Failure analysis of metal materials

Date：2022-03-09 14:55:30 Views：1289

The failure forms and causes of metal materials are closely related. The failure forms are the apparent characteristics of the material failure process, which can be observed in an appropriate way. The failure reason is the physical and chemical mechanism leading to component failure, which needs to be diagnosed and demonstrated through the investigation and research of failure process and the macro and micro analysis of failed parts. With the progress of society and the development of science and technology, metal products are more and more widely used in industry, agriculture, science and technology and people's life. Therefore, the quality of metal materials should be paid more attention.

Failure mode:Improper design, material defects, casting defects, welding defects, heat treatment defects.

The failure mechanism of metal materials is divided into:Fracture failure; Deformation failure; Wear failure; Corrosion failure and other four types.

(1) Deformation failure

The so-called deformation is usually the phenomenon that the shape and size of mechanical components change under the action of external force. Microscopically, it refers to the distortion of the lattice of metal materials under the action of external force. If the external force is eliminated and the lattice distortion is also eliminated, this deformation is elastic deformation; If the external force is eliminated and the lattice cannot be restored to its original state, that is, when the distortion cannot be eliminated, this deformation is called plastic deformation. Deformation failure refers to the excessive deformation of mechanical components in the process of use, that is, the amount of deformation when they can not meet the original design requirements. Generally, deformation failure is divided into elastic deformation failure and plastic deformation failure. Elastic deformation failure will leave no damage trace on the surface of mechanical components, only the elastic modulus of metal materials will change, which is independent of the size and shape of mechanical components; Plastic deformation failure will lead to the surface damage of mechanical components, and the shape and size of mechanical components will change.

(2) Wear failure

Wear is a phenomenon of continuous damage caused by the gradual separation of wear debris on the surface when the object moves relatively under the action of friction.

Wear failure refers to the failure of mechanical parts to reach the original design efficiency due to the occurrence of wear phenomenon, that is, they can not reach the original design level.

The types of wear failure are: ① adhesive wear failure; ② Abrasive wear failure; ③ Corrosion wear failure; ④ Deformation and wear failure;⑤ Surface fatigue wear failure; ⑥ Impact wear failure; ⑦ Micro vibration, wear and failure, etc.

(3) Fracture failure

Fracture refers to the phenomenon that metal or alloy materials or mechanical products are divided into several parts under the action of force. It is a dynamic process of crack initiation and propagation. Fracture failure refers to the failure of mechanical equipment products due to the fracture of mechanical components.

The fracture failure types are as follows: ① cleavage fracture failure; ② Dimple fracture failure; ③ Quasi cleavage fracture failure; ④ Fatigue fracture failure; ⑤ Creep fracture failure; ⑥ Stress corrosion fracture failure; ⑦ Intergranular fracture failure; ⑧ Liquid or solid metal embrittlementSexual fracture failure; ⑨ Hydrogen embrittlement fracture failure; ⑩ Slip separation failure, etc.

(4) Corrosion failure

Corrosion refers to the damage phenomenon caused by chemical or electrochemical reaction on the surface of metal or alloy materials.

Although metal corrosion plays a beneficial role in pickling, chemical power supply, electrochemical machining, metallographic etching and so on, it has caused serious losses in the national economy. Because corrosion is the phenomenon that mechanical components lose their original design function, it is called corrosion failure. The types of corrosion failure are: ① direct chemical corrosion failure; ② Electrochemical corrosion failure; ③ Pitting corrosion failure; ④ Local corrosion failure; ⑤ Intergranular corrosion failure; ⑥ Selective corrosion failure; ⑦ Crevice corrosion failure; ⑧ Biological corrosion failure; ⑨ Wear corrosion failure; ⑩ Hydrogen damage failure; Stress corrosion failure, etc.

Common means

Microstructure analysis of metal materials:

Metallographic analysis

X-ray phase structure analysis

Surface residual stress analysis

Grain size of metal materials

Composition analysis:Direct reading spectrometer, X-ray photoelectron spectrometer (XPS), Auger electron spectrometer (AES), etc

Phase analysis:X-ray diffractometer (XRD)

Residual stress analysis:X-ray stress tester

Mechanical property analysis:Universal testing machine, impact testing machine, hardness testing machine, etc

Failure analysis method of metal materials

In order to obtain better analysis results, failure analysis should not only accurately understand the product use background, but also be supplemented by a series of other inspection methods, such as nondestructive testing, mechanical property test, metallographic inspection, chemical analysis, X-ray analysis, fracture toughness test, electronic energy spectrum analysis, simulation test, etc. Finally, the results and data of the above analysis and test are comprehensively analyzed, and the improvement measures are put forward, and the failure analysis report is written.

(1) Collection of original data, all experiences of components before service, service history of components and site conditions at the time of failure, etc. In addition, samples with analytical value should be selected from scattered failure debris or associated samples.

(2) Selection and preservation of failure samples. Failure samples are the first-hand data of failure analysis and the basis of failure analysis. After failure, they should be collected carefully, properly preserved and remember to avoid pollution.

(3) Failure sample analysis in failure accidents, fracture, crack or other poor appearance are generally formed. Therefore, the analysis of bad parts is the most important analysis method of failure analysis. Fracture analysis includes macro fracture observation and micro fracture analysis.

(4) Other inspection and analysis in order to better obtain the analysis results, in addition to the observation and analysis of key parts, chemical, mechanical, physical and other experimental analysis must also be carried out. Chemical analysis includes routine, local, surface and micro area chemical analysis; Metallographic examination; Structural analysis; Simulation test, such as the simulation of the influence of environmental factors such as temperature and medium concentration on failure.

(5) When the comprehensive analysis failure analysis is carried out to a certain stage, it is necessary to conduct a comprehensive analysis and Research on the results and basic test data obtained from various inspections and tests.