Freedom is an elusive concept Freedom is an elusive concept. Some men hold themselves prisoner even when they have the power to do as they please and go where they choose, while others are free in their hearts, even as shackles restrain them -Zensunni wisdom

Dislocation interactions With tiny precipitate particles Why don't dislocs move thru precipitates? a. complex structure - poorly defined slip planes and/or b. slip planes wrongly oriented

Solid solution strengthening Solute atoms different size than solvent atoms Crystal structure distorted – slip planes less well-defined Disloc movement restricted Cu solid solutions

Strengthening methods - summary Work hardening Solution hardening Precipitation hardening Grain size reduction

Dislocations Oh, yeah….one more thing about dislocs Ease of disloc motion depends on slip plane orientation wrt applied stress direction

Dislocations Slip occurs only as a result of shear & only along slip plane in a slip direction The greater the no. of slip systems, the greater the probability some slip plane & slip direction correctly oriented

Dislocations Slip system = slip plane + slip direction ccp - 12 slip systems hcp - 3 slip systems "bcc" - 12 slip systems

Example - 718 Ni-base superalloy Composition: 52.5Ni 19Cr 3Mo 19Fe 0.4Al 5Nb-1Ti 0.04C

Example - 718 Ni-base superalloy

Example - 718 Ni-base superalloy

Example - 718 Ni-base superalloy Possibilities for strengthening 718:

Example - 718 Ni-base superalloy

Example - 718 Ni-base superalloy 52.5Ni Provides friendly matrix for alloying elements 19Cr Oxidation and corrosion resistance, solid solution strengthening 3Mo Solid solution strengthening, stabilizes chromium oxide film, carbide formation for Hi T strength 19Fe Solid solution strengthening 0.4Al Increases oxidation resistance, forms strengthening pptates 5Nb-1Ti Form strengthening pptates 0.04C Carbide formation for creep resistance

Dislocations The primary strengthening phase for alloy 718 is " with some contribution from '. The " is coherent and has a body-centered-tetragonal crystal structure, while ' has an ordered face-centered-cubic crystal structure. The stoichiometry of both can be represented as Ni3(Nb,Ti,Al). The " and ' phases in alloy 718 are both metastable. The stable precipitate phase is , which has an incoherent orthorhombic crystal structure of Ni3(Nb,Ti). It forms as intergranular lathes along (111) planes and/or at grain boundaries. ccp - 12 slip systems hcp - 3 slip systems

Dislocations 718 (Ni-18.5Fe-18Cr-5.3Nb-3Mo-0.9Ti-0.5Al-0.03C) ccp - 12 slip systems hcp - 3 slip systems