Dynamics of deformation bands and fracture of the aluminum-magnesium alloy 5556

The dynamics of deformation bands at the prefracture stage of the aluminum-magnesium alloy 5556 has been examined using the high-speed video recording. It has been revealed that, in the artificially aged and recrystallized alloys, the correlations between the propagating deformation bands and the development of the main crack are of different character.     

The behaviour of the gold 5d band in Gold-Palladium alloys

The change of bandwidth and effective spin-orbit splitting of Gold 5d bands in a number of alloy systems has been found to be dependent only on the concentration of Gold and not on the second alloy constituent. Theoretically, this has been described as the split band limit where the Gold 5d electrons interact only weakly with electrons on the other component. The binding energy shifts are found to be dependent on this interaction. In this paper we report ultraviolet photoelectron spectra from a number of Gold-Palladium alloys and compare the d-band behaviour with that in previously reported spectra. In spite of the overlapping Gold and Palladium d bands the dominant interaction is that between like atoms. We also discuss the final state of dilute Gold in the Palladium matrix.     

Cyclic deformation of aluminium and its alloys

The formation of slip bands is the main mechanism of cyclic deformation in pure Al. Their density, orientation and heights in polycrystalline Al were investigated during cycling. Types, sizes and densities of precipitates are responsible for the mode of cyclic deformation in AlCu4 pure alloy. In technical Al alloys intermetallic phases have detrimental effects on deformation homogeneity and largely govern the fatigue mechanism of the material and especially microcrack initiation.     

Serrated creep and spatio-temporal structures of macrolocalized plastic deformation

The dynamics and morphology of macrolocalized deformation bands have been investigated using a complex of high-speed in situ methods under the conditions of serrated creep of flat samples of the aluminum-magnesium alloy 5456 with different aspect ratios. It has been found that, at the front of a macroscopic plastic deformation jump, a complex structure of propagating deformation bands, which are considered as macrolocalized deformation “quanta,” is spontaneously formed in the material. It has been shown that, with an increase in the sample length, the deformation behavior of the alloy tends to the state of self-organized criticality.     

Are there phase transitions in liquid metallic alloys?

Recently, resistivity measurements of some liquid metals and metallic alloys have been obtained using an electrode technique. A marked change of the slope of the resistivity versus temperature has been observed following the history of the alloy in the liquid state and the authors conclude that there are “structural transitions in the melt”. It is of interest to examine such effects and to try to understand their origin. In this work, the resistivities of several liquid metals and metallic alloys were measured as a function of temperature. Particular attention was given to the history of the alloy, including solidification and melting conditions. We also observed “anomalies”. Our experiments lead us to conclude that they must very probably be attributed to the release of gas or vapour bubbles in the liquid alloy at the first heating, resulting from the decomposition of compounds like oxides or hydroxides of the metals, but not from a phase transition in the liquid metallic state involving “breaking” Sn–Sn covalent bands.     

非晶态合金与氢相互作用的研究进展

非晶态合金在力学性能、耐磨耐蚀性、磁性等方面比传统晶态合金具有显著优势,是一类有优良应用前景的新型结构与功能材料.非晶态合金与氢相互作用可以产生很多有趣的物理化学现象和应用.本文从物理基础和材料应用两个方面评述非晶态合金和氢相互作用的研究进展,在物理基础研究方面,从氢在非晶态合金中的存在状态出发,讨论氢在非晶态合金中的溶解、分布、占位和扩散等相关物理问题,进而分析氢对非晶态合金的热稳定性、磁性、内耗、氢脆等的影响.在材料应用研究方面,对非晶态储氢合金、非晶态合金氢功能膜、吸氢改善非晶态合金的塑性和玻璃形成能力、氢致非晶化、利用非晶态合金制备纳米储氢材料等方面的研究进展进行评述.最后总结并展望有关非晶态合金与氢相互作用的研究和应用.     

Mg-Al系工业合金牌号的成分式解析

Mg-Al系牌号是应用最广的镁基工业合金,但其牌号背后的成分根源一直未知,构成研发新合金的主要障碍.本文应用描述固溶体短程序结构特征的团簇共振模型,得到了Mg-Al二元固溶体的最理想化学结构单元[Al-Mg_(12)]Mg_1,然后对《the American Society for Testing Materials》手册中所有Mg-Al系工业合金牌号进行成分解析,得到相应团簇成分式,如AZ63A合金解析后的团簇成分式为[Al_(0.78)Zn_(0.16)-Mg_(12)]Mg_(1.04)Mn_(0.02),AZ81A合金解析后的团簇成分式为[Al_(0.97)Zn_(0.03)-Mg_(12)]Mg_(0.98)Mn_(0.02).再根据成分式与化学结构单元之间的误差,对比该牌号合金的力学性能,验证了该化学结构单元在Mg-Al体系中的准确性,揭示出看似复杂的工业合金牌号后面隐藏的简单成分规律,为发展Mg-Al体系合金指出了一个全新的途径.     

Manufacturing geometrically complex nozzle-type parts by means of selective laser melting

The possibility of manufacturing of such geometrically complex parts as nozzles via the selective laser melting of heat-resistant cobalt alloy is demonstrated. The mechanisms responsible for forming the structure of investigated alloys under the conditions of selective laser melting are characterized. The physicomechanical properties of the resulting parts are determined.     

Electrical resistivity of NaPb compound-forming liquid alloy using abinitio pseudopotentials

The study of electrical resistivity of compound-forming liquid alloy, NaPb, is presented as a function of concentration. Hard sphere diameters of Na and Pb are obtained through the interionic pair potentials evaluated using Troullier and Martinsab initio pseudopotential, which have been used to calculate the partial structure factors S(q). Considering the liquid alloy to be a ternary mixture, Ziman formula, modified for complex formation has been used for calculating resistivity of binary liquid alloys. Form factors are calculated usingab initio pseudopotentials. The results suggest that Ziman formalism, when used withab initio pseudopotentials, are quite successful in explaining the electrical resistivity data of compound-forming binary liquid alloys.     

Photoemission and electronic structure of Mo,Ru and Amorphous MoRuB and MoRuP

The electronic structures of molybdenum, ruthenium and amorphous Mo₄₈ Ru₃₂ B₂₀ and Mo₄₀ Ru₄₀ P₂₀ are investigated by the XPS and UPS techniques. The experimental results of pure elements are in agreement with previous band calculations. The valence bands of the amorphous alloys are quite comparable to those obtained from pure Mo and Ru assuming hypothetical alloys. For the investigated alloys, the electronic DOS's at the Fermi level are intermediate between those of transition metal components. The disordering on the band structure, due to alloying effects, is found to be larger for the phosphorus based alloy than for the boron one. A qualitative band model can explain the various observed properties; the experimental results are also discussed in relation with the atomic volumes.     

Plastic deformation macrolocalization during serrated creep of an aluminum-magnesium Al-6 wt % Mg alloy

The nonlinear dynamics of the space-time structure of macrolocalized deformation is studied by a set of high-speed in situ methods under the conditions of serrated creep in an aluminum-magnesium Al-6 wt % Mg alloy at room temperature. Macroscopic deformation jumps with an amplitude of several percent are detected in the creep curve of this alloy. It is found that a complex space-time structure of macrolocalized deformation bands moving in a correlated manner forms spontaneously in the material during the development of a deformation jump. The difference between the observed picture of deformation bands and the well-known Portevin-Le Chatelier classification of deformation bands is discussed.     

Laser ablation of alloys: Selective evaporation model

A mechanism of non-stoichiometric laser ablation is proposed and experimentally verified for multicomponent alloys. The analysis of four-component bronze samples in various excitation modes and the recorded laser plasma spectra revealed that disproportion of plasma elements during laser evaporation arises from selective evaporation of components at the heating-melting-evaporation stage. Correction coefficients proportional to the work function of the alloy component vapor in the heating-melting-evaporation cycle are calculated for the plasma spectrum. Correction procedure for the spectral lines leads to a good agreement of the measured sample composition with the tabulated data. To check that the proposed approach is universal, aluminum alloys and iron alloys (high-alloy stainless steels) are analyzed. It is found that selective evaporation for aluminum alloys is lower than for bronzes. Evaporation selectivity was insignificant for stainless steels. The proposed mechanism for selective evaporation during laser ablation and correction of the plasma spectrum make it unnecessary to use a standard in the quantitative elemental analysis of complex bronze and aluminum alloy samples.     

Effects of the structural state of a W — Re solid solution on the Fe-57 Mössbauer spectrum

Mössbauer spectra for iron-57 are reported for alloys containing up to 27 at.% rhenium. The cobalt-57 was introduced by diffusion annealing as the parent isotope for the iron-57. Diffusion annealing at 1080°C for 16 hr causes the cobalt to diffuse mainly along lattice defects (dislocations and grain boundaries). These defects give rise to regions whose electronic structure differs from that of the matrix. The precise type of structure and the number of such regions are complex functions of the alloy composition and structural state. Results are given on the iron-57 spectra for tungsten, rhenium, the σ phase, and an alloy in the two-phase region.     

Influence of high-power ion beam treatment on the resistance to oxidation in metals and alloys

The influence of high-power ion beam (HPIB) irradiation of metal (copper) and alloys (iron-St20 and titanium-VT6) on the resistance to oxidation has been investigated. The HPIB irradiation with the subsequent oxidation in air has been found to result in the formation of complex oxides on the surface of an alloy. The formation of discontinuous oxide films related to the crater formation under irradiation is the feature of oxidation processes of the irradiated materials. Oxidation resistance has been found to rise in the alloys containing nonmetals as the dopant.     

非晶物质中的临界现象

非晶态材料有着复杂的原子结构(短程有序、长程无序)和特殊的物理性质,其临界现象和相变问题一直受到学术界关注.非晶合金,又称为金属玻璃,是一种新型的非晶态材料,具有很高的强度和优异的弹性.从微观的角度来看,非晶合金可以看作是一个多粒子系统.临界现象的研究对认识和理解多粒子系统之间的相互作用有深刻的意义.本文主要讨论非晶合金中的临界现象,包括非晶合金从制备过程、微观结构到宏观的力学性能以及磁性方面存在的临界现象,并分析这些临界现象之间的内在联系,进而深入理解非晶合金的微观结构对其宏观性质的影响.这为认识非晶合金的形成本质,提高服役可靠性,探索具有实际应用价值的非晶合金提供理论依据.     

铀基非晶合金的发展现状

铀基非晶合金是非晶家族中的特殊成员,受限于铀元素的高活性与放射性特点,目前这类非晶材料的研究极不充分.本文结合非晶合金的最新发展动态简要介绍了铀基非晶发展历史,较系统地总结了本团队的最新铀基非晶研究工作:首先较详细地介绍了新型铀基非晶的制备技术、成分体系、形成规律与晶化行为,澄清了其形成机制与热稳定性;结合高分辨电镜分析展示了其微观结构特点;采用纳米压痕技术揭示了这类非晶的微纳力学性能;利用电化学测试方法评估了其耐腐蚀性能.这些结果丰富了非晶材料的内涵,有助于深化对非晶物理基础科学问题的理解,并推动新型铀合金材料的发展,为这种材料的潜在工程应用奠定了基础.     

Near-eutectic Zn-Mg alloys: Interrelations of solidification thermal parameters,microstructure length scale and tensile/corrosion properties

Zn-Mg alloys are considered to have potential application in bone implants, since both metals are biocompatible and have biodegradable characteristics. Adding Mg to Zn can boost mechanical and corrosion resistances. However, the literature is very limited on quantifying the interrelation of solidification parameters, microstructural features and mechanical/corrosion properties of Zn-Mg alloys. The present study examines the interrelations of alloy Mg content, macrosegregation effects, morphology and scale of the matrix and eutectic phases, nature of intermetallics and tensile and corrosion properties of near-eutectic Zn-Mg alloys. The alloys samples are obtained by unsteady-state directional solidification resulting in a wide range of solidification thermal parameters and microstructures. We examine microstructural features of both dendritic and complex regular eutectic phases. It is shown that the eutectic exhibits a bimodal pattern with neighboring areas of coarse and fine lamellae. Experimental growth laws relating the primary, secondary and eutectic spacings to the solidification cooling rate and growth rate are proposed. Hall-Petch type equations are derived expressing tensile strength and elongation to dendritic and eutectic spacings. Electrochemical parameters determined by polarization curves during corrosion tests and SEM analyses of corroded areas have shown that the alloy having an essentially eutectic microstructure is associated with better corrosion resistance.     

Thermodynamics and surface properties of liquid Al–Ga and Al–Ge alloys

The surface properties of Al–Ga and Al–Ge liquid alloys have been theoretically investigated at a temperature of 1100 K and 1220 K respectively. For the Al–Ga system, the quasi chemical model for regular alloy and a model for phase segregating alloy systems were applied, while for the Al–Ge system the quasi chemical model for regular and compound forming binary alloys were applied. In the case of Al–Ga, the models for the regular alloys and that for the phase segregating alloys produced the same value of order energy and same values of thermodynamic and surface properties, while for the Al–Ge system, the model for the regular alloy reproduced better the thermodynamic properties of the alloy. The model for the compound forming systems showed a qualitative trend with the measured values of the thermodynamic properties of the Al–Ge alloy and suggests the presence of a weak complex of the form Al₂Ge₃. The surface concentrations for the alloys show that Ga manifests some level of surface segregation in Al–Ga liquid alloy while the surface concentration of Ge in Al–Ge liquid alloy showed a near Roultian behavior below 0.8 atomic fraction of Ge.     

The surface composition of silica-supported Pt-Ni alloys

In this work we have determined the surface composition of small supported Pt-Ni alloy particles (diameter 2–5 nm) by means of infrared spectra of adsorbed CO and NO. By dosing carbon monoxide and nitric oxide in the appropriate sequence to the alloys, carbon monoxide is adsorbed selectively on the Pt atoms and nitric oxide on the Ni atoms. On the alloy surfaces no reaction occurs between these adsorbed species as the bands observed do not change upon standing in vacuo. With increasing bulk nickel concentration the intensity of the CO/Pt band drops, whereas the intensity of the NO/Ni band increases. Also the band maximum of the CO/Pt band shifts continuously to lower wavenumbers and the shape of the NO/Ni band changes. It is concluded that the composition of the surface is almost equal to that of the bulk.     

析出相在铝镁合金Portevin-Le Chatelier效应中的作用研究

本文研究了在相同退火热处理条件下,不同析出相含量的两种铝镁合金5456和5052在不同加载应变率下的P-LC效应. 结果表明析出相对两种材料的P-LC效应有明显影响,并且析出相含量的不同所产生的影响不同. 此外,析出相含量较少的5052合金的溶质原子的扩散方式是管扩散,而析出相含量较多的5456合金不再局限于管扩散的方式,而是更为复杂. 关键词： Portevin-Le Chatelier effect 动态应变时效 铝镁合金