合金化元素对NiAl电子结构的影响

 运用基于密度泛函理论的离散变分法研究了NiAl晶体及加入合金化元素钪、钛、钒、铬、锰、铁、钴、镍、铜以及锌后的电子结构。通过对NiAl和合金化元素的密立根轨道集居数、差分电荷密度、态密度以及体系结合能的分析,从微观电子结构角度探讨了其合金化的作用。结果表明,铁、钴、镍有助于NiAl晶体塑性的改善。     

电站锅炉用热挤压合结管的开发

对电站锅炉用热挤压合结管进行了系统的研制开发。经过试制，确定了最合理的加热制度、热挤压工艺、热处理工艺及酸洗工艺等。试制结果和批量生产表明，该产品的性能度表面质量都达到了用户要求，受到了用户的肯定，同时打开了电站锅炉用热挤压合结管市场。     

NiAl powder alloys: I. Production of NiAl powders

The influence of five methods of production of Ni₅₀Al₅₀ powder alloys on the processes occurring during reactive alloy formation of nickel monoaluminide during heating is considered. It is shown that, when powder mixtures obtained by agitation in ball mills and cladded composite powders with a low level of internal stresses are used, it is possible to produce a material with a nearly equilibrium phase composition in the course of reactive sintering due to an exothermic effect with the participation of a liquid phase (aluminum melt) in the reaction. The sintered material is porous and has an island structure. Mechanical alloying in a high-energy ball mill (attritor) results in the formation of layered Ni/Al granules with a developed interface and a high level of internal stresses and defects, which makes it possible to decrease the temperatures of initiation of reactive interaction by ∼300°C. This interaction develops in the solid phase according to a slow diffusive mechanism leading to the formation of intermediate nickel aluminides and hindering the achievement of equilibrium phase composition. The microingot granules (∼80 wt % particles 100–400 μm in size) produced by melt spraying by gases (N, Ar) has the composition of the melt, but grain boundaries are depleted of aluminum in comparison with the volume. The NiAl powders (∼90 wt % particles <40 μm in size) produced by combined hydride-calcium reduction are characterized by a highly homogeneous nickel and aluminum distribution, and their composition is close to equilibrium. These two types of powders are selected as the initial material for investigating the compacting and production of NiAl-based alloys.     

Cavitation erosion of NiAl

Vibratory cavitation erosion tests were carried out on as-cast NiAl intermetallic compounds containing 46.5 to 62.1 at pct Ni. The erosion rate decreased with increasing nickel content by over two orders of magnitude, from a high of 16.4 to 0.11 mg·h⁻¹. These low erosion rates exhibited by the nickel-rich alloys containing 58 and 62.1 at. pct Ni, the interruptions in their mass loss with time, and the unusual effects associated with surface finish and intensity of cavitation were found to be associated with the stress-induced martensitic transformation. Alloys containing 58 to 62 at. pct Ni have the potential for use as materials for the cavitation protection of hydraulic machinery.     

粗晶组织对6061T6大规格挤压扁棒力学性能的影响

通过试验研究并分析粗大晶粒组织对6061T6大规格挤压扁棒力学性能的影响,指出6061T6扁棒在热处理后存在晶粒粗大现象,在这些晶粒粗大组织区域,其力学显能显著低于非粗晶组织区域.要实现扁棒的高性能目标,必须通过采取措施减少材料的晶粒粗大现象.     

热处理工艺对6082铝合金挤压棒材组织和力学性能的影响

研究热处理工艺（包括挤压温度、淬火和人工时效等）对6082铝合金挤压棒材组织和力学性能的影响,总结出热处理工艺及停放时间与力学性能的关系,应用于生产现场后取得良好效果。     

Deformation in NiAl bicrystals

The effects of a concentrated local stress arising from elastic and plastic incompatibility at internal NiAl grain boundaries have been investigated in oriented NiAl bicrystals. Observations of surface slip markings and TEM characterization of the dislocations responsible for bicrystal deformation have been made. The glide of a〈110〉 dislocations on {110} planes is the primary mode of deformation in the vicinity of the oriented bicrystal interfaces investigated. The dominant mode of a〈110〉 dislocation generation is the nucleation of loops away from the bicrystal interface. The macroscopic stress required to activate these dislocations, in the presence of a stress concentration such as that produced by a dislocation pile-up at a grain boundary, is the same as that required to nucleate a〈100〉 dislocations in “soft” single crystals of NiAl. Although the statistical relevance of this phenomenon as it pertains to the deformation of NiAl polycrystals has not been established, it is speculated that the glide of non-a〈100〉 dislocations may play an important role in the ductility of polycrystalline NiAl at the ductile-to-brittle transition temperature. The movement of a〈100〉 dislocations provides the primary mode of deformation for several bicrystals investigated far (> 3 mm) from the bicrystal interface. It is suggested that the vacancies required for the extensive climb of a[100] vacancy loops is supplied by the climb of a[100] and a[010] dislocations, and that the gradient in the concentration of vacancies provides the driving force for the motion of the a[100] and a[010] dislocations.     

NiAl powder alloys: II. Compacting of NiAl powders produced by various methods

The technological properties of granulated NiAl powders produced by gas spraying of melts and NiAl powders produced by calcium hydride reduction (CHR) of mixtures of nickel and aluminum oxides are compared. The possibilities of production of compact workpieces from these powders using hydrostatic pressing, hot pressing, hot isostatic pressing, and hot extrusion are estimated. To improve compressibility, preliminary milling and/or mechanical activation of the powders are proposed. The strength properties of NiAl rods with a diameter of 20 mm extruded from a temperature of 1100°C and made from the granulated powders are slightly higher than those made from the CHR powders. At temperatures higher than 800°C the properties becomes similar. Transition point t _d.b from the ductile to brittle state of samples made from powders sprayed in nitrogen and argon is 100?C150°C higher than those made from the CHR powders. The difference in the mechanical properties is caused by the structural and chemical microheterogeneity of granules (microingots), which is inherited in the rods after hot deformation and annealing at 1200?C1400°C and is (0.67?C0.88)T _m NiAl (T _m is the melting point, K).     

Micropyretic synthesis of tough NiAl alloys

NiAl has been produced by micropyretic synthesis in a tougher state by adding Cr, V, and Fe. The mechanical properties of the alloys have been evaluated. Fracture toughness values as high as 9.5 M Pa√m have been obtained. The effect of different process variables like particle size, diluents, and extent of preheat on the process of synthesis and the microstructure have been ascertained. Diluents, when present in small quantities, have been found to enhance the combustion process in NiAl without significantly affecting the microstructure of the alloy. Preheating of the specimen prior to synthesis however had a profound influence on the microstructure. The microstructures of the alloys have been examined for chemical homogeneity and the defect structure. The sequence of steps leading to the formation of NiAl from elemental powders during the process of micropyretic synthesis has been determined.