Material Science
Prof. Satish V. Kailas
Associate Professor
Dept. of Mechanical Engineering,
Indian Institute of Science,
Bangalore – 560012
India
Chapter 13. Corrosion and Degradation of Materials
All engineering materials are subjected to numerous external mechanical and
environmental factors during their service. Those factors include temperature, chemical
attack, mechanical vibration, applied mechanical loads, etc. Under the influence of these
factors, engineering materials gets degraded i.e. they loss their potential to perform the
task. The degradation is inevitable, and may lead to catastrophes! Hence, degradation of
materials not only be monitored but also be factored into the design of different
components by engineers.
Mechanism of degradation is different for each engineering material group. Material loss
either by dissolution or by formation of nonmetallic scale/film occurs in metals, while
ceramics are relatively resistant to degradation. However, ceramics also gets deteriorated
at extreme temperatures. Polymers, on the other hand, may dissolve/distort in presence of
a liquid solvent or even when exposed to electromagnetic radiation. Degradation due to
chemical/electro-chemical factors is termed as corrosion, while oxidation refers to
formation of nonmetallic scales in metals.
13.1 Corrosion of Metals
Corrosion can be defined as unintentional deterioration of materials due to
electrochemical factors. It usually starts at the external material surface. The corrosion
resistance of metals and alloys is a basic property related to the easiness with which these
materials react with a given environment. Corrosion is a natural process that seeks to
reduce the binding energy in metals, and is of electrochemical in nature. The end result of
corrosion involves a metal atom being oxidized, whereby it loses one or more electrons
and leaves the bulk metal. The process is called oxidation, some times also called anodic
reaction. The lost electrons are conducted through th