What are the ways in which metals can be strengthened?

<>1. Solution strengthening: The solute atoms integrated into the solid solution cause lattice distortion, which increases the resistance of dislocation motion and makes it difficult to slip, so that the strength and hardness of the alloy solid solution increase.

2. Fine grain strengthening: refers to the method of improving the mechanical properties of metal materials by refining the grains, and the industry will improve the strength of the materials by refining the grains.

3. Dislocation strengthening: It is one of the most effective strengthening methods in metal materials. In metals that are prone to cross-slip, the dislocations will be arranged into three-dimensional substructures after the strain exceeds a certain level, and when the dislocation walls of these substructures are loosely tangled, they are called"Cellular structure"。

4. Work hardening: the phenomenon that the strength and hardness of metal materials increase when they are plastically deformed below the recrystallization temperature, while the plasticity and toughness decrease.

5. Second phase strengthening: It means that when the second phase is evenly distributed in the matrix phase with fine and diffuse particles, it will have a significant strengthening effect.

6. Diffusion strengthening: refers to a means of strengthening a material by adding hard particles to a homogeneous material.

The first is to improve the interatomic bonding force of the alloy, improve its theoretical strength, and make complete crystals without defects, such as whiskers. The strength of the whiskers of iron is known to be close to the theoretical value, and it can be assumed that this is because there are no dislocations in the whiskers, or only a small number of dislocations that cannot proliferate during deformation. This method of strengthening is only applied in several special metals.

Another way of strengthening is to introduce a large number of crystal defects into the crystal, such as dislocations, point defects, heterogeneous atoms, grain boundaries, etc., which hinder the movement of dislocations and will also significantly improve the strength of the metal. This has proven to be the most effective way to increase the strength of metals.

For engineering materials, it is generally through the comprehensive strengthening effect to achieve better comprehensive performance. The specific methods include solution strengthening, deformation strengthening, precipitation strengthening and diffusion strengthening, fine grain strengthening, preferential orientation strengthening, complex phase strengthening, fiber strengthening and phase transformation strengthening, etc., which often coexist.

Answer: The strength of metal materials can be improved through the following 5 ways: 1) Carry out heat treatment process, heat treatment according to the required performance and structure, quenching, tempering, and tempering.

fire, etc. Automobile parts, not only to retain the toughness of the core, but also to change the surface structure to improve the hardness is to use surface high-frequency quenching or carburizing, cyanide and other heat treatment processes to improve.

2) Shot peening on the surface can also improve the strength. The high-speed projectile flow is sprayed to the surface of the spring, so that the surface of the spring is plastically deformed, and a certain thickness of the reinforcing layer is formed, and a higher residual stress is formed in the reinforcing layer, due to the existence of compressive stress on the surface of the spring, when the spring is loaded, a part of the anti-stress can be offset, so as to improve the fatigue strength of the spring.

3) Grain boundary strengthening. Controlled rolling and controlled cooling are carried out to obtain finer grains. For example, the crawler of the tractor, the jaw plate of the crusher and the switch of the railway are strengthened by 4) dislocation strengthening by using work hardening to improve their hardness and wear resistance.

For example, some single-crystal materials have higher strength, mainly because there are fewer dislocations in them.

Strength can also be improved by reducing dislocations.

5) The strength can be improved by precipitating some compounds through deformation and aging. For example, after the alloy is quenched to form a supersaturated solid solution, it is placed at room temperature or slightly higher appropriate temperature for a long time to improve the hardness and strength of the alloy.

1.Heat treatment: use quenching + ignition to change the shape of steel carbide and refine grain 2Cold work hardening: It belongs to deformation and strengthening to change the original arrangement shape and dislocation organization 3The content of the chemical increases the C or alloy content, and the carbon effect strengthens the element with the Fe or alloy carbide.

There are many ways to improve strength, and typical processes include diffusion strengthening, co-lattice strengthening and fine-grained strengthening.

1. Carry out heat treatment process, heat treatment, quenching, tempering, normalizing, etc. according to the required performance and structure.

2) Shot peening on the surface can also improve the strength.

3. Controlled rolling and controlled cooling are carried out to obtain finer grains, which are more Hall-Page formula.

4. There are also some single-crystal materials with higher strength, mainly because there are fewer dislocations in them, so reducing dislocations can also improve strength.

5) The strength can be improved by precipitating some compounds through deformation and aging.

Mainly: fine-grained strengthening, solution strengthening, second-phase strengthening, and work hardening.

Details:

Fine-grained strengthening

By refining the grains.

The method of improving the mechanical properties of metal materials is called fine grain strengthening, and the strength of the material will be improved by refining the grains in industry.

The method of defining the improvement of the mechanical properties of metal materials by refining the grains is called fine grain strengthening, and the strength of the material will be improved by refining the grains in the industry.

Usually metals are polycrystals composed of many grains, and the size of the grains can be expressed in terms of the number of grains per unit volume, and the greater the number, the finer the grains. Experiments have shown that fine-grained metals have higher strength, hardness, plasticity and toughness than coarse-grained metals at room temperature. This is because the plastic deformation of fine grains can be dispersed in more grains due to external force, and the plastic deformation is more uniform and the stress concentration is smaller. In addition, the finer the grain, the larger the grain boundary area, and the more tortuous the grain boundary, which is not conducive to crack propagation.

Therefore, the method of refining the grain to improve the strength of the material is called fine grain strengthening.

The finer the grains, the smaller the number of dislocations (n) in the dislocation cluster, and the smaller the stress concentration according to =n 0, so the higher the strength of the material.

According to the Hall-odd relation, the smaller the average value of the grains (d), the higher the yield strength of the material.

Solution Strengthened:

Basics. Because the solute atoms enter the gap or junction of the solvent lattice, the crystal lattice is distorted, and the hardness and strength of the solid solution increase, which is called the phenomenon of solution strengthening.

The solute atoms integrated into the solid solution cause lattice distortion, which increases the resistance of dislocation motion and makes it difficult to carry out the slip, so that the strength and hardness of the alloy solid solution increase. This phenomenon of strengthening metals by incorporating a certain solute element to form a solid solution is called solution strengthening. When the concentration of solute atoms is appropriate, the strength and hardness of the material can be increased, while its toughness and plasticity are reduced.

Second phase reinforcement :

Basics. Compared with single-phase alloys, complex phase alloys have a second phase in addition to the matrix phase. When the second phase is evenly distributed in the matrix phase with fine dispersed particles, it will produce a significant strengthening effect, which is called second phase strengthening. The main reason for the second phase strengthening is the interaction between them and the dislocation, which hinders the dislocation movement and improves the deformation resistance of the alloy.

Work hardening:

Work hardening (English: work hardening) refers to the phenomenon that with the increase of cold deformation, the strength and hardness of metal materials have increased, but the plasticity and toughness have decreased, also known as cold work hardening. The degree of work hardening is usually expressed as the ratio of the microhardness of the surface layer after machining to the surface layer before machining and the depth of the hardened layer.

The reinforcement mechanism is as follows:

Solution strengthening: that is, strengthening by forming a solid solution, that is, alloying fine-grained strengthening: the grain is fine, the grain boundary increases, and the dislocation slip is prevented.

Work hardening: Increases dislocation and substructural refinement.

Diffusion intensification: The second phase is strengthened into a diffusion distribution.

Precipitation hardening: precipitation of the second phase intensifies.

Solution strengthening: The process technology of obtaining different mechanical properties indexes of the carbon content in the austenite zone under different quenching and tempering temperatures through heat treatment is one of the examples.

Precipitation, precipitation, aging) diffusion strengthening: After the plastic processing of aluminum alloy is completed, aging treatment is carried out in order to obtain appropriate machining performance.

Phase change strengthening: The normalizing treatment of the metal makes the temperature change of the metal up and down the phase change point, so that the internal structure of the metal is repeatedly dissolved and recrystallized to obtain a refined grain structure, and the strength of the material is improved.

Fine-grained grain boundary strengthening: In the same example as above, different heat treatment methods are used to improve the grain refinement and recrystallize the impurities enriched on the grain boundary during the recrystallization process, so as to maintain the grain boundary strength and reduce the influence of harmful elements.

Second phase composite strengthening: carburizing treatment.

Laser surface modification is used to inject the chemical composition of the second-phase metal into the metal surface for strengthening.

1.Strength of metallic materials.

Metals and alloys are mainly crystals that are bonded by metal bonding. The theoretical tensile strength of a perfect metal refers to the physical quantity of the material (diatomic interaction model) related to the binding bond energy (binding force and binding energy), and its influencing factors can be considered from this model (such as temperature, bond energy, atomic spacing, lattice bonding, atomic size, electronegative electron concentration, etc., which should be available in metal materials);

Because the actual metal and alloy materials are not perfect crystals, there are point, line, surface defects (vacancies, dislocations, grain boundaries and phase boundaries, etc.) or distortion, so the strength of the material is much lower than its theoretical strength. Consider material strengthening from the perspective of defects. The most widely used yield strength in engineering and application, which occurs closely related to the plastic deformation of the material, can be analyzed from the metal slip and its mechanism, (such as the dislocation mechanism, etc., the way to hinder the movement of the dislocation is the strengthening mechanism, such as fine grain strengthening, aging, solid solution, deformation strengthening).

2.How steel is strengthened:

Steel generally refers to a class of ferroalloys with a carbon content less than or equal to in the iron-carbon phase diagram; The reinforcement method can be combined with theory to generalize. In the problems related to the postgraduate entrance examination, steel with martensitic phase transformation can be used as an example.

Combination of chemical composition, strengthening mechanism - solution strengthening, phase transformation strengthening, aging strengthening, austenite fine-grain strengthening, description.

3.The ways to improve the strength are summarized according to various influencing factors (heat treatment, alloy composition adjustment, deformation hardening......）

1. Aging strengthening: It refers to the precipitation of alloying elements in high temperature in some form under normal temperature or heating conditions after the solid solution of alloying elements, forming diffusely distributed hard points, causing resistance to dislocation cutting, increasing strength and reducing toughness.

2. Solution strengthening: the presence of alloying elements in the matrix metal lattice causes the crystal lattice to be distorted, and the dislocation movement resistance increases. Usually the strength also increases and the toughness decreases.

3. Fine grain strengthening is also called grain boundary strengthening: finer grains can be obtained through deformation and recrystallization, so that the strength and toughness can be improved at the same time.

4. Deformation strengthening: With the increase of plastic deformation, the rheological strength of the metal also increases, which is called deformation strengthening or work hardening.

5. Diffusion strengthening: The method of strengthening the material through the distribution of fine diffuse second-phase fine particles in the matrix is called diffusion strengthening.

6. Fiber strengthening: The method of strengthening the matrix material by combining high-strength fibers with appropriate matrix materials is called fiber strengthening.

7. Irradiation strengthening: Because the metal produces vacancies or gap-filling atoms under strong ray conditions, the defects hinder the movement of dislocations, thus producing a strengthening effect.