Ductility refers to the ability of a material to sustain significant plastic deformation before fracture. Plastic deformation is the permanent distortion of a material under applied stress, as opposed to elastic deformation, which is reversible upon removing the stress. Ductility is a critical mechanical performance indicator, particularly in applications that require materials to bend, stretch, or deform in other ways without breaking. The extent of ductility can be quantitatively assessed using the percent elongation at break, given by the equation:
Fracture is the appearance of a crack or complete separation of an object or material into two or more pieces under the action of stress. The fracture of a solid usually occurs due to the development of certain displacement discontinuity surfaces within the solid. If a displacement develops perpendicular to the surface, it is called a normal tensile crack or simply a crack; if a displacement develops tangentially, it is called a shear crack, slip band, or dislocation.
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 in steels, as well as in iron, nickel, titanium, cobalt, and their alloys. Copper, aluminium, and stainless steels are less susceptible to hydrogen embrittlement.
Tempering is a process of heat treating, which is used to increase the toughness of iron-based alloys. Tempering is usually performed after hardening, to reduce some of the excess hardness, and is done by heating the metal to some temperature below the critical point for a certain period of time, then allowing it to cool in still air. The exact temperature determines the amount of hardness removed, and depends on both the specific composition of the alloy and on the desired properties in the finished product. For instance, very hard tools are often tempered at low temperatures, while springs are tempered at much higher temperatures.
A reactor pressure vessel (RPV) in a nuclear power plant is the pressure vessel containing the nuclear reactor coolant, core shroud, and the reactor core.
Zirconium alloys are solid solutions of zirconium or other metals, a common subgroup having the trade mark Zircaloy. Zirconium has very low absorption cross-section of thermal neutrons, high hardness, ductility and corrosion resistance. One of the main uses of zirconium alloys is in nuclear technology, as cladding of fuel rods in nuclear reactors, especially water reactors. A typical composition of nuclear-grade zirconium alloys is more than 95 weight percent zirconium and less than 2% of tin, niobium, iron, chromium, nickel and other metals, which are added to improve mechanical properties and corrosion resistance.
Transgranular fracture is a type of fracture that occurs through the crystal grains of a material. In contrast to intergranular fractures, which occur when a fracture follows the grain boundaries, this type of fracture traverses the material's microstructure directly through individual grains. This type of fracture typically results from a combination of high stresses and material defects, such as voids or inclusions, that create a path for crack propagation through the grains. A broad range of ductile or brittle materials, including metals, ceramics, and polymers, can experience transgranular fracture. When examined under scanning electron microscopy, this type of fracture reveals cleavage steps, river patterns, feather markings, dimples, and tongues. The fracture may change directions somewhat when entering a new grain in order to follow the new lattice orientation of that grain but this is a less severe direction change then would be required to follow the grain boundary. This results in a fairly smooth looking fracture with fewer sharp edges than one that follows the grain boundaries. This can be visualized as a jigsaw puzzle cut from a single sheet of wood with the wood grain showing. A transgranular fracture follows the grains in the wood, not the jigsaw edges of the puzzle pieces. This is in contrast to an intergranular fracture which, in this analogy, would follow the jigsaw edges, not the wood grain.
In materials science, intergranular corrosion (IGC), also known as intergranular attack (IGA), is a form of corrosion where the boundaries of crystallites of the material are more susceptible to corrosion than their insides.
Liquid metal embrittlement is a phenomenon of practical importance, where certain ductile metals experience drastic loss in tensile ductility or undergo brittle fracture when exposed to specific liquid metals. Generally, tensile stress, either externally applied or internally present, is needed to induce embrittlement. Exceptions to this rule have been observed, as in the case of aluminium in the presence of liquid gallium. This phenomenon has been studied since the beginning of the 20th century. Many of its phenomenological characteristics are known and several mechanisms have been proposed to explain it. The practical significance of liquid metal embrittlement is revealed by the observation that several steels experience ductility losses and cracking during hot-dip galvanizing or during subsequent fabrication. Cracking can occur catastrophically and very high crack growth rates have been measured.
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.
Radiation damage is the effect of ionizing radiation on physical objects including non-living structural materials. It can be either detrimental or beneficial for materials.
In materials science, segregation is the enrichment of atoms, ions, or molecules at a microscopic region in a materials system. While the terms segregation and adsorption are essentially synonymous, in practice, segregation is often used to describe the partitioning of molecular constituents to defects from solid solutions, whereas adsorption is generally used to describe such partitioning from liquids and gases to surfaces. The molecular-level segregation discussed in this article is distinct from other types of materials phenomena that are often called segregation, such as particle segregation in granular materials, and phase separation or precipitation, wherein molecules are segregated in to macroscopic regions of different compositions. Segregation has many practical consequences, ranging from the formation of soap bubbles, to microstructural engineering in materials science, to the stabilization of colloidal suspensions.
Microvoid coalescence (MVC) is a high energy microscopic fracture mechanism observed in the majority of metallic alloys and in some engineering plastics.
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.
In materials science, toughening refers to the process of making a material more resistant to the propagation of cracks. When a crack propagates, the associated irreversible work in different materials classes is different. Thus, the most effective toughening mechanisms differ among different materials classes. The crack tip plasticity is important in toughening of metals and long-chain polymers. Ceramics have limited crack tip plasticity and primarily rely on different toughening mechanisms.
Neutron embrittlement, sometimes more broadly radiation embrittlement, is the embrittlement of various materials due to the action of neutrons. This is primarily seen in nuclear reactors, where the release of high-energy neutrons causes the long-term degradation of the reactor materials. The embrittlement is caused by the microscopic movement of atoms that are hit by the neutrons; this same action also gives rise to neutron-induced swelling causing materials to grow in size, and the Wigner effect causing energy buildup in certain materials that can lead to sudden releases of energy.
Metal-induced embrittlement (MIE) is the embrittlement caused by diffusion of metal, either solid or liquid, into the base material. Metal induced embrittlement occurs when metals are in contact with low-melting point metals while under tensile stress. The embrittler can be either solid (SMIE) or liquid. Under sufficient tensile stress, MIE failure occurs instantaneously at temperatures just above melting point. For temperatures below the melting temperature of the embrittler, solid-state diffusion is the main transport mechanism. This occurs in the following ways:
Striations are marks produced on the fracture surface that show the incremental growth of a fatigue crack. A striation marks the position of the crack tip at the time it was made. The term striation generally refers to ductile striations which are rounded bands on the fracture surface separated by depressions or fissures and can have the same appearance on both sides of the mating surfaces of the fatigue crack. Although some research has suggested that many loading cycles are required to form a single striation, it is now generally thought that each striation is the result of a single loading cycle.
Duplex stainless steels are a family of alloys with a two-phase microstructure consisting of both austenitic and ferritic phases. They offer excellent mechanical properties, corrosion resistance, and toughness compared to other types of stainless steel. However, duplex stainless steel can be susceptible to a phenomenon known as 475 °C (887 °F) embrittlement or duplex stainless steel age hardening, which is a type of aging process that causes loss of plasticity in duplex stainless steel when it is heated in the range of 250 to 550 °C. At this temperature range, spontaneous phase separation of the ferrite phase into iron-rich and chromium-rich nanophases occurs, with no change in the mechanical properties of the austenite phase. This type of embrittlement is due to precipitation hardening, which makes the material become brittle and prone to cracking.
In materials science, a precipitate-free zone (PFZ) refers to microscopic localized regions around grain boundaries that are free of precipitates. It is a common phenomenon that arises in polycrystalline materials where heterogeneous nucleation of precipitates is the dominant nucleation mechanism. This is because grain boundaries are high-energy surfaces that act as sinks for vacancies, causing regions adjacent to a grain boundary to be devoid of vacancies. As it is energetically favorable for heterogeneous nucleation to occur preferentially around defect-rich sites such as vacancies, nucleation of precipitates is impeded in the vacancy-free regions immediately adjacent to grain boundaries
