Structure of polycrystalline Al-Ni-Fe-La alloys after quenching and plastic deformation by shear under pressure

The structure and phase composition of aluminum-based polycrystalline alloys (85 at % Al) containing transition (Fe, Ni) and rare-earth (La) metals are studied by metallography, differential scanning calorimetry, X-ray diffraction, and electron-microscopic analysis after melt quenching and subsequent severe plastic deformation (SPD) by shear under pressure. The melt-quenched alloys are shown to have a four-phase structure consisting of an aluminum-based solid solution, intermetallics Al₃Ni and Al₁₁La₃, and iron intermetallics. SPD results in the fragmentation and spheroidization of all phase constituents of the alloys and in the dissolution of the iron intermetallics. A multiphase nanostructured state forms in the alloys. The nanocrystallite sizes after SPD at various deformation parameters are determined. The microhardness is maximal after deformation corresponding to six anvil revolutions at a pressure of 8 or 10 GPa. The structural parameters and the microhardnesses are compared after SPD by shear under pressure of the alloys having the same compositions and different structural states (namely, amorphous and polycrystalline) before deformation. An amorphous-nanocrystalline structure with the minimum nanograin sizes and the maximum microhardnesses forms in the alloys having an initial amorphous structure and subjected to SPD.     

铜铬系合金研究和发展现状

铜及铜合金材料广泛应用于电子信息、电气控制、电力传输及轨道交通等领域,随着科技进步和社会发展,对高强度、高导电同时兼备耐热、耐蚀、抗应力松弛等高性能铜合金材料的需求十分迫切。目前,铜铬系合金被认为是综合性能最优异的铜合金之一。本文简要回顾了铜铬系合金的发展历史,总结了其应用现状,重点探讨了稀土元素以及Hf, Ag, Ti, In, Mg, Zr和Sn的添加对铜铬系合金组织及性能的影响规律,并按照单一元素添加、复合元素添加、稀土元素添加的方式,分别讨论了稀土元素以及Ti, Mg, Mg与Si, Ni与Si等对铜铬锆合金组织和性能的影响。通过对文献的整理发现,微量合金元素的添加可明显改善铜铬合金强度与导电匹配性,并提高合金抗软化温度。此外,添加多元微量元素对性能的提升要优于单一元素,若匹配以合适的变形加工和热处理工艺,更易获得理想材料。今后,可以在铜铬锆合金基础上添加稀土元素,找到适宜的添加量以达到在最大化提高强度与抗软化温度的同时最小化影响其导电率。     

Phase composition and mechanical properties of cerium- and yttrium-containing Al-Mg alloys subjected to heat treatments under various conditions

The phase composition and properties of Al-Mg-Ce and Al-Mg-Y alloys are studied by optical microscopy and mechanical-property measurements. Isothermal sections at 430 and 275°C that correspond to alloys having manganese concentrations of up to 16% and cerium and yttrium concentrations of up to 0.7% are constructed. The ultimate strength, yield strength, and relative elongation of quenched, worked, and aged Al-Mg-based alloys having 7.0–9.9% Mg and Ce, Y, Mn, and Zr additions are determined. The alloys are aged at 175, 200, 250, and 300°C; the time of aging corresponds to the maximum strengthening effect.     

Research of magnesium alloys of the Mg-Sm-Y system subjected to severe plastic deformation and subsequent heat treatment

The effect of severe plastic deformation and subsequent aging on the structure and properties of cast and hardened magnesium alloys containing samarium and yttrium is studied. Severe plastic deformation leads to additional hardening both before and after aging. Hardening is achieved by the formation of nanocrystalline structure in quenched alloys or submicrocrystalline structure in cast alloys. Severe plastic deformation results in the rapid decomposition of a supersaturated magnesium solid solution and additional hardening due to the formation of nano-sized particles of hardening phases.     

感应加热熔炼Cu-Cr合金的凝固行为

采用电弧熔炼和感应加热熔炼研究了不同组成Cu-Cr合金的凝固行为.结果表明:由于高温下Cu-Cr合金与坩埚材料发生反应,氧化铝坩埚中感应加热熔炼Cu-Cr合金受到污染,澄清了Müller与Li的争议;当合金中Cr的摩尔分数大于40%时,感应加热熔炼Cu-Cr合金出现了液相分离,合金与坩埚材料的反应生成物促进了Cu-Cr合金的液相分离.     

Availability of amino acids from casein proteins subjected to heating under model conditions

Localization of a radiopharmaceutical agent in a "tumor" is best conceptualized in terms of the altered regional physiology attendant to the presence of the "tumor". Such localization should be expected to occur in association with other disease states characterized by similar altered regional physiology. Neoplasms, areas of inflammation, and certain phases of infarct development are characterized by increased permeability of their capillary beds to macromolecules. This is largely due to neovascularization and the large intercapillary pores associated with new growth of capillary beds in these circumstances. Often, total perfusion to such lesions is increased in comparison to surrounding normal tissue. Thus, in all three clinical conditions, the entry of macro-molecules into the interstitial fluid space from the intravascular space is increased above that seen in normal tissue. Moreover, with neoplasms and inflammatory processes, there may be a delay in new lymphatic vessel growth adding to the residence time of the macromolecules in the interstitial fluid space. In all three conditions, the increased macrophage activity associated with tissue necrosis may result in ingestion of the labeled macromolecule by the macrophage. Pinocytosis may result in ingestion of the labeled macromolecule by other cells in the lesion, or there may be specific receptor sites on the cell membrane for the macromolecule, which may lead to fixation of the labeled macromolecule on the cell surface and possible intracellular translocation of the label itself. Radiolabeled macromolecules such as albumin, fibrinogen, or gamma globulins, and radionuclides that bind to macromolecules such as radiogallium, radioindium, and other radioelements, exhibit localizing behavior in tumors, inflammatory lesions, and during certain stages of infarcts. In the case of radiogallium and radioindium, the binding macromolecule is transferrin, and it is known that some cells have specific receptor sites for transferrin-bound iron on the cell membrane. It is possible that certain cells within these lesions have cell membrane receptor sites for radiogallium- and radioindium-labeled transferrin, and the cell erroneously accepts these radioelements from the transferrin in lieu of iron in attempting to engage in heme enzyme synthesis. Another mechanism that may be operative in the localization of agents in neoplasms, infarcts, and inflammatory lesions may be the altered cell permeability found in many cells of such lesions. It is known that many agents, such as supravital dyes, are excluded from entering normal cells by the selective permeability of normal cell membranes. When cell membrane permeability is altered, such as can be seen in traumatized, dying, or dead cells, the normally excluded agent may penetrate the abnormal cell membrane and bind, and consequently accumulate in intracellular constituents.     

Structure and physicomechanical properties of melt-spun TiNi-based alloys

The structure and physicomechanical properties (strength, plasticity, electrical resistivity, and shape memory effect) of TiNi-based binary (stoichiometric and nonstoichiometric compositions) and ternary (alloyed with copper, iron, and cobalt) alloys are studied in the initial (after melt quenching (MQ)) and annealed states. It is shown that the structural states formed upon MQ in all alloys are dependent on the cooling rate; subsequent heat treatment; and the contents of titanium, nickel, and alloying elements. Depending on the chemical compositions, MQ alloys undergo thermoelastic martensitic transformations with the formation of the R, B19′, or B19 martensite.     

Structure formation in grade 20 steel during equal-channel angular pressing and subsequent heating

The structure formation and the mechanical properties of quenched and tempered grade 20 steel after equal-channel angular pressing (ECAP) at various true strains and 400°C are studied. Electron microscopy analysis after ECAP shows a partially submicrocrystalline and partially subgrain structure with a structural element size of 340–375 nm. The structural element size depends on the region in which the elements are formed (polyhedral ferrite, needle-shaped ferrite, tempered martensite, and pearlite). Heating of the steel after ECAP at 400 and 450°C increases the fraction of high-angle boundaries and the structural ferrite element size to 360–450 nm. The fragmentation and spheroidization of cementite lamellae of pearlite and subgrain coalescence in the regions of needle-shaped ferrite and tempered martensite take place at a high ECAP true strain and heating temperature. Structural refinement ensures considerable strengthening, namely, UTS 742–871 MPa at EL 11–15.3%. The strength slightly increases, whereas the plasticity slightly decreases when the true strain increases during ECAP. After ECAP and heating, the strength and plastic properties of the grade 20 steel remain almost the same.     

过饱和Cu-Cr合金时效过程中的亚稳结构

利用气雾法制备了Cu—1．56Cr合金粉末并对其于500℃进行了时效，用高分辨电镜观察了其不同时效阶段的结构，并于时效的前期阶段观察到了两种亚稳结构且均为调制结构。利用电子衍射测定了两种结构的晶格点阵，其中调制结构I为在基体的目格点阵上进行的调制，调制结构Ⅱ为DO。型超结构且与基体之间具有N-W位向关系，是后来体心立方（bcc）单质Cr析出的母相。确定了Cu-1．56Cr合金时效过程的析出惯序为面心立方（fcc）的Cu基固溶体（无序结构）→fcc演化的调制结构I→调制结构Ⅱ（典型的DO3结构）→bcc的Cr单质析出相。此两亚稳结构为由fcc过饱和固溶体到bcc析出相的结构变迁提供了过渡。     

Characteristics of the variation in structural defects and properties of iron-based powder alloys under the influence of high-speed electric heating

We determine the magnitude of microstresses and the number of dislocations in sintered steels by x-ray analysis. We have determined that large microstresses are present in the material after sintering, and their magnitude grows with the carbon content in the material. Powder steels contain a large number of random dislocations, the density of which exceeds the dislocation wall density by two or three orders of magnitude. The presence of random dislocations has a positive effect on the mechanical properties and strength characteristics of sintered carbon steels. Sintering with electric current is better than conventional sintering in a furnace, since better mechanical properties are achieved with a shorter tempering. The improvement in properties is achiered due to formation of a considerable amount of martensite phase in the material for a fast cooling rate in electric contact sintering. Large interparticle areas are formed due to a local rise in temperature and liquid formation, and this effect also contributes to the improvement in properties. Institute of the Physics of Metals, National Academy of Sciences of Ukraine, Kiev. Institute of Materials Science, Slovak Academy of Sciences, Kosice, Slovakia. Translated from Poroshkovaya Metallurgiya, Nos. 7-8, pp. 13–21, July–August 1997.     

Structure and properties of Nb-Al alloys prepared by powder metallurgy

The structure and short-time strength of Nb-Al alloys of two compositions prepared by powder metallurgy are studied. The mechanical alloying of niobium with aluminum in a planetary ball mill in air is shown to result in simultaneous alloying of niobium with oxygen. During subsequent vacuum high-temperature sintering, disperse particles of a complex oxide, whose tentative composition is (AlNb)₂O₃, form in the alloy structure. The short-time strength at 1250°C of the prepared alloys exceeds that of nickel-aluminum superalloys.     

Structure and properties of W-Ni-Fe-Co heavy alloys compacted from nanopowders

Heavy tungsten alloy (HTA) W-Ni-Fe-Co nanopowders synthesized by a chemical-metallurgical method are used to produce a compacted material with a theoretical density and a grain size of 2.9–4.6 μm. Upon solid-phase sintering (SPS) at 1350–1450°C, the binder composition of the produced material coincides with the binder composition of the alloy fabricated by liquid-phase sintering (LPS) according to a traditional technology. The hardness of the material is 4400–3400 MPa (as compared to 1750 ± 50 and 2950 ± 50 MPa after LPS followed by a hardening treatment for a standard HTA), and its ultimate tensile strength after SPS is 950–1050 MPa (as in the case of the standard alloy after LPS). The melting temperature of the binder is 25–30°C lower than that of the traditional alloy.