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1. Crystal -- Atoms are arranged in a periodic and orderly manner in three-dimensional space, possessing a fixed melting point and anisotropy. 2. Intermediate phase -- When two components, A and B, form an alloy, in addition to the formation of solid solutions based on either A or B, a new phase may also be formed whose crystal structure is different from both components A and B. Since their positions on the binary phase diagram are always in the middle, these phases are generally referred to as intermediate phases. 3. Metastable phase – A metastable phase refers to a phase that cannot exist stably from a thermodynamic standpoint; however, during rapid cooling or heating processes, it remains temporarily stable because of thermodynamic energy barriers or kinetic factors that prevent it from transforming into a stable phase. 4. Coordination number--the number of nearest and equidistant atoms surrounding any atom in a crystal structure. 5. Recrystallization – After cold deformation, when the metal is heated to a certain temperature, new, undistorted grains are regenerated within the originally deformed structure. Consequently, its properties undergo significant changes and return to their pre-deformation state. This process is known as recrystallization. (Refers to the process by which distortion-free equiaxed new grains gradually replace the deformed grains.) 6. Pseudo-eutectic – Under conditions of non-equilibrium solidification, certain alloys with sub-eutectic or hyper-eutectic compositions can also exhibit a fully eutectic structure; such an eutectic structure formed in alloys with non-eutectic compositions is known as a pseudo-eutectic structure. 7. Cross-slip – When the movement of a certain helical dislocation is hindered on its original slip plane, it may transfer to another slip plane that intersects with it in order to continue sliding; this process is known as cross-slip. 8. Aging – After solution treatment, during the heating and holding process, GP zones, θ”, θ’, and θ precipitate successively in aluminum alloys. At the beginning of the holding stage, as the holding time increases, the hardness and strength of the material rise. However, if the holding time is too long, θ’ phases will precipitate, causing the hardness and strength of the material to decrease; this phenomenon is known as over-aging. 9. Strain strengthening – When a metal is subjected to cold plastic deformation, its strength and hardness increase while its ductility and toughness decrease; this phenomenon is known as strain strengthening. 10. Solid solution strengthening – the phenomenon in which the strength of a metal-based alloy is increased due to the addition of alloying elements (impurities). 11. Dispersion strengthening – Many materials consist of two or more phases. If one of these phases comprises fine particles that are dispersed throughout the material, the strength of the material often increases; this phenomenon is known as dispersion strengthening. 12. Partial dislocations – Dislocations whose Burgers vector is not an integer multiple of the lattice vector are called partial dislocations. 13. Extended dislocation – generally refers to the entire dislocation configuration in which a full dislocation splits into two incomplete dislocations, with a stacking fault situated between them. 14. Helical dislocation – A dislocation in which the atoms near the dislocation line are arranged in a spiral pattern is called a helical dislocation. 15. Peritectic transformation–In a binary phase diagram, a peritectic transformation is an isothermal transformation in which a crystallized solid phase reacts with the remaining liquid phase to form another solid phase. 16. Eutectic transformation – a transformation in which one liquid phase gives rise to two different solid phases. 17. Eutectic transformation – a transformation in which one solid phase decomposes to yield two other distinct solid phases. 18. Upward diffusion -- The process by which solute atoms diffuse from low concentrations to high concentrations is called upward diffusion. This indicates that the driving force for diffusion is the chemical potential gradient rather than the concentration gradient. 19. Interstitial diffusion – This is a mechanism of atomic diffusion. For interstitial atoms, due to their small size and presence in the gaps of the crystal lattice, they move by jumping from one interstitial site to an adjacent one during diffusion, thereby resulting in the movement of atoms. 20. Composition supercooling – the supercooling that occurs when the actual temperature in the liquid ahead of the interface is lower than the freezing temperature determined by the solute distribution. 21. First-order phase transition – a phase transition in which the chemical potentials of the new and old phases are equal, while their first partial derivatives are not equal. 22. Second-order phase transitions – From the perspective of phase transition thermodynamics, a phase transition is termed a second-order phase transition when the free energies (enthalpies) of the two phases before and after the transition are equal, as well as the first-order partial derivatives of the free energy (enthalpy); however, the second-order partial derivatives are not equal. Examples include magnetic transitions, order-disorder transitions, and normal-conducting-superconducting transitions. 23. Coherent phase boundary--If all atoms at the interface between two phases are in a one-to-one perfect matching relationship, that is, if the atoms at the interface lie at the nodes of both phase lattices and are shared by the adjacent crystals, such a phase boundary is called a coherent phase boundary. 24. Amplitude modulation decomposition – the process by which a supersaturated solid solution decomposes at a certain temperature into two phases with the same structure but different compositions. 25. Tempering brittleness – During the tempering process of quenched steel, generally as the tempering temperature increases, its plasticity and toughness improve. However, within certain ranges of tempering temperatures, a decrease in toughness occurs, a phenomenon known as tempering brittleness. Steel materials exhibit first and second types of temper brittleness. Their temperature ranges, influencing factors, and characteristics are different. 26. Recrystallization annealing – The so-called recrystallization annealing process generally refers to the process of heating a metal that has been cold-deformed above its recrystallization temperature, holding it at that temperature for a certain period of time, and then slowly cooling it to room temperature. 27. Tempered sorbite – a tempered microstructure formed after quenching and then heating to 400–600°C for tempering; it consists of equiaxed ferrite and fine granular (worm-like) cementite. 28. Ordered solid solution–A solid solution in which one component is dissolved in another, with the atoms of each component occupying their respective Bravais lattices, resulting in an arrangement in which the atoms of each component are ordered; the solute atoms are arranged in a fully ordered manner within the lattice. 29. Heterogeneous nucleation – the new phase nucleates preferentially at heterogeneous sites within the parent phase, that is, by attaching to impurities in the liquid phase or to foreign surfaces. 30. Martensitic transformation – The phase transformation process in which a high-hardness acicular structure is formed when steel heated to the austenitic state is rapidly quenched. 31. Bainite transformation -- The transformation of steel within the range below the pearlite transformation temperature and above the martensite transformation temperature (550°C–230°C) is referred to as bainite transformation. 32. Aging of aluminum alloys -- The phenomenon in which the strength and hardness of aluminum alloys increase significantly over time after quenching is known as aging, or the aging of aluminum alloys. 33. Thermally elastic martensite – The martensitic transformation induces elastic strain, and an applied elastic deformation can cause the martensitic transformation to reverse; such martensite is known as thermally elastic martensite. Or the martensitic phase transformation is coordinated by elastic deformation. This type of martensite is called thermally elastic martensite. 34. Köckendonk effect–reflects the diffusion mechanism of substituting atoms; two pure components form a diffusion couple, and during diffusion, the interface moves toward the side of the component with the faster diffusion rate. 35. Thermoelastic martensitic transformation–When the shape change during the martensitic transformation is accommodated through elastic deformation, it is called a thermoelastic martensitic transformation. 36. Amorphous solids – atoms are not arranged in a periodic pattern over long distances, have no fixed melting point, and are isotropic, etc. 37. Density--The percentage of the atomic volume in a crystal structure relative to the total volume. 38. Multiple slip – A phenomenon in which simultaneous slipping occurs when the resolved shear stresses exerted by an external force on several slip systems are equal and have all reached the critical resolved shear stress. 39. Undercooling -- During a phase transition, the transformation occurs after cooling to a temperature below the phase transition point; the difference between the equilibrium phase transition temperature and this actual transition temperature is referred to as undercooling. 40. Interstitial phase – When the ratio of the atomic radii of a non-metal (X) and a metal (M), rX/rM, is less than 0.59, a phase with a complex crystal structure is formed; this is commonly referred to as an interstitial compound. 106. High-angle grain boundaries – The grain boundaries between individual grains in polycrystalline materials are known as high-angle grain boundaries; that is, boundaries where the angular difference between adjacent grains is greater than 10º. 107. Low-angle grain boundaries--The phase difference between adjacent subgrains is less than 10º; such grain boundaries between subgrains are called low-angle grain boundaries, usually less than 2º, and can be classified into inclined grain boundaries, twisted grain boundaries, overlapping grain boundaries, etc. 108. Critical shear stress--the minimum shear stress required to activate a slip system ； It is a constant value that is related to the properties of the material itself, and is independent of the orientation of external forces.