material science

What is the two types of classification for materials

Atomic level classification

Atomic order

6 types of mechanical properties and examples

Mechanical=strength, toughness,ductility

Electrical =conductivity,dielectric constant

Thermal=conductivity,thermal expansion

Optical=absorption,scattering,transmission

Magnetic=ferro/dia/paramagnetic

Chemical stability=corrosion,oxidation resistance

What is the circular economy/life cycle stages and its use

Raw material,design,manufacturing,consumption,maintenance,reuse/refurbishment,residual waste or recycling

Used to make sure the material basically isn’t contributing negatively to environment and has a long term usage life

What affects the properties

Atomic structure, microstructure, processing and properties??

Atomic no (Z)

Atomic mass (A)

No of protons/electrons

No of protons and neutrons (will be the bigger no.)

Why was the Bohr model inaccurate

Couldn’t identify the trajectory (couldn’t measure)

What is the purpose of an orbital/ levels

Each orbital hav different shapes and energies and can hold only 2 electrons max

What are the energy levels

what does the letter stand for

What does the atomic number stand for

1s,2s,2p,3s,3p,4s,3d

S=1, p=3, d=5 (no of lines)

Arrows are the electrons (must have 2 to fill up so both up and down arrows)

Valence electron

What does this mean for them

Electrons in the outer shell of an atom (furthest from the nucleus)

Loosely bound to the nucleus so can be easily bonded with other to create a full outer shell (more stable)

What is electronegativity and what is the difference between electronegative and electropositive

In the periodic table, explain through the table electro-… elements

Ability to attract valence electrons, positive gives up electron to become +ion and negative gains electron to become -ion

LHS- electropositive elements and RHS-electronegative elements

LHS UP=small electronegativity (0.9) and RHS UP=large electronegativity (4.1)

Why do atoms form bonds

Have as little energy levels to be closer to the nucleus for stability

Ionic bonding properties

Between a metal (-e) and non metal (+e)

Dissimilar electronegativity

Requires electron transfer

Non-directional (forces act equally in all directions)

Between 600-1500kJ/mol

Predominant bonding in ceramics

Useful for food packaging,medicine, fire resistance

Very strong (large bond energy)

Covalent bond properties

Between either all non metals or all metals

Similar electronegativity

Shares electrons instead of transfer

Directional (forces vary with direction)

Variable (large diamond/bismuth)

Metallic properties

Bonding between all metals

Outer electrons are shared between all atoms

Non-directional

Sea of valence or delocalised electrons

Variable (large tungsten or small mercury)

Good conductivity for electricity

ionic-covalent mixed bonding equation

%IC=(1-e(-0.25)(Xa-Xb)) x 100

Where Xa and Xb are the elements electronegativities

WEAK van der waals properties (secondary bonds)

Molecular and induced dipoles

Hydrogen bridge

Very small bonding energy

Directional

Interchain (polymer)

Intermolecular

What does r, E0, Tm and a (or looks like an a) stand for and mean (what’s the equation for thermal expansion

Bond length-spacing between atoms

Bond energy-how strong the atoms are bonded together

Melting temp-subjected to thermal energy (sufficient to break bonds) and atoms will move far from its equilibrium position

Thermal expansion-how material changes size. Indirectly proportional to bond energy

Change in length/original length=thermal expansion(temp diff) or change in length/original x temp diff=thermal expansion

Types of atomic orders or crystal structures

Crystalline, non-crystalline ( or amorphous) and semi-crystalline

Lattice

1D

Collection of points,arranged periodically so surroundings of each point in the lattice are identical (think of this as the line)

One lattice where the points are equally distanced (the number= no. Of lattices/lines)

Basis/motif

Crystal structure

Group of 1 or more atoms associated with each lattice point (must contain at least 1 atom)

Lattice and motif/basis combined (larger atoms located on the lattice point and smaller are at a fixed location above each lattice point)

Proper definition for a crystal structure is an arrangement of the atom in a material into a regular repeatable lattice

Unit cell

Lattice parameter

Smallest repeating portion of a crystal lattice when stacked together in 3D to create a crystal structure

or subdivision that still remains the overall characteristics of an entire lattice

quantities specifying a unit cell or the unit of periodicity of atomic arrangement

Bravias lattice

In an atoms location all angles and length in the axis is…

Theoretical infinite arrangement of geometrically equivalent points in 3D space that represents the geometric structure of a crystal. (Only 14 due to symmetry grouped into 7 types of crystal systems with the same shape, different point arrangement)

Opposite each other just like in regular maths

Name all the group types of crystal systems and why the theoretical infinite is unrealistic

Cubic,tetragonal,orthorhombic,rhombohedral,monoclinic,triclinic and hexagonal

Translation symmetry restricts the possible unit cell geometries

Metallic crystal structure properties

Tends to be densely packed

Only one element is present so all radio are equal

Bonding is non directional

Nearest neighbour distance tends to be small in order to lower bond energy

Simple cubic structure properties

Only occupy corners of the cube

Nearest neighbour touches only along the edges

Rare due to low packing density

Atomic packing factor equation

APF=I(4/3 pi)(0.5a)³ all over a³ where I is the no. Of atoms/unit cell, a is the volume/atom and a³ is the volume/unit cell

Body centre cubic structure properties

Atoms located at the corners and 1 in the centre of cube

Touch along the cube diagonals

Body centre cubic atomic packing factor equation

BCC=2(4/3 pi)(sq root 3 x a/4)³ all over a³ where 2 is the no. Of atoms/unit cell, a is the volume/atom and a³ is the volume/unit cell

Face centred cubic structure properties

Atoms at 8 corners then one on each face at the centre (6) of the unit cell so 14 atoms altogether

Atoms touch along face diagonals

Max achievable APF equation

APF=4(4/3 pi)(sq root 2 x a/4)³ all over a³ where 4 is the no. Of atoms/unit cell, a is the volume/atom and a³ is the volume/unit cell

Theoretical density equation

(No. Of atoms per cell)(atomic mass)/(volume of unit cell)(avogadro const)

nA/VcNa

Density of various classes of materials

Metals are closely packed due to metallic bonding, large atomic mass

Ceramics are less dense and a lighter element

Polymers are low packing density (often amorphous) and a lighter element

Composite has intermediate values

Allotropy

Polymorphism

Characteristics of an element being able to exist in more than one crystal structure depending in temp and pressure

Compounds exhibiting more than one type of crystal structure

Steps for crystallography coordinates

X,y and Z will be a,b and c

Determine head and tail coordinate (the head is the arrow head point) and calculate the difference between those two coordinates

Normalise coordinates so make all x,y and Z into the smallest whole number (smallest factor by multiplying or dividing)

Final answer put into square brackets will no commas and add a bar on top of number if it is a -ve number

What is miller indices

Receptacles of the three axial intercepts for plane, cleared of fractions and common multiples

All parallel planes have the same indices

When you are calculating the crystallographic coordinates for planes, if it doesn’t touch the axis, what would you put it as?

You would put it as infinity, but when you normalise it, it’ll just equal to 0

What does it mean by a family of planes?

All planes that are crystallographically equivalent (have the same atomic packing), indicated by indices in the brackets

Quickly describe the frequency and wavelength of electromagnetic spectrum

Left to right equals increase in frequency

Right to left equals increase in wavelength

You can use x-rays to determine them crystal structure, what is an equation you can use?

n x wavelength or lamda=2dhkk sin theta

dhkl is the distance between the plane of atoms

dhkl=a/sq root(h²+k²+l²), Hal is ur crystallographic coordinates x, y and Z

In summary, what are the crystal structures reflection present?

Body Centre cubic structure (BCC)=h+k+l is ALL even

Face centred cubic structure (FCC)=h+k+l is either all odd or or even

Simple cubic= h+k+l is a mix of odd and even

Mechanical and other properties of many metals and other crystalline materials depend on

Atomic and crystal structure and bonding, green size and shape, allowing and controlling conversation, processing and deformation and heat treatment (high temp = change in structure)

Types of imperfections

Point defect (vacancy at atoms, interstitial atoms, sub interstitial atoms)

Line defects(dislocation)

Surface area defect (green boundary, stacking fault, twins) in 2D

Volume defects (pause, inclusion, cracks) in 3D

Number of defect equation

Nv=Ne(-Qv/kT)

Nv-no. Of defects

N-no. Of potential defects

Qv-activation energy (1.38×10^-23 J/atomK)

k-Boltzmann const (8.62×10^-5 eV/atomK)

T-temp in kelvin

Equation for number potential defects

Either the equation for number of defects rearranged or

N=density x (Na/A) x distance

Na is avogadro constant

A is atomic weight

Alloy, it’s benefits

Two or more metals(both different) combine with each other usually by mixing and allowing to cool/solidify

Stronger than pure metals

That has become distorted, creating a stress field to hinder dislocations, moving when load is applied

Density equation and volume conversion

Density=NA/Na

N=Atom/volume

A=atomic weight

Na=avogadro constant

1m³=1×10^6cm³

Conditions for substitutional solid solutions (what will combine and well to create an alloy?)

Atomic radius is less than 15%

Similar electronegativity

Same crystal structure for pure metals

Valency(to gain or lose elections for both full outer shells)

Plastic deformation is associated with

The slip of dislocations

The harder it is for dislocations to move, the stronger the metal is

What is Burgers vector and its properties

Measure of lattice deformation (both size and direction)

Edge dislocation line is perpendicular to burger vector

Decrease distortion equals increased distance to dislocation

Screw dislocation is parallel to burger vector

spiral planar ramp due to shear deformation

What is burger circuit?

Performed by making an number of steps in orthogonal direction around the dislocation line

Explain grains

Crystallite of atoms in which atoms pack in a repeated periodic arrangement

Grains can be equiaxed (same size in all directions) or columnar (elongated grains)

Preferably, who wanted it to be all in the same size so we use a green refiner to make it more equiaxed

Polycrystalline

Solid composed of many small grains

What is the angle of misalignment?

How the atoms of two different grains exhibit different orientations/ angle between two grain lines

What’s the difference between isotropic and anisotropic materials

Isotropic have non-directional properties (all energy is the same everywhere)

Anisotropic is directional

How can you tell if a single crystal or poly crystal is isotropic or anisotropic?

Single crystals are anisotropic and polycrystalline can vary

If grain is randomly orientated=isotropic, grains are textured=anisotropic

What is precipitation strengthening?

What is aging

what does alloying and crystal refer to

Different alloys reacting to a form a chemical compound (intermetallic compound)

Distortion and strain fields are located around and hinders movement of atoms therefore increase in yield stress/ strength

Aging is a very careful heat treatment

Alloying refer to a chemical composition (more than 1 element) and crystal refers to the microstructure

Strength

Hardness

Stiffness

The ability to withstand stress without fail

Resistance to local plastic deformation

Resistance to temporary plastic defamation

Malleability

Ductility

Toughness

Ability to plasticly deform under compression

Ability to plastic lead deform in tension

Ability to absorb energy and deformed plastically before fracture

Show the different directions for tension, compression, bending, torsion, shearing

Outwards, inwards pushing it together, bending is bending,twisting,sliding on a surface

Stress and equation

Force acting during deformation divided by the cross-sectional area

F/A

Explain a stress strain graph curve

Lower yield stress is normally taken to be the ….of the metal

Straight diagonal line is the elastic defamation region,start of curve is yield stress, the curve part is the plastic defamation region and where it stops is the sudden failure

Yield strength

Strain and its equation

Fractional amount by which a material deforms

Change in length/original length

Explain elastic deformation

For stresses less than your stress, only elastic/reversible deformation

Completely recover elastic strain on unloading

Metals have a small elastic strain of less than 1%

Hookes law

What is Young’s modulus? This isn’t really affected by…

Stress=strain x Young’s modulus

A constant for the material, measure of a material stiffness which equals the gradient of linear (hookes law) region on a stress-strain graph

It’s not affected much by alloying or heat treatment

Explain plastic/permanent deformation

Plastic yielding and work hardening starts at yield stress

Stress is greater than the yield stress causes plastic deformation and creates necking in the material

bonding wise, the planes will remain sheared

If dislocations can’t move, plastic defamation doesn’t occur

What is work hardening?

Strengthening a ductile material by plastic defamation at room temperature

Explain what happens at the upper and lower yield stress in terms of Lüder bands (stretch marks)

At upper your stress, one or more Lüder bands of plastic defamation spread across the specimen. Outside the bands it is all elastic.

I love you stress, each band stretches sideways until the entire length of specimen has yielded

Explain a continuous curve on a stress strain graph and what stress would you use in an equation?

This means that there is continuous yielding, therefore no unique yield point from elastic to plastic deformation

‘ proof stress’ will be used to measure the yield stress. The strain =0.2% typically

What is the actual definition of elastic and plastic deformation?

Initially, the material regains is exact original dimensions on unloading (hookes law region)

Start at end of purely elastic hooks law region. Occur in metals when dislocation start to move (slip),and such movement is permanent

hall-petch equation

Yield stress=initial or constant stress+k/sq root d

=initial stress+kd^-1/2

Where d is the grain size

As a test piece for sectional area decreases, the length increases this means that

True tensile stress experience locally in the centre of the piece will be greater than engineering stress and the true strain will be lower than the engineering strain

True stress and strain curve versus engineering stress and strain curve

True stress and strain equation

True stress-strain curve is higher and last longer whilst engineered is lower and fails quicker

True stress= initial stress(1+e)

True strain=ln(1+e)

For many metals, what is stress equation using work hardening

Stress=k x strain ^n

K is strain hardening constant

n is work hardening between 0.1 to 0.6

Stress and strain at ultimate tensile strength=

TRUE stress and strain at ultimate tensile strength

Strain hardening constant equation

True stress/true strain

True curve underestimates the material that’s why u need a corrected curve, why is this

Corrected true stress strain curve takes into account on the complex stress state within the next region

What is poissons ratio

What is the equation

What is avg poissons ration for elastic and plastic deformation

Positive longitude or true strain (increase in length) is strain1= ln(length/original length) and negative transverse (lateral) true strain (decrease in diameter) is straint=ln(diameter/original diameter)

-straint/strain1

Elastic,v=0.25-0.3 but volume does change

Plastic,v=0.5 for any metal (volume doesn’t change significantly

Effects on strain rate and its equation

if you pull the material quicker(faster strain rate) the material will resist strongly therefore the curve will move up the graph

Stress=coefficient(strain rate)^m, where m is less than 0.025

m=strain rate sensitivity

What is cold-working

What is work hardening equation

Work hardening and becomes stronger during plastic defamation at near room temp (T is less or equal to 0.3 melting temp)

Increase and strength and hardness, increase in ductility.This can be restored by annealing/re-crystallisation.

Differentiation of stress/strain

What is flow stress?

The stress required to continue plastic defamation at any point

What is hot forming?

Crystallisation simultaneous with plastic deformation

T is more than 0.5 melting temp

Approximate by assuming a constant mean yield (flow) stress (mean yield stress=true stress=tress at UTS

What is minerology

Tensile strength is proportional to

What is hardness an indication of

Ability to resist cutting or scratching

Brinell hardness (linear)

Indication of a materials malleability

What is UK standard measurment precedures for hardness testing

What could affect the values for hardness during testing

Vickers (HV) and Brinell (HB)

The type of inventor used since hardness is the resistance to indentation

Vickers hardness and strength is generally used for

Vickers hardness =

What is 1 kgf/mm² in pascals (pressure)

Non work-hardening materials ( doesn’t exhibit strain hardening)

About 3 x yield stress

1kgf/mm²=9.8×10^6 Pa

In a stress-straint graph, what does the area under the curve =

Is the curve ductile, tough or brittle if the curve is low but still continuing, high and still continuing or high but fails and drops down to the x-axis

Energy/unit volume or the materials toughness

Low curve means it’s ductile as its still continuing, high curve is the most tough bc it’s taking a lot of stress and the one that failed is most brittle

Why in materials would u prefer one that is most tough instead of hard

With a high toughness, you can see a physical indication one when it’s going to fail whilst it being hard is unexpected ( u can’t see when it’s gonna fail)

Ductile fracture properties

Brittle fracture properties

Slow, stable cracks (shear)

Lots of plastic deformation

Early evidence of twisting/tearing

Brittle is the complete opposite

Low energy absorption

Surface is either transgranular or intergranular

What is ductile to brittle transition temperature? (DBTT)

What is fractured toughness,Kic

Temperature range below which materials lose their toughness/transitioning from ductile to brittle, becoming more prone to failure fracture toughness

Material property which describes the inherent resistance of the material to failure in the presence of a crack-like defect(possible to compute the maximum allowable stress for a given flaw size)