Fracture analysis method of metal materials for quality identification and testing of electronic products

Date：2022-01-14 16:01:14Views：924

Fracture analysis is a subject of studying metal fracture surface and an integral part of fracture subject. A pair of mutually matched fracture surfaces and their appearance obtained after metal fracture are called fracture. Metal fracture is a common identification item in quality identification. Through the analysis of fracture, we can help us make a comprehensive analysis of the quality of electronic products. So what are the fracture analysis methods for testing metal materials?

Fracture composition analysis:

The composition analysis of fracture is very important for fracture analysis, especially the fracture caused by corrosion, inclusions, non-metallic oxides and other factors. The composition analysis at the fracture is generally quantitative analysis, which usually refers to the analysis and characterization of the average chemical composition, micro area composition, surface and line distribution of elements, the change of elements along the depth, the chemical element ratio of inclusions and other defects on the fracture surface. Many experimental equipment are used for this analysis, such as ion probe, Auger electron spectrometer, electron probe, X-ray energy spectrometer, X-ray spectrometer, etc.

Material fracture structure analysis:

The fracture surface structure analysis mainly includes the crystal plane index of the fracture surface, the structure and residual stress of the micro area on the fracture surface. The experimental equipment used in this analysis mainly includes X-ray diffractometer. The main contents of the analysis are the determination of lattice constant, phase analysis and stress measurement.

Basis of fracture analysis:

1、Color and color of fracture

When observing the luster and color of fracture surface, mainly observe whether there is oxidation color, corrosion trace, special color and other colors of inclusions; Red rust, yellow rust or rust of other colors: whether there is dark gray metallic luster, bluish color (or dark purple, purple black metallic luster), etc.

The location of fatigue source can be determined according to the brightness of fatigue fracture. If it is not corrosion fatigue, the source area is smooth.

2. Pattern on fracture

Sometimes beach stripes can be seen on the macro fracture surface of fatigue fracture, and fatigue striae can be seen on the micro fracture surface. Brittle fracture has cleavage characteristics. There are glittering small facets or herringbone and mountain stripes on the macro, while there are river stripes on the micro. Tongue pattern, etc. Ductile fracture has fibrous fracture in macro and dimples or patterns in micro.

3. Roughness on fracture surface

The surface of the fracture is actually composed of many small sections, whose size and height difference determine the roughness of the fracture. Different materials and fracture modes have different fracture roughness.

Generally speaking, the shear lip of ductile fracture belonging to shear type is relatively smooth; The fiber area of positive fracture type is rough. The crystalline fracture formed by cleavage fracture belonging to brittle fracture is rough, while the porcelain fracture formed by quasi cleavage fracture is smooth. The roughness of fatigue fracture is related to crack propagation. The faster the propagation rate is, the rougher the fracture is.

4. Angle of intersection between fracture and large normal stress

The tensile fracture of ductile materials is generally cup-shaped or 45 ° cut-off, and its plastic deformation is in the form of necking. That is, the intersection angle of fracture and tensile axial large normal stress is 45 °.

The tensile fracture of brittle materials is generally perpendicular to the large tensile normal stress, the fracture surface is flush, and the fracture edge usually has no shear "lip". There is no necking near the fracture. The torsional fracture of ductile material is cut-off. The intersection angle between fracture and torsional normal stress is also 45 °.

The torsional fracture of brittle materials is in the shape of twist, which is separated in the direction perpendicular to the large principal stress under the action of pure torque.

5. Metallurgical defects on fracture

Inclusions, delaminations, coarse grains, self spots, white spots, oxide films, porosity, pores, tears, etc. can often be found on the fracture surface of failed parts through macro or micro observation.

In short, we can study the basic problems of material fracture through the morphological analysis of fracture: such as fracture cause, fracture property, fracture mode, fracture mechanism, fracture toughness, stress state of fracture process and crack growth rate. If the influence of metallurgical and environmental factors on the fracture process is required to be deeply studied, the micro area composition analysis, main body analysis, crystallography analysis and fracture stress and strain analysis of the fracture surface are usually carried out.