Application of metallographic analysis techniques in material failure analysis

At the end of the nineteenth century, the term metallographic acquired a new meaning and became inextricably linked to the microscope tissue, and the metallographic microscope became an important tool
for studying the internal structure of metals.

Metallographic definition metallographic technology: sample preparation, microscope use, tissue identification, quantitative measurement and recording and other experimental techniques metallographic testing: the process of qualitative identification and quantitative measurement of the metallographic structure of the specimen materialographic analysis: after a wide range of metallographic tests of a certain phenomenon in material research and a certain event in quality control, the metallographic principle is used to conduct a comprehensive analysis and draw scientific conclusions The study of metallographic role multi-heat treatment process: 1 The heat treatment of steel is based on the phase change of steel in the heating and cooling process, and metallographic technology is an important test means of phase change research2 Reveals the internal relationship between material composition, structure and performanceNew material development and development quality control failure analysis Accident analysis Failure analysis and purpose, role and significance Failure analysis is a comprehensive analysis of the macroscopic and microscopic characteristics of the failure parts, materials, processes, physical and chemical properties, specified functions, stress states and environmental factors, etc.
, to determine the failure mode and cause, Technical and management activities
to propose preventive and corrective actions.

The purpose of failure analysis is to determine the object of failure analysis, judge the failure mode of the failure part, find out the cause of failure, propose improvement or preventive measures, prevent the recurrence of similar failure events, and ensure the safety
of the use of equipment.

The role and significance of failure analysis The main form of mechanical structure failure, deformation failure, fracture failure, corrosion failure, wear failure, and the advantages of failure analysis using optical microscope: the damage characteristics and locations of the failure parts can be further observed and analyzed under the stereo microscope, and the macroscopic characteristics of the failure parts (fracture origin and expansion direction, source area morphology, corrosion and wear depth and color, damage traces and characteristics, etc.
) can be used to provide
。
Metallographic inspection is an important part of failure analysis, including macroscopic inspection and microscopic examination using optical microscopy to check and analyze
the low-power microstructure, high-power microstructure, inclusions and grain size of the failed parts.

Low magnification acid erosion test: check the internal segregation, looseness, inclusion, pores and other defects of the material; Defects such as surface folding, sand inclusion, and scarring; Internal cracks, white spots, overburning, etc.
; Forging streamlines, welding quality, grinding burns, etc
.

Microscopic tissue analysis: determine whether the heat treatment or cold processing process of the failed parts is normal
.

Analyze corrosion, wear, oxidation and work hardening of failed parts under working conditions
.

1.
Simple and convenient operation, high detection efficiency 2.
Low sample preparation requirements 3.
Image mode of visible light 4.
Can meet the analysis requirements of many industrial and material samples 5.
Low cost of use, simple maintenance, less space occupancy6.
Relatively low procurement cost Light microscope identification ability The identification ability of the microscope is mainly determined by the objective lens, and the identification ability of the objective lens can be divided into planar and vertical identification ability
.

Plane identification ability: that is, the resolution of the objective, refers to the ability
of the objective to clearly distinguish the two objects in the microstructure from the minimum distance d.

d is the resolution ability (discrimination rate)
of the objective lens.

The smaller the minimum distance d between two objects, the higher
the resolution of the objective.

d=λ/2NA vertical identification ability: that is, the vertical resolution of the objective is also known as depth of field, which refers to the ability of the objective to make a clear image in terms of depth of field, that is, the maximum depth of field that can be clearly imaged vertically
, and the greater the depth, the greater the vertical identification rate.

Depth of field h is: h = n / (NA) M (0.
15 ~ 0.
30) It can be seen that the vertical identification rate of the objective lens is inversely proportional to the numerical aperture and magnification, to improve the depth of field, it is best to use an objective lens with a small numerical aperture or reduce the aperture diaphragm to reduce the working aperture of the objective, but this will reduce the resolution ability
of the objective.

Therefore, the reconciliation of this contradiction can only depend on the specific circumstances
.