A thermodynamic investigation of crystalline and amorphous Se−Te alloys

The heats of formation, referred to the component elements in their stable crystalline forms, of crystalline Se?Te alloys containing 0 to 100 at. pct Te and amorphous alloys containing 0 to 30 at. pct Te were measured by liquid metal solution calorimetry. The heats of formation of the crystalline and amorphous alloys changed nonmonotonically with composition in a parallel manner. The crystalline alloys had negative heats of formation in the range of 0 to approximately 17 at. pct Te; the largest negative value of approximately?0.235 kcal/g-atom occurred at 10 at. pct Te. At 20 at. pct Te the heat of formation was positive and had a value of approximately 0.115 kcal/g-atom and at higher tellurium concentrations it again turned negative but was very small. The heats of formation of all amorphous alloys investigated were positive. A minimum of approximately 0.810 kcal/g-atom at 10 at.pct Te and a maximum of 1.040 kcal/g-atom at 20 at. pct Te corresponded to the largest negative value and the largest positive value of the heat of formation of the crystalline alloys of the respective compositions. The temperatures of maximum rates of crystallization and fusion and the heat effects associated with the crystallization and fusion of the amorphous alloys were measured by differential scanning calorimetry. With increasing tellurium concentration the temperature of crystallization decreased and the heat effect and the temperature associated with fusion increased.     

机械合金化制备Co80Zr20非晶合金粉末

采用行星式高能球磨机，通过室温下球磨纯元素混合粉末制备出原子数分数比为Co80Zr20的非晶合金粉末。应用X射线衍射（XRD）、差示扫描量热分析仪（DSC）、扫描电镜及透射电镜对不同球磨时间的混合粉末进行了研究。结果发现，球磨时间对混合粉末的结构及颗粒形貌存在显著影响。原始混合粉末由密排六方的β-Co和α—Zr组成，经过0．5h球磨，β—Co转变为同素异构的面心立方的α—Co，随着球磨时间的增加，Co、Zr颗粒都发生严重塑性变形，并且通过冷焊团聚起来，形成具有层状结构的复合颗粒。球磨导致基体元素Co品格中的晶体缺陷密度大大增加，使得合金元素Zr原子向Co品格中扩散迁移，扩散迁移到Co晶格中的Zr原子数量随球磨时间的增加而增加，导致Co元素的品格常数单调增大。当球磨时间达到8h时，形成Co80Zr20固溶体，继续球磨至10～20h，固溶体转变为非晶。球磨20h得到的非晶粉末的玻璃化转变温度为759K，它可以在840K通过单一放热过程或者继续球磨至40h而发生晶化反应，这两种不同晶化工艺所得到的晶化产物完全相同，均为面心立方的Co23Zr6。     

The forming of Zr3Al-base alloys

Tubes have been formed from the intermediate phase Zr₃Al (L1₂ type) which is of potential use as a structural element in thermal nuclear power reactors. The procedure is to extrude Zr/Zr₂Al two-phase ingots at temperatures above 1270 K in theβ Zr + Zr₂Al two-phase field and then transform the extruded product at lower temperatures to Zr₃Al via the peritectoid transformation Zr + Zr₂Al → Zr₃Al. For small tubes (⪝ 3.2 cm OD) the extrusion constants at 1375 and 1425 K, respectively, are ≃ 400 and ≃ 300 MN/m² for the conditions chosen. The experimental extrusions indicate no fundamental barriers to forming pressure tubes from Zr-Al alloys containing 7.6 to 9.0 wt pct Al.     

温挤压法制备铝基非晶合金的研究进展

Al85Ni5Y10铝基非晶粉末在603K温挤压所得块体样品的相对密度超过98%, 抗压强度和弹性模量分别高达1470Mpa和145 Gpa, 是传统铝合金的2～3倍, 并有很好的耐磨、耐蚀性能和超塑性等, 可望在航天、航空和汽车制备等领域获得广泛的应用. 然而, 以Al85Ni5Y10为代表的这类铝基非晶合金材料获得工程应用的主要困难在于较难获得大尺寸的非晶材料. 为促进其快速研发, 该文简要地综合介绍和评述了温挤压法制备大块非晶合金的基本原理、方法和研发进展.     

铜模吸铸与高能球磨制备Zr46Cu46Al8非晶合金的组织结构及晶化动力学研究

采用铜模吸铸法制备出直径3 mm的Zr₄₆Cu₄₆Al₈块体非晶合金, 利用高能球磨法获得了不同粒径的合金粉体, 通过X射线衍射仪、示差扫描量热仪、扫描电镜等测试手段及热力学计算方法, 研究了制备方法对非晶合金组织结构及晶化动力学的影响。结果表明, 块体合金和粉体合金均可获得完全非晶结构; 块体非晶合金玻璃转变和晶化过程具有明显的动力学效应; 单因素变量法制备非晶粉体的最佳参数为: 转速300 r·min-1, 球料比30:1, 球磨时间15 h; 相同条件下, 除过冷液相区外, 块体非晶合金热力学参数普遍高于非晶粉体, 且晶化放热更剧烈; 随着加热速率增大, 二者热力学参数均向高温区移动, 过冷液相区的宽度也逐渐增加; 块体非晶合金和非晶粉体的特征温度表观激活能数值相近, 块体非晶态合金的表观激活能较非晶粉体高, 热稳定性更优。     

High strength aluminium alloys prepared by nanocrystallisation of amorphous powders using spark plasma sintering

Al based nanocrystalline alloys with high fracture strength are fabricated using consolidation and controlled crystallisation strategy of amorphous powder precursors. The sintered product exhibits high specific strength of 3.18?×?10⁵?Nm?kg^??1. The compacted microstructure and ultrafine grains caused by sufficient densification and crystallisation of Al based amorphous powders are responsible for considerable properties of the sample. Furthermore, the densification process and mechanical behaviour of the sintered Al based nanocrystalline alloy are investigated in detail. The Al based nanocrystalline alloys prepared by synergetic process of powder consolidation and crystallisation of amorphous can exhibit much improved mechanical properties compared with conventional Al alloys, which can have potential engineering applications.     

On the problem of the maximum strength of metals and alloys in crystalline,amorphous, and nanocrystalline states

The true breaking stresses and the ultimate tensile strengths of 11 metals with various structures are calculated. Moreover, the fracture strengths of these metals at 0 and 298 K are calculated in the amorphous (σ _{f, a}) and nanocrystalline (σ _f,nano^max) states formed upon severe plastic deformation. The temperature dependences of these properties are also determined. These properties are obtained for a number of alloys (TiNi, NiNb, Pd₈₀Si₂₀, Ni₆₀Nb₄₀). The values of σ _{f, a} are shown to correlate with yield strength σ_{y, nano} of nanocrystalline substances, and a hypothesis of a deviation from the Hall-Petch relation is advanced. This hypothesis is supported by the calculation of the properties and diffusion characteristics. The obtained numerical results agree satisfactorily with the experimental data and the results of other approaches to estimating these properties.     

Quasi-static constitutive behavior of Zr41.25Ti13.75Ni10Cu12.5Be22.5 bulk amorphous alloys

Mechanical tests have been performed on bulk amorphous metal alloys to determine their constitutive behavior. Based on the experimental results, it appears that amorphous metal alloys obey a Von Mises yield criterion. This result has implications in determining the micromechanisms of plastic deformation in these materials.     

Deformation behavior of Zr3Al-Nb alloys II: Indentation creep studies

The high-temperature mechanical properties of Zr₃Al, Zr₃Al-3Nb, and Zr₃Al-10Nb alloys were assessed using the indentation hardness method. All three alloys showed negligible creep up to 500 K. Using Sargent and Ashby’s approach, different creep parameters such as stress exponent, activation energy, and activation area were estimated. Using the data generated in the present study and those available in the literature, a deformation creep curve was developed. The relationship between hardness and temperature in the high-temperature region can be expressed in terms of an Arrhenious equation. The activation energy estimated from this relationship was found to be in good agreement with that obtained from the indentation creep curve. On comparing the creep behavior of Zr₃Al-Nb alloys with some other intermetallics, it was observed that Zr₃Al-based intermetallics have better creep resistance compared to other intemetallics.     

Deformation behavior of Zr3Al-Nb alloys I: Room-temperature and high-temperature deformation study

The deformation behavior of the Zr₃Al-Nb alloys was studied by measuring hardness at different temperatures, by hot rolling, and by hot pressing. Using the hardness data, elasticity and plasticity parameters were estimated and were used to determine the suitable temperature range of deformation for these alloys. Hot rolling and hot pressing were applied to determine the optimum temperatures and annealing time for carrying out deformation successfully in these alloys. Microstrural investigation of the hotdeformed samples revealed that the matrix β phase has undergone substantial deformation and the second intermetallic phase, Zr₂(Al,Nb), underwent dissolution and re-precipitation. The hardness of the fully annealed Zr₃Al-Nb alloys showed two types of temperature dependence. Transition temperatures for the change in behavior, intrinsic hardness, and softening coefficient were determined. The hardness of the fully annealed alloys rolled to different extent at various temperatures and subsequently heat treated was used to study the recovery process. The microstructural study of room-temperature deformed binary Zr₃Al alloy showed the splitting of the superlattice dislocations into partials containing superlattice intrinsic stacking faults.     

Tensile deformation of amorphous nickel-palladium-phosphorous alloys

Ni-Pd-P amorphous alloys show inhomogeneous plastic deformation, as do all other amorphous alloys. A few localized deformation bands appear macroscopically just beyond the elastic region of the stress strain curve. It is shown that two types of localized deformation bands can be produced during tensile deformation,i.e., one has sharp steps produced by plastic flow associated with a shear, and the other has interconnecting voids similar to a crazing crack in polymers.