The influence of grain size and composition on 1000 to 1400K slow plastic flow properties of NiAl

The compressive slow plastic flow behaviour of several B2 crystal structure NiAl intermetallics has been studied in air between 1000 and 1400 K ( 0.53 to 0.74T _M). Small grain-sized Ni-48.25 at % Al ( 5 and 10 µm) was found to be stronger than the previously studied 17 µm diameter material. While grain refinement improved the strength at all test temperatures, the exact mechanism is not clear. Experiments at lower temperature revealed that composition as well as grain size can be an important factor, since Ni-49.2Al was weaker than Ni-48.25 Al. Pronounced yield points were found during slow strain-rate testing at 1000 K; however, continued deformation appears to take place by the same mechanism(s) as found at high temperatures. Small changes in thermomechanical processing (TMP) schedules to fabricate Ni-49.2 Al indicated that basic deformation characteristics (stress exponent and activation energy) are not affected; however, the pre-exponential term could be modified if TMP alters the grain structure.     

1300 K compressive properties of several dispersion strengthened NiAl materials

Recently an attempt [8] to produce dispersion hardened NiAl by rapid solidification technology (RST) was discussed; however these microstructural studies and tensile testing procedures did not yield conclusive evidence of strengthening. To examine the potential of RST as a means to fabricate dispersion strengthened aluminides, cylindrical compression samples were machined from the gauge section of their tensile specimens and tested in air at 1300 K: in addition, considerable materialography, including light optical, scanning electron and transmission electron microscopy techniques, of the as-fabricated and compression tested materials was conducted. While microscopy indicates that RST can produce fine dispersions of TiB₂, TiC and HfC in a NiAl matrix, the mechanical property data reveal that only HfC successfully strengthens the intermetallic matrix. The high stress exponents (> 10) and/or independence of strain rate on stress for NiAl-HfC materials suggest elevated temperature mechanical behaviour similar to that found in oxide dispersion strengthened alloys. Furthermore an apparent example of departure side pinning has been observed, and as such, it is indicative of a threshold stress for creep.     

Effect of composition and grain size on slow plastic flow properties of NiAl between 1200 and 1400 K

A series of 15 m diameter, polycrystalline B2 crystal structure NiAl alloys ranging in composition from 43.9 to 52.7 Al (at%) have been compression tested at constant velocities in air between 1200 and 1400 K. All materials were fabricated via powder metallurgy techniques with hot extrustion as the densification process. Seven intermediate compositions were produced by blending various amounts of two master heats of prealloyed powder; in addition a tenth alloy of identical composition, 48.25 AI, as one of the blended materials was produced from a third master heat. Comparison of the flow stress-strain rate behaviour for the two 48.25 AI alloys revealed that their properties were identical. The creep strength of materials for AI/Ni 1.03 was essentially equal, and deformation could be described by a single stress exponent and activation energy. Creep at low temperatures and faster strain rates is independent of grain sizes and appears to be controlled by a subgrain mechanism. However, at higher temperatures and slower strain rates, diffusional creep seems to contribute to the overall deformation rate.     

Elevated temperature slow plastic deformation of NiAl-TiB2 particulate composites at 1200 and 1300K

Elevated temperature compression testing has been conducted in air at 1200 and 1300K with strain rates varying from 10^–4 to 10^–7sec^–1 on NiAl-TiB₂ particulate composites. These materials, which consisted of a B2 crystal structure intermetallic Ni-50at% Al matrix and from 0 to 30 vol % of approximately 1 m diameter TiB₂ particles, were fabricated by XD synthesis and hot pressed to full density. Flow strength of the composites increased with volume fraction of the strengthening phase with NiAl-30TiB₂ being approximately three times stronger than NiAl. Comparison of the light optical and transmission electron microstructures of asreceived and tested samples revealed that reactions did not occur between the two phases, and NiAl-TiB₂ interfaces were not cracked during deformation. Additional transmission electron microscopy indicated that the particles stabilize a vastly different microstructure in the NiAl matrix of the composites than that formed in unreinforced NiAl.     

Some properties of slow plastic scintillators

The decay times for two new plastic scintillators, the Nuclear Enterprises NE115 and the Bicron BC444, have been measured. They were determined to be 344 and 287 ns respectively. The light yield from an NE115 scintillator was also measured as a function of energy in the range 22.3–59.8 MeV. A good fit to these data points was obtained with the polynomial y = ax^1.06, indicating minimal nonlinear effects for this scintillator in this energy range.     

Laser Interferometric Dilatometer Applicable to Temperature Range from 1300 to 2000 K

A laser interferometric dilatometer has been developed for measuring the thermal expansion of high-temperature solids in the temperature range 1300 to 2000 K. The dilatometer consists of a double-path optical heterodyne interferometer, a spectral-band radiation thermometer, and a vacuum chamber with carbon-composite heaters. The performance of the dilatometer has been assessed on the basis of measurements of linear thermal expansion coefficients for glassy carbon. The relative standard deviation of the measured values from those calculated from the fitting polynomial is 0.63% over the temperature range investigated. The combined standard uncertainties in the measured values are estimated to be less than 1.3% over this range. The process of sample relocation predominantly affects the reproducibility of the experimental results.     

Mechanical properties of extruded dual-phase NiAl Alloys

The mechanical behaviour of dual-phase microstructures, consisting of elongated primary NiAl grains aligned with an intergranular NiAl/X eutectic phase, produced by extrusion of cast NiAl-X (whereX=Cr and W) alloys, has been examined. Chromium, added to create a dual-phase NiAl-based aligned microstructure, resulted in large increases in the yield strength, but only marginal improvement in the toughness. In contrast, tungsten alloying leads to ductility or toughness increases with no significant strengthening. The constitutional hardening rate due to deviations from stoichiometry in Ni rich NiAl was estimated to be about 66 MPa (Ni^–1 at%).     

Linear Thermal Expansion Coefficient of Silicon from 293 to 1000 K

As a part of the program to establish a thermal expansion standard, the linear thermal expansion coefficients of single-crystal silicon have been determined in the temperature range 293 to 1000 K using a dilatometer which consists of a heterodyne laser Michelson interferometer and gold versus platinum thermocouple. The relative standard deviation of the measured values from those calculated from the best least-squares fit was 0.21%. The relative expanded uncertainty in the measurement was estimated to be 1.1 to 1.5% in the temperature range, based upon an analysis of thirteen standard uncertainties. The present data are compared with the data previously obtained by similar dilatometers and the standard reference data for the thermal expansion coefficient of silicon, recommended by the Committee on Data for Science and Technology (CODATA). The present data are in good agreement with the most recently reported data but not with the earlier high-temperature data used to evaluate the standard reference data, which suggests a need for the reevaluation of the standard reference data for the thermal expansion coefficient of silicon at temperatures above 600 K.     

The equations of state and the thermodynamic properties of inert gases in the interval from the normal boiling point to 1300°k at pressures below 1000 bar

Statistical processing on a computer of the most reliable p, v, and T data provided the basis for the plotting and discussion of the equation of state for gaseous krypton with T = 120–1300°K and p = 1-1000 bar.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol.16, No.3, pp. 504–509, March, 1969.     

The compression strength of unidirectional carbon fibre reinforced plastic

A simple compression test, suitable for quality control measurements on unidirectional carbon fibre composite, is described. The specimen, a plane bar, with aluminium end tabs attached, is compressed by applying shear forces over the ends. With either type 1 or type 2 treated fibre the failure mode is one of shear over a plane at approximately 45° to the fibre axis. With untreated type 1 material failure is due to delamination. The variation of the compression strength of treated material with fibre volume loading is linear, the values being considerably below those predicted by buckling theory. Increasing void content causes a steady decrease in compression strength, and off-axis strength values are above those given by the maximum work criterion. The present work supports the recently proposed view that the compression strength of unidirectional carbon fibre composites at room temperature is not governed by fibre buckling but is related to the ultimate strength of the fibre.     

Inferences on plastic properties and coefficient of friction during simultaneous compression deformation of dissimilar sintered powder metallurgical preforms

Abstract

Plastic working of powder metallurgical (PM) material necessitates the development of fundamental data such as flow stress, densification behaviour, coefficient of friction, apparent strength coefficient, apparent strain hardening exponent, plastic Poisson's ratio, etc. In the present work compression and standard ring compression tests have been carried out to generate the fundamental data for simultaneous deformation of sintered steel and copper powder metallurgical preforms. The results reveal that the behaviour of individual materials during simultaneous deformation is strongly influenced by local micromechanical interactions at the metal - metal interface. In addition to this, the test conditions (iso-stress and iso-strain) strongly influence the severity of interaction. The interfacial friction coefficients are less than that of the same material when tested between hard tools. The optimal process parameters with higher interfacial friction, which can enhance the solid state joining of dissimilar materials, have been identified. The flow stress of the composite (steel - copper combination) during simultaneous deformation can be estimated if the flow stress of the individual materials comprising the combination/composite are known. With these studies, it should be possible to extend the inferences to the major deformation processes.     

热场发射公式在1000 K以下时的数值分析

对热场发射公式在 10 0 0K温度以下进行了数值计算 ,发现计算结果与一些文献推导的、用于计算温度在 10 0 0K以下的近似公式计算结果出现偏差 ,而且随着阴极材料的不同 (逸出功不同 ) ,偏差也不同 ;文中给出了几种常用阴极材料的计算结果 ,对实际工作具有一定的指导意义     

Inhomogeneous microstructure and mechanical properties of friction stir processed NiAl bronze

As-cast Cu–9Al–4.5Ni–4Fe NiAl bronze (NAB) alloy was subjected to friction stir processing (FSP) in a wide range of tool rotation rates of 800–2000 rpm and traverse speeds of 50–200 mm/min. After FSP, the initial coarse microstructure of the as-cast NAB was transformed to fine structure, and the porosity defects were eliminated. However, the stir zones were characterized by inhomogeneous structure and could be divided into four regions: fine Widmanstätten primary α phase in the surface layer, banded primary α and β′ phases in the subsurface layer, equiaxed α and β′ phases in the center, and streamlike α and β′ phases at the bottom. The heterogeneous microstructure could be alleviated by adjusting the FSP parameters, but could not be completely eliminated under investigated FSP parameters. The FSP NAB exhibited significantly improved hardness, tensile strength, and ductility compared to the base metal. When the NAB was subjected to two pass FSP, its microstructure was further homogenized, resulting in apparently increased ductility with similar hardness and tensile strength.