#martensite

Scientists achieve giant magneto-superelasticity in metal crystal

Recently, a research group developed a giant magneto-superelasticity of 5% in a Ni34Co8Cu8Mn36Ga14 single crystal. This was achieved by introducing arrays of ordered dislocations to form preferentially oriented martensitic variants during the magnetically induced reverse martensitic transformation. The research was published in Advanced Science. Elasticity is the ability of materials to return to their original shape after deformation, typically with a strain of 0.2% in most metals. Shape memory and high entropy alloys can exhibit superelasticity with strains of several percent, usually triggered by external stresses. Magneto-superelasticity, induced by a magnetic field, is crucial for contactless material operation and the development of new large stroke actuators and efficient energy transducers.

Not quite studyblr pretty, but I'm proud anyway.

Martensitic Phase Transformations

A martensitic phase transformation is a first order, solid-solid, displacive (or diffusionless) shear transformation. Though the term martensite was originally used to refer to the specific steel microstructure formed as a result of this transformation, the term came to apply to the transformation itself. A martensitic transformation can be triggered by temperature, external stress, or both and is not possible in all materials. Shape memory alloys, in particular, rely on martensitic transformations.

Sources/Further Reading: (University of Cambridge) (IUCr) (1996 article) (dierk-raabe.com)

Hot compression bonding helps achieve seamless CLAM steel joint

China low activation martensitic (CLAM) steel, as a typical reduced activation ferritic/martensitic steel, is the main candidate structural material for fusion reactors due to its low activation, high mechanical properties, irradiation resistance and corrosion resistance. However, weld uniformity is difficult to achieve with a conventional welding method, which tends to coarsen the martensitic slat, and the performance of the joints is usually lower than that of the base material. In view of this, a research team led by Prof. Huang Qunying from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences (CAS), in collaboration with researchers from the Institute of Metal Research of CAS, has conducted a study on the evolution of interfacial microstructure and oxides in CLAM steel by hot compression bonding (HCB). The study is published in the journal Materials Characterization. They developed the HCB method to realize effective joining of components by promoting the interfacial grain boundary migration and recrystallization under the combined effect of thermal coupling. The results showed that the interfacial oxide and micro-voids could be eliminated after the HCB process. The atomic-scale interfacial bonding could be achieved so that the bonding interface would be completely healed.

Adolf Martens (6 March 1850 – 24 July 1914)

A German metallurgist, Adolf Martens was primarily involved in the iron and steel industries, working on bridges and other metallic structures as well as rail lines, before he became a professor in Berlin. Martens is most famous for his work on steel microstructures - in particular, the phase (martensite) that was named in his honor. (Though at the time, martensitic transformations were unknown and Martens didn't actually publish any studies connected to martensite, he did sketch microstructures that could have been what we now call martensite.) As well as studying microstructures, relating structure to properties, he also studied fracture surfaces and developed and improved versions of optical microscopes.

Novel durable copper-aluminum-zinc shape memory alloys for energy-efficient refrigeration

The elastocaloric effect is a phenomenon where a material displays a temperature change when it is exposed to a mechanical stress. The change in temperature occurs due to an entropy difference resulting from a martensitic transformation accompanied by material's crystal structure change under stress.

An analogous effect is observed when the rubber band is stretched: its polymer chains line up in an ordered manner, causing its entropy to decrease. This leads to the rubber band discharging heat to its surroundings and becoming warmer. When the rubber band is released, the opposite occurs, and the rubber band cools down.

Like rubber bands, metallic superelastic shape memory alloys (SMAs) can also utilize the elastocaloric effect for cooling. Copper (Cu)-based SMAs consisting of Cu, aluminum (Al), and zinc (Zn) are particularly promising due to their low cost and modest stress demands for triggering the temperature lift. However, Cu-Al-Zn SMAs suffer from cyclical fatigue issues as their coarse crystal grains and numerous grain boundaries are susceptible to fracture from repeated expansion and contraction.

Researchers at Tokyo Institute of Technology and the National Institute for Fusion Science have clarified the chemical compatibility between high temperature liquid metal tin (Sn) and reduced activation ferritic martensitic, a candidate structural material for fusion reactors. This discovery has paved the way for the development of a liquid metal tin divertor, which is an advanced heat-removal component of fusion reactors. A device called a divertor is installed in the fusion reactors to maintain the purity of the plasma. For divertors, there has been demand for liquid metals that can withstand extremely large heat loads from high-temperature plasma.

Background

Fusion reactors are being actively developed throughout the world as a form of sustainable zero-carbon energies because their fuel can be extracted from an inexhaustible supply of seawater. Also, they do not emit greenhouse gases. In addition to the construction of the tokamak (ITER), which is being constructed through collaboration of seven of the world's leading countries and regions (Japan, EU, United States, South Korea, China, Russia, and India), fusion development by the private sector is also accelerating.