In this article we will discuss about the atomic approach to elastic deformation of metals. At absolute zero, the two neighbouring atoms in a metal are in stable equilibrium state when the distance between them is r0. Fig. 6.11 illustrates this schematically. At large distance of separation between two atoms, the main force is of attractive nature, FA (negative). When [...]
In this article we will discuss about the plastic deformation of metals with its diagram. Referring to Fig. 6.2 the deformation of the specimen is elastic up to the yield point (or elastic limit) and it becomes plastic, i.e. the linear elastic region is followed by a nonlinear plastic region. Although yield strength is an important design parameter for machine [...]
In this article we will discuss about:- 1. Introduction to Corrosion 2. Classification of Corrosion 3. Rate 4. Corrosion Rates from Polarisation and Mixed Potential Theory. Introduction to Corrosion: Corrosion is responsible for colossal loss of materials occurring everywhere every moment involving billions and billions of rupees annually. It is one of the most serious destructive agents, and is one [...]
Corrosion occurs when metals come in contact with a corrosive atmosphere. Thus, corrosion can be prevented by: 1. Geometrical Design 2. Proper Selection of Material 3. Modification of corrosive environment 4. Cathodic Protection 5. Anodic Protection. The most effective and economical method of preventing corrosion is to choose the most suitable geometrical design, most suitable material and then choose most [...]
Corrosion is a very complex phenomenon. However, depending on the form, appearance and the distribution of the attack, corrosion is classified industrially in following types: 1. Uniform Corrosion 2. Atmospheric Corrosion 3. Inter-Granular Corrosion 4. Pitting Corrosion 5. Crevice Corrosion 6. Stress-Corrosion Cracking 7. Hydrogen-Embrittlement 8. Corrosion-Fatigue 9. Erosion-Corrosion and Few Others. Types # 1. Uniform Corrosion: If corrosion is [...]
In this article we will discuss about:- 1. Meaning of Oxidation 2. Mechanism of Oxidation 3. Kinetics. Meaning of Oxidation: Oxidation is a type of corrosion involving the reaction between a metal and air or oxygen at high temperatures in the absence of water or an aqueous phase. It is also called dry-corrosion. At normal temperatures, the oxides of the [...]
Hot working is defined as the plastic deformation of a material at a temperature above its recrystallisation temperature, whereas working below this temperature is called cold working. The literal meaning of the words, hot and cold in ordinary sense does not apply here. For example, the working of lead and tin at room temperature is called hot working as their [...]
Cold-working produces structural changes in polycrystalline metals and alloys, which can be broadly classified in three categories: 1. Changes in Shape and Size of Grains 2. Changes in Orientation of Grains 3. Changes in Internal Structure of the Grains. Category # 1. Changes in Shape and Size of Grains: Commercial metals and alloys are polycrystalline in nature in which the [...]
Plastic deformation occurs by the following modes: 1. Slip 2. Twinning 3. Kink. Mode # 1. Slip: The surface of a crystalline solid which has been polished, Fig. 6.14 (a) and then plastically deformed, generally gets covered with one or, more sets of parallel lines, Fig. 6.14 (c). At high magnifications, these 'slip lines' are found to be steps on [...]
When a single crystal is continued to be deformed in the plastic range beyond the yield point, the shear stress required to produce further deformation continues to increase. The increase in the stress required to continue the deformation because of the previous plastic deformation is called as strain-hardening, or work-hardening. As the dislocation density also increases simultaneously with strain (dislocation [...]