Physical Metallurgy - What is Slip systems and Surface Defects

A: Slip systems are crucial because plastic deformation in metals primarily occurs through the motion of dislocations along slip systems. The ease of dislocation movement depends on the availability and orientation of slip systems relative to the applied stress. Materials with multiple active slip systems can accommodate deformation more uniformly, leading to better ductility and toughness. The concept of critical resolved shear stress (CRSS) helps quantify the stress needed to activate slip on a particular system. Understanding slip systems enables engineers to predict material behavior under mechanical loads and design alloys with desired mechanical properties. References include "Mechanical Behavior of Materials" by Norman E. Dowling.

A: In body-centered cubic (BCC) metals, the primary slip systems involve {110}, {112}, and {123} slip planes with <111> slip directions. Although BCC metals have several potential slip systems, their activation is influenced by temperature due to higher Peierls-Nabarro stress compared to FCC metals. In contrast, FCC metals primarily deform by slip on {111} planes in <110> directions, which are close-packed and allow for easier dislocation movement even at lower temperatures. This difference explains why BCC metals often exhibit a ductile-to-brittle transition temperature, while FCC metals remain ductile over a wide range of temperatures. More can be read in "Introduction to Dislocations" by D. Hull and D.J. Bacon.

A: Slip systems refer to specific combinations of slip planes and slip directions along which dislocation motion occurs most easily in a crystal lattice, leading to plastic deformation. Each slip system consists of a slip plane, which is the plane with the highest atomic density, and a slip direction, which is the direction in the plane with the highest atomic density. The number and type of slip systems determine the ductility and deformation behavior of a material. For example, face-centered cubic (FCC) metals typically have 12 slip systems, which contributes to their high ductility. More information can be found in classic materials science textbooks such as "Materials Science and Engineering: An Introduction" by William D. Callister.

A: Surface defects in metals are irregularities or imperfections located at or near the surface of a material. These include surface roughness, steps, ledges, grain boundaries that intersect the surface, as well as vacancies and adatoms on the surface. Surface defects can have a significant impact on properties such as corrosion resistance, fatigue life, and catalytic activity. For instance, grain boundaries at the surface can act as sites for corrosion initiation, and surface steps can influence how dislocations move during deformation. Detailed explanations can be found in "Physical Metallurgy" by Peter Haasen and resources such as the ASM Handbook on Surface Engineering.