Polycrystalline Ceramics: Sub Grain Structure

Pure un-doped zirconia is a polymorph which includes three allotropes specifically: Monoclinic, Tetragonal and lastly Cubic. These phases tend to enhance into each other when subjected to certain temperature amounts and such change is important for the processing and mechanical properties of zirconia. The monoclinic period of genuine un-doped zirconia is secure at room temps and remains so up to about 11700C, where it then changes into tetragonal phase. It becomes stable tetragonal at this heat range and remains so up to 23700C, where it turns to cubic. The cubic stage occurs up to the melting temperature of 26800C.

Monoclinic phase

The monoclinic form generally known as baddeleyite, is a thermodynamically stable period at a temp range between room temps and about 9500C. It includes four ZrO2 molecules per product cell and has a space group of P21/c. Physique 2. 1 shows the lattice parameter of monoclinic form. Its composition is referred to as a distorted fluorite (CaF2 structure). It is difficult to explain the crystal composition of monoclinic zirconia because of its complexity as well as the problem of making a monoclinic single crystal with the reasonable qualities credited to: micro-cracking, low purity, twinning and disproportionate stable solution creation.

Tetragonal phase

This is a high temperature phase (t) firstly uncovered by several scientist during its change from the lower temperature monoclinic stage over a temperature of about 11500C. Number 2. 1 shows the lattice parameter of tetragonal form. The structure is comparable to that of monoclinic polymorph in the sense that it is also distorted CaF2 structure. Hence, tetragonal zirconia (t-ZrO2) can be identified using the face centred tetragonal Bravais lattice as oppose to the body centred tetragonal lattice, which has a unit cell with volume twice the size of the primitive cell. (3) Shape 2. 2b shows a straightforward schematic of the tetragonal product cell. Its framework consists of eight oxygen ions encompassing a zirconium ion, with 1 / 2 far away of 0. 2455nm forming an elongated tetrahedron and the remaining four are at a distance of 0. 2065 creating a flattened tetrahedron (the elongated and flattened tetrahedron are rotated 900 to one another). The transformation from tetragonal to monoclinic can start (Ts) and finish off (Ts) over a variety of temperature. This reaction can be measured using the following experimental techniques: DTA, XRD and dilatometry. (3)

Cubic phase

Unlike the other structures, the cubic polymorph is quite easy to clarify as it has a fluorite composition (CaF2). Figure 2. 2c shows a straightforward schematic of a tetragonal product cell. It has a lattice parameter of the order 0. 508nm (this however is determined by the temperatures purity of zirconia that is partly stabilised zirconia at room temperatures or 100 % pure zirconia at increased temperatures) and a crystal symmetry of Fm3m.

The martensitic transformation

For a martensitic change to occur, a change in shape is necessary which must produce a aircraft that will not change during transformation. This is such that it is common to the phase produced as well as the mother or father phase. The phase change in zirconia entails a change in level of between 4 to 5%. The matrix inhibits the altered particle of zirconia leading to a partial condition change. However, the change creates a tension which is presented in the monoclinic and its surrounding grains. Because of this, researchers attended up with the idea that transformation stresses are relieved by deformation twinning. At these times, most of the lattice stress is then limited to the monoclinic/matrix software. Micro-cracks can be developed as of this matrix/monolithic software or in the monoclinic particle if this lattice strain rises. The twinning within monoclinic is brought on by deformation twinning, as the researchers have witnessed using TEM that a section of any risk of strain related to the transformation happens therefore of a device known as slip. (3)

The phase change particularly from tetragonal to monoclinic is of great importance, as it attributes the zirconia's excellent properties. [from fulltext. pdf] It had been firstly found out by Garvie et al that the transformation of metastable tetragonal phase to monoclinic phase operates as a toughnening mechanism to crack propagation level of resistance in zirconia. The transformation is quick and results in a 4 to 5 percent increase in volume which contributes to development of micro-cracks and eventually macro-cracks in the material. This process induces compressive tensions and thus toughens the materials. Gupta et al guaranteed this theory up. Studies proved that the transformation mechanism is highly reliant on grain size and by doping the ceramic material with stabilisers. Examples of stabilisers are yttria (Y2O3), magnesia (MgO), calcia (CaO), etc. Y-TZP ceramics is in the category of these toughened materials. Tetragonal zirconia doped with Yttria (Y-TZP) has great power of over 1000MPa and toughness weighing between 6 and 10 MPa. m1/2. This helps it be an excellent contender in medical applications, especially in hip joints.

ZrO2 - Y2O3

The period diagram shown in body 3 was first of all learned by Scott (1975), this study was decided and utilized by many more experts. The tetragonal phase field is the main aspect of physique 3. It shows that up to about 2. 5mol% of Yttria can be stated in stable solution in addition with the reduced eutectoid temperature leading to the forming of a fully tetragonal ceramic, this may happen so long as the grain is of a proper size.

The theory of transformation toughening produced some enjoyment in the materials industry however this enjoyment came up to a halt when Kobayashi et al uncovered a flaw in Y-TZP ceramics. Y-TZPs undergoes low heat degradation during ageing at temperatures which range from 100 to 4000C, this is specially enhanced when it is exposed to water or is in humid conditions. This degradation is due to the forming of flaws such as micro-cracks and macro-cracks (mentioned previously) at the top which gradually switches into the majority of the material. These flaws are due to the spontaneous transformation from tetragonal phase to monoclinic stage.

Material experts have documented literature regarding the degradation however there were contradictory views as to the mechanism of the phenomenon. Shape 4 is a graphshowing the low heat range degradation of different types of TZPs. Figure 5 shows ageing heat against surface monoclinic levels. Some of these researchers centered on the interaction between normal water (or water vapour) and YTZP, whilst others focused on ways to prevent this from occurred.

Sato et al came up with a theory where in fact the hydroxyl group from drinking water (H2O) reacts with zirconia from the bonds between zirconia and air (that is Zr-O-Zr bonds) forming Zr-OH bonds at crack tips. This accelerates the pace at which the metastable tetragonal period transforms to monoclinic at low conditions. They came up with the conclusion that there surely is a stress which stabilizes the tetragonal stage, however under certain circumstances it is released and with the combination other pre existing defects accelerates the change.

The theory submit by Yoshimura et al is similar to that of Sato et al in the sense that the Zr-OH bonds are also shaped. However, the effect process which causes the same final result is exactly what differentiates the two ideas. Their research revealed an evaluation of the changed monoclinic phase to the untransformed tetragonal ZrO2. Hydroxyl (OH-) is at the monoclinic ZrO2 whereas there was no track in the latter. Due to their findings, they developed the idea that the degradation process took place in periods: upon contact with drinking water, Zr-OH bonds are produced therefore of H2O being adsorbed on the YTZP surface. This creates a stress site which accumulates as the OH- ions diffuse through the surface and lattice triggering the formation of nucleation sites for the stage change. This occurs until the stress reaches split level triggering the transformation to occur at the surface leading to the formation of micro and macro splits all the way through to the majority.

Lange et al [7] observed ±-Y(OH)3 crystallites of about 20 - 50 nm in size forming and developed the theory that the hydroxide formed creates a monoclinic nuclei by detatching Yttria from the grains of the tetragonal phase on the surface. As Yttria has been withdrawn, expansion of the nuclei continues until a crucial size where it'll grow spontaneuously, resulting in the transformation of tetragonal grains to monoclinic. Micro cracks and macro-cracks begin to occur as the transformed grain gets large enough. This technique happens over and over again as the micro and macro-cracks act as a site for water molecules to penetrate into to the grains. This technique occurs only if the grains are larger than the critical size. However, if they're smaller, the transformation will be affected by the diffusion of Yttria on the surface. Other experts such as Winnubst and Burggraf support this theory, as they found traces of Yttria on surface layer of the YTZP specimen. Their specimen was exposed to temperature of 1770C in a nitrogen environment for over 5hrs and using an auger electron microscope, they found a yttrium abundant surface part.

The listed theories were predicated on YTZP's mechanism during degradation. Whalen et al identified that the reason for this degradation is the spontaneous transformation from tetragonal stage to monoclinic stage at the top which then eventually spreads to the majority. They developed the thought of stabilising the tetragonal phase. This may be done by either of the next two methods: the chemical factor which is increasing the stabiliser content on the surface or the microstructural solution which is lowering the grain size at the surface. The latter was decided after which was done by the process of post sintering grinding followed by annealing treatment.

2. 45mol% Y2O3/ZrO2 was the material mixed up in research. Samples of the material were made using isostatic pressing at pressure of 275MPa and then sintered at a temperature of 15000C for a time amount of 2hrs. A 2mm drive was formed which its two factors had different areas treatments, One side being refined and the other being surface grounded. The stage compositions at surfaces were then reviewed using XRD. The XRD effect indicated there is a big change in the period composition of both attributes. The ground part showed little change change whereas there is 50% increase in monoclinic stage after annealing. This provided evidence that the ground and annealed surface hindered the procedure of phase transformation from tetragonal to monoclinic at the top. As a result of this, there have been no micro-cracks shaped at the top and hence the expected mechanical properties were achieved.

Talk and compare it to mine later (TEM as oppose to XRD, advantages of process)

The aim of this project is to provide evidence (if any) of the event of enhanced grains (recrystallization) in Y-TZP constructions because of this of deformation. The ideology used to make clear the idea of recrystallization in metals may be used to explain its occurrence in ceramics as this is a new phenomena in the ceramic industry.

Grain refinement requires certain conditions in its publicity in polycrystalline ceramics and they're: plastically deforming the materials (due to applying a stress) and followed by heat treatment.

Deformation is actually an alteration in body shape which occurs therefore of an applied power. Materials may experience either elastic which is impermanent deformation that upon the release of applied stress is recovered or plastic material deformation which is permanent deformation that is non recoverable when a stress is applied. YTZP's recrystallization behaviour can be discussed by its capacity to plastically deform. The stress and strain behaviour of a materials is used to look for the start and the degree of vinyl deformation.

Figure 6 shows an example of a typical stress and pressure curve. Produce tensile durability is the point at which stretchy deformation ends and the materials starts to plastically deformation. Most polymers and metals undergo elastic accompanied by clear plastic deformation but this isn't the situation for ceramics. They undergo elastic deformation followed by fracture with little or no plastic material deformation. YTZP has superplasticity properties and this nature may be used to make clear refinement in its microstructure.

Plastic deformation is governed by the activity of large numbers of dislocations. Hindering dislocation movement will increase a material's strength. Ceramics are inorganic materials kept along by both ionic and covalent bonds. The bonding mixture leads to hindering the action of dislocations, hence their high strength but brittle behavior.

Dislocation is an important factor in understanding vinyl deformation therefore certain elements have to be examined to be able to understand the idea. Most materials comprise of an arrangement of atoms known as a crystal composition (these can either be sole or polycrystalline that is having multiple crystals as the name advises). This task will give attention to polycrystalline zirconia, however understanding solo crystals help in explaining the behavior of polycrystalline materials. All crystal structures have imperfections that distort the standard design of the atoms. These imperfections can either be point defect (that is they may have vacancies or interstitials), surface, brand (dislocations) and level defects. The actions and ramifications of all these imperfections are interconnected thus the importance in the need to understand them.

As the dislocations move, they have a tendency to interact with one another however this conversation is a complicated as an amount of dislocations (rephrased from pdf). The collective motion of dislocations causes gross plastic deformation.

http://composite. about. com/collection/PR/2001/blmpi1. htm

Dislocations can either be screw, edge or a hybrid of both.

Edge dislocation: in this dislocation, the line of defect is parallel to the shear stress. The dislocation movement is comparable to that of a caterpillar in the sense that the motion is in smaller amounts at a time. Figure 7shows a typical schematic of the motion of dislocations. A is the extra half airplane of atoms. As shear stress is applied, the connection between the top and lower part of B is broken. The extra atom planes of atom A bonds with the low part of B switching the low part to an extra half planes. This motion causes the top one half to move with respect to the bottom one half.

Screw dislocation: this is comparable to that of advantage in the sense it also occurs with shear stress however, the defect lines is perpendicular to the shear stress as oppose to being parallel. Just like the border dislocation only a minute small fraction of bonds are damaged at confirmed time.

Although the movements are different, the overall vinyl deformation for both dislocations is the same. The primary mechanism that causes plastic deformation in crystals is named slip. As dislocations move over the crystals, they shear the crystals along their planes of action.

Slip System

The amount of ease of action of dislocations differs with in every crystallographic directions and crystallographic planes of atoms. Normally dislocation action occurs in a preferred planes and within that airplane there are specific guidelines at also which it occurs. The combination of the aircraft and direction is known as a slip system. The plane of which this movement occurs is referred to as slip planes, and the route is known as slip course. The slip system is determined by the crystal structure of the materials. Slip is only going to occur when the worthiness of applied the shear stress surpasses a certain critical value. The mechanism at which slide occurs differs in sole crystals that of polycrystalline materials. Schmid described the critical shear stress in sole crystals as shown in physique 9:

Deformation is much more complicated in polycrystalline materials as the crystallography orientations of several grains need to be considered. This orientation is arbitrary and therefore causes the course of slip to vary in one grain to another. Its complexity extends in addition to the grain boundaries which works as obstacles to dislocation motion.

Twinning is another system at which clear plastic deformation may appear. The idea of twinning in vinyl deformation is to allow further slip that occurs by producing changes in aircraft orientations. It occurs when a small fraction of the crystals adopts an orientation that is correlated to the orientation of the rest of the untwined lattice within an exact proportioned way. Shape 10 shows an illustration of an un-deformed crystal with one undergoing slip and twinning.

There is a definite difference between slip and twinning. The crystal orientation in a slip is the same above and below the slide planes whereas in twinning differs across the twin plane. More differences is illustrated in amount 11

Slip

Twinning

Where it occurs

Widely multiply planes

Every plane of region is involved

Occurrence

On many multiple slip systems simultaneously

On a specific plane for each crystal

Time required

Milli seconds

Micro seconds

Size (in terms of inter atomic distance)

Multiples

Fractions.

ANNEALING PROCESS LEADING TO Restoration, RECRYSTALLIZATION AND GRAIN GROWTH

Annealing is a high temperature process that triggers changes in a material's framework, leading to alterations in its properties. Whenever a material is plastically deformed, most the is dissipated as warmth, but one minute small percentage is stored in the material as stress energy which is associated with a range of lattice flaws established consequently of deformation. The deformation process as well as a number of various factors (such as heat and rate of deformation) decides the quantity of energy stored in the material. A reduction in deformation and an increase in intensity of deformation cause a vast upsurge in the quantity of maintained energy.

The release of stored energy

There are two main techniques of releasing the energy retained by a materials due to cheap deformation and they are an-isothermal annealing and isothermal annealing. Anisothermal annealing occurs when the materials is continuously heated from a lower temperature compared to that of an increased one (the energy discharged is determined as a function of heat range) whereas, Isothermal annealing occurs when the heat range is constant.

The material's microstructure will undertake either or maybe many of these three restoration operations: recovery, recrystallization and grain expansion. The magnitude of plastic deformation can sometimes determine the mechanisms of restoration and recrystallization. These processes require heat therapy to cause rearrangement of grain restrictions and dislocations.

Recovery

It is the original stage of annealing that occurs at the reduced temperature level of annealing. As being a material is plastically deformed, a minute portion of mechanical energy is stored which exists in crystals as stacking faults, point problems (such flaws are interstitials and vacancies) and dislocations. When a materials is plastically deformed, it is at a thermodynamically unpredictable status of higher energy. That is converted to lower energy states by the application of annealing leading to a change in microstructure.

There are two process involved with recovery: slide annihilating and polygonization. Slide annihilation occurs when dislocations of complete opposite symptoms (that is in the case of border dislocations, the fusion of the positive and the negative edge dislocation or regarding screw in which the right hands screw merges with the left hand screw) combine together in doing so cancelling one another out. Polygonization is the rearrangement of dislocation after annihilation recovery to a lesser energy configuration.

During restoration, this tension energy developed is relieved somewhat by dislocation movement, due to improved atomic diffusion at high temperature. Recovery causes physical properties like thermal and electrical conductivities being retrieved to their pre worked claims. [ggbk]

Recrystallization

After restoration, grains aren't entirely strain free. This is the energy express of the grains is relatively high. New models of strain free grains having near equal dimensions everywhere with low dislocation densities are formed. This process is recognized as recrystallization. This system of producing new equaxed grains is driven by the difference in interior energy between your unstrained and strained materials. The procedure of recrystallization may appear after or during deformation. The manner at which recrystallization occurs is of two types which range with materials. First of all a continuing manner, of which the microstructure little by little evolves into a recrystallized one or a discontinuous manner at which distinct new grains nucleate and develop Recrystallization after deformation is referred to as static whereas the second option is recognized as dynamic.

The extent of which recrystallization occurs would depend on two factors namely: time and recrystallization heat range. The temperature of which recrystallization is completed in an hour is referred to as recrystallization temperature. It is usually a 3rd to half the materials melting temps. The rate at which recovery process occurs is inversely proportional to time (that is it reduces with increasing time). Recrystallization has an totally different kinetic. Through the isothermal annealing, recrystallization starts very slowly and gradually then accumulates gradually up to certain point where it slows down. This can be shown in amount 13

In some circumstances it could be as high 0. 7th the melting temperatures. An illustration of the relationship between recrystallization temperatures and percentage cool work is shown in amount 14. It is realized that as the ratio cold work raises, the recrystallization heat range decreases.

Other factors affect the rate and event of recrystallization. The annealing temp is one of a few factors that have an impact on recrystallization. A materials recrystallization temperature reduces annealing time. The stress applied is another factor both recrystallization and temperature, a rise in stress applied means a lower temperature must activate the process. Also, the deformation on the materials must be enough to permit nucleation and expansion.

A process known as grain development occurs in a polycrystalline materials after recrystallization provided the annealing temps is preserved. The restoration device does not require prior deformation or recrystallization and therefore will occur during annealing in their absence in a polycrystalline material. Grain boundary is the driving a vehicle force for recovery.

Stored energy produced consequently of a materials being plastically deformed is released during the process of annealing causing a change in microstructure. This energy released is because of this of varied mechanisms due to crystal defect relationships:

A decrease in crystal defects due to their reactions with one another.

Dislocations with complete opposite signs interacting causing their annihilation and dislocation loop shrinkage.

Relocation of dislocations triggering the forming of lower energy configurations such as grain boundaries with low sides.

The formation of grain restrictions with high sides.

These reactions arise during the recovery process of restoration. After this process, the following can occur:

Dislocations as well as point flaws being absorbed consequently of the migration of high perspective grain boundaries.

A decrease in the entire grain boundary area.

These micro-structural changes appear during the repair process of recrystallization and restoration. Due to these micro-structural changes, an ideal classification of recrystallization comes from:

Along with the micro-structural changes, the properties of the specimen also change correspondingly. Thus, deformation and annealing are essential processing methods for producing desired properties of the material by handling its microstructures.

Recrystallization mechanism

The start of recrystallization is referred to as nucleation and occurs when dislocations are rearranged in order to form low dislocation density areas that have a high position grain boundary with great flexibility and so is with the capacity of quick movement within the strained region or recovered matrix. Recrystallization has a low driving power and high grain boundary energies; therefore of the characteristics, thermal modifications cannot explain parts surrounded by high viewpoint grain limitations that are clear of defects after annealing. Therefore, the formation of recrystallized grains will not occur during annealing but recently is present in the deformed state. Three methods can be used to describe nucleation and they are:

Movement of high position boundaries that already are present before annealing: this happens when pre existing grain boundaries transfer to grains that are highly strained as illustrated in shape 16 this process takes a favourable energy balance between a rise in the entire grain boundary surface and a decrease in stored energy as a result of the removal defects triggered by the migration of the boundary.

Movement of sub boundaries (that is low perspective limitations): this model is based on the idea of polygonization where stored energy is reduced during annealing as a result of rearrangement and removal of problems. It occurs when sub grain boundaries besiege regions formulated with low dislocation densities. Upon creation of sub grains, by using sub grain boundary movement, they are able to grow at the trouble their neighbouring grains. Dislocations are consumed by migrating sub restrictions and as a result of this, their freedom, orientation dissimilarities and energies are increased until their transformation into high viewpoint restrictions, thus illustrating nucleation.

Sub grains coalescence: this occurs when two neighbouring subgrains combine resulting in their crystal lattices coinciding. It really is seen as a slow process but when in comparison to migration of sub grains is favoured for annealing at low conditions. it is illustrated in amount 17.

In this method, stored energy is reduced leading sub boundaries disappearing, sub grains growing and increase in orientation variations between coalescence communities and their neighbouring sub grains. These lead to the forming of high angle limitations which move at high speeds and cause the process of recrystallization nucleation.

It is essential to identify the actual fact that the total energy balance that will take the disappearance of sub boundaries into consideration with the increase and orientation difference is favourable (that could it be leads to a decrease in total free energy). This system is illustrated in number 18.

The occurrence of these three models is relatively diverse and they will therefore happen under different conditions. The essential requirement for the occurrence of the motion of pre existing grain limitations that is the existence of distinctions in large stress between neighbouring grains is well accepted by research workers. However, there is certainly conflict concerning when the mechanisms sub grain restrictions migration and the coalescence of sub grains take place. Researchers thought the coalescence of sub grain restrictions are linked with large dispersion of sub grain angles distribution, relatively moderate strain, and moderately low annealing temps. Whereas the mechanism of sub grain migration is linked with high annealing heat, strains that are relatively high and large dispersion in the syndication in sub grain size.

Growth of recrystallized regions

The basic device causing recrystallization and grain expansion is the migration of grain limitations with high perspectives. However their travelling force is what differentiates them from one another. The energy of the high angled grain boundaries is the key driving drive for grain progress whether it being irregular or normal expansion. Whereas that for recrystallization is the energy stored during straining came out as crystalline problems. In defect free parts that are encircled by boundaries with high position, recrystallization advances by enlargement of this nucleus on the non recrystallized medium. Grain expansion and recrystallization's migrating high perspective boundary curvature signal is another essential aspect that differentiates the two.

http://asmcommunity. asminternational. org/website/site/www/AsmStore/ProductDetails/?vgnextoid=a75a7dcbe4e18110VgnVCM100000701e010aRCRD

ASM Handbook Level 14A, Metalworking: Mass Forming (ASM International)

http://www. accuratus. com/zirc. html

http://www. totaljoints. info/ceramic_for_total_hips. htm#2

http://www. azom. com/details. asp?ArticleID=940

http://books. google. co. uk/catalogs?id=eUZw4SgqaPYC&pg=PA126&lpg=PA126&dq=phase+transformation+mechanism+leading+to+microcracks+zirconia&source=bl&ots=fCFhf-satf&sig=WNiOjbUtX06mA_d1NkXIEEHcOss&hl=en&ei=r568S9zCKJHFsgaxkd3lCQ&sa=X&oi=book_result&ct=result&resnum=4&ved=0CBYQ6AEwAzgK#v=onepage&q&f=false

EXPERIMENTAL PROCEDURE

Equipment

Three examples of YTZP, 0ne made from 3mol Y2O3/ZrO2 powder and the other two made from the same powder but by two other manufacturers.

Focused Ion Beam (FIB): is a technique used by materials scientists in the research of the materials microstructure. the examples obtained can either be analysed immediately using the FIB or transferred and seen under a TEM or SEM. This process is similar to that of an SEM however ions (specifically gallium ions) rather than electrons.

Figures 19a and b show the way the FIB operates. The surface of the sample being tested is subjected to principal gallium ion beams. This spits a tiny area of the material, leading to the forming of either secondary ions (either positive or negative) or neutral atoms on the surface. Extra electrons (e) are also produced from the gallium beam. That is gathered as well as the indication from the break up ions to form a graphic which is either examined using the FIB itself, SEM or TEM.

http://www. fibics. com/fib/tutorials/introduction-focused-ion-beam-systems/4/ images is from here.

GNU image manipulation program (GIMP): can be an image editing and enhancing software used to assess grain sizes.

Vickers indentation: is utilized to create indentations that are viewed and analyzed under an optical microscope. A square imprint is created from the Vickers indenter, where the two diagonal measures are measured. With this project, the Vickers indentation can be used to form plastic deformation. The top flaws such as scratches and unevenness need to be controlled, hence the reason for polishing.

High temps furnace: used for sintering and annealing.

TEM

Cold isostatic pressing

Sample preparation

Three mol% Y2O3/ZrO2 stable solution natural powder was used in this experiment. The powder was pressed into a disc at 200MPa, then sintered at 14500C for 2 time. Two discs were produced, each pressed with lots 7. 5 lots and 5 loads respectively. The strain was reduced to 5 inorder to lessen the chance of lamination, as it took place with the 7. 5.

Measurements and dimensions

Sample 1: broken

Sample 2

Weight

25. 7711g

19. 6836g

Diameter

39. 23

39. 11

Height (thickness)

7. 1

6. 51

Dimensions after sintering

Weight

25. 515g

19. 487g

Diameter

29. 66

6. 52

Height (thickness)

29. 23

4. 82

Sintering information : it took like 24hrs to sinter.

Heating and chilling rate 30C/min

Temperature 14500C

Time 2hrs

Polishing

Machine used: Kemet 15 lapping machine

Information:

Iron plate 45 microns precious stone suspension

Polished for 2hrs up to now (focusing on the others)

For last polishing:

Copper plate diamond suspension system of 8 microns and 3 microns

Objective

Use Vickers hardness to create an indentation

View micro-structural images using SEM, TEM and Targeted Ion Beam

Compare the microstructure of the indented area with the un-indented area.

Calculating the average grain size using GIMP software.

PROCEDURE

Place prepared test on screening machine.

Force the indentor into the surface of the sample under the action of a static weight.

An stretchy region and plastic region will be shaped.

Use a focused ion beam to mill the indented surface for browsing in a transmitting electron microscope.

Do the same for an un-indented section.

Compare the microstructures of the plastic region, flexible region as well as the un-indented section.

Figure 23

Materials technology & anatomist an intro

Deformation r, r, g pdf and old products as well as pdf.

Rephrase

http://www. scielo. br/scielo. php?pid=S1516-14392005000300002&script=sci_arttext

change from microstructure book

standard deviation for grain sizes.

Errors

Recrystallization website

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