Heat nickel-based alloys

It is used in certain nickel-based alloys, such as the "Hastelloys(R)" which are heat-resistant and corrosion-resistant to chemical solutions. Molybdenum oxidizes at elevated temperatures. The metal has found recent application as electrodes for electrically heated glass furnaces and foreheaths. The metal is also used in nuclear energy applications and for missile and aircraft parts. Molybdenum is valuable as a catalyst in the refining of petroleum. It has found applications as a filament material in electronic and electrical applications. Molybdenum is an... 

Many instances of intergranular stress corrosion cracking (IGSCC) of stainless steel and nickel-based alloys have occurred in the reactor water systems of BWRs. IGSCC, first observed in the recirculation piping systems (21) and later in reactor vessel internal components, has been observed primarily in the weld heat-affected zone of Type 304 stainless steel. 

HEAT RESISTANT NICKEL-BASE ALLOYS AND THE PRODUCTS OF THEIR CORROSION COMPOSITION DETERMINATION... 

Silver-palladium-manganese brazes possess excellent creep characteristics and have been developed for high-temperature applications involving the use of cobalt or nickel-based alloys, heat-resistant steels, molybdenum and tungsten. Their liquidus temperatures lie in the range 1 100-1 250°C. 

Cyclic Oxidation In many industrial applications it is particularly important for the component to be resistant to thermal shock for example, resistance-heating wires or blading for gas turbines. Chromia, and especially alumina, scales that form on nickel-base alloys are prone to spalling when thermally cycled as a result of the stress build-up arising from the mismatch in the thermal expansion coefficients of the oxide and the alloy as well as that derived from the growth process. A very useful compilation of data on the cyclic oxidation of about 40 superalloys in the temperature range 1 000-1 I50°C has been made by Barrett et... 

In contact with molten salts, the nickel-base alloys behave much more satisfactorily than is the general experience with molten metals. For this reason they are considered as structural materials in atomic reactors using fluoride mixtures as coolants and are used as vessels for heat-treatment salt baths, as thermocouple sheaths and in similar applications. 

For several years, additions of Be to commercial copper- and nickel-based alloys have enabled these materials to be precipitation-hardened to strengths approaching those of heat-treated steels. Yet Cu-Be alloys retain the corrosion resistance, electrical and thermal conductivities, and spark resistance of copper-based alloys. 

Takeda et al. [141] described the conditions applied for the diffusion bonding of nickel-based alloys (Hastelloy). A test piece of a plate and fin heat exchanger (dimensions 40 mm x 40 mm x 3 mm, channel dimensions 1000 pm x 1000 pm) was first cleaned with a 1% solution of nitric acid and hydrogen fluoride to remove the oxidation layer. A pressure as low as 6 mPa was necessary to run the process. For NiCrFe and other materials, other authors claim that an even lower pressure of 1 pPa is required. A welding temperature of 1 150 °C and a contact pressure of... 

The discovery of Cr began with a curious red lead found in Siberia. In 1797 itwas shown that the mineral contained not only lead but also another unknown element, which was isolated a year later. Today chromium is used in various steels - spring, nickel-chromium, and stainless, and in heat-resistant nickel-based alloys. My own generation of automobiles was adorned with chrome (chromium-plated) bumpers and fender and window trims - an excess that staggers the mind attuned to today s automobile manufacturing. 

Some practical cases are determination of residual stress in steel springs, the effect of mechanical loading on stress relaxation of machined and shot-peened nickel-base alloys,65 determination of residual stress level in turbine engine disks as they accumulate engine cycles,65 66 effect of manufacturing processes on residual stress, measurement of stress gradients in mechanical, electronic and structural components, effect of heat treatment on residual stress in steel coil springs, effect of variable heat treatment temperature on residual stress in iron alloys, measurement of stress in multiphase materials and composites and stress measurements at locations of stress concentrations. 

Corrosion Resistance of Nickel-based Alloys. Nickel-based alloys are solid solutions based on nickel. Nickel-based alloys used for low-temperature aqueous or condensed systems are generally known as corrosion-resistant alloys (CRA), and nickel alloys used for high-temperature applications are known as heat-resistant alloys (HRA), high-temperature alloys (HTA), or superalloys. The corrosion performance could change due to the presence of second phase or a weld seam. (Rebak)5... 

Corrosion of iron-base and nickel-base alloys by liquid metals used as heat transfer agents (e.g., liquid sodium, potassium, and lithium)... 

Because of the broad variation in composition and response to thermal treatment of the nickel-base alloys, it is not possible to generalize mechanisms responsible for developing susceptibility to intergranular corrosion. Therefore, the following discussion of the behavior of a Ni-Mo-Cr alloy is used to illustrate the complexity of an interrelationship between alloy composition, heat treatment, corrosion environment and corrosion rate. The alloy has the nominal composition in weight percent of 14.5 to 16.5 Cr, 15 to 17 Mo, 3 to 4.5 W, and 4 to 7 Fe with maximum limits on carbon and silicon. The alloys for which the corrosion data are shown in Fig. 7.59 contained 0.045 to 0.06 wt% carbon and 0.53 to 0.80 wt% silicon and were initially quenched from 1225 15 °C (2235 25 °F), which produced a dispersion of M6C type carbides (M = Mo, W, Si) in austenite (Ref 94). These carbides were not involved in the subsequent corrosion behavior or heat treatments. Heat... 

Pyromet . [Carpenter Tech.] Nickel-base alloy for heat shiel(Is, furnace hardware, gas turbine engine ducting, combustion liners, chemi( l plant hardware, seawater applies. 

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