embrittlement


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Related to embrittlement: caustic embrittlement

embrittlement

[‚em′brid·əl·mənt]
(mechanics)
Reduction or loss of ductility or toughness in a metal or plastic with little change in other mechanical properties.

Embrittlement

A general set of phenomena whereby materials suffer a marked decrease in their ability to deform (loss of ductility) or in their ability to absorb energy during fracture (loss of toughness), with little change in other mechanical properties, such as strength and hardness. Embrittlement can be induced by a variety of external or internal factors, for example, (1) a decreasing or an increasing temperature; (2) changes in the internal structure of the material, namely, changes in crystallite (grain) size, or in the presence and distribution of alloying elements and second-phase particles; (3) the introduction of an environment which is often, but not necessarily, corrosive in nature; (4) an increasing rate of application of load or extension; and (5) the presence of surface notches.

Low-temperature embrittlement results from a competition between deformation and brittle fracture, with the latter becoming preferred at a critical temperature. For a material to be useful structurally, it is desirable that this critical temperature be below the minimum anticipated service temperature; in most cases, this is room temperature. At high temperatures, internal structural changes that lead to intergranular embrittlement can occur. Embrittlement usually occurs in the creep temperature range, a temperature at which deformation can occur under very low stresses; and the two processes are believed to be connected.

In many metals, particularly structural steels, annealing or heat treating in certain temperature ranges sensitizes the grain boundaries in such a way that intergranular embrittlement subsequently occurs during service. To reduce the brittleness, the steel undergoes an annealing treatment called tempering, which, while decreasing the strength, usually increases the toughness. The exception to this trade-off occurs when the steel is tempered at 1000°F (538°C). This can lead to a mode of intergranular fracture called temper embrittlement; such a process has led to catastrophic failures in turbines, rotors, and other high-strength steel parts. In other metals, there are less specific but similar types of embrittlement resulting from critical heat treatments. See Heat treatment (metallurgy), Tempering

Metals can fracture catastrophically when exposed to a variety of environments. These environments can range from liquid metals to aqueous and nonaqueous solutions to gases such as hydrogen.

If a thin film of a liquid metal is placed on the oxide-free surface of a solid metal, the tensile properties of the solid metal will not be affected, but the fracture behavior can be markedly different from that observed in air. Although many different liquid metals are capable of inducing embrittlement in a variety of solid metals, some of the more common couples, many of which have important engineering and design consequences, are mercury embrittlement of brass, lead embrittlement of steel, and gallium embrittlement of aluminum.

Stress corrosion cracking can occur when a metal is stressed and simultaneously exposed to an environment which may be, but is not necessarily, corrosive in nature. Both stress and environment are required; if only one of these elements is present, the metal usually displays no embrittlement. See Corrosion

Hydrogen embrittlement is a form of embrittlement often considered to be a type of stress corrosion cracking. Hydrogen atoms can enter a metal, causing severe embrittlement, again with little effect on other mechanical properties. This phenomenon was originally observed, and is most critical in, steels, but it is not documented to occur in titanium and nickel alloys, and may lead to cracking in other alloy systems as well.

Factors such as notches and the rate of application of stress can modify the response of a material to a specific type of embrittlement. In general, notches or surface flaws always enhance embrittlement, both by acting as a stress raiser and by providing a preexisting crack.

References in periodicals archive ?
The successful alloying of high manganese steels with Al, which reduces the weakness against hydrogen embrittlement, suggests studying the effect of Al on the different aspects of hydrogen in Fe-Mn systems.
1 wt% generates copper-rich precipitates that are responsible of irradiation embrittlement in reactor pressure vessel materials [10].
Hydrogen embrittlement is an old mystery," says Song.
That is, embrittlement with annealing is quite obvious for high-speed testing.
Looking first at mechanisms of hydrogen interactions with metals, then at modeling hydrogen embrittlement, they consider such topics as bulk thermal desorption spectroscopy methods of analyzing hydrogen in metals, controlling hydrogen embrittlement of metals by chemical inhibitors and coatings, the influence of hydrogen on the behavior of dislocations, continuum mechanics modeling of hydrogen embrittlement, and developing service life prognosis systems for hydrogen energy devices.
Silva, A Study of Internal Hydrogen Embrittlement and Environmental Hydrogen Embrittlement of API 5L X60 Steel, Memorias del 20[grados] Congreso Brasileno de Ingenieria Mecanica, Gramado, Brasil, 15 al 20 de noviembre (2009).
It is often considered to be interchangeable with "hydrogen-induced cracking (HIC)" and/or "hydrogen embrittlement (HE)".
Embrittlement by hydrogen can manifest itself in the form of reduced ductility and notch strengths or subcritical crack growth under monotonic loading, which is called "hydrogen embrittlement" (HE), and increased fatigue crack growth (rate(s)) (FCG(R)).
Results from the lab tests are used for computer simulation, where hydrogen embrittlement in the metals is calculated.
Unlike traditional PCs, new Lexan DMX resin provides exceptional clarity and resistance to haze/reduced light transmission and embrittlement from prolonged ammonia exposure for extended luminaire life and reduced energy consumption.
They consider such aspects as the International Atomic Energy Agency's coordinated research projects on the structural integrity of reactor pressure vessels, the embrittlement correlation method for the Japanese reactor pressure vessel materials, irradiation-induced grain-boundary solute segregation and its effect on the ductile-to-brittle transition temperatures in reactor pressure vessel steels, inter-relationships between true stress-true strain behavior and deformation microstructure in the plastic deformation of neutron-irradiated or work-hardened austenitic stainless steel, and the influence of neutron irradiation on energy accumulation and dissipation during plastic flow and hardening of metallic polycrystals.