For studying materials, this is essential foundational knowledge

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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 alloys are formed from two components, A and B, in addition to solid solutions based on A or B, new phases with a crystal structure different from that of both A and B may also be formed. Since their positions on the binary phase diagram are always in the middle, these phases are commonly referred to as intermediate phases. 3. Metastable phase: A metastable phase refers to a phase that cannot exist stably from a thermodynamic perspective, but temporarily remains stable during rapid cooling or heating due to thermodynamic barriers or kinetic factors, preventing it from transforming into a stable phase. 4. Coordination number: The number of nearest-neighbor atoms at equal distances from any given atom in a crystal structure. 5. Recrystallization: When a metal that has been cold-deformed is heated to a certain temperature, new grains free from distortions form within the originally deformed structure. The properties of the metal change significantly as it returns to its state before deformation; this process is known as recrystallization. (Refers to the process by which distortion-free equiaxed new grains gradually replace the deformed grains.) 6. Pseudeutectic: Under conditions of non-equilibrium solidification, certain alloys with sub-eutectic or hyper-eutectic compositions can also develop a fully eutectic structure; such an eutectic structure formed in alloys with non-eutectic compositions is known as a pseudeutectic structure. 7. Cross-slip: When the movement of a 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. Ageing: After solution treatment, during the heating and holding process, GP zones, θ”, θ’, and θ will precipitate successively in the aluminum alloy. 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: After cold plastic deformation, metals experience an increase in strength and hardness, along with a decrease in ductility and toughness; 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 are composed of two or more phases; if one of these phases consists of fine particles that are dispersed throughout the material, the strength of this material tends to increase, a phenomenon known as dispersion strengthening. 12. Partial dislocation: A dislocation whose Burgers vector is not an integer multiple of the lattice vector is called a partial dislocation. 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 areas of low concentration to areas of high concentration 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 one of the mechanisms of atomic diffusion. For interstitial atoms, due to their small size, they reside in the interstices of the crystal lattice. During diffusion, click to download eighteen essential software programs. Interstitial atoms jump from one interstitial site to an adjacent one, resulting in the movement of atoms. 20. Composition supercooling: The supercooling that occurs when the actual temperature of the liquid at the front edge of the solidification front 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 old and new phases are equal, but the first partial derivatives of their chemical potentials are not equal. 22. Second-order phase transition: From the perspective of phase transition thermodynamics, a phase transition is considered a second-order phase transition when the free energy (enthalpy) of the two phases before and after the transition is equal, and the first derivatives of the free energy (enthalpy) are equal; however, their second derivatives are not equal. Examples include magnetic transitions, order-disorder transitions, and normal-conducting to 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, then 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 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 in quenched steel after it is heated and tempered at temperatures ranging from 400–600°C. It consists of equiaxed ferrite and fine granular (worm-like) cementite. 28. Ordered solid solution: When one component dissolves in another, a solid solution is formed in which the atoms of each component occupy their respective Bravais lattices, resulting in an arrangement in which the atoms of each component are ordered; the solute atoms are arranged in a completely 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 needle-like and plate-like 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 quenched aluminum alloys significantly increase over time 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. Click to download 18 essential software programs. Or the martensitic phase transformation is coordinated by elastic deformation. This type of martensite is called thermoelastic martensite. 34. The Kirkendall effect reflects the diffusion mechanism of substituting atoms. When two pure components form a diffusion couple, during the diffusion process, 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 materials: atoms are not arranged in a periodic pattern over long distances; they have no fixed melting point and are isotropic, among other characteristics. 37. Density: The percentage of the atomic volume within a crystal structure relative to its total volume. 38. Multiple slip: When the resolved shear stresses of an external force on several slip systems are equal and all reach the critical resolved shear stress simultaneously, the phenomenon of simultaneous slip occurs. 39. Supercooling: During a phase transformation, the transformation occurs when the temperature is cooled below a certain value corresponding to the phase transition point. The difference between the equilibrium phase transition temperature and this actual transformation temperature is known as supercooling. 40. When the ratio of the atomic radii of the non-metal (X) to that of the metal (M), i.e., rX/rM, is 0.59 or greater, a phase with a complex crystal structure is formed, which 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 10°. 107. Small-angle grain boundaries: The phase difference between adjacent subgrains is less than 10°; such grain boundaries between subgrains are called small-angle grain boundaries, usually less than 2°. They can be classified into tilted grain boundaries, twisted grain boundaries, overlapping grain boundaries, etc. 108. Critical shear stress: The minimum shear stress required for a slip system to activate ； It is a constant value that depends on the properties of the material itself and has nothing to do with the orientation of external forces.