Indian Research Forum

Solid solubility is defined as the amount of solute that is soluble in solvent. Solid solubility of any alloy depends upon atomic size, valencies, and crystal structure and electronegativity parameters. Solid solubility limits is decided on the basis of the Hume–Rothery rules for solid solution formation. Solid Solubility limit is the limit to which one metal is capable to form solid solutions with respect to other metal. In case of solid dissolved in liquid water, the solid solubility increases because of increase average kinetic energy of the solute molecules with increment of temperature.

Diffusion is the process of movement of atoms from high concentration to low concentration in a material. Adolf Fick first discussed the molecular diffusion in binary components. Fick’s first law of diffusion for a binary mixture depends on flux, diffusion velocity, molar concentration, and temperature gradient. In the diffusion process, atoms change their original positions relative to the adjacent atom due to gradients. The gradient can be a concentration gradient, magnetic gradient, temperature gradient or stress gradient. Diffusion mechanisms involve vacancy diffusion, interstitial diffusion, substitutional diffusion, self-interstitial, self-diffusion, etc. Diffusion process can be either steady-state or non-steady-state process, which depends on flux i.e. the net number of atoms crossing a unit area per unit time in a particular direction. Some important factors that influence diffusion are diffusing material, temperature, crystal lattice, defects, etc.

Corrosion fatigue is mechanical degradation process in both a corrosive and under cyclic loading conditions. Corrosion fatigue can occur in most of the materials. In corrosion fatigue, the crack propagates by the means of the trans-granular mechanism through the grain surface. Corrosion fatigue generates brittle fracture conditions. It increases the rate of crack propagation and changes the stress cycle frequency. Corrosion fatigue decreases the fatigue life of the metal. Corrosion fatigue can be prevented by vibration controlled conditions, proper material selection, proper design to reduce stress, use of inhibitors and coatings etc.

Hydrogen embrittlement is an undesirable process resulting loss of ductility of metal, decrease of the toughness and reduction of load-bearing capability occurs due to the absorption of hydrogen atoms by the metal. So that there is crack formation in metal component and fracture at lower stresses conditions. There are mainly two types of Hydrogen embrittlement. The first one is internal  hydrogen  embrittlement, It occurs when the hydrogen dissolved in molten metal which becomes supersaturated with hydrogen immediately after solidification.  And the second type is environmental  hydrogen  embrittlement, which results from by hydrogen absorption by the solid metal. This condition can occur during high-temperature thermal treatment & during electroplating, during corrosion reactions, during cathodic protection, operating hydrogen in high-pressure conditions etc.

Sensitization means precipitation of carbides present at the grain boundaries in alloy and causing the alloy to be susceptible to intergranular corrosion. Intergranular corrosion is caused by the segregation of impurities and precipitates at the grain boundaries or by enrichment or depletion in the grain boundary. Sensitization in aluminum composites is an serious problem which is identified by the gradual formation and growth of beta phase Mg 2 Al 3 at grain boundaries, which increases the susceptibility of alloys to intergranular corrosion (IGC) and intergranular stress-corrosion cracking (IGSCC)

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