Final answer:
When dislocations in a material attract and come into contact, they can either form a larger dislocation or annihilate each other, resulting in a decrease in the total number of dislocations and affecting the material's mechanical properties.
Step-by-step explanation:
The statement 'Where dislocations attract they may create a single dislocation or annihilate, hence reducing the dislocation density in the material' indicates that when dislocations of opposite signs come together in a crystalline material, they can either form a larger dislocation or cancel each other out completely. This process lessens the overall number of dislocations in the material, which can alter its mechanical properties. Dislocations are line defects that represent a misalignment in the orderly array of atoms, often leading to ductility and malleability of the material. These defects can move under stress, contributing to plastic deformation. The movement and interaction of dislocations are crucial for understanding the mechanical behavior of crystalline solids. The attraction between dislocations, followed by their potential annihilation, plays an essential role in the material's ability to deform and its overall strength. It is a fundamental concept in materials science and metallurgy.
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