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HI all
Why is fcc more ductile than bcc although bcc has greater number of slip planes than fcc?
Why is fcc more ductile than bcc although bcc has greater number of slip planes than fcc?
http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Structure/solidstate.htmCrystalline structure is important because it contributes to the properties of a material. For example, it is easier for planes of atoms to slide by each other if those planes are closely packed. Therefore, lattice structures with closely packed planes allow more plastic deformation than those that are not closely packed. Additionally, cubic lattice structures allow slippage to occur more easily than non-cubic lattices. This is because their symmetry provides closely packed planes in several directions. A face-centered cubic crystal structure will exhibit more ductility (deform more readily under load before breaking) than a body-centered cubic structure. The bcc lattice, although cubic, is not closely packed and forms strong metals. Alpha-iron and tungsten have the bcc form. The fcc lattice is both cubic and closely packed and forms more ductile materials. Gamma-iron, silver, gold, and lead have fcc structures. Finally, HCP lattices are closely packed, but not cubic. HCP metals like cobalt and zinc are not as ductile as the fcc metals.
http://www.exo.net/~jillj/activities/mechanical.pdfIn fcc metals, the flow stress, i.e. the force required to move dislocations, is not strongly
temperature dependent. Therefore, dislocation movement remains high even at low
temperatures and the material remains relatively ductile.
In contrast to fcc metal crystals, the yield stress or critical resolved shear stress of bcc
single crystals is markedly temperature dependent, in particular at low temperatures. The
temperature sensitivity of the yield stress of bcc crystals has been attributed to the
presence of interstitial impurities on the one hand, and to a temperature dependent
Peierls-Nabarro force on the other. However, the crack propagation stress is relatively
independent of temperature. Thus the mode of failure changes from plastic flow at high
temperature to brittle fracture at low temperature.
P and S are generally considered impurities in most alloys, particularly structural materials. Both can increase notch sensitivity, or conversely reduce fracture toughness, particularly at cold temperatures.Enthalpy said:Hence my claim that essentially the alloying elements (C, P, S...) determine ductility.
FCC (face-centered cubic) metals have a higher ductility because their crystal structure allows for more dislocation movement when a force is applied. This means that the atoms can shift and slide past each other more easily, allowing the metal to be stretched without breaking.
In an FCC structure, the atoms are arranged in a close-packed lattice, with atoms at each corner of the cube and in the center of each face. This arrangement provides more open spaces or "slip planes" for dislocations to move through, making it easier for the metal to undergo plastic deformation.
Yes, there are other factors that can affect the ductility of a metal, such as the type and amount of alloying elements present, the temperature at which the metal is tested, and the presence of impurities or defects in the crystal structure. These factors can all influence the ability of the metal to undergo plastic deformation before breaking.
Yes, the ductility of a metal can vary depending on the conditions it is subjected to. For example, increasing the temperature can make a metal more ductile, while decreasing the temperature can make it more brittle. Additionally, the presence of impurities or defects in the crystal structure can also affect the ductility of a metal.
Ductility is an important property of metals as it allows them to be formed into various shapes and sizes without breaking. This makes them useful in many applications, such as in construction, manufacturing, and engineering. Additionally, metals with high ductility tend to be more malleable and can undergo significant plastic deformation before reaching their breaking point.