （250.94 g kg-1） was in the SIR and the lowest （78.67 g kg-1） was in the NIR, but in the upland filed, the surface soil （0-20 cm） of the SIR and the 40-60 cm soil layer for the NIR had the highest （177.13 g kg-1） and the lowest （59.96 g kg-1） values of gravel content, respectively. The distribution of gravel and sand decreased with depth in the three influenced regions, but silt and clay showed the inverse change. In the paddy field, the average of sand content decreased from 58.6 （in the SIR） to 49.0% （in the NIR）, but the silt content was in a reverse order, increasing from 27.9 to 36.9%, and the average of the clay content of three regions showed no significant variation （P〈0.05）. But in the upland filed, the sand, silt and clay fluctuated in the NIR and the WIR. Soils in the paddy and upland field were highly acidic （pH〈5.2） in the SIR and WIR; moreover lower nutrient contents （soil organic matter （SOM）, total N and available N, P, K） existed in the SIR. In the 0-20 cm soil layer of the paddy field, compared with the NIR and the WIR, collapsing gully erosion caused a very sharp decrease in the SOM and total N of the SIR （5.23 and 0.56 g kg-1, respectively）. But in the surface soil （0-20 cm） of the upland field, the highest SOM, total N, available N, available P and available K occurred in the NIR, and the lowest ones were in the SIR. Compared with the NIR, the cation exchange capacity （CEC） in the SIR and WIR was found to be relatively lower. These results suggest that collapsing gully erosion seriously affect the soil physical and chemical properties of farmland, lead to coarse particles accumulation in the field and decrease pH and nutrient levels.

Gravity erosion and lithology in Pisha sandstone in southern Inner Mongolia

Pisha sandstone is a soft rock found in the southern zone of the Inner Mongolia Autonomous Region of Inner Mongolia. The presence of soft Pisha sandstone in the middle reaches of the Yellow River coincides with large areas of bedrock erosion in the river’s basin, with the average total erosion modulus as high as 44 570 t/(km^2·a). Such high levels of erosion are one of the main sources of coarse mud and sands in the Yellow River. Erosion by gravitational forces such as snow glide and landslip are the main erosion types in Pisha sandstone region. The gravity erosion modulus can be as high as 25 615 t/(km^2·a), accounting for 30.6% of the total average erosion. Our paper investigates the characteristics of Pisha sandstone in relation to the development of gravity erosion mechanisms. We conducted field investigations in Pisha sandstone region for original state rock sampling. Test results from analyses of the rock properties indicate that the mineral composition, structure and microstructure characteristics of Pisha sandstone determine its varying capacity to resist weathering. Degrees of weathering in slightly different lithological layers of Pisha sandstone lead to different erosion rates. In this way, erosion forces combined with the varying lithological strata in the rock aggravate gravitational erosion in Pisha sandstone.

Enhanced cavitation erosion resistance of a friction stir processed high entropy alloy

Friction stir processing of an Al0.1CoCrFeNi high entropy alloy(HEA)was performed at controlled cooling conditions(ambient and liquid submerged).Microstructural and mechanical characterization of the processed and as-cast HEAs was evaluated using electron backscatter diffraction,micro-hardness testing and nanoindentation.HEA under the submerged cooling condition showed elongated grains(10μm)with fine equiaxed grains(2μm)along the boundary compared to the coarser grain(~2 mm)of as-cast HEA.The hardness showed remarkable improvements with four(submerged cooling condition)and three(ambient cooling condition)times that of as-cast HEA(HV^150).The enhanced hardness is attributed to the significant grain refinement in the processed HEAs.Cavitation erosion behavior was observed for samples using an ultrasonication method.All of the HEAs showed better cavitation erosion resistance than the stainless steel 316L.The sample processed under a submerged liquid condition showed approximately 20 and 2 times greater erosion resistance than stainless steel 316L and ascast HEA,respectively.The enhanced erosion resistances of the processed HEAs correlate to their increased hardness,resistance to plasticity,and better yield strength than the as-cast HEA.The surface of the tested samples showed nucleation and pit growth,and plastic deformation of the material followed by fatigue-controlled disintegration as the primary material removal mechanism.

Soil Loss by Wind Erosion for Three Different Textured Soils Treated with Polyacrylamide and Crude Oil, Iraq

The study is conducted to estimate the resistance of three soils (EL Hartha clay loam, Barjisiya sandy loam and the soil near the sand dunes in Sheikh sa'ad area sandy soil) to wind erosion, it is also aimed at getting full acquaintance of the relationship between the soil loss and the physical and chemical features of soil. In addition to the experiment of some soil stabilizers, polyacrylamide (PAM) concentration of 0.2 % and crude oil in concentration of 1 % in order to reduce or prevent wind erosion. The study shows that the amendment increased the dry soil aggregate >1 mm, mean weight diameter and soil moisture. It is clear that polyacrylamide had greater effect than that of crude oil, besides the great effectiveness of these amendments in decreasing bulk density and relations of soil loss.

Influence of austenization temperature on the erosion behavior of austempered ductile irons

The erosion behavior of austempered ductile irons austenized at different temperatures was studied. The results indicate that the erosion rate well correlates with the mechanical properties. At high impact angles, increasing ductility and mechanical energy density results in decreasing erosion rate, whereas increasing hardness reduces the erosion rate at low impact angles. 2008 University of Science and Technology Beijing. All rights reserved.

Mechanical Properties and Erosive Wear Resistance of Zirconia Toughened Al_2O_3-TiC Ceramics

The effect of ZrO2, content on the fracture toughness, flexural strength and Vickers hardness as well as the erosive wear resistan properties of zirconia toughened Al2O3-TiC ceramic composites has been investigated. The results showed that the improvement in fracture toughness and flexure strength of composites with the content of zirconia less than 50% and 10% in mass fraction respectively,is primarily attributed to stress-induced transformation toughening by the analyse of X-ray diffraction. The dependance of erosion wear resistance on the attak angle and the content of ZrO2, panicles of the composites was also revealed. It is found that the erosion rate of the composites has a sharp rise at a attack angle over 65°. This phenomenon is due to a brittle response to the erosion test by microsmictural observation on eroded surface.

Characterisation and Corrosion-Erosion Behaviour of Carbide based Thermal Spray Coatings

Thermal spraying has emerged as a suitable and effective surface engineering technology and is widely used to apply wear, erosion and corrosion protective coatings for various kinds of industrial applications. Cr3C2-based coatings have been applied to a wide range of industrial components. Cr3C2-NiCr coatings offer greater corrosion and oxidation resistance, also having a high melting point and maintaining high hardness, strength and wear resistance up to a maximum operating temperature of 900 °C. The corrosion resistance is provided by NiCr matrix while the wear resistance is mainly due to the carbide ceramic phase. This paper reviews the performance, developments and applications of Cr3C2-NiCr thermal spray coatings for corrosion/erosion-corrosion under different types of environments and outlines the characterization of Cr3C2-NiCr coatings with respect to their microstructure and mechanical properties, together with some brief characterisation work by the author for HVOF sprayed 75Cr3C2-25NiCr coating on T91 boiler steel.

Effect of Filler Content and Alkalization on Mechanical and Erosion Wear Behavior of CBPD Filled Bamboo Fiber Composites

In this study the mechanical and erosion wear behavior of bamboo fiber reinforce epoxy composites filled with Cement By-Pass Dust (CBPD) were studied. The effect of CBPD content and alkalization on the various properties of these composites was also investigated. Taguchi’s orthogonal arrays are used for analysis of experiential results. It identifies significant control factors influencing the erosion wear and also outlines significant interaction effects. Analysis of variance (ANOVA) test has also been performed on the measured data to find the most significant factors affecting erosion rate. Finally, eroded surfaces of both untreated and alkali treated bamboo fiber reinforced composites were characterized using SEM.

秸秆覆盖免耕对坡耕地土壤理化性质及水土流失的影响

为探究秸秆覆盖免耕对坡耕地土壤理化性质的影响及该措施下的水土保持效益。通过设立秸秆覆盖免耕和传统耕作田间试验区,探究土壤孔隙结构、土壤含水量、化学性质、产流产沙情况。结果表明:秸秆覆盖免耕处理后,土壤深度(h)为0<h≤10 cm处土壤密度增加了14.16%,总孔隙度及非毛管孔隙度分别降低了10.85%、27.11%。土壤深度为0<h≤20 cm处土壤有机质及全氮流失量减少,有效改善了土壤养分含量及分布。土壤深度为10、20、30、40 cm处土壤含水量分别提高6.30%、5.78%、7.57%、9.03%。在相同降雨条件下,土层越深土壤水分滞留时间越短。秸秆覆盖免耕处理减弱了降雨侵蚀力对产流产沙的影响,产流产沙次数及数量较传统耕作处理有明显降低,产流、产沙次数分别减少3、5次,产流、产沙量分别减少53.07%、71.87%。秸秆覆盖免耕能够有效降低降雨对产流产沙的驱动力,减少土壤有机质及氮流失,调节土壤结构。

Changes in soil properties and erodibility of gully heads induced by vegetation restoration on the Loess Plateau, China

Soil erosion on the Loess Plateau of China is effectively controlled due to the implementation of several ecological restoration projects that improve soil properties and reduce soil erodibility. However, few studies have examined the effects of vegetation restoration on soil properties and erodibility of gully head in the gully regions of the Loess Plateau. The objectives of this study were to quantify the effects of vegetation restoration on soil properties and erodibility in this region. Specifically, a control site in a slope cropland and 9 sites in 3 restored land-use types （5 sites in grassland, 3 in woodland and 1 in shrubland） in the Nanxiaohegou watershed of a typical gully region on the Loess Plateau were selected, and soil and root samples were collected to assess soil properties and root characteristics. Soil erodibility factor was calculated by the Erosion Productivity Impact Calculator method. Our results revealed that vegetation restoration increased soil sand content, soil saturated hydraulic conductivity, organic matter content and mean weight diameter of water-stable aggregate but decreased soil silt and clay contents and soil disintegration rate. A significant difference in soil erodibility was observed among different vegetation restoration patterns or land-use types. Compared with cropland, soil erodibility decreased in the restored lands by 3.99% to 21.43%. The restoration patterns of Cleistogenes caespitosa K. and Artemisia sacrorum L. in the grassland showed the lowest soil erodibility and can be considered as the optimal vegetation restoration pattern for improving soil anti-erodibility of the gully heads. Additionally, the negative linear change in soil erodibility for grassland with restoration time was faster than those of woodland and shrubland. Soil erodibility was significantly correlated with soil particle size distribution, soil disintegration rate, soil saturated hydraulic conductivity, water-stable aggregate stability, organic matter content and root characteristics （including root average diameter, root length density, root surface density and root biomass density）, but it showed no association with soil bulk density and soil total porosity. These findings indicate that although vegetation destruction is a short-term process, returning the soil erodibility of cropland to the level of grassland, woodland and shrubland is a long-term process （8-50 years）.

Fatigue Property of Basalt Fiber-Modified Asphalt Mixture under Complicated Environment

The fatigue property of asphalt mixtures under complicated environment （low-temperature bending performance, chloride penetration, freezing-thawing cycle and their coupling effect） and the improvement effect for relevant property of basalt fiber-reinforcing asphalt mixture under complicated environment are studied. Two grading types of asphalt mixtures, AC-16I and AC-13I, are chosen, whose optimum asphalt-aggregate ratio and optimum dosage of basalt fiber are determined by the Marshall test. The standard specimens are made firstly, and then the low temperature bending tests of asphalt mixture and basalt fiber-reinforced asphalt mixture under the coupling effect of the chloride erosion and freezing-thawing cycle have been carried out. Finally, the fatigue property tests of asphalt mixture and basalt fiber-reinforced asphalt mixture under complex environment are performed on MTS material testing system. The results indicate that the tensile strength, the maximum curving tensile stress, the curving stiffness modulus, and fatigue properties of asphalt mixture are influenced by the coupling effect of the chloride erosion and freezing-thawing cycle. The low-temperature bending performance and fatigue property of asphalt mixtures under complicated environment can be greatly improved by adding moderate basalt fiber. The dense gradation asphalt mixture possesses stronger ability to resist adverse environmental effects under the same condition.

Study of Changes in Physiochemical Properties of Soil by the Addition of Cement

The effect of cement on physiochemical properties of three types of soils i.e garden soil, agricultural soil and roadside soil was investigated. The ordinary Portland cement was used. The amount of cement added to soil samples, as dry mass percentage was 20%. The results of analysis showed that the addition of cement is capable of bringing about changes in physiochemical properties of soil. The electrical conductivity and organic matter content in three soils get decreased by the addition of cement. While the pH, bulk density and water holding capacity of soils after the addition of cement gets increased. The soil found most suitable to be treated with cement was roadside soil. It was concluded that cement can be used to change the physiochemical properties of soil and this technique has great utility in improving the quality of problematic soils.

植被恢复边坡土壤抗蚀性及其影响因子耦合协调分析

为了给边坡植被恢复设计等提供参考和技术支撑,基于内江市境内公路边坡经0、5、7、15、20 a植被恢复的样地野外调查资料,以土壤颗粒(团聚体)平均质量直径和水稳性指数为土壤抗蚀性指标,以土壤粒径≥0.25 mm的大团聚体含量、容重、有机质含量、碱解氮含量、速效磷含量、速效钾含量等6个土壤理化性质指标为土壤抗蚀性影响因子,采用主成分分析、耦合协调度分析等方法,探究不同植被恢复年限的边坡土壤抗蚀性与其影响因子的耦合协调关系,得到以下主要结论:1)不同植被恢复年限的土壤抗蚀性指标及其影响因子具有显著差异,随着植被恢复年限的延长,土壤大团聚体含量和养分含量呈增加趋势,土壤容重呈减小趋势,土壤抗蚀性呈增强趋势;2)碱解氮含量、有机质含量、速效磷含量、大团聚体含量、容重是不同植被恢复年限土壤抗蚀性的主要影响因子;3)土壤理化性质指标中,化学指标(速效磷含量、碱解氮含量、有机质含量、速效钾含量)对土壤抗蚀性的影响大于物理指标(大团聚体含量、容重)的影响,进行植被护坡设计时应当注重有机质和速效肥料的保持;4)土壤理化性质指标与土壤抗蚀性指标的耦合协调度随植被恢复年限的延长而提高,植被恢复15 a时二者的耦合协调类型仍属弱协调、植被恢复20 a时二者的耦合协调类型尚属中度协调,为了进一步改善边坡土壤的理化性质、促进稳定土壤结构的形成、增强土壤抗蚀性,还需更长时间的植被恢复。

盐冻循环作用下水泥稳定碎石混合料的宏细观性能

为研究盐分和冻融循环耦合侵蚀作用下水泥稳定碎石混合料的力学性能、疲劳特性及微细观空隙结构衰减规律,在冻融条件下对不同初始含盐量的水泥稳定碎石混合料开展无侧限抗压强度试验、弯拉强度试验、动态压缩模量试验和三分点加载疲劳试验。基于工业CT无损检测技术研究了盐冻耦合作用下水泥稳定碎石混合料微细观空隙结构衰减规律;提出了盐冻循环次数与盐溶液浓度对水泥稳定碎石混合料力学性能、疲劳性能和微细观空隙直径期望值的衰减公式;建立了微细观空隙结构与宏观力学性能、疲劳性能之间的拟合关系。结果表明:盐冻耦合侵蚀作用加速了水泥稳定碎石混合料力学性能与疲劳特性衰减,随着盐冻循环次数增加,水泥稳定碎石混合料的无侧限抗压强度与动态回弹模量呈指数模型衰减,弯拉强度与疲劳寿命呈三次函数模型衰减;盐冻损伤主要集中在集料边缘的原生空隙部位,微细观等效空隙直径期望值和空隙级配中小于0.1 mm3的空隙数量随着盐冻耦合侵蚀作用次数增加而增大;硫酸钠盐溶液浓度越大,经历相同盐冻循环后水泥稳定碎石混合料力学性能和疲劳性能损伤度越高,微细观等效空隙直径期望值随着硫酸钠盐溶液浓度增大呈线性关系增大;随着等效空隙直径期望值增大,水泥稳定碎石混合料的动态回弹模量、无侧限抗压强度和弯拉强度均呈线性关系减小,同时疲劳寿命呈指数函数关系降低;盐冻耦合侵蚀作用改变了水泥稳定碎石内部微细观空隙结构,是盐冻耦合侵蚀作用导致水泥稳定碎石混合料力学性能和疲劳性能下降的原因之一。