Behaviour of Inclusions in Beryllium under Compression at Room Temperature

The behaviour of inclusions in the vacuum-melted beryllium specimens which were made from pebble and flake metals with or without addition of aluminium, silicon, beryllium oxide, or air has been investigated. Inclusions are round- and stringer-shape aluminium-, silicon-, and iron-rich phases, angular carbide phase, cluster of oxide, and nitride needle. Inclusions of all kinds of shapes except some small ones interact with slip and twin deformation. The following phenomena have been observed : (a) Coherent deformation of the aluminium-rich phase. (b) Separation of inclusions from the matrix. (c) Cleavage of inclusions. (d) Initiation of new slip and twinning in the matrix at the boundary between the inclusion and the matrix. (e) Occurrence of cracks from the boundary into the matrix. (f) When a crack approaches inclusions including a cluster of oxide, the crack is developed, with further deformation accompanying the separation of the inclusions from the matrix and/or the cleavage of the inclusions. (g) However, the crack which causes the metal to fracture is not necessarily a crack such as is developed by an inclusion

Strain Hardening and Recovery in High-Temperature Deformation by Pure-Metal Mode

By a new method using the stress relaxation test, the coefficient of strain hardening without recovery (h) and the rate of recovery without strain hardening (r) are estimated in high-temperature deformation of fcc aluminum and b c c iron, where the internal stress is confirmed to be nearly 100% of the flow stress. Both h and r are dependent on applied stress σ and temperature T in a steady-state deformation, and are represented by h=h_0(σ/E)^m exp(-Q_h/RT) and r=r_0 (σ/E)^l exp (-Q_r/RT), where h_0 and r_0 are constants, E is Young\u27s modulus and m=-0.88(-1.5), l=4.3(3.2), Q_h=-22(-76) kJ/mol, Q_r=88(132) kJ/mol for aluminum(iron). During a transient state of tensile deformation in the constant strain-rate test, h and r are nearly independent of strain. The activation energy for recovery (Q_r) is found to be appreciably smaller than that of self-diffusion, and then possible roles of pipe-diffusion and strain-enhanced diffusion in dynamic recovery are discussed

Precipitation in Beryllium-Iron Alloys

Hardness measurements and microscopic observations by both optical and transmission electron microscopy were carried out mainly on a beryllium-3wt% iron alloy. The alloy was solution-treated at 1150℃, followed by oil-quenching, and aged at 400°to 700℃ for a various time. In the quenched specimens, helices and loops of dislocations were observed. The ageing treatment resulted in climbing of the dislocations and also preferential precipitation on dislocations as well as at grain-, twin-, and sub-boundaries. Although the change in hardness due to ageing was not so large, two different stages were found in the ageing process, and it was considered that the first stage was associated with the climbing of dislocations and preferential precipitation onto dislocations, and the second stage with effective homogeneous precipitation. The composition of precipitates was identified to be Be_Fe, and the crystal structure of the precipitates and their orientation relationship with the matrix were the same as those reported by Rooksby

Precipitation in Quenched and Aged Beryllium Containing Small Amounts of Iron

Hardness test, electrical resistivity measurement, and electron microscope observation were carried out on arc-melted beryllium specimens with up to 0.2 wt % iron which were heat-treated at 900℃ and aged at 400°to 700℃ for various times. From the results it was deduced that the amount of small dislocation loops produced probably by precipitation of excess quenched-in vacancies increased with increasing iron content, and that the vacancies combined preferentially with iron atoms, which resulted in the slowing down of their migration rate. The amount of the loops increased by the subsequent ageing, accompanied with the precipitation of iron onto the loops as well as onto other defects such as grain boundaries and dislocation lines

Diffusion of Hydrogen at High Temperatures in the Group V Transition Metals and Alloying Effect on the Diffusion (Metallurgy)

application/pdfDiffusion coefficients of hydrogen in the Group V transition metals, i.e. vanadium, niobium and tantalum, and those in vanadium alloys containing chromium, iron, niobium and titanium were measured in the temperature range of 500～1100℃ by the absorption method. The following results were obtained : (1) Diffusion data at high temperatures in the Group V transition metals in the present experiment coincided well with data obtained at low temperatures by different methods, e.g. electrical resistivity, etc., but not with data at moderate temperatures measured by the same absorption method. (2) Below some critical temperature of the metals (540 to 700℃), the values of diffusion coefficient deviated downward from the linearity of Arrhenius plots. This deviation might be attributed to the effect of surface layers, probably oxide films, of the specimens, which would depress the absorption process of hydrogen in the metals. (3) The diffusion coefficient of hydrogen in vanadium was decreased by alloying chromium, iron or niobium, but increased by addition of 40at.% titanium. (4) Variations of the vibrational frequency term, D_0, and the activation energy, ΔHD, with the alloy concentration were almost parallel to that of the electric specific heat coefficient so far reported. Therefore, it was concluded that the screening of proton by electrons seemed to play an important role in the diffusion process, as with the case of the solubility of hydrogen in the metals.紀要類(bulletin)76810 bytesdepartmental bulletin pape

Strengthening of Vanadium Alloys by the Internal Oxidation Process(Metallurgy)

Fundamental experiments on the internal oxidation process of vanadium alloys, were carried out for the improvement of high temperature strength of the alloys, and the following results were obtained : (1) Zirconium and silicon were alloyed to vanadium, respectively, as an internally-oxidizing element. The former element was more favorable than the latter from the point of view of high temperature strength. (2) Excess of oxygen, supplied by decomposition of NiO, increased the amount of oxygen dissolved in solid-solution in the internally-oxidized alloys, which caused strengthening of the alloys not at high temperature but at low temperature, accompanied by brittlement. (3) Optimum zirconium contents of internally-oxidized V-Zr alloys was in the range of 0.3 and 1.0 wt%. (4) Strength of V-Zr alloys internally oxidized at a temperature above 980℃ was greater than those internally oxidized below this temperature. This fact was attributed to the volume expansion of ZrO_2 due to the β-α transformation when the alloy was cooled down through the transformation points of 980 to 1100℃. (5) Zirconium oxide particles formed by internal oxidation were appreciably stable at temperature around 1000℃, but they grew obeying Seybolt\u27s law at 1300℃ and then dissolved into the matrix above 1500℃

Effect of Hydrogen on the Tensile Properties of Vanadium at Moderate Temperatures (Metallurgy)

Tensile tests in the temperature range of 293 and 573K and microscopic observations were carried out on vanadium and V-high hydrogen concentration (1240-3410 wt ppm H) alloys. Examining the true stress (σ)-true plastic strain (ε_p) curves and the temperature and strain-rate dependence of the tensile properties, the following results were obtained : (1) The relation between σ and ε_p was well represented by the equation σ=Kε^m_p, where K is a constant and m is the strain hardening exponent. The value of m was measured to be 0.34 for vanadium and 0.11～0.15 for V-H alloys at 293K, which slightly increased with increase in test temperature up to 473K for vanadium, but decreased for V-H alloys. This decrease of m for V-H alloys might involve the resolution of hydride : under the tensile test at a temperature where hydride is completely resolved into the matrix, the alloys show the same behavior as vanadium subjected to prestraining to a stress level equal to the yield stress of the alloys at the specified temperature ; consequently the value of m for the alloys is smaller than that of vanadium. This fact was attributed to the dislocation structure which formed when the hydride was produced and still remained after the hydride was resolved ; the existence of the structure was confirmed by electron microscopy in the dehydrogenated alloy. Hydride, if it exists in the alloys, contributes to the strengthening of the alloys but induces embrittlement. (2) The temperature and hydrogen concentration dependence of the tensile properties were also explained by consideration (1) mentioned above. (3) As the ductile-brittle transition temperature of the alloys was lower than the solvus temperature at which hydride precipitates, it was considered that the hydride itself contributed mainly to the embrittlement of the alloys. (4) Anomalous embrittlement of V-H alloys containing about 3000 wt ppm or more H was observed at 423K, where all the hydrogen atoms should be in solution