Fatigue crack growth resistance of SiC<Subscript>p</Subscript> reinforced Al alloys: Effects of particle size,particle volume fraction,and matrix strength

The main aim of this work was to study the effects of particle size, particle volume fraction, and matrix strength on the long fatigue crack growth resistance of two different grades of Al alloys (Al2124-T1 and Al6061-T1) reinforced with SiC particles. Basically, it was found that an increase in particle volume fraction and particle size increases the fatigue crack growth resistance at near threshold and Paris regimen, with matrix strength having a smaller effect. Near final failure, the stronger and more brittle composites are affected more by static modes of failure as the applied maximum stress intensity factor (K _max) approaches mode I plane strain fracture toughness (K _IC).     

改善颗粒增强金属基复合材料塑性和韧性的途径与机制

评述了影响颗粒增强金属基复合材料塑性和韧性的各种因素,在此基础上深入研究了颗粒形状对ＳｉＣｐ／ＬＤ２复合材料塑性和断裂韧性的影响规律。采用有限单元法分析不同形状的ＳｉＣ颗粒增强的ＬＤ２复合材料的微区力学环境和整体力学行为,结果表明颗粒的尖锐化导致基体内应变集中和颗粒尖端断裂的可能性加剧,因而降低材料的塑性;而在外加载荷的作用下,由于复合材料基体整体均处于较高的加工硬化状态,因此颗粒形状对材料断裂韧     

室温微成形尺寸效应对材料强韧性影响的研究现状

重点梳理了近年来微成形尺寸效应理论的研究进展,归纳总结了现有文献中关于微成形中变形行为的各种尺寸效应与材料屈服强度、塑性、抗拉强度、断裂韧性的关系,包括:晶粒尺寸、厚度尺寸以及两者之间的比值对屈服强度有重要影响;伸长率随厚度的增加而增加;抗拉强度与厚度尺寸和晶粒尺寸之间存在复杂关系;材料的断裂韧性与各种尺寸有密不可分的关系。并分析了这些研究结论存在差异的原因,同时,指出现有微成形尺寸效应机理目前存在有争议和亟待解决的关键问题。     

Production and mechanical properties (strength, wear, and fracture toughness) of chilled aluminum-quartz castable particulate composite

Structural composite materials offer an excellent opportunity to produce components that achieve weight savings and improved mechanical properties. This paper describes a chilled Al-quartz particulate composite that can be cast using metallic and nonmetallic chill blocks, much like nonreinforced aluminum, using conventional aluminum casting equipments. Unlike other metal matrix composites (MMCs), this material is produced economically by a simple ingot metallurgical process. An overview of the production process is given along with the techniques used for fabricating the chilled composite. The material’s mechanical properties, particularly its strength, wear resistance, fracture toughness, and hardness, are discussed in some detail. These properties offer attractive design opportunities for a variety of automotive, aerospace, and structural applications. The composite developed is shown to provide significant weight savings over ferrous metals. The present investigation aims at producing cast aluminum alloy-quartz particulate composites in molds, containing metallic and non metallic chill blocks, by dispersing quartz particles in molten aluminum alloy, above the liquidus temperature, the size of the particles dispersed being between 60 and 100 μm. The dispersoid being added ranges from 3 to 9 wt.% in steps of 3%. The resulting composites cast using chill blocks were tested for thier mechanical properties.     

Effects of silver powder particle size on the microstructure and properties of Ag-Yb<Subscript>2</Subscript>O<Subscript>3</Subscript> electrical contact materials prepared by spark plasma sintering

Ag-Yb₂O₃ electrical contact materials were fabricated by spark plasma sintering (SPS). The effects of silver powder particle size on the microstructure and properties of the samples were investigated. The surface morphologies of the sintered samples were examined by optical microscope (OM), and the fracture morphologies were observed by scanning electron microscopy (SEM). The physical and mechanical properties such as density, electrical resistivity, microhardness, and tensile strength were also tested. The results show that the silver powder particle size has evident effects on the sintered materials. Comparing with coarse silver powder (5 μm), homogeneous and fine microstructure was obtained by fine silver powder (≤0.5 μm). At the same time, the electrical conductivity, microhardness, and tensile strength of the sintered samples with fine silver powder were higher than those of the samples with coarse silver powder. However, silver powder particle size has little influence on the relative densities, which of all samples (both by fine and coarse silver powders) is more than 95%. The fracture characteristics are ductile.     

多级强化固溶处理对7050铝合金厚板强度和断裂韧性的影响

采用光学金相、示差扫描量热分析、扫描电镜、室温拉伸及断裂韧性实验,研究多级固溶处理对7050铝合金强度和断裂韧性的影响。结果表明:7050铝合金厚板经多级强化固溶后,随最后一级温度的增加,可溶性粗大第二相减少,其强度和断裂韧性增加,当最后一级温度为493℃时,合金的断裂韧性和强度达到峰值,其断裂韧性(KIC)、屈服强度(σ0.2)和抗拉强度(σb)分别为37.4 MPa.m1/2、500.6 MPa和534.0 MPa;当最后一级温度超过493℃时,由于再结晶分数急剧增加、晶粒快速长大,断裂韧性和强度又逐渐降低;当多级固溶最后一级的温度和时间与单级固溶一致时,经多级强化固溶后的7050铝合金具有比单级固溶时更高的断裂韧性和强度。     

Tensile properties and fracture behavior of Ti2AlNb based alloys at room temperature

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Effects of particle size on residual stresses of metal matrix composites

A finite element analysis was carried out on the development of residual stresses during the cooling process from the fabrication temperature in the SiCp reinforced AI matrix composites. In the simulation, the two-dimensional and random distribution multi-particle unit cell model and plane strain conditions were used. By incorporating the Taylor-based nonlocal plasticity theory, the effect of particle size on the nature, magnitude and distribution of residual stresses of the composites was studied. The magnitude thermal-stress-induced plastic deformation during cooling was also calculated. The results show similarities in the patterns of thermal residual stress and strain distributions for all ranges of particle size. However, they show differences in magnitude of thermal residual stress as a result of strain gradient effect. The average thermal residual stress increases with decreasing particle size, and the residual plastic strain decreases with decreasing particle size.     

热处理对SiCp/Al复合材料强度和塑性的影响

采用粉末冶金法制备了d300 mm的15%SiCp/Al(体积分数)复合材料坯锭,研究了挤压态和T4态复合材料的力学性能和断裂特点,揭示了基体强度和颗粒开裂对复合材料强度与塑性的影响规律。结果表明:复合材料T4态拉伸强度保持在560 MPa的水平下,延伸率仍高达7%以上;与挤压态相比,T4态复合材料拉伸强度和屈服强度分别提高了68.5%和105%,但塑性保持在同一水平。断口观察表明:挤压态复合材料以基体断裂为主,而T4态复合材料除了基体断裂外,还存在SiC颗粒开裂现象;基体强度严重影响复合材料的断裂形式,颗粒开裂有利于提高复合材料的塑性。     

Tensile and fracture properties of Ti-62A alloy plate with different microstructures

Ti-62A alloy plates with three different types of microstructure,fully equiaxed,bimodal,and Widmanst(a)tten,were obtained by various heat treatments to investigate the effects of microstructure on the tensile and fracture properties at room temperature.The results reveal that Widmanst(a)tten microstructure exhibits good damage tolerance behavior considering strength,fracture toughness,and fatigue crack growth behavior,while the bimodal microstructure shows good comprehensive properties considering the plasticity synthetically.Optical microscopy (OM) and scanning electron microscopy (SEM) microstructure analyses on fracture and fatigue crack path demonstrate that the dependence of mechanical properties and fatigue crack growth behavior on microstructural feature are attributed to the α lamellae width and the α colony size.     

新型高强韧铝锂合金的显微组织和性能

通过室温拉伸试验、热稳定化试验、扫描电镜(SEM)以及透射电镜(TEM)等方法对人工时效状态下新型高强韧铝锂合金厚板室温拉伸性能、热稳定性、断口形貌以及微观组织进行了研究。结果表明,合金进行室温拉伸试验时,厚板T/2厚度位置处的强度和伸长率均高于T/4厚度位置,这是由于板材进行轧制变形时,T/2厚度位置处变形量较大,位错密度更高,后续时效处理时会析出更多的强化相;稳定化时间一定时,随稳定化温度的升高,合金强度先增加,稳定化温度超过175℃后,强度逐渐降低,合金的热稳定性主要取决于稳定化处理后析出相的变化,稳定化温度低于150℃时,T₁相具有较好的耐热性,析出相的尺寸和数量变化较小,稳定化温度进一步升高后,T₁相数量逐渐减少。     

Improvement of high-temperature strength of 6061 Al matrix composite reinforced by dual-phased nano-AlN and submicron-Al2O3 particles

Nano-AlN and submicron-Al₂O₃ particles were simultaneously utilized in a 6061 Al matrix composite to improve the high-temperature strength. According to the SEM and TEM characterization, nano-AlN and submicron- Al₂O₃ particles are uniformly distributed in the Al matrix. Brinell hardness results indicate that different from the traditional 6061 Al matrix alloy, the aging kinetics of the composite is obviously accelerated by the reinforcement particles. The T6-treated composite exhibits excellent tensile properties at both room temperature and elevated temperature. Especially at 350 °C, the T6-treated composite not only has a high yield strength of 121 MPa and ultimate tensile strength of 128 MPa, but also exhibits a large elongation of 11.6%. Different strengthening mechanisms of nano-AlN and submicron-Al₂O₃ particles were also discussed in detail.     

Effect of graphite particle size on wear property of graphite and Al_2O_3 reinforced AZ91D-0.8%Ce composites

The graphite particles and Al_2O_3 short fibers reinforced AZ91D-0.8%Ce composites were fabricated by squeeze-infiltration technique.The researches about the effects of different graphite particle sizes on the microstructure and wear property of the composites were performed under the condition of constant contents of graphite particles and Al_2O_3 short fibers.The results reveal that the grain size of the composites changes less when the graphite particle size descends.Moreover,Ce enriches around the gr...     

Effect of particle size on the microstructure and thermal conductivity of Al/diamond composites prepared by spark plasma sintering

Spark plasma sintering (SPS) was used to fabricate Al/diamond composites. The influence of diamond particle size on the microstructure and thermal conductivity (TC) of composites was investigated by combining experimental results with model prediction. The results show that both composites with 40 μm particles and 70 μm particles exhibit high density and good TC, and the composite with 70 μm particles indicates an excellent TC of 325 W·m⁻¹·K⁻¹. Their TCs lay between the theoretical estimated bounds. In contrast, the composite with 100 μm particles demonstrates low density as well as poor TC due to its high porosity and weak interfacial bonding. Its TC is even considerably less than the lower bound of the predicted value. Using larger diamond particles can further enhance thermal conductive performance only based on the premise that highly dense composites of strong interfacial bonding can be obtained.     

基体合金对连续Al2O3f/Al复合材料微观组织及拉伸强度的影响

选用Nextel610型Al2O3纤维作为增强体,采用真空气压浸渗法制备了纤维体积分数40%、基体合金分别为1A99、ZL210A、ZL301及7075合金的单向连续Al2O3f/Al复合材料,并用NaOH溶液萃取出Al2O3纤维,研究了基体合金对连续Al2O3f/Al复合材料的致密度、纤维损伤及拉伸强度的影响。结果表明：基体合金对连续Al2O3f/Al复合材料的致密度和微观组织有明显影响,其中连续Al2O3f/ZL301复合材料致密度最高为99.2%,组织缺陷最少;连续Al2O3f/1A99复合材料致密度最低为96.8%,这种差异是由于不同基体与纤维之间润湿性不同导致的。不同基体与纤维发生了不同程度的界面反应,最后表现为对纤维的损伤程度不同。连续Al2O3f/1A99、Al2O3f/ZL210A、Al2O3f/ZL301及Al2O3f/7075四种复合材料的拉伸强度分别为465MPa、479MPa、680MPa和389MPa,缺陷、纤维损伤和界面结合强度是影响连续Al2O3f/Al复合材料强度的主要因素。     

Effects of SiC volume fraction and aluminum particulate size on interfacial reactions in SiC nanoparticulate reinforced aluminum matrix composites

The SiC nanoparticulate reinforced Al-3.0 wt.% Mg composites were fabricated by combining pressureless infiltration with ball-milling and cold-pressing technology at 700 °C for 2 h. The effects of SiC nanoparticulate volume fractions (6%, 10% and 14%) and Al particulate sizes (38 μm and 74 μm) on interfacial reactions were investigated by SEM, TEM and X-ray diffraction. The results show that the MgO at the interface between SiC nanoparticulate and molten Al can provide a barrier for the diffusion of Si, C and Al. Using Al particulate (74 μm) as raw material, the Al₄C₃ phase was not found in the composites containing 6 vol.% and 10 vol.% SiC, but presented in the composites containing 14 vol.% SiC. When SiC content up to 14 vol.%, the products of MgO around SiC nanoparticulate are not enough to provide effective protection from the reaction between SiC and molten Al, therefore the diffusion of Si, C and Al can take place to produce Al₄C₃ and Si phases. Using 38 μm Al particulate as raw material, the fine Al particulate possesses the high reaction activity and can easily be embedded into the gap among the big Mg particulate segregated at the interface, resulting in the appearance of exposure surface of SiCp to the Al and the forming of diffusion channels for the atomics C, Si and Al. So, the formations of Al₄C₃ and Si phases were occurred.     

Si3N4颗粒体积分数对Si3N4/Al复合材料微观组织和力学性能的影响（英文）

采用压力浸渗法制备Si3N4体积分数分别为45%、50%和55%的颗粒增强铝基复合材料(Si3N4/Al)。研究Si3N4体积分数和T6热处理对Si3N4/Al复合材料微观组织和力学性能的影响。结果表明:Si3N4颗粒分散均匀,Si3N4/Al复合材料浸渗良好,没有明显的孔洞和铸造缺陷;在Si3N4颗粒附近的铝基体中,可以观察到高密度位错;Si3N4/Al复合材料的弯曲强度随着Si3N4体积分数的增大而降低;T6热处理能提高复合材料的强度;复合材料的弹性模量随着Si3N4体积分数的增加而线性增加;在低Si3N4体积分数时,可以观察到更多的撕裂棱和韧窝;T6热处理对断口形貌的影响较小。     

Preparation,characterization and electrochemical properties of mesoporous LiFe<Subscript>0.99</Subscript>Mo<Subscript>0.01</Subscript>PO<Subscript>4</Subscript>/C

A mesoporous LiFe_0.99Mo_0.01PO₄/C composite was synthesized by the sol-gel method using (NH₄)₂MoO₄ as a doping starting material. The formation of conductive carbon, metal doping and mesopores was achieved simultaneously in the prepared material. The characterizations of crystal structures and microstructures were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), extended X-ray-absorption fine-structure (EXAFS) and X-ray-absorption near-structure spectroscopy (XANES), while the surface area was determined using N₂ adsorption techniques. Cyclic voltammetry (CV) and charge-discharge cycling performance were used to characterize its electrochemical properties. The sample possessed uniformly distributed mesopores with an average pore size of 4 nm, and the specific surface area was about 69.368 m²/g. The results show that the reversible capacity of mesoporous LiFe_0.99Mo_0.01PO₄/C is about 160 mAh/g at 0.1C, 135 mAh/g at 1C and 90 mAh/g at 5C, respectively. The capacity fading is neglectable.     

X80管线钢组织和有效晶粒对慢拉伸行为的影响

对系列X80管线钢研究表明,该材料组织特征为含有粒状贝氏体的针状铁素体;粒状贝氏体越细小弥散,其强韧性匹配越好。粒状贝氏体中,M-A岛的作用为阻碍裂纹的扩展;晶粒边界和M-A岛边界易萌生裂纹源。管线钢的有效晶粒决定了材料的塑韧性。具体表现为,当有效晶粒减小时,材料韧脆转变温度降低,断面收缩率提高。随着慢拉伸速率的提高,材料的断裂方式将发生改变。当拉伸速率为0.1 mm/s时,管线钢的延性最佳,而对强度的影响不大。这说明在管线钢富气服役状态下,富气压力有一个最佳值。拉伸速率升高后,断裂逐渐向脆性方式转变。