MEEN Nanoscale Issues in Manufacturing

Transcription

1 MEEN Nanoscale Issues in Manufacturing Equal Channel Angular Extrusion (ECAE) Lecture 1 : Bulk Nanostructured Materials 1-ECAE 1

2 Bulk Nanostructured Materials Theme 2: Fabrication of bulk materials through severe plastic deformation and nanoparticle consolidation Fabrication methods for structural materials Why nano?? Evidence for ultrahigh strength and ductility when building blocks are in the nano range. Building blocks? Grains, layers, particles, etc. How do we make building blocks in nano range? How do we connect the building blocks? Bulk? In cm range Properties: bullet proof aluminum? 2-ECAE 1

3 Theme 1 vs. Theme 2 Theme 1 - Lithography: Making engineering parts and devices smaller Theme 2 is different: Microstructural design for properties, making building blocks submicron scale. What kind of properties we are interested in? Structural: Magnetic: Electrical (ferroelectrics) (thermoelectrics) grain size and texture is important 3-ECAE 1

4 Why is grain size important for structural applications? Cu Ni Hall-Petch Relation: σ y = σ 0 + k y d 4-ECAE 1

5 Why is texture important for structural applications? Crystal Orientation Dependence 50.8%Ni-Ti Compression- Aged K [001] [111] [112] 1500 [148] Strain (%) 5-ECAE 1

6 Why is texture and grain size important for functional properties? Grain size: might be a solution for brittleness in thermoelectrics and ferroelectrics Magnetization Applied Magnetic Field Typical thermoelectric cooler for electronics 6-ECAE 1

7 What is the mechanism for grain boundary strengthening in nanocrystalline materials? Hall-Petch Relation: Work-hardening: τ σ y = σ 0 + = τ 0 k y d + αgb ρ 7-ECAE 1

8 What is the mechanism for grain boundary strengthening in nanocrystalline materials? Two-phase model Grain-boundary sliding model 8-ECAE 1

9 Top Down or Bottom Up? Both work to make bulk nanocrystalline materials Decreasing the grain size of already bulk materials: Severe Plastic Deformation (SPD) Consolidation of nanograins (particles). 9-ECAE 1

10 Top down approach to bulk nanocrystalline materials fabrication Main principles of Severe Plastic Deformation (SPD): Increase dislocation density by heavily deforming materials (uniformity! Cross section!), form dislocation walls, transform dislocation walls into grain boundaries (high angle boundaries) Is there any intrinsic limitation? 10-ECAE 1

11 Severe Plastic Deformation (SPD) 11-ECAE 1

12 Why SPD? Think about materials that must be heavily mixed during processing Concrete Bread Samurai Sword Steel (Damascus Steel) Piano Wire Superalloy Components in Jet Engines Superconductors Sheet Stock for Auto Bodies Sheet Stock for Beer Cans 12-ECAE 1

13 Why SPD? Why do this mixing? To Refine/Homogenize the Microstructure To Strengthen the Material To Enhance the Properties Examples Work Hardening Grain Refinement Development of Special Microstructures Development of Special Textures 13-ECAE 1

14 SPD provides increase in both strength and ductility True Stress, MPa Bulk Cu 101 Tension Experiments at RT True stress versus true strain ECAE at RT, 1A ECAE at RT, 2C ECAE at RT, 4C ECAE at RT, 8A ECAE at RT, 8E ECAE at RT, 16E Annealed Cu 101 (grain size: 75µm) As received True Strain, % ECAE 1

15 SPD provides increase in both strength and ductility 15-ECAE 1

16 Unconventional SPD Techniques Equal Channel Angular Extrusion High Pressure Torsion Accumulative Roll Bonding Repetitive Corrugation and Straightening 16-ECAE 1

17 Conventional Methods of SPD Process Characteristics Load Change in Geometry Uniformity of Plastic Strain Rolling V. High Decrease in thickness Only after SPD Extrusion High Decrease in cross- Can be with special die sectional area design Drawing Low Decrease in cross- Higher at surface sectional area Forging V. High Usually Usually not 17-ECAE 1

18 Bottom Up Approach Nanoparticle Consolidation (Problems with nanopowders?) Hot isostatic pressing (HIP) (good for ceramics) Cold isostatic pressing (CIP) + Sintering (good for ceramics) Conventional Extrusion Consolidation Equal Channel Angular Extrusion Consolidation (scale up is easier) 18-ECAE 1

19 Nanoparticle Fabrication Methods Vaporization methods Free jet expansion method Laser vaporization Spark erosion Electro explosion of wires Chemical vapor deposition etc. Mechanical Attrition 19-ECAE 1

20 Equal Channel Angular Extrusion (ECAE) Material Properties Improved strength, ductility and toughness Superplasticity Engineered microstructures Engineered textures Materials Extruded Alloys Polymers Intermetallic compounds Composites 20-ECAE 1

21 Description of ECAE Die Inlet Die Chamber Channel Billet Shear Zone (P) Punch Die Exit Channel Die Angle Conditions 1. Inlet and outlet channels have nearly the same dimensions 2. Channel intersection is abrupt 3. Lubrication and other means are used to reduce friction 21-ECAE 1