Ambarish Maji Reg. No.: 120503430 M Tech. (Manufacturing Engg. & Technology)

Under the guidance of

Dr. H.S. Tripathi (Guide) Dr. Anoop Mukherjee (Co Guide) Mr. Ankur Srivastava Principle Scientist Chief Scientist Assistant Professor (Refractoty Div.), CGCRI (CSIR) (Mechanical Lab), CGCRI (CSIR) (Mech. Engg. Dept.), MUJ

Microstructure and mechanical properties of Alumina Zirconia ceramic composites

Final Dissertation Report

INTRODUCTION• Ceramics - A ceramic is an inorganic, nonmetallic solid prepared by the action

of heat and subsequent cooling.

• The word "ceramic" comes from the Greek word keramikos or keramos means potter’s clay.

• Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous (e.g. Glass).

• Ceramic products are usually divided into four sectors

a. Structural

b. Refractories

c. White wares

d. Advanced ceramics

REFRACTORIES• Refractories are high temperature resistant materials which retain their

strength at high temperatures.

• They are used to make bricks, cements, crucibles and to make refractory linings, which line furnaces, kilns and incinerators.

• Properties of refractories

(I) Refractory materials must be chemically and physically stable at high temperatures.

(II) They are resistant to thermal shock and chemically inert.

• The oxides of Aluminium (Alumina), Silicon (Silica) and Magnesium (Magnesia) are the most important materials used in the manufacturing of refractories.

Alumina Zirconia ceramics• In today’s world Alumina Zirconia composite plays a big role in medical and

mechanical industries. There are two types of alumina zirconia composites.

(i) Alumina Toughened Zirconia (ATZ)

(ii) Zirconia Toughened Alumina (ZTA)

• Alumina Toughened Zirconia (ATZ) ceramics are attractive materials for biomedical implants and other engineering applications requiring high strength and abrasion resistance at ambient temperature.

• It is a composite ceramic material consisting of small (order of magnitude 1 μm after firing) alumina particles in a very fine matrix of (nanosized) zirconia particles.

ATZ• ATZ consists of two different ceramic materials.

(i) Alumina (Al2O3)

(ii) Zirconia (ZrO2)

Alumina• Aluminium oxide is a chemical compound of Aluminium and Oxygen with the

chemical formula Al2O3. It is the most commonly occurring of several oxides of Aluminium, and specifically identified as Aluminium Oxide (Alumina).

• Properties of Alumina

• Formula: Al2O3

• Melting point: 2,072°C • Molar mass: 101.96 g/mol • Density: 3.95 g/cm³ • Boiling point: 2,977°C

Zirconia• Zirconium Dioxide (Zirconia), is a white crystalline oxide of Zirconium. The

word “Zirconium” comes from Arabic word “Zargon” which means “golden in color”. Its most naturally occurring form, Its most naturally occurring form, with a monoclinic crystalline structure, is the mineral Baddeleyite. Zirconium dioxide is one of the most studied ceramic materials.

• Properties of Zirconia

• Formula: ZrO2

• Melting point: 2715°C • Density: 5.68 g/cm³ • Molar mass: 123.218 g/mol • Boiling point: 4300°C • Soluble in: Water

Zirconia (Continued)• Zirconia consists of three different phases.

1. Monoclinic < 1170°C2. Tetragonal =1170°C - 2370°C3. Cubic > 2370°C

• Zirconia is used in this research is not pure Zirconia but it is Yttria stabilized Zirconia (3Y-TZP) [3 mol% Yttria stabilized Tetragonal Zirconia Polycrystal].

• ZrO2 adopts a monoclinic crystal structure at room temperature and transitions to tetragonal and cubic at higher temperatures. The volume expansion caused by the cubic to tetragonal to monoclinic transformation induces large stresses, and these stresses cause ZrO2 to crack upon cooling from high temperatures.

• When the zirconia is blended with some other oxides, the tetragonal and/or cubic phases are stabilized.

OBJECTIVE• The main objectives of the work are

1. To develop Alumina Toughened Zirconia (ATZ) by different sintering route.

2. To evaluate mechanical properties like hardness, fracture toughness, and calculate the same.

3. Microstructures can be evaluated to observe grains and grain boundaries in FESEM (Field Emission Scanning Electron Microscope).

4. AP (Apparent Porosity) and BD (Bulk Density) test can also be done to visualize how AP and BD of ATZ changes through various sintering routes.

5. Specific Gravity of Alumina and Zirconia are to be found out through specific gravity test.

6. To analyze the phases of alumina, zirconia and sintered ATZ through X Ray diffraction.

Tools and Methodologies• The project is divided into 4 categories such as

1. Product preparation: Alumina and Zirconia powders are mixed with each other.

2. Fabrication of shapes: Bars and Discs are made of this ceramic composite by mixing binders and processed through uniaxial pressing and isopressing.

3. Sintering: Sintering is done though different sintering route.

4. Evaluation: Evaluate the physical and mechanical properties and microstructures of ATZ.

Product preparationXRD (X Ray Diffraction) Analysis• Alumina and Zirconia powders are collected and sent them to XRD (X Ray

Diffraction) analysis to know the phase of Alumina and Zirconia. Pure Alumina in room temp. is at monoclinic phase and stabilized zirconia in tetragonal phase.

• Alumina: The most common form of crystalline aluminum oxide is known as Corundum. Generally Alumina exists in α Al2O3 phase ( monoclinic phase).

• Zirconia: In Zirconia three phases are shown: Monoclinic < 1170 °C, Tetragonal 1170°C - 2370°C, and Cubic > 2370 °C. A few percentages of the oxides of calcium or yttrium stabilize the cubic phase. In this experiment Yttria Stabilized Zirconia powder is in Tetragonal phase at room temperature.

• ATZ: Zirconia in ATZ posses tetragonal and alumina posses monoclinic phase.

XRD (Continued)

XRD (Continued)

• It has been observed that alumina posses all monoclinic (Corundum) phase

• Yttria stabilized zirconia posses 86% of tetragonal (Zirconium oxide) phase, 13% of monoclinic (Zirconium oxide) phase and 1% of cubic (Yttrium zirconium oxide) phase.

• ATZ posses 64% of tetragonal (Zirconium oxide) phase, 19% of monoclinic (Aluminum oxide) phase, 14% of monoclinic (Baddeleyite) phase and 2% of cubic (Yttrium zirconium oxide) phase.

XRD Machine

• XRD Machine: X ray is a highly energized electromagnetic radiation. All electromagnetic waves undergo diffraction or scattering.

• X-rays have a similar nature to visible light rays, but have a much shorter wavelength.

• X-ray wavelengths are comparable to the distances between atoms in molecules, rays scattered by different atoms ‘interfere’ with each other.

• If they are out of step, they cancel each other out and if they are in step, they reinforce each other.

• In this Experiment X-ray pass through ceramic powder at desired angle. The interference of X-ray passing through the powder shows the graph and the peak.

XRD Machine (Continued)

XRD machine

Working process of XRD

XRD machine working process• XRD works following Bragg’s law

• When a monochromatic x-ray beam with wavelength λ is incident on the lattice planes in a crystal planes in a crystal at an angle θ, diffraction occurs only when the distance traveled by the rays reflected from successive planes differs by a complete number n of wavelengths.

• λ is kept constant by using filtered X- ray radiation that is approximately monochromatic.

• d may have value consistent with the crystal structure.

• θ is the variable parameters, in terms of which the diffraction peaks are measured.

nλ =2dsinθ

Chemical Analysis• Alumina: The most common form of crystalline aluminum oxide is known as

corundum. The oxygen ions nearly form a hexagonal close-packed structure with aluminum ions at the centre.

Al

O

ChemicalComposition Al2O3 SiO2 Fe2O3 Na2O

Amount 99.0% 100 ppm 100 ppm 0.5%

Its grain size is ≥ 0.2 µm

Chemical Analysis (Continued)• Zirconia: Pure zirconium dioxide undergoes a phase transformations like• Monoclinic (1173°C) ↔Tetragonal (2370°C) ↔Cubic (2690°C) ↔melt

• Materials related to YSZ (Yttria Stabilized Zirconia) include Calcia, Magnesia, Ceria, Hafnia or alumina as stabilization factor.

ChemicalComposition ZrO2 Y2O3 HfO2 Al2O3 Other

Oxides

Amount 93% 4.9% 2% 0.1% < 0.1%

Its grain size is 0.15 to 0.2µm

Fabrication of shapesAttrition Milling

• Alumina and Zirconia powders are mixed with each other at different proportion and make 6 different batches where alumina proportion increases from 0 to 30.

• Six different batches are ZA0, ZA10, ZA15, ZA20, ZA25, ZA30 [Z stands for zirconia and A stands for alumina].

• It means in 1st batch alumina is 0%, in 2nd batch 10% and so on.

• Then each batch is grinded and mixed in attrition mill in which both powders are mixed properly and powder particles are grinded by zirconia balls inside attrition mill.

• As a result particle size of the powder is reduced and it becomes fine.

Attrition Mill Machine• Attrition Mill: It is a machine where powders are mixed and grinded into

smaller particle size with the help of rotating zirconia balls.

• There is a cylindrical case in which a huge numbers of tiny zirconia balls are placed. A shaft with multiple arms is inserted inside the case and the shaft is driven by the motor.

• As the shaft rotates, zirconia balls around the shaft also rotate and powders inside the case are grinded and mixed.

• In this project Ethyl Alcohol (CH3CH2OH)is poured inside the case to mix with powder and make a solution, because Ethyl Alcohol does not react with Zirconia.

• Motor rotates at 400 rpm for 2hrs. After this process solution is taken out and collected in a container. While drying Alcohol evaporates and fine powder is collected.

Attrition Mill Machine

Attrition Mill Machine

Inside of Attrition Mill cylinder case

Uniaxial pressing and Isopressing

• Powders mixture of each batch is mixed with PVA (Poly Vinyl Alcohol) which acts as a binder and pour it in different geometrical mould.

• when pressure is applied in the mould from one direction they are bonded and take the shape of the mould.

• Particular numbers of bars and palettes of suitable geometrical shape are made by pressing machine.

• These bars and palettes are wrapped with rubber caps and put it in a big mould. Fill the mould with the oil and apply pressure from one side for isopressing operation.

• Better bonding is provided in bars and palettes.

Pressing and Isopressing (Continued)

ATZ Bars and Palettes made by pressing

1 2 1. Bar pressing mould

2. Palette pressing mould

Uniaxial Pressing Machine• Pressing machine is a machine ceramic powder mixed with binder is inserted into

the mould of a particular shape.

• Pressure is applied from one direction and material comes out from that mould in its shape when pressure is released.

• In this experiment 2 tons of pressure is applied.

Pressing Machine

Isopressing Machine• A particular geometrical shaped material wrapped up by rubber cap is inserted into the

mould of Isopressing machine. The remaining of mould is filled up with viscous oil. Around the mould lid two rubber bands are attached.

• Then a huge amount of pressure (80 tons) is applied from one direction to the mould and the pressure is equally spread in the oil in all direction and through that oil equilibrium pressure applied on the material. As a result bonding of the material gets firm.

Iso Pressing Machine

Sintering• Sintering is a method for creating objects from powders, including metal and

ceramic powders.

• It is based on atomic diffusion. Diffusion occurs in any material above absolute zero, but it occurs much faster at higher temperatures. In most sintering processes, the powdered material is held in a mold and then heated to a temperature below the melting point.

• The atoms in the powder particles diffuse across the boundaries of the particles, fusing the particles together and creating one solid piece.

• In this experiment ceramic bars and palettes are sintered at different temp. like (1350, 1450, 1500, 1550, 1600, 1650)°C for AP and BD test.

• In each sintering furnace is programmed as up to 1000°C temp. rises at 5°C /min and after 1000°C to final temp. it increases at 3°C /min. Then dwelling is for 2hrs. At this time furnace temp. is constant at highest programmed point. Then it goes down gradually.

Sintering Furnace

Sintering Furnace with Control BoardHeating coils inside furnacechamber

Evaluation• There are four tests are done and their results are observed

and evaluated.

1. AP (Apparent Porosity) & BD (Bulk Density) test

2. Specific gravity test

3. Hardness and fracture toughness test

4. Observation of microstructure in FESEM

Apparent Porosity (AP) & Bulk Density (BD) Test

• Sintered materials from different temperatures are examined for AP and BD test.

• AP and BD are measured in 4 steps.

1. Dry weight (D) of sintered material is calculated.

2. These materials are wrapped in a cloth and put in water. Water is boiling for 2 hours. As a result the pours of the materials are filled with water.

3. Then suspended weight (S) of the material is calculated under water. Its value is less than dry weight value.

4. At last surface water these wet materials are soaked by wet cloth one by one. Then soaked weight (W) of those materials are measured one by one. Which is greater than dry weight because its pours are filled with water.

AP & BD Test• AP and BD are calculated from three weight values and using two different

formulas. Those two formulas are:

• Porosity decreases and Density increases in a ceramic material as sintered temperature increases.

AP & BD Result

AP & BD Result (Continued)

Specific Gravity Test• Specific Gravity of Alumina and Zirconia are measured. Kerosene is used for this

experiment because zirconia reacts with water and form zirconia hydroxide.

• It is tested in 4 steps:

1. Dry bottle weight (W1) is measured.

2. A few amount of powder is poured in bottle and again bottle with powder weight (W2) is measured.

3. Then kerosene is poured in bottle fully and bottle with powder and kerosene weight (W3) is measured.

4. After this bottle is cleaned properly and dried in hot drier totally. Then bottle is filled with kerosene only and weight (W4) of bottle with kerosene is measured.

Specific Gravity Result• Specific gravity is calculated using following formula:

• Density of Yttria Stablized Zirconia is 5.9 gm/cc. and density of Alumina is 3.95 gm/cc. theoretically.

Hardness and Fracture toughness test• Hardness is a measure of how resistant solid matter is to various

kinds of permanent shape change when a force is applied. In this experiment Vickers hardness test is done through micro indentation process.

• Fracture toughness is a property which describes the ability of material containing a crack to resist fracture, and is one of the most important properties of any material for many design applications.

• The linear-elastic fracture toughness of a material is determined from the stress intensity factor (K) at which a thin crack in the material begins to grow. It is denoted by KIc and has units of

Hardness and Fracture toughness test (continued.)

• The Vickers test is often easier to use than other hardness tests since the required calculations are independent of the size of the indenter, loads of various magnitudes are applied to a flat surface through indenter depending on the hardness of the material to be measured.

• The HV number is then determined by the ratio F/A, where F is the force applied to the diamond in kilograms- force and A is the surface area of the resulting indentation in square millimeters. A can be determined by the formula.

or where d is the average length of

the diagonal left by the indenter in millimeters.

• So , where HV is Vickers hardness no. and its unit

is kgf /mm2.

Hardness and fracture toughness result

Sample Load (Kgf) Time (sec.) Hardness (Gpa) Fracture toughness (Mpa.m0.5)

ZA0 5 10 5.8±0.6 8.6±0.3

ZA10 5 10 6.4±0.9 8.37±0.92

ZA15 5 10 7.3±0.2 8.11±0.95

ZA20 5 10 7.43±0.31 7.9±0.9

ZA25 5 10 7.66±0.45 6.53±0.17

ZA30 5 10 7.63±0.24 6.8±0.14

ZA0 ZA10 ZA15

ZA20 ZA25 ZA30

Hardness and fracture toughness result (continued.)

•

• Hardness graph

Fracture toughness graph

Microstructure observation through FESEM• Field emission microscopy (FEM) is an analytical technique used in materials

science to investigate molecular surface structures and their electronic properties. Microscopy techniques are used to produce real space magnified images of a surface showing what it looks like.

• A Field Emission Microscope consists of a metallic sample in the form of a sharp tip and a conducting fluorescent screen enclosed in ultrahigh vacuum. The tip radius used is typically of the order of 100 nm. It is composed of a metal with a high melting point.

• The sample is held at a large negative potential (1-10 kV) relative to the fluorescent screen. This gives the electric field near the tip apex to be the order of 1010 V/m which is high enough for field emission of electrons to take place.

Microstructure observation result• Field emission scanning electron microscopy (FESEM) provides

topographical and elemental information at magnifications of 10x to 300,000x, with virtually unlimited depth of field.

• Compared with convention scanning electron microscopy (SEM), field emission SEM (FESEM) produces clearer, less electro statically distorted images with spatial resolution down to 1 and 1/2 nanometers three to six times better.

• Here are microscopic structures of different samples.

ZA0 ZA10 ZA20

• Grain size of alumina and zirconia are measured for each image and calculated results are displayed in a table

Sample Grain size (µm)Alumina Zirconia

ZA0 0 0.36

ZA10 0.67 0.31

ZA20 0.78 0.26

Parameters effecting the change of properties of ceramic composites• Parameters those effect in the change of the properties of ceramic

composites are

1. Sintering temperature: As sintering temperature rises, porosity of the material reduces and bulk density increases.

2. Alumina-Zirconia mixing Ratio: As alumina percentage increases in alumina-zirconia mixing ratio, porosity decreases and bulk density increases.

Flow Chart of Project Work

• All mechanical properties and microstructures are yet to be tested.

Upcoming Expected Results

• Mechanical properties characterization: Mechanical properties like hardness, bending strength and fracture toughness should increase with increasing of alumina percentage in ATZ.

• Microstructure observation: The number of alumina grains within zirconia grains should increase with increasing of alumina zirconia proportion in ATZ.

Applications

• Alumina-Zirconia ceramic composite is used mostly in biomedical application and orthopedic field.

• This composite offers several advantages allowing the coupling of good properties of alumina, and the hardness, chemical inertia, biocompatibility and toughness of zirconia.

• Recently CeramTec (Plochingen, Germany) has commercialized BIOLOX delta, a composite material consisting of 80 vol.% Al2O3, approximately 18.5 vol.% ZrO2, and 1.5 vol.% of mixed oxides (CrO2 & Y2O3) characterized by strength higher than 1150 MPa and toughness of 8.5 MPa/m1/2. It is made by alumina-zirconia ceramic composites.

Conclusion• In this project alumina and zirconia powders are characterized through XRD and

chemical analysis. • They are mixed with each other in 6 different ratios to make 6 different batches.

• This ATZ composite is isopressed and sintered in different route to calculate AP and BD.

• The crystal structure of grains and chemical composition can be known from above work.

• The sp. gravity of the materials and the change of porosity and density with temperature change can be observed from the above work.

• In future mechanical properties and microstructures of ATZ will be tested to find out what the behavior of this ceramic is and what will be its application.

Reference

• [1]. N.P. Bansal, Dongming Zhu, “Thermal Conductivity of Alumina Toughened Zirconia Composites”, NASA/TM, 2003, 1-8.

• [2]. Yong-Qi Zaho, Li Jiang et al., “Shear bond strengths between alumina toughened zirconia cores and veneering ceramics and their susceptibility to aging”, Asia Pacific Journal of Tropical Medicine, 2012, 402-405.

• [3]. E. Camposilvan, F.G. Marro et al., “Mechanical properties of alumina infiltrated zirconia nanocomposites”, XIII National Congress of Mechanical Properties of Solids, Institute of Materials Technology of the UPV, Spain, 2012, 203-207.

• [4]. Willi Pabst, Eva Gregorova et al., “Alumina Toughened Zirconia made by room temperature extrusion o f ceramic pastes”, Dept. of Glass and Ceramics, Institute of

Chemical Technology, Czech Republic, 2000, 41-46.

• [5]. Jyoti Prakash et al., “Mechanical Behavior of Alumina- Zirconia composite by slurry method”, International Journal o f Engineering Science and Technology, 2011, 1359 -1367.