1. INTRODUCTION:
The material are broadly divided into two groups, Metal and Non-Metal. The metals are usually solid at room temperature and are malleable and ductile, and have good electrical and thermal conductivity. The other properties of metals include lustre, high density, high melting point, good strength and hardness, low specific heat etc. Most of the metals are found to be elastic to a certain limit and they deform plastically at higher stresses. A metal can exist in the solid, liquid or gaseous states depending upon the temperature and pressure exerted on the metal. some of the common metals and alloys are iron, copper, aluminium, nickel, tin, brass and bronze etc.
The non-metals in the solid state are mostly brittle and are poor electrical and thermal conductivity. They do not form alloy but combine chemically to form compound. Some of the non-metals are glass, plastics, wood, concrete etc.
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2. STRUCTURE OF SOLIDS:
All solid substances are either amorphous solids or crystalline solids. In the amorphous solids, the atoms are arranged chaotically, i.e., the atoms are not arranged in a systematic order.
The common amorphous solids are wood, plastics, glass, paper, rubber etc. In crystalline solids, the atoms making up the crystals arrange themselves in a definite and orderly manner and form. All solid metals such as iron, copper, aluminum etc. are crystalline solids.
SPACE LATTICE:
All solid metals are made up of a number of crystals arranged themselves in a definite and orderly manner and form and each crystal consists a large number of atoms. This definite and orderly manner and form of atoms producing a geometrical shape in the aggregate is called space lattice.
ATOMIC PACKING FACTOR:
The atomic packing factor is defined as the ratio of the volume occupied by the atoms to the total volume of the unit cell.
GRAINS FORMATION IN MOLTEN METALS:
The molten metal start solidification from nuclei. Two axis growth starts from nuclei and it connects all nearby nuclei one by one and the process spread in all area of molten metal rapidly. The process when continues to the multiple time, it gave a tree like crystal, which known as dendrites. This process of solidification is termed as dendritic solidification.
On the broader prospects solidification or grain formation begins with formation of the small nuclei scattered in the surface of molten metal. This nuclei grow as more atom join them to form larger grains. Atoms starts grow in an orderly arrangement to give unit cube structure and the growth takes place in three dimension.
Each crystal or the grain is built up of thousands of small unit cells or cubes. The axis of cubes are all points in the same direction, but this direction varies from one crystal to another.
GRAIN SIZE DETERMAINE MECHANICAL PROPERTIES:
The grain size plays an important role to shape the metals mechanical properties such as strength, hardness, weir resistance, elasticity etc. Heat treatment is one of the main factor to determine the grain size. Smaller grain size increase a material strength and hardness because they provide more grain boundaries to impede free movement, while larger grain size lead to higher ductility and toughness but lower strength and hardness.
BONDS IN SOLID:
We are already know atoms rarely exist independently, most of the elements exist in cluster and electrically neutral.