Metals Flashcards
What does galvanised mean
Coated in zinc to prevent corrosion
What was the first 3 metals in order of use that was used by man to any significant capacity
copper from malachite (copper carbonate hydroxide), then bronze then iron
What are the three main types of crystalline structure present in metals
Face centred cubic (atom in each corner of the cube as well as one in the middle of the face)
hexagonal closed packed (two forms ABC in which the second layer atoms directly above the gaps of the first layer and the third layer lie directly above the gaps of the third layer and the ABA form in which the third layer is a repeat of the first layer)
body centred cubic (atom in each corner of the cube as well as one in the centre of the whole cube)
What are the 5 types of imperfections that can form in metals
substitutional atoms, interstitial atoms, dislocations, vacancies, grain boundaries
how do grain boundaries form
Metallic crystals each grow from their nucleation sites but when they meet there is a difference in orientation between the metals from different origin points.
How do imperfections increase the yield stress and toughness of metals
Dislocation cause high toughness by allowing stress to be relieved. Imperfections as well as other dislocations can obstruct dislocations, which increases yield stress, as the movement of dislocation causes permanent deformation (yield stress is the stress at which the material begins to deform plastically)
What is the composition of steel
Carbon 2%, 1% manganese small amounts of silicon, phosphorous, sulfur and oxygen and mainly iron
How many grades of steel are there
3500 and ongoing.
How much steel is produced per year
Around 1.9 billion tonnes
How can grains be altered to increase yield stress
Create smaller grains as the dislocations will have more grain boundaries to overcome as grains become smaller
Why did hammering steel increase its strength
Hammering increases the number of dislocations which serve as obstructions to other dislocations, increasing the yield stress
What is solid solution strengthening
The introduction of different atoms other than the metal into its structure which causes obstruction to dislocation motion
What is the precipitation strengthening
The introduction of a group of atoms which are not the metal atom into its structure which causes obstruction to dislocation motion
What does W/t % C mean
Weight percent of carbon
What is austenite
The face centred cubic phase of iron
