Lecture 1 Materials Engineering Introduction

1. Lecture 1 Materials Engineering Introduction Ahmad Asadi (MSc, BEng Civil & Structural) ENG-1020: Introduction to Materials Engineering

2. About this Course

3. Contents • Material Engineering • How to make useful things • Materials • Material properties • Processes • How to shape / join materials • Design • What choices of materials & processes to produce a thing of value.

4. History of Materials • Materials have been used to advance / change society • Functional reasons: do new things, Do old things better or more efficiently • Human reasons: psychological, societal, Power, status • We talk of the “Stone Age”, the “Bronze Age” and the “Iron Age” • These refer to the dominant materials that defined these societies • Today we might be in the “Silicon Age” - but things are changing so quickly that Ages are becoming Decades • Most of the materials we use today have been developed in the past 100 years!

5. History of Materials • Next slide shows the development of materials over time. • Materials of pre-history are on the left and occur naturally • The development of chemistry and polymers enabled man-made materials shown in the coloured zones on the right.

6. Timeline of Materials

7. History of Materials • 10000 years ago most of the materials were naturally occurring • Some processes were developed such as Weaving, brickmaking, cloth making, tool making. • As each Age came, new processes allowed the development of new materials. A few hundreds more materials perhaps • In the past 100 years this small number has grown enormously – we now have 160,000 different materials that we have developed and “know” • Light alloys (new to this century – 1000's) • High performance composites (new to this century – 100's) • Synthetic Polymers and elastomers gels and foams (new to this century – 45000) • This wealth of choice is a key problem. We need to know: • Broad categories of materials , categorized by useful properties • How to select the “best” material for a purpose

8. History of Materials e.g., airplane design Over one generation of airplanes, engineering has changed dramatically:

9. History of Materials • The forces for change are many • Power, political, military, economic • Human / social, recreational • Need • Food • Clothing • Shelter • Protection from elements, disease, enemies • Curiosity

10. Materials, Process and Design • Making useful things is a three-part process • The parts are not independent • Ultimately, you need to make something that will be economically viable • i.e., it makes money as a regular commercial item • or... governments (who have lots of money) are willing to buy it • The broad flow of the design process might be as follows:

11. The Design Process & Its Inputs

12. People and the Market • In developed countries there are many technically good products • It is often desire (not need) which drives markets • Greater functionality, or cross functionality “Mash-Ups” • Novel behaviour get valued – they have a “Cool factor” • Designers sometimes respond to market needs • Customer surveys, etc. • Exploration of human behaviour to understand what people want, need, and can become entrenched in their normal life • “Design Research” / “Human Factors Design”

13. People and Markets • But some products are truly revolutionary and take everyone by surprise. • Designer identifies an unknown “need” or “desire” • Creates a product that meets the need • Then with the right marketing, the need is felt through the society and a new market is born • Watches, iPhones, iPod's, Walkman's etc.

14. Other Design Drivers • Science and Technology • Continue to expose new opportunities by advances in material and processes • Being able to maintain a set of ideal properties over a wide range of environmental conditions is the ultimate goal. e.g., Tires that don't melt in driving across lava. • Miniaturization • Efficiency

15. Other Design Drivers • Sustainability and the Environment • Human activity has an impact on all life • Some of this can be absorbed without upsetting the balance of nature • This has become untrue more frequently in the past 100 years • Legislation is becoming a hard condition which must be met and so can have impact on any design • Environmental friendliness however can be a goal of “eco” companies and can become a driver of design in its own right

16. Other Design Drivers • Economics and Investment Climate • The time needs to be right for certain investments • Investment in a new product requires confidence in the product and the general economic and political climate • Patent issues are also important – is development protected for some time? • Products are economically viable if their value in the marketplace is greater than the cost by a significant margin • This is the cost of “risk” • How much can you sell, and for what price? Some products have value to some of the market, but different value to other parts of the market • Titanium bicycle: valuable to cycling enthusiasts, but not to grandma who goes shopping at low speed

17. Other Design Drivers • Aesthetics, Behaviour and Overall Design • Aesthetics inspire, excite. Aesthetically pleasing products want to be touched and used. They feel good, smell good. • They stimulate your senses - so that you want them, so that you get memories, feelings: • Touch – Warm / Cold / Soft / Hard/ Flexible/ Stiff • Sight – Clear / transparent / translucent / opaque / reflective / glossy / matte / textured • Sound – Muffled / Dull / Sharp / Resonant / Ringing / Low Pitch / High Pitch • Taste / Smell – bitter / sweet / natural / industrial

18. Other Design Drivers • “Form follows function”. i.e., you need to have a product that functions properly. Then you give it a form. But the form can actually be quite important: • Product differentiation • Simple interfaces / ease of use (“It just works”) • Corporate or brand identity • Product life: “iconic” designs last well beyond their design life (classic cars, etc)

19. Gold, Sand and String • Gold sand and string are just some of the materials around us • They are dissimilar and so deserve special stories • They represent the metallic, the inorganic and the organic resources of the world • Gold → bronze → iron → modern metals • Sand → stone → clay → silicon • String → rope → cloth → rubbers and elastomers

20. Gold • Pure gold coins stamped with a lion and a bull were made in Anatolia in the 6th century BCE under the rule of King Croesus • “rich as Croesus” • Each weighs about 8gm • Like a jelly bean, with 25 billion x trillion atoms of gold (Au) • Gold has only one stable isotope, so the atoms are all the same

21. Gold • The coins were made by melting gold and then stamping them with the images • When the gold cooled the gold settled into an arrangement which is called “crystalline” • Atoms are regularly arranged in a crystal pattern • X-ray diffraction shows this clearly • Gold is a “cubic” pattern (face-centred cubic, fcc) • From the X-ray analysis we know that the edge of each face is 0.41 nm

22. Gold • But it's not just one big crystal! • Crystallization starts at the same time at many places in the liquid gold • Lots of little crystals form, and they meet up at crystal boundaries • Each little crystal has a random orientation and usually doesn't match its neighbours • Get crystal boundaries

23. Gold • Naturally occurring gold is usually not pure. King Croesus' gold was about 25% silver • He was able to make pure gold by refining: • Beat the gold into thin sheets • Place in layers with salt and other materials • Heat to just below melting point of gold about 1000 C – the salt combines with the silver and leaves behind the gold • The remaining gold has lots of little tunnels but is made pure and solid by beating it

24. Gold • Other atoms might be in gold too: • Copper (found in Egyptian rose gold – 10% Cu) and iron (Fe) will dissolve in gold • The Cu, Fe are about the same size as a gold atom and so can be substituted into the crystal matrix • Platinum, osmium, iridium – can be found mixed in but do not dissolve – they are usually separate particles • The overall composition of a metal can identify where it is from – most places have a unique signature for the amount of additional trace elements that they contain • e.g, 8th century gold coins in Spain had a markedly lower tin content (Sn) than previously – indicative of the Arab conquest because the gold came from West Africa

25. Bronze Bells • Copper is abundant but soft • Melts at a fairly low temperature (1100 C) which can be achieved with primitive furnaces • Discovered that bronze could be made: an alloy of copper and tin • Much harder, useful for weapons and tools • 4 parts Cu, 1 part Sn • Bells made of bronze don't crack when struck, and retain an audible ring for up to a minute after being struck • Has to do with the speed of sound in the alloy • Now have many other Cu alloys: • Zinc-Cu (“brass”), Nickel bronze, Aluminum bronze, silicon bronze, phosphor bronze etc. • All are used in mechanical engineering

26. Copper • Huge increase in Cu production in 19th century • Copper is an excellent conductor • People found uses for electricity including telephone cables • Transatlantic cable laid but it was unreliable • Didn't understand the resistivity of the copper was strongly affected by impurities – higher purity, higher conductivity (lower resistance) • Developed methods for making 99.999% pure copper – dissolve in acid bath, and redeposit the Cu ions on the cathode of a battery

27. Steel • Small scale steelmaking by blacksmiths has been done for a long time – knowledge of forging, annealing, quenching, tempering was well known • Iron melts at 1500 C which is much hotter than primitive furnaces can be • “Big Steel” started in the 1850's when blast furnaces were built to perform molten steelmaking. • Steel is Iron with embedded carbon. • There are many, many kinds of steel • But it is very complicated and exactly how you make it will control what you get

28. Steel • Other iron alloys were also made • Iron + Manganese (Mn) – strong and tough • Iron + Chromium (Cr) – resists rust • Iron + Tungsten (W) – extremely hard even at high temperatures • Big picture eventually followed: • Steel is made by reducing carbon content from 4% to lower value • Steel properties depend on exactly how much carbon (or other elements) there is, plus how it is made in terms of temperature and process

29. Sand • Silicon (Si) and oxygen (O) are the most common elements on earth, and together form quartz crystals, sand (Si-O-Si) • Quartz is a crystal – but is difficult to make! • Requires very slow cooling of quartz – geological time. • Too rapid cooling – and a glass is formed. • Glasses are not crystalline – but “nearly” • They are actually extremely thick, viscous liquid: glass “flows” • Cathedral windows which are 500 years old are turned upside down to get the glass to flow the other way: the glass was getting noticeably thinner at the top and thicker at the bottom

30. Sand • Calcite / sand are used in the making of cement and concrete • Clay is another natural material that is actually made of nano-particles – little crystalline plates • Under right heat conditions, these can be made to form new materials like ceramics • Clay is combined with limestone to make Portland cement- the key ingredient in making concrete (together with sand and water) • Under right heat conditions – about 1400 C – the calcium silicates produced are the key ingredients in cement.

31. Strings • Long “macromolecules” were first discovered about 100 years ago – cellulose • It is the main component of all green plants. • Cellulose is very long – in cotton it can be 10,000 units long. • It is not branched • Contains O and H – and so when cellulose molecules lie side-by-side they get linked by relatively strong chemical forces • Parallel chains will pack tightly in a crystalline way

32. Strings • Rubber is also a long stringy molecule • It is a hydrocarbon, with no oxygen and so the chemical forces between the chains is very small (van der Waals forces) • Rubber molecules are like chains of spaghetti, all mixed up and tangled

33. Strings • Cellulose goes to making wood and paper • Other fibrous materials like cotton, wool, silk – have similar properties and great importance • Strong in tension, not so good in compression • Side-bonding between chains makes a lot of difference in the material behaviour

34. Others Materials? • Not everything is a metal, polymer or ceramic. • Water • Diamond? • Semiconductors • In general the periodic table has metals in the left side, toward the right are the non-metals and the far right column is the noble gases. • Any new materials we make will depend on the proportion and arrangement of specific atoms, as well as how we “cook” the final product.