STRUCTURE AND PROPERTIES OF MATERIALS

STRUCTURE AND PROPERTIES OF MATERIALS

LECTURE 4: MANIPULATION OF MECHANICAL PROPERTIES

Mechanics of Materials

  • Institution: TU/e, Eindhoven University of Technology

PREVIOUSLY DISCUSSED TOPICS

  • Atomic bonds

  • Crystals

  • Defects Energy

    • Body-Centered Cubic (BCC), Face-Centered Cubic (FCC), Hexagonal Close-Packed (HCP)

    • Microstructure consists of lattice + defects (e.g., dislocations)

CONTENTS OF THIS LECTURE

  • 4.1 Manipulation of Properties

  • 4.2 Cold Work

  • 4.3 Grain Size

  • 4.4 Recrystallization

  • 4.5 Strengthening in Alloys

MANIPULATION OF STRENGTH

Strength Characteristics

  • Significant differences in strengthening mechanisms due to defects and microstructure:

    • Yield stress and tensile strength vary as follows:

    • Metal: 300 - 1500 MPa

    • Steel: 35 - 500 MPa

    • Aluminum: 28 - 1,400 - 1,700 MPa

    • Yield strength (σy) can be related to critical resolved shear stress (\tau{crss}): \sigmay = 2-3 \times \tau_{crss} for pure single crystal

    • Reference: (Zaat, 1974)

Methods for Improving Strength

  1. Preventing Dislocation Movement:

    • Utilize barriers to impede movement by obstacles.

    • Create elastic lattice distortions which interact with dislocations.

  2. Cold Work

  3. Grain Refinement

  4. Solid Solution Strengthening

  5. Multi-phase Systems

  6. Precipitation Hardening

Manipulating Ductility

  • Aim for improved ductility to promote dislocation movement.

  • Noteworthy conflict: Improved strength may reduce ductility.

COLD WORK

Definition

  • Plastic deformation resulting in increased dislocation density.

  • Leads to an increase in yield strength, also termed **