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In materials science, a dislocation or Taylor's dislocation is a linear crystallographic defect or irregularity within a crystal structure that contains an abrupt change in the arrangement of atoms. The movement of dislocations allow atoms to slide over each other at low stress levels and is known as glide or slip. The crystalline order is restored on either side of a glide dislocation but the atoms on one side have moved by one position. The crystalline order is not fully restored with a partial dislocation. A dislocation defines the boundary between slipped and unslipped regions of material and as a result, must either form a complete loop, intersect other dislocations or defects, or extend to the edges of the crystal. A dislocation can be characterised by the distance and direction of movement it causes to atoms which is defined by the Burgers vector. Plastic deformation of a material occurs by the creation and movement of many dislocations. The number and arrangement of dislocations influences many of the properties of materials.
Hydrogen embrittlement (HE), also known as hydrogen-assisted cracking or hydrogen-induced cracking (HIC), is a reduction in the ductility of a metal due to absorbed hydrogen. Hydrogen atoms are small and can permeate solid metals. Once absorbed, hydrogen lowers the stress required for cracks in the metal to initiate and propagate, resulting in embrittlement. Hydrogen embrittlement occurs most notably in steels, as well as in iron, nickel, titanium, cobalt, and their alloys. Copper, aluminium, and stainless steels are less susceptible to hydrogen embrittlement.
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In metallurgy and materials science, annealing is a heat treatment that alters the physical and sometimes chemical properties of a material to increase its ductility and reduce its hardness, making it more workable. It involves heating a material above its recrystallization temperature, maintaining a suitable temperature for an appropriate amount of time and then cooling.
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Embrittlement is a significant decrease of ductility of a material, which makes the material brittle. Embrittlement is used to describe any phenomena where the environment compromises a stressed material's mechanical performance, such as temperature or environmental composition. This is oftentimes undesirable as brittle fracture occurs quicker and can much more easily propagate than ductile fracture, leading to complete failure of the equipment. Various materials have different mechanisms of embrittlement, therefore it can manifest in a variety of ways, from slow crack growth to a reduction of tensile ductility and toughness.
In metallurgy, solid solution strengthening is a type of alloying that can be used to improve the strength of a pure metal. The technique works by adding atoms of one element to the crystalline lattice of another element, forming a solid solution. The local nonuniformity in the lattice due to the alloying element makes plastic deformation more difficult by impeding dislocation motion through stress fields. In contrast, alloying beyond the solubility limit can form a second phase, leading to strengthening via other mechanisms.
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In materials science, grain-boundary strengthening is a method of strengthening materials by changing their average crystallite (grain) size. It is based on the observation that grain boundaries are insurmountable borders for dislocations and that the number of dislocations within a grain has an effect on how stress builds up in the adjacent grain, which will eventually activate dislocation sources and thus enabling deformation in the neighbouring grain as well. By changing grain size, one can influence the number of dislocations piled up at the grain boundary and yield strength. For example, heat treatment after plastic deformation and changing the rate of solidification are ways to alter grain size.
Oxide dispersion strengthened alloys (ODS) are alloys that consist of a metal matrix with small oxide particles dispersed within it. They have high heat resistance, strength, and ductility. Alloys of nickel are the most common but includes iron aluminum alloys.
Dynamic strain aging (DSA) for materials science is an instability in plastic flow of materials, associated with interaction between moving dislocations and diffusing solutes. Although sometimes dynamic strain aging is used interchangeably with the Portevin–Le Chatelier effect (or serrated yielding), dynamic strain aging refers specifically to the microscopic mechanism that induces the Portevin–Le Chatelier effect. This strengthening mechanism is related to solid-solution strengthening and has been observed in a variety of fcc and bcc substitutional and interstitial alloys, metalloids like silicon, and ordered intermetallics within specific ranges of temperature and strain rate.
Iron–hydrogen alloy, also known as iron hydride, is an alloy of iron and hydrogen and other elements. Because of its lability when removed from a hydrogen atmosphere, it has no uses as a structural material.
References
- ↑ Figueroa, D.; Robinson, M.J. (2008-04-01). "The effects of sacrificial coatings on hydrogen embrittlement and re-embrittlement of ultra high strength steels". Corrosion Science. 50 (4): 1066–1079. doi:10.1016/j.corsci.2007.11.023. ISSN 0010-938X.
- ↑ Takai, K.; Shoda, H.; Suzuki, H.; Nagumo, M. (2008-10-01). "Lattice defects dominating hydrogen-related failure of metals". Acta Materialia. 56 (18): 5158–5167. Bibcode:2008AcMat..56.5158T. doi:10.1016/j.actamat.2008.06.031. ISSN 1359-6454.
- ↑ Effect of temperature on the susceptibility of VT6ch alloy to hydrogen embrittlement
- ↑ Zhou, Chengshuang (2019). "Effects of internal hydrogen and surface-absorbed hydrogen on the hydrogen embrittlement of X80 pipeline steel". International Journal of Hydrogen Energy. 44 (40): 22547–22558. doi:10.1016/j.ijhydene.2019.04.239. S2CID 181515850.
- ↑ Liu, Qian; Atrens, Andrej (2015-07-01). "Reversible hydrogen trapping in a 3.5NiCrMoV medium strength steel". Corrosion Science. 96: 112–120. doi:10.1016/j.corsci.2015.04.011. ISSN 0010-938X.
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