This thread got moved out of General Engineering to GD, but it would be more appropriate in Materials & Chemical Engineering.
Anyway, marie_curie, what is it that you wish to know about material engineering or materials science.
Since mankind uses a variety of materials in a variety of products and in a variety of environments, one must know how that material performs - so there is a discipline of materials engineering or science devoted to understanding materials from a microscopic, was well as macroscopic, standpoint.
In addition to understanding the physical (including thermophysical), mechanical, and chemical (and electrochemical) properties of a material in order to know how it will perform, one must also understand how the material is manufactured. Often, how a material is made will affect how it performs.