含Nd镁铝合金电子结构计算与强化机制分析

基于EET理论,计算了Nd元素加入Mg-Al合金后形成的Mg-Al-Nd固溶体,第二相Al2Nd,Al3Nd价电子结构,研究了价电子结构与合金固溶强化、第二相强化、高温稳定性和晶粒细化的关系.Mg-Al-Nd最强键共价电子对数nA值和共价电子密度ρCV值均大于α-Mg的nA值和ρCV值,表明Nd的固溶有利于基体强度的提高;第二相Al2Nd最强键(nA=0.44396)与Al3Nd最强键(nA=0.38949)的键合强度均远大于基体α-Mg(nA=0.11199)的键合强度,因此,Al2Nd和Al3Nd极大地阻碍了位错的运动,提高了合金的强度;Al2Nd和Al3Nd的单位体积成键能力FV值分别为145.91和242.35,与γ-Mg17Al12(Fγ-Mg17Al12V＝44.22)相比较,它们的高温稳定性更好,其存在有利于改善Mg-Al合金的高温性能;Nd提高了液态合金中邻近原子间键合强度,增加了基体的形核率,减缓了晶粒长大速度,进而细化了晶粒,提高了合金的力学性能.     

Nd对AZ91镁合金组织和高温力学性能的影响

研究了Nd对AZ91镁合金组织和高温力学性能的影响.结果表明,稀土Nd(1%～4%(wt))的加入明显细化了AZ91镁合金的铸态组织,减少了β(Mg17Al12)相的析出.随着稀土Nd含量的增加,室温、150℃和250℃等3个温度下的强度都是先升后降,Nd含量为1%时合金的强度均达到最大值,特别是150℃下其强度高达203MPa;Nd含量的增加对AZ91镁合金的延伸率影响规律也是先升后降,高温下当Nd含量为2%时合金的延伸率达到最大值,表现出良好的韧性,同时也具有较高强度.     

挤压AM50(-Ca)镁合金的显微组织与力学性能研究

研究了挤压AM50(-Ca)镁合金的微观组织和力学性能.研究发现添加钙在AM50合金中生成新的Al2Ca相,并细化合金的晶粒尺寸.大于2wt.%的钙使铸态AMS0的晶粒尺寸从200 μm减小到40 μm,使挤压态AM50的晶粒尺寸从15 μm减小到7.5 μm.含钙量较少时,晶粒内仍含有少量的Mg17Al12相,Al2Ca相主要分布在晶界;含钙量多于2wt.%时,合金中的Mg17Al12完全消失,除晶界处的Al2Ca相外,在晶粒内部出现大量的针状Al2Ca相.加钙提高了AM50合金的低温抗拉强度,同时在所有试验温度下合金的屈服强度得到提升.     

Si对AM50力学性能和高温蠕变性能的影响

在基体合金AM50中分别加入Si和Ca,研究了Si和Ca对AM50-xSi合金的微观组织、力学性能及蠕变性能的影响.结果表明:加入Si后,合金高温蠕变性能随Si量的增加而增加并超过了AS41的水平;在AM50-xSi中加入微量Ca以后,合金中的Mg2Si相得到细化,从汉字状转变成颗粒状,室温及150℃拉伸性能明显提高.     

合金元素对AM60B镁合金性能的影响

为提高镁合金的力学性能,将元素Sr和稀土元素Y、Nd加入到AM60B中.采用X光荧光和X射线衍射对合金的化学成分和物相组成进行了分析,研究了合金元素对AM60B镁合金力学性能的影响,采用扫描电子显微镜对合金试样的断口表面进行了观察,对其断裂行为进行了探讨.研究结果表明,Sr和稀土元素Y、Nd使AM60B镁合金的力学性能得到改善,含Sr和稀土元素Nd的AM60B镁合金的断裂强度和延伸率最高,分别达到224.57 MPa和9.25%,比AM60B镁合金分别提高了32%和38%,合金的屈服强度也得到改善.稀土元素Y和Nd的加入,使AM60B镁合金表现出较大的塑性变形能力.     

含钇Mg-Al系镁合金的研究现状和进展

综述了钇(Y)对Mg-Al系合金的组织、室温和高温力学性能、铸造性能以及耐腐蚀性能的影响.添加适量Y不仅可以细化镁舍金的基体组织,生成高熔点强化相Al2Y,还可以改善β相(Mg17Al12)的形态,有利于铗合金室温力学性能的提高,而Y的固溶强化作用和Al2Y颗粒相的弥散强化作用既有利于室温力学性能的提高,又有利于合金高温力学性能的提高.添加适量Y也可以改善Mg-Al系合金的铸造性能和耐腐蚀性能.Y和Ce、Ca和Nd等合金元素的复合加入可有效改善镁合金的力学性能.指出了含钇Mg-Al系合金目前存在的问题,并展望了其发展前景.     

Sr对AM50显微组织和力学性能的影响

研究了不同含量Sr对AM50合金微观组织和力学性能的影响.结果表明,添加Sr后,AM50合金铸体组织β-Mg17Al12变得细小,晶粒明显细化;Sr基本上与Al结合生成高熔点、高稳定的Al4Sr相,能够强化晶界并阻碍位错滑移,从而强化合金.适量的Sr明显提高了室温下合金的屈服强度和抗拉强度,而且不影响合金的延伸率,而过量的Sr会导致AM50延伸率和轻度的降低.含0.5%Sr的铸态合金可得到最高抗拉强度233MPa,屈服强度90MPa,延伸率16.3%的性能.     

Bi对Mg-3Al-3Nd合金显微组织和力学性能的影响

使用扫描电子显微镜(SEM)和光学显微镜(OM)观察、X-射线衍射(XRD)分析以及力学性能测试等手段研究了Bi含量对Mg-3Al-3Nd合金的显微组织和力学性能的影响。结果表明：添加Bi元素可细化Mg-3Al-3Nd合金的组织。当Bi含量(质量分数)为1%时晶粒最小,晶粒尺寸从1854±58 μm减小到890±64 μm;Mg-3Al-3Nd合金由呈网状分布在晶界的Al₁₁Nd₃相和分布在晶内的颗粒状Al₂Nd组成;随着Bi含量的提高Al₁₁Nd₃相和Al₂Nd相的数量减少,晶内的BiNd相数量增加;Bi能明显改善Mg-3Al-3Nd合金室温和高温力学性能,Bi含量为1%时其室温和高温力学性能最佳。室温抗拉强度和延伸率分别为167±2.3 MPa和(16.1±0.3)%,高温抗拉强度及延伸率分别为136±1.7 MPa和(19.3±0.3)%。     

高Nb-TiAl合金的凝固组织与力学性能研究

研究了Al含量变化对高Nb-TiAl合金的凝固组织与力学性能的影响.结果表明:随着Al含量的增加,TiAl合金晶粒尺寸呈增加趋势;当Al含量为45.7%时,凝固过程中局部区域发生包晶转变,使晶粒尺寸显著增大;室温及700℃高温拉伸强度随着Al含量的增加而呈增加的趋势,但发生包晶转变致使室温及700℃高温拉伸强度下降约200MPa;Al含量对延伸率不敏感,持久性能随Al含量的增加呈增加趋势.为控制铸锭凝固后的组织与力学性能,尽量避开包晶转变区,合金中Al含量应低于45.7%.     

ZL211A合金组织与性能研究

研究了ZL211A合金的铸造状态和热处理状态的组织和力学性能,进行了合金熔炼、铸造、热处理、力学性能测试、微观组织和拉伸断口形貌观察等试验.结果表明,ZL211A合金的铸态金相组织主要由α(Al)、CuAl2和T(Al12CuMn2)相组成,力学性能较低,不能满足航空结构材料的要求,必须经热处理强化后才能使用;热处理状态的金相组织主要由α(A1)、T(Al12 CuMn2)相、θ″相和θ′相组成,经过二级固溶处理再人工时效后,即在535℃±5℃,保温7h,再升温到545+3-5℃,保温7h,淬入50～60℃的热水中,然后在165℃±5℃人工时效7h,可获得优良的综合力学性能.ZL211A合金拉伸试样断口表现为延性断裂,其微观形貌均为韧窝和撕裂棱,韧窝的大小和深浅有所不同.     

Mechanical properties of

The ultimate values for compressive strength, Young's modulus, and toughness of cylindrical specimens of unitary aspect ratios and uniform grain-size distributions were extrapolated for hydroxyapatite (HAP) to 70 MPa, 9.2 GPa, and 0.36 J cm-3, and for tricalcium phosphate (TCP), to 315 MPa, 21 GPa, and 2.34 J cm-3. For total volume porosities of 50%, the corresponding values were determined: for HAP, 9.3 MPa, 1.2 GPa, 0.042 J cm-3, for TCP, 13 MPa, 1.6 GP, 0.077 J cm-3. Porosities of HAP specimens ranged from 3%–50%; TCP from 10%–70%. Two pore-size distributions were employed. Exponential dependencies of the mechanical properties were found upon porosity (p0.0001). No differences in measured mechanical properties, as determined in compression, could be attributed to pore size. The superiority of TCP increases with density and suggests that a larger or more selective pore-size distribution could be effectively employed in TCP biological implants. This work also suggests the dominant role of secondary calcium phosphates in increasing compressive strengths. © 1999 Kluwer Academic Publishers     

Flexural properties and dynamic mechanical properties of glass fibre-epoxy composites

The viscoelastic behaviour of glass fibre (GF)-epoxy composites was studied by flexural tests and dynamic mechanical measurements. In relation, the influence of surface treatment of GF on viscoelastic behaviour was also examined. Using the results of flexural tests under a variety of constant temperature and strain rate, master curves of flexural strength () and flexural strain () were obtained for matrix epoxy and GF composites. The magnitudes of the master curves were different between matrix epoxy and GF composites. The fracture mode was influenced by temperature, strain rate, and G F surface treatment. The magnitude of storage modulus and effectiveness of adhesion at the GF-matrix interface were also influenced by GF surface treatment. Relationship between the results of flexural strain and loss modulus were considered for GF composites.     

Effective thermal properties of viscoelastic composites having field-dependent constituent properties

This study introduces a micromechanical model for predicting effective thermal properties (linear coefficient of thermal expansion and thermal conductivity) of viscoelastic composites having solid spherical particle reinforcements. A representative volume element (RVE) of the composites is modeled by a single particle embedded in the cubic matrix. Periodic boundary conditions are imposed to the RVE. The micromechanical model consists of four particle and matrix subcells. Micromechanical relations are formulated in terms of incremental average field quantities, i.e., stress, strain, heat flux and temperature gradient, in the subcells. Perfect bonds are assumed along the subcell’s interfaces. Stress and temperature-dependent viscoelastic constitutive models are used for the isotropic constituents in the micromechanical model. Thermal properties of the particle and matrix constituents are temperature dependent. The effective coefficient of thermal expansion is derived by satisfying displacement and traction continuity at the interfaces during thermo-viscoelastic deformations. This formulation leads to an effective time–temperature–stress-dependent coefficient of thermal expansion. The effective thermal conductivity is formulated by imposing heat flux and temperature continuity at the subcells’ interfaces. The effective thermal properties obtained from the micromechanical model are compared with analytical solutions and experimental data available in the literature. Finally, parametric studies are also performed to investigate the effects of nonlinear thermal and mechanical properties of each constituent on the overall thermal properties of the composite.     

Free-volume properties of epoxy composites and its relation to macrostructure properties

Some characteristics of epoxy composites are discussed based on the results of positron annihilation lifetime spectroscopy (PALS), electrical and mechanical measurements. The effect of different types and wt% of fillers such as aluminium oxide (Al₂O₃), titanium oxide (TiO₂) and silicon carbide (SiC) on the epoxy structure and hence free volume, physical, electrical, and mechanical properties is presented. The results showed that the electrical properties are improved at high wt% of filler, while mechanical properties are improved at low wt% of filler. Furthermore, a similar trend is observed for all fillers but with a systematic shift to high influence when Sic added to cured epoxy. On the other hand, adding SiC as a filler on epoxy improved the resistance to water absorption.The role of PALS as a sensitive probe for changes in microstructure of epoxy composites is confirmed during the correlation between the free-volume parameters and the other measurements.     

Thermodynamic properties of n-pentane

Specific volumes and isobaric heat capacity measurements are reported for n-pentane. The measurements were made in the liquid and vapor phases at temperatures ranging from the triple point (173 K) to the onset of dissociation temperature (700 K) and pressures up to 100 MPa including a wide region around the critical point. We are able to fit our data, as well as those of a number of other authors, to a single equation of state with 30 constants. This equation yields the density of n-pentane in the temperature range from 280 to 650 K at pressures up to 80 MPa and the caloric properties up to 500 K. Additional experimental investigations of the thermodynamic properties are required for temperatures above 500 K. Interpolating equations for the caloric properties on the saturated line and in the critical region are also presented.     

Piezoelectric properties,hysteresis behaviour and dielectric properties of PMN-PZT ceramics

Ferroelectric and piezoelectric properties ofxPb(Mg_1/3Nb_2/3)O₃−(1−x)Pb (Zr_0·55Ti_0·45)O₃ system have been investigated. X-ray diffraction patterns indicate rhombohedral and cubic structures. Maximum dielectric constant and piezoelectric properties are exhibited by 0·5–0·5 PMN-PZT composition.P _r is high in 0·6–0·4 PMN-PZT composition.     

磺化改性对聚醚砜力学性能和抗凝血性能的影响

对磺化改性后聚醚砜的力学性能和抗凝血性能进行了测试 ,结果表明 :磺化改性后聚醚砜材料的力学性能有一些改善 ,抗凝血性能也有一定提高     

Thermodynamic properties of n-hexane

Specific volumes and isobaric heat capacity measurements are reported for n-hexane. The measurements were made in the liquid and vapor phases at temperatures from the triple point and also cover a wide region around the critical point. The thermal, caloric, and acoustic data from our own investigation as well as those of a number of other authors are fitted to a single equation of state with 32 constants. This equation yields to all thermodynamic properties of n-hexane in the temperature range 180 to 630 K and pressures up to 100 MPa. The data in the critical region have been analyzed in terms of a scaled equation of state.     

Antifouling properties of hydrogels

Marine sessile organisms easily adhere to submerged solids such as rocks, metals and plastics, but not to seaweeds and fishes, which are covered with soft and wet ‘hydrogel’. Inspired by this fact, we have studied long-term antifouling properties of hydrogels against marine sessile organisms. Hydrogels, especially those containing hydroxy group and sulfonic group, show excellent antifouling activity against barnacles both in laboratory assays and in the marine environment. The extreme low settlement on hydrogels in vitro and in vivo is mainly caused by antifouling properties against the barnacle cypris.     

Thermodynamic properties of aluminum

This work reviews and discusses the data on the thermodynamic properties of aluminum available through May 1984. However, two papers dated 1985 which are useful to this work are also included. These properties include heat capacity, enthalpy, enthalpy of transition and melting, vapor pressure, and enthalpy of vaporization. The recommended values for heat capacity cover the temperature range from 0.1 to 2800 K. The recommended values for enthalpy, entropy, Gibbs energy function, and vapor pressure cover the temperature range from 298.15 to 2800 K.