Every material, made up of one or more than one element, is used directly or indirectly by mankind for one or another purpose. For the sake of convenience, solid materials useful to human beings are referred to as engineering materials. It does not mean that liquid and gaseous materials are not useful to mankind. The concept of engineering materials helps in restricting the field of study of materials. A major fraction of engineering materials utilizes the elements in combined form as alloys, compounds or mixtures.