Alloys +

Useful information
Kit List: 

Cutlery, cheap stainless set more expensive stainless set (all spoons)
NiTinol springs
NiTinol Magic Tricks (Bending Paperclip and Heart Wire)
Normal steel spring
Heat gun and tongs
Other lumps of metal could be good needs more thought

Packing Away: 

This experiment now lives in the new small blue box called 'Periodic Table, Alloys and Carbon Allotropes', all three experiments may be done in combination. It's contained in a small Tupperware and a pencil case.
This experiment used to live in Misc box.

Frequency of use: 

EDIT: I (Yaron) am on tour at the moment but when I get back I will be working on a major overhaul for this experiment. Firstly, we'll be using cigarette lighters to heat the Nitinol because it's just so much more convenient than a kettle with water.

"But Yaron", I hear you say. "Won't the metal oxidise?" As Stephen Hawking used to say, "yes, probably." But we can replace it all when it stops working. We have loads of Nitinol, it can't be that expensive.

Also, I really want to take all the knives and forks out of the experiment since a kid threatened to STAB ME earlier. And we should replace the spoons with less rusty ones because it's difficult to demonstrate that stainless steel is oxidation resistant when all your SS samples have rusted.

Depending on how much steel is already in the demonstration, one could acquire a pearlite and martensite sample and compare their physical properties (strength, stiffness, hardness). This may have previously been a part of the demonstration but has since been taken out.

Finally, we should get a couple more samples to talk about because the demonstration is a little short. Perhaps an Al-Cu alloy to talk about age hardening? Can anyone convince the Materials Department to donate a single crystal turbine blade?
UPDATE: Yes, we may be able to get a defective sample from Rolls Royce. I discussed it briefly with Dr Catherine Rae (cr18) and she says it can be arranged. Will need to email at some point.

OLD RA. Updated on 20/01/2019 for use in its current state:

What is an alloy? A metal which is a metal mixed with something. More rigorously: A metallic solid or liquid that is composed of a mixture of two or more metals, or of metals and nonmetal or metalloid elements, usually for the purpose of imparting or increasing specific characteristics or properties.

Alloys may be homogenous or inhomogenous depending on how the different metals interact. This will have a large effect on the properties of the alloy, so alloying additions need to be carefully chosen to ensure you optimise the properties and don't ruin the stock.

The composition and manufacturing conditions of the alloy will determine which phases are present in the metal. A phase is the specific arrangement of atoms in the unit cell of a crystal lattice. For example in steels, the austenite phase is a face-centred cubic arrangement of iron atoms while the ferrite phase (typically more stable at room temperature) is body-centred cubic.

There is (or should be) a few phase diagrams in the box, which could do with laminating, that can be used to illustrate the different regions and what phases you'd expect to find in under certain conditions. Ask what they expect a material to look like under a microscope - all the same or different regions? Then introduce the micrographs and what they can see in them (also could do to be laminated, I can't remember exactly which ones I left in there...). They should notice the grains, some annealing twins in a brass, the grain boundaries and possibly notice the different appearances of the different phases. You can talk about how different phases form different grains, and discuss solidification if they're really keen.

There's a model of some hcp layers (looks like a Christmas tree kinda) that you can use to illustrate the idea of bcc, hcp and fcc structures. You can use this to explain the twins you see in the brass micrograph - they occur due to a stacking fault. Stacking faults can be illustrated by organising the layers of "atoms" in the model out of sequence to show that they can stack in different ways. The "twin" comes from the symmetry that arises either side of the twin boundary:



Note the shape of the twins - they're squarish. Compare to the idea of deformation twins, which are lenticular. Annealing twins arise from growth accidents at high temperatures. Deformation twins need to be lenticular to minimise strain energy, whilst annealing twins don't need to do this because there's no strain energy associated with their formation.

Say that you can tell how expensive someone's cutlery is from whether it is magnetic. Good stainless steel contains Cr and Ni, the Ni stabilizes austenite phase, which is not magnetic. Bad stainless steel contains just Cr, this means the ferrite (magnetic) phase is stable and therefore cheap cutlery is magnetic. The proportions are usually 18:10, 18:8 or 18:0 Cr:Ni - the higher the Ni content the higher the quality. Show that the good John Lewis stainless steel is non-magnetic and the cheap Asda stainless steel is magnetic. The result of this means the Asda cutlery scratches more easily, which makes it look less shiny.

(Look at other properties. Ask if they know the difference between hardness and toughness? Most won't, toughness is a measure of the amount of impact energy it can take before fracturing, whereas hardness is a measure of its how difficult it is to scratch. This is related to strength, which is a measure of how hard it is to permanently plastically deform.)

Finally, demonstrate the shape memory alloys. Ask members of the audience to deform the NiTinol wire sample. After this, tell them you will return it to its original shape. Heat up using the heat gun, holding the wire using a pair of tongs. If the wire has been tangled by an ambitious member of the audience, you may need to untangle it, as this may prevent the wire from uncoiling fully. The ideal geometry is to curl the wire into a spring.

Risk Assessment
Date risk assesment last checked: 
Sun, 20/01/2019
Risk assesment checked by: 
Yaron Bernstein
Date risk assesment double checked: 
Mon, 21/01/2019
Risk assesment double-checked by: 
Grace Exley
Risk Assessment: 


Hazard Risk Likelihood Severity Overall Mitigation Likelihood Severity Overall
Heat gun Fire risk and also the possibility of burns. 3 3 9 Demonstrator to control heat gun. Do not leave on. Keep flammable material away from the heat gun. Use stand instead of lying heat gun on a surface. Do not touch the heat gun.
In case of burns, run affected area under cold tap for 10 minutes. Call a first aider. Follow venue RA protocols in case of fire.
2 3 6
NiTinol wire and tongs hot when heated Risk of burns. 3 3 9 Do not let anyone near the heated wire. The wire is thin and should cool within a few seconds, but care should be taken with the tongs. If possible, obtain a heat-resistant mat to lay the tongs/wire on after heating.
In case of burns, run affected area under cold tap for 10 minutes. Call a first aider. Follow venue RA protocols in case of fire.
2 3 6
Cutlery Stabbing self/others 4 3 12 Don't use any knives or forks. 4 1 4
Magnets Skin getting caught between cutlery and magnet 3 3 9 Use weak magnet so won’t cause harm if occurs 3 1 3