11-Dispersionhardening.ppt-MechanicalandAerospace.pptVIP

Solid Solution Hardening Solid Solution Hardening Solid Solution Hardening Precipitate or Dispersion Hardening Precipitate or Dispersion Hardening-Small particles Precipitate or Dispersion Hardening-Small particles Precipitate or Dispersion Hardening- Big Particles Precipitate or Dispersion Hardening- Big Particles Precipitate or Dispersion Hardening - Big Particles Precipitate or Dispersion Hardening - Particle Size Effect Mechanical Aerospace Engineering West Virginia University Dispersion and Solution Hardening - Impurity atoms go into either substitutional or interstitial solid solution. Lattice strain field interacts between dislocations and these impurity atoms result, and consequently, dislocation movement is restricted. - The strain (or stress) field “roughen” the lattice structure and hinder the dislocation movement. Solid solution hardening in brass There is an interaction between the strain fields about a solute atom and the strain fields about the dislocations. Solid Solution Hardening Example – Al Alloys 1.8% 5000 series Aluminum Alloys (Al-Mg) Hold at 450C (Solution Heat Treatment) Cool moderately quickly to room temperature Solid Solution Hardening – Al Alloys Dispersion Strengthening - Strengthening by the introduction of a second phase. Precipitation Strengthening - Through the formation of extremely small uniformly dispersed particles of a second phase within the matrix Particle Cutting Particles should be small enough to be cut. Large size particles offer more resistance to dislocation motion. Strengthening Particle Radius Strengthening effect can be estimated as: G – Shear Modulus r – Particle radius b – Burgers vector f – volume fraction of particles - strain field factor Dislocation Bypass by the Orowan Bowing Mechanism: The stress required to bypass in this manner is given by the line tension when the dislocation is bowing at the maximum curvature – Depends then on the distance between particles (L): ?? - S