Editing Metal (section)

===Post-World War II developments===

====Superalloys====
{{Main|Superalloy}}

[[File:ریخته گري دقیق سوپرآلیاژهای نیکل.jpg|thumb|Heat treating superalloy turbine blades]]
Superalloys composed of combinations of Fe, Ni, Co, and Cr, and lesser amounts of W, Mo, Ta, Nb, Ti, and Al were developed shortly after World War II for use in high performance engines, operating at elevated temperatures (above 650&nbsp;°C (1,200&nbsp;°F)). They retain most of their strength under these conditions, for prolonged periods, and combine good low-temperature ductility with resistance to corrosion or oxidation. Superalloys can now be found in a wide range of applications including land, maritime, and aerospace turbines, and chemical and petroleum plants.

====Transcurium metals====
The successful development of the atomic bomb at the end of World War II sparked further efforts to synthesize new elements, nearly all of which are, or are expected to be, metals, and all of which are radioactive. It was not until 1949 that element 97 ([[Berkelium]]), next after element 96 ([[Curium]]), was synthesized by firing alpha particles at an americium target. In 1952, element 100 ([[Fermium]]) was found in the debris of the first hydrogen bomb explosion; hydrogen, a nonmetal, had been identified as an element nearly 200 years earlier. Since 1952, elements 101 ([[Mendelevium]]) to 118 ([[Oganesson]]) have been synthesized.

====Bulk metallic glasses====
{{Main|Metallic Glass}}
[[File:Metalic Glas Vitreloy4.jpg|thumb|Metallic Glass Vitreloy4]]

A metallic glass (also known as an amorphous or glassy metal) is a solid metallic material, usually an alloy, with a disordered atomic-scale structure. Most pure and alloyed metals, in their solid state, have atoms arranged in a highly ordered crystalline structure. In contrast these have a non-crystalline glass-like structure. But unlike common glasses, such as window glass, which are typically electrical insulators, amorphous metals have good electrical conductivity. Amorphous metals are produced in several ways, including extremely rapid cooling, physical vapor deposition, solid-state reaction, ion irradiation, and mechanical alloying. The first reported metallic glass was an alloy (Au<sub>75</sub>Si<sub>25</sub>) produced at [[Caltech]] in 1960. More recently, batches of amorphous steel with three times the strength of conventional steel alloys have been produced. Currently, the most important applications rely on the special magnetic properties of some ferromagnetic metallic glasses. The low magnetization loss is used in high-efficiency transformers. Theft control ID tags and other article surveillance schemes often use metallic glasses because of these magnetic properties.

====Shape-memory alloys====
{{Main|Shape-memory alloy}}
A shape-memory alloy (SMA) is an alloy that "remembers" its original shape and when deformed returns to its pre-deformed shape when heated. While the shape memory effect had been first observed in 1932, in an Au-Cd alloy, it was not until 1962, with the accidental discovery of the effect in a Ni-Ti alloy that research began in earnest, and another ten years before commercial applications emerged. SMA's have applications in robotics and automotive, aerospace, and biomedical industries. There is another type of SMA, called a ferromagnetic shape-memory alloy (FSMA), that changes shape under strong magnetic fields. These materials are of interest as the magnetic response tends to be faster and more efficient than temperature-induced responses.

====Quasicrystalline alloys====
{{Main|Quasicrystal}}
[[File:Ho-Mg-ZnQuasicrystal.jpg|thumb|A Ho-Mg-Zn icosahedral quasicrystal formed as a pentagonal [[dodecahedron]], the [[dual polyhedron|dual]] of the [[icosahedron]]|alt=A metallic regular dodecahedron]]
In 1984, Israeli metallurgist [[Dan Shechtman]] found an aluminium-manganese alloy having five-fold symmetry, in breach of crystallographic convention at the time which said that crystalline structures could only have two-, three-, four-, or six-fold symmetry. Due to reservation about the scientific community's reaction, it took Shechtman two years to publish the results&nbsp;for which he was awarded the Nobel Prize in Chemistry in 2011. Since this time, hundreds of quasicrystals have been reported and confirmed. They exist in many metallic alloys (and some polymers). Quasicrystals are found most often in aluminium alloys (Al-Li-Cu, Al-Mn-Si, Al-Ni-Co, Al-Pd-Mn, Al-Cu-Fe, Al-Cu-V, etc.), but numerous other compositions are also known (Cd-Yb, Ti-Zr-Ni, Zn-Mg-Ho, Zn-Mg-Sc, In-Ag-Yb, Pd-U-Si, etc.). [[Quasicrystal]]s effectively have infinitely large unit cells. [[Icosahedrite]] Al<sub>63</sub>Cu<sub>24</sub>Fe<sub>13</sub>, the first quasicrystal found in nature, was discovered in 2009. Most quasicrystals have ceramic-like properties including low electrical conductivity (approaching values seen in insulators) and low thermal conductivity, high hardness, brittleness, and resistance to corrosion, and non-stick properties. Quasicrystals have been used to develop heat insulation,&nbsp;LEDs, diesel engines, and new materials that convert heat to electricity. New applications may take advantage of the low coefficient of friction and the hardness of some quasicrystalline materials, for example embedding particles in plastic to make strong, hard-wearing, low-friction plastic gears. Other potential applications include selective solar absorbers for power conversion, broad-wavelength reflectors, and bone repair and prostheses applications where biocompatibility, low friction, and corrosion resistance are required.

====Complex metallic alloys====
{{Main|Complex metallic alloy}}
Complex metallic alloys (CMAs) are intermetallic compounds characterized by large unit cells comprising some tens up to thousands of atoms; the presence of well-defined clusters of atoms (frequently with icosahedral symmetry); and partial disorder within their crystalline lattices. They are composed of two or more metallic elements, sometimes with metalloids or [[chalcogenides]] added. They include, for example, NaCd2, with 348 sodium atoms and 768 cadmium atoms in the unit cell. [[Linus Pauling]] attempted to describe the structure of NaCd<sub>2</sub> in 1923, but did not succeed until 1955. At first called "giant unit cell crystals", interest in CMAs, as they came to be called, did not pick up until 2002, with the publication of a paper called "Structurally Complex Alloy Phases", given at the ''8th International Conference on Quasicrystals.'' Potential applications of CMAs include as heat insulation; solar heating; magnetic refrigerators; using waste heat to generate electricity; and coatings for turbine blades in military engines.

====High-entropy alloys====
{{Main|High-entropy alloy}}
High entropy alloys (HEAs) such as AlLiMgScTi are composed of equal or nearly equal quantities of five or more metals. Compared to conventional alloys with only one or two base metals, HEAs have considerably better strength-to-weight ratios, higher tensile strength, and greater resistance to fracturing, corrosion, and oxidation. Although HEAs were described as early as 1981, significant interest did not develop until the 2010s; they continue to be a focus of research in materials science and engineering because of their desirable properties.

====MAX phase====
{| class="wikitable plainrowheaders" style="float:right; margin-left:2em; margin-top:-2em;"
|+ MAX phase<br />alloy examples
!scope="col"| MAX
!scope="col"| M
!scope="col"| A
!scope="col"| X
|-
!scope="row"| Hf<sub>2</sub>SnC
| Hf || Sn || C
|-
!scope="row"| Ti<sub>4</sub>AlN<sub>3</sub>
| Ti || Al || N
|-
!scope="row"| Ti<sub>3</sub>SiC<sub>2</sub>
| Ti || Si || C
|-
!scope="row"| Ti<sub>2</sub>AlC
| Ti || Al || C
|-
!scope="row"| Cr<sub>2</sub>AlC<sub>2</sub>
| Cr || Al || C
|-
!scope="row"| Ti<sub>3</sub>AlC<sub>2</sub>
| Ti || Al || C
|}
{{Main|MAX phases}}
In a Max phase, '''M''' is an early transition metal, '''A''' is an A group element (mostly group IIIA and IVA, or groups 13 and 14), and '''X''' is either carbon or nitrogen. Examples are Hf<sub>2</sub>SnC and Ti<sub>4</sub>AlN<sub>3</sub>. Such alloys have high electrical and thermal conductivity, thermal shock resistance, damage tolerance, machinability, high elastic stiffness, and low thermal expansion coefficients.<ref>{{Cite journal |last1=Hanaor |first1=D.A.H. |last2=Hu |first2=L. |last3=Kan |first3=W.H. |last4=Proust |first4=G. |last5=Foley |first5=M. |last6=Karaman |first6=I. |last7=Radovic |first7=M. |date=2016 |title=Compressive performance and crack propagation in Al alloy/Ti2AlC composites |url=https://linkinghub.elsevier.com/retrieve/pii/S0921509316307419 |journal=Materials Science and Engineering: A |language=en |volume=672 |pages=247–256 |doi=10.1016/j.msea.2016.06.073|arxiv=1908.08757 }}</ref> They can be polished to a metallic luster because of their excellent electrical conductivities. During mechanical testing, it has been found that polycrystalline Ti<sub>3</sub>SiC<sub>2</sub> cylinders can be repeatedly compressed at room temperature, up to stresses of 1 GPa, and fully recover upon the removal of the load. Some MAX phases are also highly resistant to chemical attack (e.g. Ti<sub>3</sub>SiC<sub>2</sub>) and high-temperature oxidation in air (Ti<sub>2</sub>AlC, Cr<sub>2</sub>AlC<sub>2</sub>, and Ti<sub>3</sub>AlC<sub>2</sub>). Potential applications for MAX phase alloys include: as tough, machinable, thermal shock-resistant refractories; high-temperature heating elements; coatings for electrical contacts; and neutron irradiation resistant parts for nuclear applications.