Essential basic knowledge for materials science

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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 an alloy is 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 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, preventing it from transitioning into a stable phase. 4. Coordination number: The number of nearest and equidistant atoms surrounding any 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 in which distortion-free, equiaxed new grains gradually replace deformed grains.) 6. Pseudo-eutectic: Under non-equilibrium solidification conditions, certain alloys with hypoeutectic or hypereutectic compositions can also exhibit a completely eutectic structure. This eutectic structure formed in alloys with non-eutectic compositions is known as pseudo-eutectic. 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. Over-aging: After solution treatment, GP zones, θ”, θ’, and θ will successively precipitate during the heating and holding process of aluminum alloys. At the start of the heat treatment phase, as the treatment time increases, the hardness and strength of the material rise. However, if the treatment time is too long, θ’ phases will form, 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 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 vectors are called partial dislocations. 13. Extended dislocation: Generally refers to the overall dislocation configuration in which a full dislocation splits into two partial dislocations, with a stacking fault situated between them. 14. Screw dislocation: A dislocation in which the atoms near the dislocation line are arranged in a helical pattern is called a screw dislocation. 15. Peritectic transformation: In a binary phase diagram, a peritectic transformation is an isothermal transformation in which the 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. Uphill diffusion: The process by which solute atoms diffuse from areas of low concentration to areas of high concentration is called uphill 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, during diffusion, click to download eighteen essential software applications. Interstitial atoms jump from one interstitial site to another adjacent site, 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 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 their first-order partial derivatives of free energy (enthalpy); however, their 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, 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. Temper brittleness: During the tempering process of quenched steel, generally speaking, its plasticity and toughness increase as the tempering temperature rises. However, within a specific range of tempering temperatures, there is a phenomenon where toughness actually decreases; this is known as temper brittleness. For steel materials, there are Type I and Type II 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 cold-deformed metal above its recrystallization temperature, holding it at that temperature for a certain period of time, and then slowly cooling it down to room temperature. 27. Tempered sorbite: The microstructure that forms in quenched steel after it is tempered at temperatures of 400–600°C; it consists of equiaxed ferrite and fine granular (worm-like) cementite. 28. Ordered solid solution: When one component dissolves in another, the atoms of each component occupy their respective Bravais lattices, resulting in a solid solution in which the atoms of each component are arranged in an orderly manner; the solute atoms are arranged in a completely ordered structure 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 aging of aluminum alloys. 33. Thermelastic martensite: The martensitic transformation induces elastic strain, and an applied elastic deformation can cause the martensitic transformation to reverse; such martensite is known as thermelastic 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 substituent 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. Thermelastic martensitic transformation: When the shape change during the martensitic transformation is accommodated through elastic deformation, it is called thermelastic martensitic transformation. 36. Amorphous solids: Atoms do not have a long-range periodic arrangement; they have no definite melting point and are isotropic, etc. 37. Density: The percentage of the atomic volume within a crystal structure relative to the total volume. 38. Multiple sliding: When the shear stresses exerted by external forces on several slip systems are equal and all reach the critical shear stress at the same time, multiple simultaneous slippages occur. 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. A interstitial phase is formed when the ratio of the atomic radii of the non-metal (X) to that of the metal (M), rX/rM, is 0.59 or greater; such phases have complex crystal structures and are commonly referred to as interstitial compounds. 106. High-angle grain boundaries: The grain boundaries between individual grains in polycrystalline materials are referred to 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 angular difference between adjacent subgrains is less than 10º. Such grain boundaries between subgrains are referred to as low-angle grain boundaries; typically, this angle is less than 2º. They can be classified into tilt boundaries, twist boundaries, coincidence boundaries, etc. 108. Critical resolved shear stress: The minimum resolved shear stress required to activate a slip system ； 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.