Structure-Property Correlation [1] Structure-processing-properties-performance relation

Transcription

1 MME 297: Lecture 04 Structure-Property Correlation [1] Structure-processing-properties-performance relation Dr. A. K. M. Bazlur Rashid Professor, Department of MME BUET, Dhaka Topics to discuss today... Study microstructures, starting with the smallest, and working up Understand the structure-properties-processing-performance tetrahedron Connect how microstructure relates to properties Look at the effect of processing on microstructure and properties References: 1. Callister & Rethwisch. Materials Science and Engineering An Introduction, 9th Ed, Wiley, pp /32

2 Materials Science and Engineering The discipline of materials science and engineering can be divided into materials science and materials engineering subdisciplines. Materials science involves investigating the relationships that exist between the structures and properties of materials. Materials engineering involves, on the basis of these structure property correlations, designing or engineering the structure of a material to produce a predetermined set of properties. From a functional perspective, the role of a materials scientist is to develop or synthesize new materials, whereas a materials engineer is called upon to create new products or systems using existing materials and/or to develop techniques for processing materials. 3/32 definitions of terminology Composition means the chemical make-up of a material. Structure means a description of the arrangements of its internal components (atoms, ions, etc.). Synthesis is the process by which materials are made from naturally occurring or other chemicals. Processing means different ways for shaping materials into useful components or changing their properties. Properties is a material trait in terms of the kind and magnitude of response to a specific imposed stimulus (which is made independent of material shape and size) 4/32

3 What are Structures? Electronic structure electrons and nuclei (protons and neutrons) Atomic structure organization of atoms or molecules Crystal structure organisation of atoms into a 3D space Microscopic structure groups of atoms that are normally agglomerated together Macroscopic structure viewable with the un-aided eye 5/32 terminology and unit of structure mil = inch = 25.4 µm micrometer = 1,000,000-1 meter = 1µm Angstrom = 10,000,000,000-1 meter = 1Å 1 Micrometer is Two Wavelengths of Green Light Long An 1 micron wide line on a CD is the same scale as a 100 foot wide road on North America A hair is 50 micrometers in diameter 6/32

4 logarithmic scale of structures size, m Atomic structure Crystal structure X-ray & neutron diffraction (XRD) Microstructure Macrostructure Transmission electron microscopy (TEM) Scanning electron microscopy (SEM) Optical microscopy (OM) 7/32 Optical Microscope Microstructure of steel (0.8% C) Microstructure of brass (70Cu-30Zn) 8/32

5 Scanning Electron Microscope (SEM) Carbon nanotube Zika virous 9/32 Transmission Electron Microscope (SEM) Electron diffraction pattern Zika virous 10/32

6 X-Ray Diffractometer Bragg s law X-ray pattern 11/32 The Structures - Property - Processing - Performance Tetrahedron The field of Materials Science and Engineering is devoted to Performance understanding and controlling of the performance of useful solid materials through the study of interrelationships between materials synthesis, structure, and properties Properties Structure Processing 12/32

7 application of materials tetrahedron to automotive steels chassis Performance / Cost What is the strength-to-density ratio? What is the formability? How does this relate to the crashworthiness of the vehicle? What is the cost of fabrication? A: Compositions Iron-based? Aluminium-based? What alloying element should be used? What quantities? B: Microstructure What features of the structure limit the strength and formability? What controls the strength? C: Synthesis and Processing How can the steelmaking be controlled so as to provide a high level of toughness and formability? How can be the aerodynamic car chassis be formed? 13/32 application of materials tetrahedron to transparent ceramics Single crystal (a high degree of perfection) which gives rise to its transparency. Composed of numerous and very small single crystals that are all connected; the boundaries between these small crystals scatter a portion of the light reflected from the printed page, which makes this material optically translucent. Composed of many small, interconnected crystals and a large number of very small pores or void spaces, which effectively scatter the reflected light and render this material opaque. 14/32

8 structure : examples 15/32 property : examples 16/32

9 processing : examples 17/32 From Structures to Properties To understand the properties of engineering materials, it is necessary to understand their structure on the atomic and/or microscopic scale. crystalline amorphous atomic-level structure (x10 7 ) microscopic-level structure (x10 3 ) 18/32

10 Case study -1: Atomic-scale architecture Ductility of aluminium and magnesium tensile testing specimen tensile testing machine 19/32 brittle fracture broken tensile test pieces of Al and Mg ductile fracture Why is aluminium more ductile than magnesium? 20/32

11 FCC Aluminium HCP Magnesium 21/32 principles of atomic packing Many crystals structures can be described as stacking arrangements of atoms in 2-D lattices or, nets. Structures based on the square net Simple cubic (SC) Body-centred cubic (BCC) Structures based on the close-packed net Face-centred cubic (FCC) Hexagonal close-packed (HCP) 22/32

12 square net close-packed net 16 lattice points in shaded area lattice points in shaded area more efficient packing in the closed-packed net 23/32 why are we interested in packing sequence of crystals? It is easier for crystal lattice deformation to occur in the direction that is close packed. The number and direction of close-packed planes vary according to packing sequence of crystal /32

13 HCP Cell 3 slip systems (1 plane x 3 directions) small lattice deformation FCC Cell 12 slip systems (4 plane x 3 directions) high lattice deformation Thus, Aluminium (FCC) is more ductile than Magnesium (HCP) 25/32 Case study - 2: Microscopic-scale architecture Making of transparent ceramics high temperature sodium vapour lamp polycrystalline alumina containing porosity 15 lumens/w polycrystalline alumina plus 0.1 wt.% magnesia with near pore-free structure 100 lumens/w 26/32

14 Ferrite (almost pure iron; very soft) C < 0.80% Pearlite (an intimate mixture of Ferrite and Cementite) C = 0.80% C > 0.80% Cementite (an intermetallic compound, Fe 3 C, very hard and very brittle) chains stampings rivets wire nails screws tinplate structural steels axles gears shafts tires screw drivers rails wire ropes drills taps dies shear blades clod chisels some hand tools structure - properties relationship of ordinary steels knives broaches reamers saws razors 27/32 From Processing to Structures rolling extrusion During rolling and extrusion, the grains of material are deformed and become elongated along the rolling direction, which imparts directional properties to the material. During casting, the liquid metal cools from three directions and grains of uniform shape are created, which imparts non-directional or isotropic properties to the material. 28/32

15 From Processing to Properties 29/32 electrical resistivity of copper Adding impurity atoms to Cu increases resistivity Deforming Cu increases resistivity 30/32

16 Properties depend on structure. Ex: hardness vs. structure of steel Processing can change structure. Ex: structure vs. cooling rate of steel 31/32 Next Class MME 297 Lecture 05 Structure-Property Correlation [2] Atomic bonding and material properties