mechanism and rate of solidification of metals and alloys
TRANSCRIPT
College of Engineering
Mechanical Eng. Dept.
Mechanism and rate of solidification of metals and alloys
Ch3
Many liquid metals are actually so full of sundry solid phases floating about, that they begin to more closely resemble slurries than liquids.
Introduction
It is sobering to realize that many of the strength related properties of liquid metals can only be explained by
assuming that the melt is full of defects.
It is not easy to quantify the number of nonmetallic inclusions in liquid metals.
Solidification of metals and alloys
Solidification of metals and alloys
Solidification of metals and alloys
Solidification of metals and alloys
Where T is under cooling
Solidification of metals and alloys
Homogeneous nucleation
Homogeneous nucleation occurs when are no special Objects inside a phase which can cause nucleation
Gibbs Free Energy
Energies Involved in Homogeneous Nucleation
Critical Radius
Energies Involved in Homogeneous Nucleation
Heterogeneous Nucleation
Critical Radius of Nuclei VS. Undercooling
Rapid Solidification (105 K/s)
Rapidly cool or quench to produce amorphous or glassy structure (metallic glass)
Rapid Solidification
Cooling Rate >104 -107 oK/s
By processes such as: Atomization, melt spinning, roller-quenching or plasma spray or laser or electron beam surface treatment
Non-eqm phase, no thermo. Restrictions, exceed solubility limits, melt solidifies without any chem changes.
Crystalline or amorphous (improved mech. properties)
Microsegregation-free structures
Using powder metallurgy to process the materials.
Micro-segregation
Macro-segregation
