1 / 15

530.352 Materials Selection

530.352 Materials Selection. Lecture #17; Strengthening Mechanisms Monday October 24 th , 2005. Strengthening Mechanisms :. Lattice Friction Solid Solution Strengthening Precipitation Hardening Strain Hardening and Recovery Grain Boundary Strengthening. Lattice Friction:. FCC.  H.

bat
Télécharger la présentation

530.352 Materials Selection

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 530.352 Materials Selection Lecture #17; Strengthening MechanismsMonday October 24th, 2005

  2. Strengthening Mechanisms : • Lattice Friction • Solid Solution Strengthening • Precipitation Hardening • Strain Hardening and Recovery • Grain Boundary Strengthening

  3. Lattice Friction: FCC H Easy BCC H Hard

  4. Refractory Metals : • Tungsten, molybdenum, tantalum, niobium, columbium • High Tmelting • Very good high T strength !!! • Limited RT ductility -- hard to form • Poor oxidation resistance !!!

  5. Lattice Friction: Crystal Structure Slip systems Friction FCC 12- {111}<110> very low BCC 12- {110}<111> high Diamond cubic 12- {111}-like very high(w covalent bonding) HCP basal slip 2- (0001)<1120] very low othersvery high

  6. H Cu Zn Zn Not as easy Solid Solution Strengthening: y C1/2

  7. Examples of solute strengthening

  8. Precipitation strengthening: Solution,Quench,Heat treat: - forms  precipitates in the  matrix L 700 600 500 400 300 1.   Temperature  3. 2. Al % Cu

  9. Nucleation and Growth: Atoms in Nucleation More nucleation Growth of solution of precipitates until exhausted precipitates

  10. Surface Energy drives growth: For a fixed volume fraction: L ? L L Most surface area -> Least surface area Higher energy-> Lower energy

  11. The mechanical properties: cutting bowing precipitates get too big,i.e. spacing (L) too large. 50 40 30 no precipitates y (ksi) precipitates form and grow y Gb / L Heat Treating Time

  12. Cutting precipitates: When too small - dislocations can cut them:

  13. Bowing: dislocations bow past precipitates precipitates slow dislocations y Gb / L

  14. Yielding: • Single crystalsy b = Ffriction + Fsol’n + Fprec + Fwork hardening • Polycrystals • Yielding starts in some grains before others • General yielding occurs aty = 3y • Grain boundaries add strength

  15. Grain Boundary Strengthening: • dislocations pile up at boundary. • stress builds up. • dislocation motion initiated in neighboring grain. Hall - Petch relation: y = i + ky d -1/2

More Related