[en] The formation of brittle phases during brazing very often causes a reduction of strength and toughness of the joint. In order to escape from this problem defined long time heat treatments at rather high temperatures are successfully applied after brazing. However, by modifying the process a direct influence on the brittle phase formation during brazing is rendered possible, so that the disadvantageous effect on the joint is completely suppressed. Strength tests provide information about suitable joining parameters. (orig.)

[en] To predict the life of a component of an engineering system, it is essential to compute the stresses and strains to which the material will be subjected. In this work described the validity of these methods was tested under conditions in which the stress distribution in the component is changing with time. The experiment was simple in concept. A thick-walled cylindrical specimen of Nimonic 80A was placed in an evacuated furnace. An electric-resistance heater was mounted concentrically inside the specimen and the walls of the furnace were water-cooled to provide a heat sink. Insulating blocks were placed at the ends of the cylinder to minimise the axial temperature gradients in the specimen. The temperature distribution in the cylinder was in the range 700⁰C to 815⁰C, which is the temperature range over which the creep behavior of this material is well documented. The initial stress distribution, described by the Lame equations, was modified by creep. The temperature distribution in the specimen was maintained for 500 hours, after which the specimen was cooled, in a controlled manner, to room temperature. The stress redistribution due to creep during the prolonged heating, and the final residual stress distribution were computed, assuming various models of creep behavior. The residual stresses were measured by a modified Sachs layer-removal procedure, in which the layers of material were removed by acid etching in order to avoid the development of additional machining stresses. This paper includes results from several specimens subjected to identical load sequences. Repeatable results were obtained, indicating that the random errors are small. Attempts to predict the results by computer have been less encouraging

[en] Moessbauer measurements made on the Inconel-600 (Ni-72%, Cr-18%, Fe-10%) show that isomer shift and line width increase with the decrease of temperature. From the area under the resonance curve the Debye temperature theta is determined to be near 400 K. A brief description of the Moessbauer effect is included. (author)

[en] Creep behaviors of solution treated, solution and precipitation heat treated, and solution, precipitation and carburization treated Nimonic 86 alloys were compared. Solution treatments were carried out at 1150 deg C for 2 hours and precipitation treatments were performed at 900 deg C for 200 and 1000 hours. Carburization treatments were performed during precipitation treatment using carburizing atmosphere. Creep tests were carried out up to 1200 hours at 850 and 950 deg C. Precipitation heat treatment decreased the creep resistance compared to the solution treatment, and the carburization treatment significantly increased the creep resistance, especially at 950 deg C. The results were explained by the relative amounts, size, and distribution of carbide precipitates. (Author)

[en] The time-load relationships produced experimentally correspond to those experienced in practice in reactor and turbine components. The creep properties of the basic materials here used - in this case NiCr20TiAl - are known. In brazed joints using nickel-based brazing alloys the major parameters of influence are the width of the braze gap and the number and type of phases occuring within it. Hard phases within the braze seam lead to accelerated breakage of the joint. The cohering carbides and silicides dissipate to form discrete particles under heat treatment at around 1000₀C, and subsequent strength tests show marked improvement of the strength properties. If a crack is present in the braze seam, these discrete particles have the effect of making the crack grow unstably. The time-stress loading was applied in the operating range of temperature, i.e. between 500₀C and 800₀C. The basic investigations of creep behaviour were carried out using NiCr20TiAl as the material to be joined and a nickel-based brazing metal containing no boron, BNi 5. The strength properties are described and are compared with the corresponding microstructure states. The creep resistance of the samples of brazing metal is compared with that of the materials to be joined, and possible hypothesis to explain failures are discussed. (orig.)

No abstract available

[en] This report considers the possibility of high temperature rupture occurring by a grain boundary diffusional mechanism. It is assumed that a pre-existing, intergranular crack grows by loss of atoms from the crack tip to the grain boundary. Rupture occurs when the crack has grown to a critical length. A theoretical treatment of the kinetics of crack growth is presented and equations are derived for the crack velocity and time to rupture. A comparison is made with a previous theoretical model developed by Charles, together with rupture data obtained experimentally for the nickel-based alloy, Nimonic 80A. We conclude that experimental verification of the theoretical models requires a comparison with crack velocity data rather than time to rupture data. (author)

[en] Cold drawn INCONEL 600 samples had been submitted to creep rupture tests with constant load at 650⁰C. The controlling creep mechanism had been characterized in that condition. Some aspects of the mechanical and structural behaviour of the material after the creep rupture tests had been compared with those observed in the same material after the simple submission its to isothermal treatment. (Author)

[en] For the purpose of improving the cyclic oxidation resistance of Ni-base superalloy, Inconel 600, aluminide coating methods are studied. The formation rate of aluminide coating layers is measured as a function of time and pack composition to find out the optimum coating condition. The evaluation of cyclic oxidation is established by the change in weight, the microphotography and EPMA of cross sectional area during 200 deg C - 950 deg C and 200 deg C - 1100 deg C, respectively. The thickness of coating layer and weight gains are parabolic behavior in propotion to time and Al contents. In pack of low aluminum contents, 2wt%, however, weight gain is decreased when activator, NH₄Cl is higher than 2 wt%. The cyclic oxidation resistance of the coatings carried out at 1100 deg C are superior to those of the coatings diffusion-treated after pack cementation at 800 deg C. Aluminide oxide, which is formed in external scale, is barrier to the cyclic oxidation. (Author)

[en] The effect of prior hot plastic deformation, (prestrain), on the subsequent creep properties of Nimonic 80A has been investigated. It has been found that prestraining at temperatures up to 700⁰C can have a serious detrimental effect on the subsequent creep performance at 750⁰C. The reduction in the creep ductility has been attributed to enhanced grain boundary cavitation which has been studied in the crept specimens using optical microscopy. The submicron grain boundary cavities formed during the hot prestraining have also been examined using high voltage electron microscopy. (author)