0: Introduction to Materials Science

Summary

Ce module introduit la science des matériaux en abordant brièvement les quatre étapes clés de son étude : le traitement, la structure, les propriétés et les performances. Le traitement des matériaux influence leur structure, qui à son tour détermine leurs propriétés, et ces propriétés affectent leur performance dans des applications pratiques. L'accent est mis sur la compréhension des liens entre microstructure et propriétés, et comment le traitement peut modifier la microstructure pour obtenir des propriétés désirées. Les principaux types de matériaux abordés sont les métaux, les polymères et les céramiques, et l'importance de la variabilité des propriétés est soulignée.

Takeaways

• 🔬 La science des matériaux étudie le traitement des matériaux et son impact sur leur structure.
• 📐 Les propriétés des matériaux sont influencées par leur structure, qui à son tour est affectée par le traitement.
• 🔩 Les propriétés telles que le point de cession, le module d'elasticité, la résistance à la rupture ou la ductilité peuvent être modifiées par le traitement.
• 🔧 Le module d'elasticité est principalement déterminé par le matériau choisi, tandis que la résistance à la rupture ou la ductilité peuvent être significativement contrôlées par le traitement.
• 🔄 Le comportement de la fatigue des matériaux peut être modifié en changeant leur structure grâce au traitement.
• 🏗️ Les propriétés des matériaux déterminent leur performance dans des applications telles que les engrenages ou les lames de turbine à gaz.
• 📊 Les diagrammes de phases, comme celui du fer-carbone, sont essentiels pour comprendre comment ajuster la microstructure et les propriétés des matériaux.
• 🤔 Deux questions fondamentales seront abordées : comment la microstructure influence-t-elle les propriétés, et comment le traitement influence-t-elle la microstructure.
• 🧐 La classe explorera la raison pour laquelle certaines propriétés, comme la résistance à la rupture du fer comparée au fer pur, sont différentes.
• 🌟 Les trois grandes catégories de matériaux sont les métaux, les polymères et les céramiques, chacun ayant des propriétés distinctes et des applications spécifiques.
• 📊 Il existe une grande variabilité dans les propriétés des matériaux, allant de la rigidité à la densité, et la classe vise à expliquer les raisons de cette variabilité.

Q & A

Quel est le premier stade du cycle de la science des matériaux mentionné dans le script?

Le premier stade mentionné est le traitement, illustré par l'exemple de métal chauffé dans un four puis trempé dans un bain d'huile.

Comment le traitement des matériaux affecte-t-il leur structure?

Le traitement des matériaux, comme le chauffage et le trempage d'un métal, peut influencer l'arrangement atomique et la taille des grains, ainsi que la formation des limites de grains.

Quels sont les deux grands types de structures mentionnés dans le script qui sont affectés par le traitement des matériaux?

Les deux types de structures mentionnés sont l'arrangement atomique et les grains avec leurs limites de grains.

La structure influence-t-elle les propriétés des matériaux?

Oui, la structure influence les propriétés des matériaux, comme le point de cession, le module d'elasticité, la résistance à la rupture et la ductilité.

Quels sont les exemples de propriétés des matériaux qui peuvent être facilement ajustées par le traitement?

Les propriétés telles que la résistance à la rupture, la force de cession et la ductilité peuvent être significativement ajustées par le traitement des matériaux.

Comment le script relie-t-il les propriétés des matériaux à leur performance dans des applications?

Le script indique que les propriétés des matériaux, une fois obtenues, déterminent leur performance dans des applications telles que les engrenages ou les lames de turbines à gaz.

Quelle est la différence clé entre l'approche de ce cours et les cours précédents sur la mécanique des matériaux?

Dans ce cours, l'accent est mis sur la façon dont le traitement et la composition des matériaux influencent leurs propriétés, plutôt que de calculer la réaction des matériaux à un chargement donné.

Quels sont les deux questions fondamentales abordées dans le cours?

Les deux questions fondamentales sont comment la microstructure affecte les propriétés et comment le traitement affecte la microstructure.

Quels sont les trois grands types de matériaux discutés dans le script?

Les trois grands types de matériaux discutés sont les métaux, les polymères et les céramiques.

Comment le script explique-t-il la variabilité des propriétés des matériaux?

Le script montre que les propriétés des matériaux, comme le module d'Young, varient considérablement et souligne la nécessité de comprendre pourquoi cela se produit et comment on peut les modifier.

Outlines

00:00

🔬 Introduction à la science des matériaux

Le premier paragraphe introduit la science des matériaux comme un domaine d'étude qui se concentre sur le traitement des matériaux, l'effet de ce traitement sur leur structure, et comment cette structure influence les propriétés. On explique que les sciences des matériaux examinent les transformations à l'échelle atomique, comme l'arrangement des atomes et la formation de limites de grains, qui sont influencées par les processus de traitement. Les propriétés telles que le point de cession, le module d'Young, la résistance à la rupture et la ductilité sont mentionnées, soulignant que certaines propriétés peuvent être ajustées par le traitement. Le paragraphe conclut en soulignant que les sciences des matériaux étudient la manière dont les propriétés des matériaux sont affectées par leur structure et leur traitement, et comment ces propriétés influencent leur performance dans des applications pratiques.

05:02

🔧 Comment le traitement influence la microstructure

Le deuxième paragraphe se concentre sur la relation entre le traitement des matériaux, leur microstructure et leurs propriétés. Il est expliqué que le traitement, comme le chauffage et le refroidissement rapide (trempage), peut changer la structure interne des matériaux, affectant ainsi leurs propriétés mécaniques telles que la résistance à la rupture et la ductilité. Le paragraphe met en avant l'importance de comprendre comment le microstructure, qui peut inclure des arrangements atomiques et des structures de grains plus larges, influence les propriétés des matériaux. De plus, il souligne que le cours ne se concentrera pas sur les calculs quantitatifs, mais plutôt sur la compréhension conceptuelle de la manière dont les matériaux se comportent.

10:03

📚 Catégories de matériaux et leurs propriétés

Le troisième paragraphe présente une vue d'ensemble des principales catégories de matériaux : les métaux, les céramiques et les polymères. Chaque catégorie est décrite en termes de leurs propriétés générales, telles que la force, la ductilité, la densité, la conductivité thermique et électrique, et les propriétés optiques. Les métaux sont décrits comme étant généralement forts et ductiles, avec une haute conductivité thermique et électrique, tandis que les polymères sont faibles, flexibles et ont une faible densité et des propriétés de conductivité réduites. Les céramiques sont décrites comme étant fortes mais cassantes, avec une faible conductivité thermique et électrique, et des propriétés optiques variables. Le paragraphe illustre également la variabilité des propriétés des matériaux en montrant un exemple de la variété des modules d'Young en fonction de la densité pour différents types de matériaux.

Keywords

💡Traitement des matériaux

Le traitement des matériaux est un processus par lequel les matériaux sont transformés pour améliorer leurs propriétés ou les adapter à des applications spécifiques. Dans le script, l'exemple donné est celui de métal chauffé dans un four et ensuite trempé dans un bain d'huile, ce qui montre comment le traitement peut influencer la structure et les propriétés du matériau.

💡Structure

La structure fait référence à l'organisation des atomes dans un matériau, y compris leur arrangement atomique et la distribution des grains. Dans le contexte du script, la structure est cruciale car elle est directement influencée par le traitement des matériaux et détermine les propriétés du matériau.

💡Propriétés

Les propriétés sont les caractéristiques physiques et chimiques d'un matériau qui déterminent son comportement et son utilisation. Elles sont influencées par la structure du matériau, comme l'indique le script, et peuvent inclure la résistance à la rupture, le module de Young ou la ductilité.

💡Performance

La performance d'un matériau fait référence à la manière dont il se comporte dans des applications réelles, telles que la résistance à la fatigue ou la capacité à supporter des charges. Le script mentionne que les propriétés, qui sont influencées par le traitement et la structure, déterminent finalement la performance du matériau dans des applications telles que les engrenages ou les lames de turbine.

💡Phase diagramme

Un diagramme de phase est un outil utilisé pour représenter les états de la matière sous différentes conditions de température et de composition. Dans le script, il est mentionné que les diagrammes de phase, comme celui de fer et de carbone, sont utilisés pour comprendre comment ajuster la microstructure et, par conséquent, les propriétés des matériaux.

💡Microstructure

La microstructure est la structure d'un matériau à une échelle plus petite que celle visible à l'œil nu, y compris les grains et les grain boundaries. Le script explique que la microstructure affecte les propriétés des matériaux et que le traitement des matériaux peut changer la microstructure.

💡Traitement thermique

Le traitement thermique est une méthode de traitement des matériaux qui implique des opérations telles que la chauffe et le refroidissement rapide (trempage) pour modifier la structure et les propriétés du matériau. Le script mentionne le trempage comme un exemple de traitement thermique qui affecte la structure et les propriétés du métal.

💡Alliage

Un alliage est un matériau composé de deux ou plusieurs métaux, ou d'un métal et d'un non-métal, qui ont été fusionnés pour créer une nouvelle substance avec des propriétés différentes de ceux des métaux purs. Le script souligne que les alliages sont souvent utilisés plus fréquemment que les métaux purs en raison de leurs propriétés améliorées.

💡Céramiques

Les céramiques sont un type de matériau inorganique non métallique, souvent utilisé pour ses propriétés de résistance à la température élevée et de résistance mécanique. Le script les décrit comme étant dures mais cassantes, avec une faible conductivité thermique et électrique.

💡Polymères

Les polymères sont des matériaux organiques composés de grandes chaînes moléculaires formées par des liens covalents répétés. Dans le script, ils sont décrits comme étant généralement faibles, ductiles et de faible densité, avec des propriétés optiques et de conductivité qui varient largement.

Highlights

Introduction to material science and its focus areas.

Material science encompasses four different stages: processing, structure, properties, and performance.

Processing of materials affects their atomic structure and grain boundaries.

The atomic arrangement and grain structure can be impacted by processing methods like heating and quenching.

Properties of materials, such as yield point or modulus, are influenced by their structure.

Some material properties are easier to control through processing, like yield strength or ductility.

Fatigue behavior of materials can be altered by changing their structure through processing.

Application of materials with desired properties in real-world scenarios like gears and gas turbine blades.

The course focuses on understanding how processing affects material properties rather than just calculating stresses and strains.

Phase diagrams, like the iron-carbon phase diagram, are essential tools for understanding material properties.

The class aims to answer fundamental questions about how microstructure affects properties and how processing affects microstructure.

Examples of questions explored: Why is steel stronger than pure iron, and why do alloys have different properties than pure metals?

Material properties can vary greatly, and the class will explore why and how we can control these variations.

Overview of the three broad classes of materials: metals, ceramics, and polymers, and their general properties.

Metals are typically strong, ductile, and have high density, thermal, and electrical conductivity.

Polymers are generally weak, ductile, low density, and have low thermal and electrical conductivity.

Ceramics are strong but brittle, have medium to high density, and low thermal and electrical conductivity.

The class will cover the processing, microstructure, and properties of metals, polymers, and ceramics.

Material properties can span a wide range, such as the seven orders of magnitude difference in Young's modulus.

The course will explore the reasons behind the variability in material properties and how we might change them.

Transcripts

in this module i want to give you just a

a very

a brief and high level introduction to

material science and

and kind of tell you what what the focus

of it is

so let's let's let's begin it actually

encompasses in this case

sort of four different

stages i guess if you will or steps the

first

is processing and i'm showing you here

somebody putting metal into a furnace

and then

in the next image uh it's it's taking

that hot metal and dunking it into an

oil bath so that's just an example of

processing

so material sciences is fundamentally

interested in the processing of

materials

specifically for what the processing

does to the structure

so if i do in this case

a heating and quenching of a metal for

example

what happens to the structure and why so

in this case i'm showing you here um

in these images uh you can see that this

is a atomic arrangement so these are

this is actually a high resolution

electron micrograph of uh or microscope

image rather of

an atomic configuration those the atomic

configuration itself can be

impacted by the processing as well as

the arrangement of what are called

grains

we'll talk about that later on in this

class but essentially it's it's

an arrangement of different orientations

of

groupings of orientations of atoms so

they come together to form grain

boundaries and that's what you're

looking at there

the processing that we might do to a

material affects everything at the

the atomic level but even up to a little

bit more macroscopic level you have like

a one millimeter

scale bar on that image the

the next um facet that we want to focus

on after structure

is the properties right so the

processing influences the structure

and the structure influences the

properties so you could think of

properties very simply as something like

the

the yield point or the modulus or

something like that and some properties

are going to be more easy to tune

and easy to control than others for

example modulus

is not something that we can easily

control it's pretty much dictated by the

the material that we choose whereas

something like

um yield strength or ultimate strength

or ductility

those are things that we can control uh

significantly with the

processing so that's that's that's one

component the other image

i'm showing you here on the far right

this is just a

typical fatigue curve so you have stress

on the the

y-axis and number of cycles on the the

x-axis so this is showing you

differences in materials

of their fatigue behavior and we can use

processing to change the structure

to change the fatigue behavior of the

material

and then finally once we have uh the

properties that we want we can apply

them in some sort of a

an application so we can look at the

performance whether it's gears

like i'm showing you on the left or on

the right i'm showing you a

uh the hot stage blade of a gas turbine

engine

um so those are that's sort of the

the way that we think in material

sciences

processing affects structure structure

effects properties and properties affect

performance

and that's what we're going to focus on

in this class but i would say too that

as you enter this class

i want you to be aware of some

differences from from previous classes

so

in your previous courses this is maybe

taken from a mechanics of materials

course

you were given some shape some material

properties some load scenario

and then you're asked something like

what's the maximum stress or strain or

what's the deflection that's achieved

under a particular force

okay so that that's that's a very

valuable engineering skill to have

that isn't the focus of this course okay

in this course

we're going to say given some material

composition and processing

what are the material properties and

then and then beyond that

how might we change them for for our

purposes

um and so what i'm showing you here and

i don't expect you to have seen this

before on the left hand side

this is what's called a phase diagram

we're going to spend a long time

working with these you're going to

become very familiar this is the iron

carbon phase diagram so

uh we're gonna we're gonna talk about

how we can use these kinds of

um uh this kind of information to

understand a little bit about

uh how to tune the microstructure and

then ultimately the properties

of something like steel again i'm just

showing you here a grain structure of

of steel uh and and the focus of this

class is how are we going to be able to

change those

all of that at least as far as this

problem above is concerned

is to say well we could change the

elastic modulus because we are going to

potentially change the atomic

arrangement

we could also change if we were actually

trying to solve for something like

strength

we could change the strength we could

change the ductility we could

so in the problem above with the this um

simply supported beam we could we could

focus on something like how could we

uh prevent failure or or make the

make the apart more robust so so our

focus though is going to be on how can

we change those material properties

and it's going to be a little bit less

quantitative than you're probably used

to

so we're going to talk about what

happens and why it changes the

properties

but it's it's not going to be a memorize

the method

and then apply it in different scenarios

it's going to be conceptual

trying to understand what is it that

makes materials behave the way that they

do okay

so the i would say that if i want to

really boil it down there are two

fundamental questions that we're going

to ask

in this class the first is how does

microstructure

affect properties so this is gonna this

is gonna take the form of

questions like the following why is the

yield strength of steel

higher than pure iron maybe you didn't

know that but that is the case

what is it about steel that makes it

different

in fact what does what what is what

allows the material to yield anyway

we're going to talk about that

another question that might be along

these same lines why do we oftentimes

see alloys being used more often than

pure metals what is that what is that

doing for us

we're gonna talk about that in this

class

and then something that maybe you've

never thought of why is it that glass

shatters and copper bends you know

ceramics in general glass in particular

has a very high strength

so why is it that we don't build um

bridges out of glass and would you feel

comfortable

driving over one i surely wouldn't um

so so we want to ask questions about

what is it about their

uh what is it about their structure that

gives them properties that make them

suitable for some purposes and not

others

um another simple one why are rubber

materials

uh lighter and more ductile than metals

you know i think everybody knows the

that they are right i would say all of

these for the most part people

realize that they are but i don't think

very many people can tell you why

we're going to be able to do that by by

the end of this class

okay so that that one the one

fundamental question that we'll be

asking throughout the class is how does

microstructure affect properties

and we'll look at microstructures that

range from atomic arrangements all the

way up to a lot more large scale

microstructural features

the second question is how does

processing affect microstructure

so those are that's really where we're

going to hone in on so

for example just a couple brief

questions why is it that we quench

steels after we heat them up

what is it that we're doing to them how

does that processing affect the

microstructure

and then finally uh why why would be we

expect or see the grains again you don't

necessarily know what grains are but

it's a it's a larger scale feature of

the microstructure

why are they larger in annealed aluminum

than heat treated aluminum

um we're going to be able to answer

those questions and and of course

uh in addition you'll know why one gives

you different mechanical properties

than the other so globally i want you to

come away with the idea that we're going

to study

why materials behave the way that they

do and we're going to ask how we can

control that behavior

okay all right so i want to give you

a brief overview of categories of

materials

so and i think again some of this stuff

you know we're just going to put a

little bit of

sophistication on your knowledge here so

uh

i think you're familiar with metals

ceramics and polymers

these are the three really broad classes

of materials that are out there

and if i were to show you a picture of a

metal this widget whatever it is

uh you'd be able to look at it and say

yeah that's a metal and

and uh in part i'm asking you why how do

you know what

what makes a metal different than a

polymer what makes a polymer different

than a ceramic

and and we also know something about

these broad classes of materials have

relatively consistent properties for

example

we know that metals are typically strong

in ductile right

and and we also know that they are high

density

if we're talking about thermal

conductivity just leave a fork in a

pan pot of boiling water for a while and

grab the end of it and you'll see that

it has high

uh thermal conductivity uh similarly if

if you've ever been shocked before you

know that we of course run wires with

metal because they are also electrically

conductive so it has thought

high thermal and electrical conductivity

looking at it probably when i first

popped this image up you could tell it

was a metal why

because it was opaque and typically

metals are optically reflective so it's

a bit shiny right

how about polymers well they have

another sort of set of properties

so here i'm just showing you an isla a

nylon rope but in general when you think

of polymers you probably think of them

as

weak and relatively ductile and that's

typically the case that's not to say

that we can't make a

very brittle polymer um in general we

still can't make a super strong polymer

maybe i'll just there's there's a couple

small

classes where that might be true maybe

in things like

armor and toe straps but as a general

rule uh polymers are are pretty weak

they're typically low density that's

that's what makes them nice to use in a

lot of applications

they also have low thermal and

electrical conductivity um

and they're you they can vary all over

the map in terms of their

their optical properties right they

could be opaque um they could be

translucent or they could be transparent

all right we we've we've seen things

that are

like um polycarbonate or something like

that but we can see through okay so

so that's a second class and our final

class is ceramics here i'm showing you

just a couple coffee cups obviously that

are ceramics

some things that you probably know about

ceramics they're strong

but they're brittle right they snap they

don't bend very well

uh they have they typically are high

density but i would call them medium to

high density

because in general they don't achieve

the density of metals but they're

significantly heavier than than polymers

and if you're if you're drinking a cup

of coffee uh the conductivity is of

importance to you

you'd like that to be low so it has low

thermal conductivity right so it doesn't

burn your fingers

in contrast to if you're a hiker or

something and you use those ridiculous

tin cups for hiking and

you pour a cup of hot coffee in there

and then probably burn your fingers off

i don't understand the purpose of that

but nevertheless

uh we don't typically drink hot drinks

out of

high conductivity materials so you know

that ceramics don't conduct well they

also don't conduct

electrically very well in fact they if

you look up on uh

your power poles you'll see big ceramic

uh

insulators on there

and in terms of the optical properties

of ceramic

uh they can they can span the spectrum

so they can be opaque like the coffee

cups here

or they can be transparent like your

glass windows okay

so those are the broad categories of of

materials

we're going to talk about each of them

we're going to spend the bulk of our

time on metals since

for most engineering applications they

probably are

are the dominant material but we're

going to talk uh significantly still

about polymers and ceramics

both in terms of processing

microstructure and

properties okay i want to just give you

a little example to kind of show you the

the the diversity of properties that we

have

in materials so what i'm showing you

here is the stiffness on the the y-axis

uh or you can think of that as the

young's modulus in gigapascals

and then on the x-axis is giving you

density and just showing you that

uh for the for materials we actually

have a seven

order of magnitude difference in uh

the young's modulus and and you can see

that

in general lower density materials have

a lower modulus but

but not universally so right you can

have

elastomers which have relatively low

modulus and then higher densities

but then we get up into the metals high

densities and high modulus

ceramics are in this regime polymers are

in this sort of intermediate regime

where they're lower density but also

lower modulus

so i just want to show you that there's

a tremendous variability in material

properties

and what we want to be able to answer

clearly is why is that

and then maybe we could change some of

that so why why do we see

that and then looking at density it

varies here by four orders of

magnitude why is that um we're going to

talk a lot about

these things as we move forward in the

class but i just wanted to wet your

appetite

and give you a little bit of a flavor

for for what you can expect

in the class going forward