Supervisor: STEFANO SGOBBA

ELISA GARCIA-TABARES VALDIVIESO UNIVERSIDAD COMPLUTENSE DE MADRID 4º COURSE OF MATERIAL ENGINEERING

INDEX

1. CERN PRESENTATION

2. INTRODUCTION: THE N-TOF EXPERIMENT

3. AIMS OF THE PROJECT

4. DESCRIPTION OF THE MATERIALS TO BE CHARACTERIZED.

4.1 Aluminium alloy 5083 H111 4.2 Pure lead 99.99%

5. DESCRIPTION OF THE TEST:

5.1 Test for the lead:

5.1.1 Creep test: • Creep Room temperature test • Creep High temperature test

5.1.2 Structural test

5.2 Tests for the aluminium 5083 alloy

5.2.1 Flexural test

5.3 Test for the Aluminium/Lead pair

5.3.1 Corrosion tests

6. OVERALL CONCLUSION

7. ACKNOWLEDGEMENT

ANNEX 1: DESCRIPTION OF THE MOST RELEVANT EQUIPMENT INVOLVED IN THE PROJECT ANNEX 2: MEB OBSERVATIONS OF THE SAMPLES

ANNEX 3: QUALITATIVE ANALYSIS

1. PRESENTATION OF THE CERN:

CERN, the European Organization for Nuclear Research, is one of the world’s largest and most respected centers for scientific research. Its business is fundamental physics, finding out what the Universe is made of and how it works. At CERN, the world’s largest and most complex scientific instruments are used to study the basic constituents of matter the fundamental particles. By studying what happens when these particles collide, physicists learn about the laws of Nature.

The instruments used at CERN are particle accelerators and detectors. Accelerators boost beams of particles to high energies before they are made to collide with each other or with stationary targets. Detectors observe and record the results of these collisions.

Founded in 1954, the CERN Laboratory sits astride the Franco–Swiss border near Geneva. It was one of Europe’s first joint ventures and now has 20 Member States.

The convention that established CERN in 1954 clearly laid down the main missions for the Organization.

Primarily, the Convention states;

“The Organization shall provide for collaboration among European States in nuclear research of a pure scientific and fundamental character (...). The Organization shall have no concern with work for military requirements and the results of its experimental and theoretical work shall be published or otherwise made generally available”.

Today it is the contents of the nucleus – the basic building blocks of the Universe that provide the key to unlock the frontier of fundamental research, but CERN’s main mission remains essentially the same.

The Convention also states that CERN shall organize and sponsor international co-operation in research, promoting contacts between scientists and interchange with other laboratories and institutes. This includes dissemination of information, and the provision of advanced training for research workers, which continue to be reflected in the current programmes for technology transfer and education and training at many levels.

• Research: Seeking and finding answers to questions about the Universe

• Technology: Advancing the frontiers of technology • Collaborating: Bringing nations together through science • Education: Training the scientists of tomorrow

CERN is an international laboratory for particle physicists, providing some of the most technologically advanced facilities for their research into the basic building blocks of the Universe. Specialist facilities that

would otherwise be difficult or impossible for individual nations to build include advanced particle accelerators, such as the Large Hadron Collider, and facilities for the production of exotic forms of matter, including antimatter.

CERN has established a reputation at the forefront of research, proven through its experiments, past and present. The Laboratory is a vibrant meeting place for discussion and debate; around half of the world’s particle physicists come here for their research. This is reflected in the experiments, which are usually run by international collaborations, bringing together teams of physicists from different institutes towards a common goal.

While the main focus of research at CERN has moved in recent years towards the Large Hadron Collider (LHC), experiments at other accelerators and facilities remain an important part of the laboratory’s activities.

In the ‘fixed-target’ experiments, a single beam of particles from anaccelerator strikes a ‘target’, which can be in the form of a solid, liquidor gas. In some instances, the target is itself part of the detectionsystem.

The COMPASS experiment is studying the structure of hadrons particles made of quarks – at the Super Proton Synchrotron. DIRAC isinvestigating the strong force between quarks at the Proton Synchrotr(PS). Also at the PS, the CLOUD experiment is investigating a possiblink between cosmic rays and cloud formation. ACE, ALPHA, ASACUSand ATRAP are all making use of antiprotons at the AntiprotonDecelerator.

In addition, the CAST experiment, which uses a prototype dipole magnefor the LHC, is looking for hypothetical new particles coming, not from collisions at CERN, but from the Sun.

–

on le A,

t

2. INTRODUCTION: THE N-TOF EXPERIMENT 2.1 Description of the experiment The n-tof project is an experiment which has been developed by the TS/MME/MM department in the CERN during the last years. On May of 2002 the experiment begun, but the appearance of some failures, caused the decommissioning of the project. On November of 2008 the experiment will be restarted with some improvements such as the introduction of the cooling in the water in order to decrease the corrosion of the target. The following figure shows the scheme of the n-tof II

The experiment consist of a pure lead block (99.99%) which was situated inside a EN-AW 5083 aluminium alloy pool, which contained agitated water at 20 degrees. A proton beam with a momentum of 20 GeV/c hits the target made from lead (80*80*40 cm3) and generates neutrons by the spallation reaction*. The spallation neutrons emerging from the lead target are moderated by cooling water in contact with the target and then enter the evacuated time-of-flight tube in angle of 100 to the proton beam direction.

P=1bar T= RT

P>1 Bar T= 20ºC

p n

Proton Beam Tube Lead Target

TOF Tube

Aluminum Alloy Pool

P=1bar T= RT

Refrigeration Circuit

Al 5083 Window

Spallation reaction*: In general, spallation is a process in which fragments of material (spall) are ejected from a body due to impact or stress. In nuclear physics, it is the process in which a heavy nucleus emits a large number of nucleons as a result of being hit by a high-energy particle, thus greatly reducing its atomic weight. In the context of impact physics it describes ejection or vaporization of material from a target during impact by a projectile.

The aim of the ese neutrons through the mea course.

As can be in contact with two differe-The HNO3 and el; the acid was generated du-The HBO3 put m quality of the neutron signal. The follow the n-tof experiment.

experiment is to estimate the time of flight of thsuring of the time wasted on do a determinate

en observed in the previous picture, the pool was nces environments: the air recreated the atmosphere of the tunn

e to the radiation there was inside the tunnel. oderation for the neutron and improved the

ing picture shows the internal structure of

2.2 Developed problems during the first phase: The old target was removed from the pit and brought on the surface for visual inspection and sample taking The followings problems were observed: -Displacement of the block: This effect was due to the crrep in lead and to the non monolithic structure of the target. A system based on laser scanning is revealing displacements > 1cm -Hole in the lead at the proton impact area: After study of the possible corrosion mechanism and analysis of the samples taken, the conclusion is that the hole in the lead is due to the pit corrosion induced by the local boiling of the water in the proton impact area due to the relative small beam cross section. -Oxidation: Various lead oxides have been identified on the lead surface as a result of the corrosion phenomena aching on the lead target and a galvanic corrosion at the interface between Pb and stainless steel (stainless steel support). The reasons for the problems encountered could be summarized as follows:

• Insufficient water flow compared to the energy deposition concentrated in the proton impact area.

• Uncontrolled water chemistry generating the release of spallation products due to the increased solubility of the lead oxides resulting from corrosion of the lead.

2.3 Possible problems in the second phase: The main problems which took place on the n-tof were the followings:

- Gradient temperature:

Due to the dissipation of the proton’s energy, the temperature inside the block of lead increased and was difference from the surface of the block, which was at 60º C. This fact generated a temperature gradient between the inner and the outer parts of the block. This gradient involves the apparition of some stress in the material. The maximum value of the stress which could appear for this gradient is 1MPa, while the minimum stress could be developed was 0.25 MPa due to the own weight of the lead.

- Pressure gradient:

While around the lead the pressure is always the same, the aluminium alloy window was submitted to a pressure gradient due to the difference between the interior (pressurized water) and the exterior (atmospheric pressure) of the container.

According to the norms, the ultimate stress at 20ºC for the EN-AW 5083 H111 is 275 MPa, while the yield stress at the same temperature for the same alloy is 125 MPa.

- Corrosion levels: The corrosion was going to be developed on both materials (Pb block and Al alloy) not only due to the galvanic pair formed but also due to the oxidation of the material in contact with the water.

- Characterization of the lead:

The study of the micro-structure of this material was important to understand and predict the results of some test such as the creep or the conductivity, due to the influence of the micro-porosity or the size of the grains on these parameters.

3. AIMS OF THE PROJECT: My work here consists of study the magnitude of all the problems which were going to take place on the ntof experiment by the unrolling of some representative test. These tests and the reason why they had been carry out, were: -Creep test: This test tries to simulate the conditions in which ones the block of lead was going to be put under in the ntof experiment. As it was said, the temperature gradient in the block was going to develop some stress inside the material, reason why the creep was going to appear. The experiment was made for two differences temperatures (room temperature and 100ºC) and for two differences pressures (0.25 MPa and 1MPa). -Flexural test: Due to the pressure gradient in the aluminium wall of the container, some stress was going to appear. The aim of the flexural test was to recreate this stress which was generated between both sides of the container in order to predicted the results of this stress in the material. -Corrosion rates: In order to understand and to predict the corrosions levels which were going to be detected in the ntof experiment some experiments were carry out. To achieve that, a pool made of the same aluminium alloy of the ntof and containing a small block of lead (10 dm2), was installed in the Prevessin lab.

-Structural characterization of the lead: The study of the lead micro-structure was going to be helpful to estimate the magnitude of the creep which was going to be developed on the lead block. This characterization had also the aim of determinate the micro-porosity of the material we were studying, because as it was said, the n-tof reaction was between a proton beam and the lead target, what means that as much holes we had, few successfully was the reaction. Furthermore the holes impeded the conductivity on the block.

4. DESCRIPTION OF MATERIALS TO BE CHARACTERIZED: 1. Aluminium alloy 5083 H111: First of all, a short introduction of the aluminium:

Aluminium is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13. It is not soluble in water under normal circumstances. Aluminium is the most abundant metal in the Earth's crust, and the third most abundant element therein, after oxygen and silicon. It makes up about 8% by weight of the Earth’s solid surface. Aluminium is too reactive chemically to occur in nature as the free metal. Instead, it is found combined in over 270 different minerals.[1] The chief source of aluminium is bauxite ore.

e s

ry s

cal to

Aluminium is remarkable for its ability to resist corrosion (due to thphenomenon of passivation) and its low density. Structural componentmade from aluminium and its alloys are vital to the aerospace industand very important in other areas of transportation and building. Itreactive nature makes it useful as a catalyst or additive in chemimixtures, including being used in ammonium nitrate explosivesenhance blast power.

Sensitization: The aluminum alloy 5083 (Al-4.4Mg-0.7Mn-0.15Cr) is a nonheat-treatable aluminum alloy known for its excellent corrosion resistance. However, it can become susceptible to intergranular stress corrosion cracking (IGSCC) when exposed to temperatures ranging from 50 °C to 200 °C for sufficient lengths of time. This IGSCC is widely believed to be associated with dissolution of the electrochemically active β phase, Al3Mg2, which is precipitated on grain boundaries. Recently, alternative mechanisms have been invoked related to hydrogen effects and/or free Mg segregation or depletion in the grain-boundary regions. To establish a baseline for the sensitization effect, constant-extension-rate tests (CERTs) were conducted under open-circuit conditions and under potential control in 3.5 pct NaCI on samples isothermally treated at 150 °C. To aid in interpreting the CERT results, grain-boundary precipitation and solute depletion were characterized by transmission electron microscopy (TEM). Additionally, the electrochemical behavior of the β phase was characterized by anodic polarization of the intermetallic compound synthesized in bulk form. In CERTs under open-circuit conditions, the measured ductility depended strongly on sensitization time, reaching a minimum at 189 hours, followed by a slight increase at longer times. This trend correlated well with the fractional coverage of β phase on grain boundaries, which increased up to 189 hours, where it existed with nearly continuous coverage. At longer times, this film coarsened and became discontinuous. Correspondingly, some resistance to IGSCC was recovered. In polarization experiments, bulk synthesized β phase was found to be spontaneously passive from its corrosion potential (-1.40 VSCE) up to about -0.92 VSCE, where passivity was observed to break down. Sensitized AA5083 samples polarized below the β-phase breakdown potential showed almost no evidence of IGSCC, indicating that a high β dissolution rate is a requirement for IGSCC. Mg-depleted zones were observed along grain boundaries in sensitized alloys, but a clear role for solute depletion in IGSCC could not be defined on the basis of the results developed in this study.

Chemical Composition of Aluminum Alloy 5083

Element Present Si 0.4% Fe 0.4% Cu 0.1% Mn 0.4-1.0% Mg 4.0-4.9% Zn 0.25% Ti 0.15% Cr 0.05-0.25% Al Balance

Properties of Aluminium Alloy 5083

Mechanical Properties of Aluminium Alloy 5083

Temper H111

Proof Stress 0.2% (MPa) 145 Tensile Strength (MPa) 300 Shear Strength (MPa) 175

Elongation A5 (%) 23 Hardness Vickers (HV) 75

Physical Properties of Aluminium Alloy 5083

Property Value

Density 2.65 g/cm3 Melting Point 570°C

Modulus of Elasticity 72 GPa Electrical Resistivity 0.058x10-6 Ω.m

Thermal Conductivity 121 W/m.K Thermal Expansion 25x10-6 /K

Fabrication of Aluminium Alloy 5083

Welding

When welding Aluminium 5083 to itself or another alloy from the same sub-group, the recommended filler metal is 5183.

Fabrication Response

Process Rating

Workability – Cold Average Machinability Poor

Weldability – Gas Average Weldability – Arc Excellent

Weldability – Resistance Excellent Brazability Poor

Solderability Poor

Temper

The most common tempers for Aluminium 5083 are: · 0 – Annealed wrought alloy · H111 – Some work hardening imparted by shaping processes but less than required for a H11 temper. · H32 – Work hardened and stabilised with a quarter hard temper.

Applications of Aluminium Alloy 5083

Aluminium 5083 is typically used in: · Shipbuilding · Rail cars · Vehicle bodies · Tip truck bodies · Mine skips and cages · Pressure vessels

2. Pure lead 99.9%:

Lead is a main group element with a symbol Pb (Latin: plumbum). Lead has the atomic number 82. Lead is a soft, malleable poor metal, also considered to be one of the heavy metals. Lead has a bluish white color when freshly cut, but tarnishes to a dull grayish color when it is exposed to air and is a shiny chrome silver when melted into a liquid. Lead is used in building construction, lead-acid batteries, bullets and shot, weights, and is part of solder, pewter, and fusible alloys. Lead has the highest atomic number of all stable elements, although the next element, bismuth, has a half-life so long (longer than the estimated age of the universe) it can be considered stable. Like mercury, another heavy metal, lead is a potent neurotoxin that accumulates in soft tissues and bone over time.

Characteristics

Lead has a dull luster and is a dense, ductile, very soft, highly malleable, bluish-white metal that has poor electrical conductivity. This true metal is highly resistant to corrosion, and because of this property, it is used to contain corrosive liquids (e.g., sulfuric acid). Because lead is very malleable and resistant to corrosion it is extensively used in building construction, e.g., external coverings of roofing joints. Lead can be toughened by adding a small amount of antimony or other metals to it. It is a common misconception that lead has a zero Thomson effect. All lead, except 204Pb, is the end product of a complex radioactive decay (see isotopes of lead below). Lead is also poisonous.

Properties of Lead

Mechanical Properties

Mechanical Properties Lead

Hardness, Brinell 4.20 Hardness, Vickers 5.00

Tensile Strength, Ultimate 18.0 MPa Modulus of Elasticity 14.0 GPa

Poissons Ratio 0.420

Physical Properties

Mechanical Properties Lead

Phase solid

Density (near r.t.) 11.34  g·cm−3

Liquid density at m.p. 10.66  g·cm−3

Melting point 600.61 K

Boiling point 2022 K

Heat of fusion 4.77  kJ·mol−1

Heat of vaporization 179.5  kJ·mol−1

Specific heat capacity (25 °C) 26.650  J·mol−1·K−1

Production and recycling

Worldwide production and consumption of lead is increasing. Total annual production is about 8 million tonnes; about half is produced from recycled scrap. Top lead producing countries, as of 2008, are Australia, China, USA, Peru, Canada, Mexico, Sweden, Morocco, South Africa and North Korea.[8] Australia, China and the United States account for more than half of primary production.[10]

• 2007 mine production: 3,595,000 tonnes • 2007 metal production: 8,127,000 tonnes[11]

At current use rates, the supply of lead is estimated to run out in 42 years.[12] Environmental analyst, Lester Brown, however, has suggested lead could run out within 18 years based on an extrapolation of 2% growth per year.[13] This may need to be reviewed to take account of renewed interest in recycling, and rapid progress in fuel cell technology.

5. DESCRIPTION OF THE TEST: In order to predict the results of the n-tof experiments, some test were made recreating the conditions of this experiment. These ones consist of mechanical, structural and metrological test.

5.1. TEST FOR THE PURE LEAD

5.1.1.CREEP TEST The aim of this experiment is to study the creep which was developed due to the conditions in which ones the lead block was put under in the n-tof. This creep appears in the real experiment due to the temperature gradient which is generated as well by the proton beam. In order to understand the experiment, could be advisable to give the mean of the creep: The creep can be defined as the deformation which appears when a particular material is submitted to a constant effort and temperature. In metals, the creep usually appears only in high temperatures, while the room temperature creep is more common in plastics materials. The data we obtain from the test are usually plot in front of time in temperature and effort constant. The slope of the curve is the speed of the creep and the last point is the time of breakage. As we can observe in the follow diagram, the creep is divided in 3 steps.

o The first one is the first creep and begins with a high speed but decreases with the time.

o The second one has a uniform speed. o And the third one has a high speed of creep and ends due to a

me.

The aim of this experiment is to measure the lead’s creep, that is to say, to measure the deformation this material suffer when we apply a pressure on it during some period of time in constant temperature. We studied the creep which appears in 4 cubs of lead for two different temperatures: room temperature (25ºC) and high temperature (100ºC) and for two different pressures: 0.25MPa and 1 MPa. Each experiment consist of 4 lead’s cubes of 10 mm of height, and over them we put some blocs of lead which produce the deformation in the cubes due to the compression. All the datas were taken by an acquisition system, by means of the LVDTs (linear variable differential transformer) which were situated above each cub.

problem in the material in the breaking ti

The acquisition system gave us the relative position of each LVDT, so that with the initial position of each LVDT, we can estimate the displacement of each one. The compression force produced by the blocs could be calculated with the definition of force and pressure: The total support surface is the amount of the 4 cube’s area, which is equal to= 4*(10E-3) 2=4E-04 m2 With the previous formula we could deduce the expression to calculate the mass of the blocs: Where: Mblocs = the mass we need to produce this deformation (Kg) σ =0.25 MPa o 1 MPa S = support surface (m2) g = gravitational force (m/s2) With those datas, we obtain the following results: Mblocs =10,2Kg for σ =0.25 MPa and Mblocs= 40.8 Kg for σ =1 MPa

CREEP ROOM TEMPERATURE TEST.

1Pa=1N/1m2 1N=1kg*g=1kg*1m*1s-2 g= 9.80665 m/s2

Mblocs = (σ*S)/g

The following picture shows the experiment, the equipment of the left is the 0.25 MPa creep, while the right one is the 1MPa creep.

As we can observe in each corner there is a LVDT which takes the datas; Furthermore there is in the top of each experiment a clock which measures the net displacement (between the start of the experiment and the end of that).

The experiment began the 8th April 2008 and ended on 12th August 2008. The pictures obtained when we stopped the experiment were the followings:

CREEP HIGH TEMPERATURE TEST.

As in the other case, this experiment was made for two different pressures; on the left we can observe the 0.25 MPa and on the right is the 1 MPa experiment.

th April of 20August where the following pictures were taken.

The experiment began on the 25 08 and finished on 29th of

CREEP TEST REPRESENTATIONS

The figure number 1 shows the variation of the displacement with the time for all the experiments.

The figure number 2 shows the relation between the epsilon and the time for all the experiments, being epsilon the developed deformation. Epsilon= Final position- Initial position= l-lo/l For ξ=10 para σ =0.25 MPa y ξ=10.01 para σ =1 Mpa The έ corresponds with the speed of creep value, which has been calculated as the last epsilon value divided by the time.

έ= 8.70E-10 s-1

έ= 4.83E-10 s-1

έ= 3.18E-10 s-1

έ= 2.35E-10 s-1

For conclude, the following picture shows the relation between epsilon and epsilon´ for the different experiments.

creep which has been developed s has to be compared with the

the temperature eed can be

Shear stress= MN/m2

25º C Shear stress=0.1 MN/m2 100º C Shear stress=0.4 MN/m2

CONCLUSIONS

In order to know the magnitude of the on the block, the experimental valueexpected ones.

Knowing the shear stress andfor each experiement, the creep spdeterminated using the Ashby diagrams.

According to the diagrams the values for the creep speed for grains of 10 µm are of the order of 10-8 s-1 for HT and 10-10 s-1 for RT while these values are lower than 10-10 s-1 for 1mm grains.

These results entail that higher grains you have, lower speed of creep will be appeared.

The experimental results are of the order of 10-10 s-1, which are agreed with the expected ones.

According to the structural characterization have be done in the lead which are going to be used in the n-tof, the size of the grains is of the order of 10mm thus the expected speed of creep in this case will be lower than in our test.

OF5.1.2. LEAD OF THE N-T

s is to observe the micro e porosity of the material which is going to first one is related with the creep behaviou proton capture and the thermal conductivity.

PREPARATION OF THE SAMPLES

The company D´Huart has produced th to use in the n-tof project.

During the producing phase, they have made some prototypes in order to make some studies on that.

This prototype consists on a big cylinder of lead. We cut two samples of that, one of this was the top of the ingot (the real surface of the cylinder) while the other belows to the interior of the cylinder.

The aim of these studie structure and th be used in the ntof since ther and the second one with the

e final lead which we’re going

When a ultrasonic control was made, we observed that both samples didn’t have the same behaviour; that fact was the reason to do an analysis of the microstructure with the aim of understand the reason why this difference appeared.

In both case the initial shape was the same (triangle), but in the sample A, we did a cross section and we cut it in three parts (as we can observe in the picture) in order to make easier the analysis. When we had the three parts cut, we made 3 different resins, to do the polishing easier.

Sample B (Top of the ingot)

Sample A (Interior del cilindro)

Then, we polish* the samples until we got to observe the grains well-defined in the optical microscope. In order to make easier this work, we combine the polishing with etching with a solution (2:1) of acetic acid and oxygen peroxide. *POLISHING AND ETCHING: Polishing is the final step in production a surface that is flat, scratch free, and mirror like in appearance. Such a surface is necessary for subsequent accurate metallographic interpretation, both qualitative and quantitative. The polishing technique used should not introduce extraneous structure such as disturbed metal, pitting, dragging out of inclusions, comet tails and staining. Before final polishing is started, the surface condition should be at least as good that obtained by grinding with a 400-grit (25 microns) abrasive. Although certain information may be obtained from as-polished specimens, the microstructure is usually visible only after etching. Only features which exhibit a significant difference in reflectivity (10% or greater) can be viewed without etching. This is true of microstructural features with strong color differences or with large differences in hardness causing relief formation. Cracks, pores, pits, and nonmetallic inclusions may be observed in the as-polished condition. In most cases, a polished specimen will not exhibit its microstructure because incident light is uniformly reflected. Since small differences in reflectivity cannot be recognized by the human eye, some means of producing image contrast must be employed. Although this has become known as

"etching" in metallographic, it does not always refer to selective chemical dissolution of various structural features. There are numerous ways of achieving contrast. These methods may classified as optical, electrochemical (chemical), or physical, depending on whether the process alters the surface or leaves if intact. Chemical etching is based on the application of certain illumination methods, all of which use the Kohler illumination principle. This principle also underlies common bright-filed illumination. These illumination modes are dark field, polarized light, phase contrast and interference contrast. They are available in many commercially produced microscopes, and in most cases, the mode may be put into operation with few simple manipulations. There is distinct advantage in employing optical etching rather than those techniques which alter the specimen surface. Chemical and physical etching requires considerable time and effort and there is always a danger of producing artifacts which lead to misinterpretations.

OPTICAL MICROSCOPE

The following pictures correspond with the photograph we took in the optical microscope.

In the top of the picture we can observe the little grains which were developed due to the cut we made in the cylinder in order to obtain the sample A. The real microstructure is the one we can observe in the picture close to the little grains, but in this case the size of the grains are of the order of 10mm. In the sample B, the grains could be observed at first sight without the optical microscope, therefore we hadn’t to cut the sample to observe those grains. The size of the grains is also of the order of 10 mm. When we observed the grains in the microscope we realised that many microporosity appeared, as we can see in the follow picture.

We could deduce that the main reason why the US control had a different behaviour for two samples of the same material is the microporosity we found in one of them.

CONCLUSION

The appearance of some microporosity in the top of the ingot can explain the fact of the attenuation of the ultra sonic control.

Thanks to the structural analysis made, we could observe the size of the grains in the lead is of the order of 10mm. This fact is relevant for the creep test because, as can be observed later, the size of the grains has a direct relation with the creep which is going to be developed in the material.

5.2. TEST FOR THE ALUMINIUM 5083 H111:

5.2.1.FLEXURAL TEST

DESCRIPTION

The aim of this experiment was to study the size of the craks which were developed in an aluminium sample when we submitted it to a 3 points flexural test. Those test were made with anodised aluminium samples (that is to say the aluminium was recovered with an alumina layer of 15-20 µm of thickness), and without anodized samples in order to know if this oxide layer is favorable or not. Depends on the deep of the cracks which were developed in the material, the corrosion that appears in the aluminum is going to be higher or lower. In order to reproduce the real conditions in which ones the block was in the n-tof, we etched some samples with HNO3 0.1%

The flexural test consists of a 3 points system in which one we applied pairs of force perpendicular to the longitudinal axis of the sample. The pressure we applied was 500 N and then we made a cycle of fatigue of +/- 100N at 0.25 Hz during 900 times. Knowing that:

l= (D+3a) ± a/2

We could calculate the value of the l, that is = 29 ± 1.5mm; we approximated this value to 30 mm in order to make easier the work. With the following expression we could determinate the force we need to apply to obtain the permanent deformation of 0.2%.

σP= (1.5 Pp*l)/ (b*a2)

Working with the previous formula, we get the follow expression:

Pp= (σP*b*a2) / (1.5 *l)

Where we could determinate the value of the force, that is 500 N. This force is one of the variables we had to fit on the flexural test, the variation of the force had to be 20% of the highest applied force, so the range of variation was ±100 N. The following picture shows a flexural test; in which one we can observe the 900 cycles generated around the balance position.

l=distance between two support points. D= diameter of the cylinder=20mm a= thickness of the sample=3mm

σP = necessary tension we have to apply to have a constant deformation of 0.2%=125 MPa. Pp = necessary force we have to apply in order to have this deformation. a= thickness of the sample=3mm l= distance between 2 support points=30mm

Sample nº: Treatment

Differents experiments were made varying some aspects of the sample like the presence of the aluminium layer, or the etching with nitric acid. The following table shows the differents experiments took place. 1,2,3 4,5,6 7,8,9 10,1

1,12 Anodisation

NO YES NO YES

Nitri acid

NO NO YES YES

Test 3points flexural test + cycle of fatigue

3points flexural test + cycle of fatigue

3points flexural test + cycle of fatigue

3points flexural test + cycle of fatigue

σP 125 MPa

125 MPa

125 MPa

125 MPa

Force vs Time

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0 5 10 15 20 25 30 35 40

Time(s)

Forc

e(kN

)

45 50

Force vs Time

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

183.5 184 184.5 185 185.5 186 186.5 187

Time(s)

Forc

e(kN

)

187.5

The followings graphs show the two different parts of the test:

1. Flexural test:

2. Cycle of fatigue:

ANALYSIS AND RESULTS IN THE MEB

Once finished the entire test, the study of the samples in the MEB began. Comparing the results before and after the test, the influence of the deformation on the development of the cracks could be done. The obtain images were the following: Samples 1, 2 and 3 (neither anodisation nor nitric acid).

Samples 4, 5 and 6 (nor anodisation but nitric acid).

i

Samples 7, 8 and 9 (anodized aluminum w thout nitric acid).

0 2 4 6Energy (keV)

0

20

40

60

cps

C

O

Mg

Al

S

Samples 10, 11 and 12 (anodized aluminum with nitric acid).

nate that in the free anodized tail the development of

tween the oxidized state we can

important facts: veloped before the

ce. s of two different cid(blue color) while

Looking at the pictures we could determilayer samples, the pressure of the test doesn’t encracks in the surface of the material, the only difference bepictures of before and after the test is the moreappreciate in the last one. Although, with the anodized samples there are two-As we can observe, some cracks has already deflexural test -After the test, some news cracks appear in the surfaThe following graphic compare the compositionsamples: one of them has been exposed to nitric athe other hasn’t been(red color).

CROSS SECTION:

To study the deep of the cracks that have been developed in the anodized layer is helpful to make a cross section in the sample. We worked with two different samples (one of them with nitric acid and the other without it). With a jigsaw we remove of each sample two pieces (one of the middle of the sample (which means that it had been deformed) and the other of the exterior zone which hadn’t been deformed))

Once we had the new samples, we prepared two different resins in order to observe them in the optical microscope. In the following picture, the different zones of the experiment are explained.

Non-deformed zone

External face (compression)

Deformed zone Internal face (tension)

The following pictures correspond with the analysis we made in the MEB. -Sample of anodized aluminum with nitric acid, deformed zone and internal face.

-Sample of anodized aluminum with nitric acid, deformed zone and external face.

ALUMINUM

RESIN

ALUMINA

ALUMINUM

RESIN

ALUMINA

ALUMINUM

RESIN

ALUMINA

RESIN ALUMINA

ALUMINUM

- Sample of anodized aluminum with nitric acid, non deformed zone (internal face).

- Sample of anodized aluminum without nitric acid, deformed zone and internal face.

RESIN

ALUMINA

ALUMINUM

RESIN

ALUMINA

ALUMINUM

RESIN

ALUMINA

ALUMINUM

- Sample of anodized aluminum without nitric acid, deformed zone andexternal face.

ALUMINUM

RESIN

ALUMINA

-Sample of anodized aluminum without nitric acid, non-deformed zone (internal face).

CONCLUSIONS:

-The samples presented cracks even before they were under pressure. -The difference between (HNO3) exposed samples and non exposed ones were not particularly important. -The opening of the cracks in deformed zone is bigger than those in the non deformed zone. -The depth of the cracks which have been developed in the internal face (tension) is bigger than that for the external zone (compression).

ALUMINUM

RESIN

ALUMINA

ALUMINUM

RESIN

ALUMINA