Metal defects: from atomic to volumetric level

Metals, despite the seeming perfection of their crystal structure, contain many “flaws” — defects that affect their properties and performance characteristics. Understanding the nature and types of defects is key to improving the quality of products, and PZPS pays special attention to this at every stage of production.

The concept of a defect in metals

A defect in metals is any deviation from the ideal periodicity crystal lattice or a violation of the uniformity of the structure. Such disorders can be natural (for example, during radiation exposure) and technological (plastic deformation, contamination with impurities) that occur during the production, processing or operation of metal products. Defects can occur at various levels — from atomic to volumetric — and have a significant impact on the physical, chemical and mechanical properties of the metal.

Defects in metals are classified according to their level of manifestation:

1. Atomic level. Point defects are disorders localized within one or more atoms. These include vacancies, interstitial atoms, and impurities.
2. Crystal lattice level. Linear defects — these are disorders that spread in one dimension, for example, dislocations. Surface defects are disorders located in two dimensions, for example, grain boundaries or phase boundaries.
3. Volume level. Volume defects — these are violations that take up a significant amount of material. These include cracks, pores, and inclusions.

This classification helps to systematize various types of defects and understand their impact on the properties of metals, depending on the scale of their occurrence.

Defects at the atomic level

Point defects are microstructural changes in a metal that directly affect its macroscopic properties. These include:

• Vacances — absence of atoms in the nodes of the crystal lattice.
  
  • Reasons: thermal vibrations of atoms, radiation or impurities.
• Interstitial atoms — atoms located between the lattice nodes. They create local stresses and prevent dislocations from sliding.
  
  • Reasons: plastic deformation, radiation, or diffusion of atoms through the metal surface.
• Impurity — atoms of other elements embedded in the crystal lattice. They can both reduce and improve the quality of the material, for example, improve corrosion resistance, strength and other properties. There are:
  
  • intentional are formed as a result of alloying steel;
  • random appear due to contamination of the material.

Point defects have a significant impact on the properties of steels and alloys.

The effect of point defects:

• Mechanical properties: defects at the atomic level prevent the movement of dislocations, changing the strength and plasticity of the metal.
• Electrical properties: point defects change the concentration of charge carriers, which affects the electrical conductivity of steel or alloy.
• Thermal properties: defects within one or more atoms disrupt their orderly movement, which can lead to a decrease in thermal conductivity.

Analysis methods:

• X-ray and neutron diffraction make it possible to determine the structure of the crystal lattice and identify the presence of defects.
• Infrared and combinational spectroscopy help analyze atomic vibrations in the crystal lattice.
• Nuclear magnetic resonance (NMR) allows you to analyze the local structure and dynamics of atoms in metal.

Defects at the level of the crystal lattice

Crystal defects are violations of the ideal periodicity and correct arrangement of particles in crystals. They affect the plasticity, strength and reliability of metals. They can be linear and superficial.

• Dislocations — these are lines along which the correct location of the crystal lattice is disturbed. Refer to linear defects. They can be marginal, helical or mixed. Dislocations play an important role in the processes of plastic deformation and hardening of materials.

• Grain boundaries — these are areas between grains where the crystal lattice changes its orientation. They are like linear and superficial defects. They can affect the mechanical (strength, hardness and plasticity) and physical (electrical and thermal conductivity) properties of the material.
• Phase boundaries are interfaces between different phases in the material, for example, between solid and liquid states or between various crystalline modifications. Refer to superficial defects. They affect properties such as strength, plasticity and corrosion resistance.

The effect of crystal lattice defects on the mechanical and physical properties of metals:

• Strength and plasticity — linear defects change the material's ability to recover from deformation. The more defects, the higher the strength and the lower the plasticity of the metal.
• Electrical and thermal conductivity — lattice defects can change the electronic structure of the metal and its ability to conduct heat and electricity.
• Corrosion resistance — defects can change the surface of the metal, thereby increasing or decreasing its corrosion resistance.

Research methods:

• X-ray diffraction analysis (SAR) determines the structure of the crystal lattice and reveals linear defects.
• Electron microscopy It allows you to obtain high-resolution images of the crystal lattice and identify any defects in it.
• Electron diffraction makes it possible to study the structure of the crystal lattice and identify grain dislocations and boundaries.

Volumetric defects

Cracks, pores and other heterogeneities in the structure have the greatest impact on the physical and mechanical properties of the material.

Volumetric defects include:

• Cracks — ruptures in the material may be superficial and internal. They occur due to fatigue loads, residual, reactive, thermal stresses, corrosion damage and other factors. They lead to a decrease in the strength and durability of the material.
• Pores — voids in the material resulting from gas and non-metallic inclusions and other factors. They reduce the density, strength and other mechanical properties of the material and can act as corrosion centers.
• Inclusions — foreign particles that enter the material during its manufacture or use. They can be metallic or non-metallic. They reduce the physical and mechanical properties of steels and alloys.

The effect of volumetric defects on the performance properties of metals:

• Decrease in strength and stiffness by creating local weakening in the material structure.
• Reducing fatigue strength, which leads to the destruction of the metal under cyclic loads in places where pores and cracks exist.
• Reducing stiffness, which contributes to the deformation of the material under load.

Control methods:

• Visual inspection and microscopy make it possible to detect surface cracks and other visible defects.
• Ultrasonic flaw detection — is based on the use of ultrasonic waves to detect internal defects in the material.
• Magnetic flaw detection It is used to detect defects in ferromagnetic materials using magnetic fields.

The choice of a method for studying and evaluating volumetric defects depends on the type of material, its structure and the requirements for the accuracy and reliability of the results.

Methods for preventing metal defects

Material quality control:

• Input control incoming materials for compliance with standards and specifications. It includes analysis of chemical composition, mechanical properties, microstructure and the presence of defects.
• Sort and exclude materials with identified defects or inappropriate characteristics.

Process control:

• Development and compliance with technological regulations and processing parameters (temperature, pressure, time, etc.) in order to minimize the likelihood of defects.
• Continuous monitoring and prompt adjustment technological processes and parameters to prevent defects.
• Use of high-tech modern equipment, which ensures high accuracy and repeatability of operations.

High-quality alloys produced by PZPS

Thanks to high-precision modern equipment, its own laboratory and strict control of technological parameters at each stage of production, PZPS produces materials with maximum uniformity and a minimum number of defects. Here you can buy cold-rolled strip from:

• precision alloys for elastic elements, for example, 17HNGT et 40KHNM;
• corrosion-resistant steels 12X18H10T, 20X13 and others;
• electrical steel, for example, 20895, 20860, 21880;
• precision alloys with high electrical resistance X23YU5T, X20N80N, X15N60N and others;
• soft magnetic alloys, including 49K2FA-VI, 81NMA.

PZPS employees carefully monitor the appearance of various defects in the metal and promptly eliminate them, which makes it possible to produce high-quality productsthat meets strict industry standards. Contact our expertsto get advice and place an order for special steels, precision alloys or production services.