Pour fabriquer le caisson-coeur du futur réacteur expérimental Jules Horowitz (RJH), un assemblage de viroles est effectué à l'aide d'un procédé haute énergie : le soudage par faisceau d'électrons (FE). L'aluminium 6061-T6 qui a été choisi pour la fabrication de ces viroles est un alliage à durcissement structural, ce qui signifie que ses propriétés mécaniques sont très fortement dépendantes de son état de précipitation. Lors du soudage des viroles, l'état microstructural du matériau est affecté : on assiste notamment à une dégradation de l'état fin de précipitation (T6). Les conséquences de cette dégradation microstructurale sont diverses. Notamment, l'évolution de l'état de précipitation au cours du soudage engendre une variation du comportement mécanique et impactera donc la distribution des contraintes résiduelles. De plus, les propriétés mécaniques en service à proximité du joint soudé seront grandement modifiées, on assiste par exemple à une chute de la limite d'élasticité. Dans ce travail, des essais cycliques ont été effectués après des chargements thermiques représentatifs d'une opération de soudage mais aussi pendant des essais isothermes. L'analyse de ces résultats et la confrontation à des mesures de Diffusion de Neutrons aux Petits Angles (DNPA) et de Microscopie Electronique en Transmission (MET) permettent de comprendre les effets de la précipitation sur la loi de comportement de l'alliage. Afin de prédire les évolutions microstructurales et mécaniques dans l'alliage 6061, un logiciel de précipitation a été implémenté et couplé à un modèle élastoplastique à base physique. Les résultats obtenus permettent de représenter la grande variété de comportement observé lors de la campagne expérimentale. Un couplage entre simulation éléments finis thermique et précipitation a été effectué et permet d'ouvrir des perspectives de simulations plus physiques pour ce type d'alliage. / In order to assemble the pressure vessel of experimental Reactor Jules Horowitz (RJH) of France in the future, the electron beam welding process will be used. Several ferrules in a 6061-T6 age hardening aluminum alloy are used for manufacturing this vessel. The fine precipitation state (T6) is affected significantly by the electron beam welding process. Consequently, this microstructural degradation leads to an evolution of the mechanical behaviour and thus will affect the distribution of residual stresses. Moreover, the mechanical properties of the weld joint at ambiant temperature can be modified, such as the yield stress that may drop from 280 MPa to 55 MPa. In this work, cyclic tensile tests have been performed after anisothermal histories representative of welding and during isothermal treatments. The analysis of these results is compared with Small Angles Neutrons Scattering (SANS) and Transmission Electron Microscopy (TEM) characterizations that allow to understand the effect of the precipitation on the material behaviour. To predict the microstructural evolutions in the 6061 structure, a precipitation model has been developped. The precipitation software "PreciSo" coupled with a Finite Element thermal simulations and elastoplastic models allows to open new prospectives in the physical-based simulations domain.

L'objectif de cette thèse est l'étude de la déformation, à l'échelle microscopique, de la phase MAX Ti2AlN, synthétisée par métallurgie des poudres. Ce travail se divise en trois parties : une première dans laquelle l'accent a été mis sur l'hystérèse mécanique des phases MAX via des essais cyclés, en nanoindentation sphérique et compression ex-situ de micro-piliers, sur des grains d'orientations différentes déterminées par l'EBSD. Dans la deuxième nous nous sommes intéressés à la déformation de micropiliers via des essais de compression cyclés in-situ couplés à la micro-diffraction Laue. L'objectif a été d'analyser les taches diffraction au cours de la déformation du pilier afin de mettre en évidence les mécanismes de déformation élémentaires mis en jeu et d'observer les structures finales via des images MEB post-mortem des piliers. Enfin, une dernière dans laquelle l'objectif a été l'étude des mécanismes de déformation en température à l'échelle microscopique via des essais de nano-indentation allant jusqu'à 800°C. La caractérisation des lignes de glissement en surface et des configurations microstructurales sous l'empreinte a été réalisée par AFM et MET respectivement. Toutes les données recueillies par ces divers essais aux petites échelles, ont permis d'affiner notre compréhension des mécanismes de déformation du monocristal de phase MAX, notamment vis à vis des modèles usuellement proposés dans la littérature. / The thesis's goal is to study the deformation, at microscopic scale, of the MAX phase Ti2AlN synthesized by powder metallurgy. This work is divided into three parts: in the first part, the interest has been put on the hysteretic behavior of the MAX phases via cyclic mechanical solicitations, during spherical indentation tests and ex-situ compression of micro-pillars, on differently orientated grains beforehand determined by EBSD. In the second part, we were interested into the micro-pillar's deformation via insitu cyclic compression tests coupled with Laue micro-diffraction. The goal was to analyse the evolution diffraction lines during the pillar's deformation in order to highlight the elementary deformation mechanisms and to observe the finale structures via the post-mortem SEM imaging of the pillars. Finally, a last part was devoted to study the deformation mechanisms in temperature at microscopic scale via nano-indentation tests up to 800°C. The characterization of the slip lines on the surface has been revealed by AFM and that of t he microstructural configurations (dislocations) under the indent has been done by TEM. All data collected by these various tests at the small scales have refined our understanding of the deformation mechanisms of crystal MAX phase, particularly with respect to the models usually proposed in the literature.

The primary goal of this study was to develop a preliminary tool to determine caregivers’ needs regarding the management of a person with a traumatic brain injury (TBI), during the acute rehabilitation period. The potential impact of TBI on family dynamics, interpersonal relationships and functional independence is well documented.To facilitate achievement of the main goal this study was divided into two phases. In the first phase, caregivers’ needs were determined by means of both qualitative and quantitative measurements in the form of structured and unstructured observations, the implementation of a “Needs Questionnaire”, a focus group and semi-structured interviews. The results obtained during this phase indicated that caregivers have needs for support from professionals and the community, as well as needs regarding the general management of the person with a TBI and the management of the potential communication difficulties associated with TBI. Based on these needs, a preliminary tool, namely the “Needs questionnaire for caregivers of a person with a traumatic brain injury”, was developed. During the second phase of the study, this tool was administered to caregivers of individuals with TBI before and after the presentation of a workshop to determine whether there is a change in caregivers’ needs once they have received information. A pretest-posttest, experimental design was thus implemented during the second phase of this study. Although further research is required for the qualitative and quantitative validation of this tool, the use of this tool has implications for providing a better understanding of caregivers’ needs during the acute rehabilitation period after TBI. The results of this study further emphasize that improved service delivery in the South African context is reliant on the early identification, by the professional team, of the needs that caregivers of individuals with TBI have. / Dissertation (M (Communication Pathology))--University of Pretoria, 2007. / Speech-Language Pathology and Audiology / unrestricted

AFRIKAANS: In hierdie navorsing is die huwelik met voorskoolse kinders in Suid-Afrika aan die begin van die een-en-twintigste eeu ondersoek. Hierdie huweliksfase, met sy vele uitdagings en huwelikstake, word beskou as die fase met die laagste huweliksaanpassing en die hoogste voorkoms van egskeiding. Die sin en betekenis van hierdie uitdagings (spirituele intelligensie of SQ), sowel as die emosionele belewenis, verstaan en hantering hiervan (emosionele intelligensie of EQ), asook die rol wat dit in huweliksaanpassing speel, is ondersoek. Eerstens is ’n vraelys ontwikkel wat SQ-eienskappe kan meet (MMV-SQ-vraelys), naamlik: (i) die vind van sin en betekenis in ’n gegewe situasie, (ii) motiveringsbronne van gedrag, en (iii) die waardes wat uitgeleef word. Data van 198 respondente het gedui op betroubaarheid van subskale wat wissel van 0.47 tot 0.80. Bevredigende konstrukgeldigheid is verkry deur die verhouding tussen die subskale van die SQ-vraelys en waardeskaal te ondersoek (r het gevarieer van 0.15; p ≤ 0.05 tot 0.54; p ≤ 0.01). Sowel kwantitatiewe as kwalitatiewe navorsing is vervolgens gebruik. In die kwantitatiewe navorsing is die MMV-SQ-vraelys, die huweliks-aanpassingsvraelys van Spanier (Dyadic Adjustment Scale), asook die SSRI (Schutte Self-Report Inventory) op 84 deelnemers toegepas. Die deelnemers het 84 getroude persone, waaronder 34 egpare ingesluit. Die verband tussen huweliksaanpassing en EQ is ondersoek deur korrelasies te bereken tussen die subskale van die DAS en SSRI. Dit het geblyk dat ʼn optimistiese gemoedstemming ʼn verband toon met al die subskale van huweliksaanpassing. Die herkenning van die eie en die huweliksmaat se gevoelens, sosiale vaardighede, en die toepassing van emosies blyk verband te hou met hoër huwelikstevredenheid asook huwelikskonsensus. Sosiale vaardighede het ook ʼn verband getoon met affeksionele uitdrukking. EQ het egter nie ’n sterk verband met huwelikskohesie getoon nie. Die verband tussen die subskale van die DAS is vervolgens vergelyk met dié van die MMV-SQ-vraelys. Betekenisvolle korrelasies tussen enkele skale van huweliksaanpassing en SQ het voorgekom, veral wat die motiveringskaal betref: egpaarlede wie se gedrag deur die motiveringsbron bemeestering gemotiveer word, blyk ʼn hoër mate van huweliksaanpassing te hê, terwyl die negatiewe motiveringsbronne, waaronder selfgesentreerdheid, drange en vrees, ’n negatiewe verband met huweliksaanpassing toon. Min verbande is egter gevind tussen huweliksaanpassing, en sin en betekenis (wel tussen meditatiewe bewustheid en huwelikskonsensus, asook tussen empatiese aanvaarding en openheid, en affeksionele ekspressie). Geen verbande is ten opsigte van waardes gevind nie. Verskille tussen mans en vroue se EQ en SQ is ook ondersoek, maar geen groot verskille is verkry nie. Deur ’n meervoudige regressie is enkele verdere biografiese veranderlikes geïdentifiseer wat ʼn verband met huweliksaanpassing toon. In die kwalitatiewe navorsing is verskeie aspekte ondersoek en bespreek: die rolverdeling ten opsigte van kinderopvoeding en huistake, die balans tussen beroep en gesin, persoonlike tevredenheid (SQ) in die huwelik, asook die begrip en hantering van gevoelens (EQ). Die waarde van hierdie navorsing lê veral in die grondleggingswerk van die SQ-vraelys, asook bruikbare inligting ten opsigte van die huwelik met voorskoolse kinders in Suid-Afrika. Leiding aan egpare in die hantering van gevoelens (EQ), asook insig in hulle motiveringsbronne (SQ) behoort dus hulle huweliksaanpassing te verhoog. ENGLISH: In this research, the South-African marriage with preschool children was investigated. This phase of marriage, full of challenges and marital tasks, is regarded showing the lowest degree of marital adjustment and the highest incidence of divorce. The meaning, (spiritual intelligence or SQ), emotional experience, understanding and dealing with these challenges (emotional intelligence or EQ), as well as the relation to marital adjustment, were investigated. Firstly, a questionnaire was developed that could measure the characteristics of SQ, namely: (i) finding purpose and meaning in a given situation, (ii) motivations of behaviour, and (iii) values. Data from 198 respondents indicated the reliability of the subscales, which vary from 0.47 to 0.80. Satisfactory construct validity was obtained by researching the relation between the subscales of the SQ questionnaire and the value scale (r varied from 0.15; p ≤ 0.05 to 0.54; p ≤ 0.01). Next, both qualitative and quantitative research were utilised. In the quantitative research, the MMV SQ questionnaire, the marital adjustment questionnaire of Spanier (Dyadic Adjustment Scale), as well as the SSRI (Schutte Self-Report Inventory) were completed by the respondents. The respondents were 84 married individuals, including 34 couples. The relationship between marital adjustment and EQ was investigated by calculating correlations between the subscales of the DAS and SSRI. It transpired that an optimistic frame of mind showed a correlation with all the subscales of marital adjustment. It also appeared that the recognition of the own and the spouse’s feelings, social skills, and the application of emotions were related to increased marital satisfaction as well as marital consensus. Social skills also displayed a correlation with affectional expression. EQ, however, did not show a strong correlation with marital cohesion. Next, the relation between the subscales of the DAS was compared to that of the MMV-SQ questionnaire. Meaningful correlations between some scales of marital adjustment and SQ occurred, in particular with regard to the motivational scale: couples whose behaviour are motivated by mastering, appear to display a higher degree of marital adjustment, while the negative sources of motivation like self-centredness, craving and fears, display a negative correlation with marital adjustment. Few correlations were found between marital adjustment and purpose and meaning (between meditative awareness and marital consensus; between empathetic acceptance and openness, and affectional expression). No correlation was found with regard to values. Differences between the EQ and SQ of men and women were also investigated, but no major differences were observed. By means of multiple regressions it was indicated that some biographic variables did show a correlation with marital adjustment. Valuable information was obtained in the qualitative research regarding the couple’s roles in child-raising and domestic chores, the balance between career and family, personal satisfaction (SQ) in the marriage, as well as the understanding and handling of feelings (EQ). The value of this research lies in the foundational work of the SQ questionnaire in particular, as well as useful information with regard to South African marriages with preschool children. Guiding couples in their dealing with feelings (EQ), as well as providing an insight into the sources of motivation (SQ), should therefore enhance their marital adjustment. / Thesis (PhD)--University of Pretoria, 2010. / Psychology / unrestricted

After the democratic election of 1994, a new and integrated education system was developed in South Africa in accordance with international trends and the stipulations of the South African Bill of Rights with regard to equality, human dignity, basic education and equal access to education. According to the inclusive education system, learners with learning and developmental barriers should be accommodated within the mainstream of education. In order for inclusive education to succeed, a network of support was developed on departmental, provincial, district and school level. At school level, the school-based support team is directly responsible for supporting learners with learning and developmental barriers, educators and parents/caregivers. The effectiveness of these school-based support teams will, eventually, determine the quality of this inclusive education approach. The question which guided this research, is: How effectively does the school-based support team fullfil its function in the teaching and learning of learners with learning and developmental barriers within the framework of inclusive education? A qualitative research design was chosen which is exploratory, descriptive and explanatory. After an initial literature study in which international and national trends in this field were investigated, five primary mainstream schools were selected in the Western Cape according to certain criteria. A pilot study was conducted in another school to refine data collection strategies. Information was then gathered in the five schools by means of structured questionnaires, individual and focus group interviews, field notes and the study of appropriate documents. In order to evaluate these teams, eleven criteria were designed to serve collectively as an evaluation instrument. The effectiveness of the school-based support teams in the five schools were subsequently assessed and placed in various categories according to a conceptual framework. It was found that the school-based support teams function relatively effectively in most areas. The composition of the teams is effective. However, the teams function ineffectively with regard to the orientation and training of their members, as well as of the teachers and parents/caregivers of learners with learning and developmental barriers / Thesis (PhD (Educational Psychology))--University of Pretoria, 2008. / Educational Psychology / unrestricted

Please read the abstract in the section 07back, of this document / Thesis (DEd)--University of Pretoria, 2008. / Orthopaedic Surgery / unrestricted

AFRIKAANS : In die studie word gepoog om aan te dui op watter ingrypende maniere die Afrikaner se problematiese verlede altyd weer opduik in die hede, en op watter maniere hierdie verlede die groei en ontwikkeling van ’n nuwe Suid-Afrikaanse identiteit kan verhinder, of andersins, hoe ’n grondige en bewuste Auseinandersetzung met die verlede kan lei tot beter begrip, nie alleenlik van die verlede nie, maar ook van die hede en (ideaalgesproke) van die toekoms. Daar word geredeneer word dat ’n proses van bewuste konfrontasie met die verlede noodsaaklik is vir die ontwikkeling van ’n lewensvatbare identiteit. Hierdie proses sluit in ’n bewuswording en ontleding van die houdings van skuld (ook kollektiewe skuld), verlies en melancholie jeens die verlede. ’n Belangrike newe-komponent van die verhandeling is om hierdie proses te koppel aan verhaaltegniese middele wat aangewend word in die bundel vertellings onder bespreking. Daar word gepoog om ’n noodwendige verband te lê tussen tematiek en narratiewe tegnieke. In die verhandeling word aandag gegee aan die temas van skuld en verlies in die verhale, asook die vele motiewe wat gekoppel kan word aan hierdie twee temas. Daar word ook aandag gegee aan verteltegnieke soos tydsvorme, assosiatiewe skryfwyse, vertellingstrant en die stem van die verteller, wat aangewend word om die konfrontasie met en houdings jeens die verlede uit te beeld. Daar word geargumenteer in die verhandeling dat die prosa in hierdie bundel as vertellings gereken moet word, eerder as kortverhale (of meer spesifiek, short stories), en wel omdat die temas en die verteltegnieke bymekaar aansluit met die oog op ’n spesifieke leserrespons wat ’n grondige konfrontasie met en bestekopname van die verlede behels. ENLISH : The study focuses on the inescapable presence of a problematic past in contemporary South Africa, and the ways in which this past prevents the development of a new South African identity. It argues that a fundamental reckoning with the past will lead to a better understanding of the present and the future, and is essential to the development of a viable South African identity. This process of reckoning with the past involves an awareness and analysis of attitudes towards the past, which includes guilt (also collective guilt), loss and melancholy. The process of Auseinandersetzung with the past is then linked to specific narrative techniques which are employed in the collection of short prose under discussion. It is argued that there exists a connection between theme and narrative technique. Narrative techniques under discussion include tense (past and present tense), associative writing, narration and voice. It is argued that the short prose in the collection under discussion should be defined as (oral) narratives (vertellings), rather than Short Stories. The reader response towards an (oral) narrative differs from the response towards a Short Story, and the difference is essential in the process of confrontation with the problematic past/history. Copyright / Dissertation (MA)--University of Pretoria, 2010. / Afrikaans / unrestricted

Des nuances d’aciers à moyen carbone, microalliés au vanadium, ont été élaborées avec l’objectif d’obtenir de nouvelles microstructures, majoritairement constituées de ferrite aciculaire (FA). Le contrôle de la composition chimique (0.1-0.3 % V) et la vitesse de refroidissement (2.0 °Cs-1) conduit à des fractions de FA atteignant 80 %. Un paramètre empirique, le pouvoir ferritisant, P, a été introduit pour évaluer l’effet combiné de la composition chimique et de la vitesse de refroidissement sur la fraction de FA. Les caractérisations par MEB et MET montrent que la FA se développe à partir de la ferrite proeutectoïde recouvrant les inclusions de MnS. Une précipitation interphase de carbonitrures de vanadium, V(C,N), serait à l’origine d’un appauvrissement local en carbone de la matrice austénitique autour des aiguilles de FA, favorisant une germination autocatalytique. Le caractère fractal de la FA a été mis en évidence par des caractérisations morphologiques. Les dimensions fractales, D, et les longueurs de coupure ont été déterminées par la méthode de comptage de boîtes à partir d’images MEB. Des essais mécaniques isothermes-quasistatiques révèlent des propriétés mécaniques équivalentes à celles des microstructures bainitiques. Les courbes contrainte-déformation montrent un comportement mécanique de type Hollomon. Les structures de ces aciers présentent des taux de consolidation qui augmentent avec l’accroissement de la fraction de FA. Une corrélation entre les propriétés mécaniques et la dimension fractale a été établie. Ce lien s’exprime par des relations de type exponentiel : [delta]M = c exp [[alpha](D -2)] où M représente? les propriétés mécaniques (Re, Rm, etc.) et c? et ?[alpha] des constantes / Medium carbon vanadium microalloyed steels have been developed to obtain new microstructures, mainly formed of acicular ferrite (AF). Controlling the chemical composition and (0.1-0.3 % V) and the cooling rates (2.0 °Cs-1) lead to AF fractions up to 80 %. An empirical parameter, the ferritisant power, P, has been introduced to evaluate the combined effect of chemical composition and cooling conditions. Scanning (SEM) and transmission (TEM) electron microscopy investigations indicate that AF develops from proeutectoid ferrite enveloping MnS inclusions. An interphase precipitation of vanadium carbo-nitrides, V(C,N) has been identified. It is suggested that this precipitation is at the origin of carbon depletion in the austenitic matrix surrounding the AF plates. The formation of the AF is then enhanced by an autocatalytic effect. The fractal nature of AF has been determined by SEM and TEM characterisations. Fractal dimensions, D, and cut off lengths have been derived by the counting box method applied to SEM images. Mechanical tests conducted in isothermal and quasistatic conditions reveal that mechanical properties of AF are of the same grade of that of bainitic microstructures. Experimental strain-stress curves are described by the Hollomon law. The work hardening of the studied microstructures increases with the AF fraction. The mechanical properties have been linked to the fractal dimension by the following exponential relation : [delta]M = c exp [[alpha] (D -2)], where M represents the mechanical property (Re, Rm, etc.) and c and [alpha] are constants parameters

In hierdie studie is psigoterapeutiese uitkoms navorsing gedoen (Lindegger, 1999). Die navorser het as intern opvoedkundige sielkundige ‘n groepgebaseerde gestalt-dramaterapie program van 12 sessies ontwikkel ten einde selfagting-ontwikkeling by die kind met leerhindernisse aan te spreek. Gebrekkige motivering, ongunstige selfagting, sowel as problematiese sosiale vaardighede word geassosieer met leerhindernisse (DSM-IV-TR, 2000). Die Self-Esteem Index (SEI) is as meetinstrument gebruik en met aanvang en terminering van die intervensie afgeneem. Sekere strategieë is toegepas ten einde leerhindernisse te akkommodeer tydens die afneem van die meetinstrument. Na afloop van die intervensie, wat hoofsaaklik bestaan het uit dramatisering en rollespelle in kleingroep-verband, is die versamelde data statisties geanaliseer ten einde te bepaal of die intervensie moontlik tot die ontwikkeling van gunstige selfagting by die betrokke leerdergroep bygedra het. Die steekproef (n=17) is vanuit die SEI-vraelysdata van die Afrikaanssprekende Graad 4-leerders (tussen die ouderdomme van 10 tot 12 jaar) verbonde aan die betrokke remediërende skool, wie aan die LOD-program deelgeneem het, op sistematiese wyse getrek. Gepaarde t-toetse is gedoen ten einde te bepaal of daar enige statisties betekenisvolle verskille tussen die voortoets-/natoets-data bestaan. Die terapeutiese proses waartydens die data gegenereer is vir hierdie studie, was soortgelyk aan die pre-eksperimentele een groep voortoets-/natoets ontwerp. Die navorsingsresultate het aangedui dat die nulhipotese nie verwerp kan word nie. Die alternatiewe hipotese moet dus verder ondersoek word en vele moontlikhede vir toekomstige navorsing het vanuit die studie ontwikkel. ENGLISH : In this study psychotherapy outcome research was conducted (Lindegger, 1999). The researcher developed a group based gestalt drama therapy program during her internship as educational psychologist in a remedial school. The main therapeutic aim was to develop the self-esteem of the child with barriers to learning. Demoralization, low self-esteem, and deficits in social skills may be associated with barriers to learning (DSM-IV-TR, 2000). The intervention was facilitated over 12 sessions and all the Grade 4 pupils of the specific school participated in the intervention. The Self-Esteem Index (SEI) was administered during the beginning and at the end of the intervention. Certain strategies were used to accommodate barriers to learning during the administration of the SEI. After termination of the intervention the data were statistically analysed. The pretest/posttest results were compared in order to determine if the intervention contributed to self-esteem development of the participants. A data-sample (n=17) was systematically drawn from the Afrikaans speaking Grade 4 learner participants’ (between the ages of 10 to 12 years) SEI questionnaires. The therapeutic process during which the data was generated resembled a pre-experimental one group pretest/posttest design. Paired t-tests were used and the research results indicated no statistical significance which means that the null hypothesis could not be rejected. This resulted in the formulation of further hypothesis. The aim of this study therefore was to explore the possible effect of the intervention on the self-esteem development of the child with barriers to learning. Possibilities for further research emerged from this research study. Copyright / Dissertation (MEd)--University of Pretoria, 2010. / Educational Psychology / unrestricted

Les aciers appelés ODS (pour Oxide Dispersion Strengthened), renforcés par une dispersion homogène de nano-oxydes, sont des matériaux de structure avancés pour les futurs réacteurs nucléaires de fusion et de fission. En effet ces nano-oxydes, à base d’Y et Ti, servent comme centres de recombinaison de défauts ponctuels et d'obstacles aux mouvements des dislocations, améliorant de ce fait leur résistance aux radiations et aux températures élevées. La fabrication conventionnelle des aciers ODS est réalisée par broyage mécanique suivi de traitements thermo-mécaniques, et ne permet pas facilement de comprendre les mécanismes physiques conduisant à la précipitation des nano-oxydes, ce qui serait potentiellement utile pour optimiser leur production. La cinétique de formation de ces nano-oxydes peut être étudiée en utilisant une technique alternative, à savoir la synthèse par faisceaux d’ions, qui présente de nombreux avantages, notamment le contrôle précis des paramètres expérimentaux et la possibilité de décorréler divers facteurs contribuant à la cinétique de précipitation. Au cours de cette thèse, cette technique a été utilisée pour étudier la coprécipitation d'ions métalliques (Y et/ou Ti) et d'oxygène implantés dans un alliage modèle Fe-Cr de composition proche de celle typique des aciers ODS commerciaux. Des ions de Y, Ti et O à basse énergie ont été implantés dans des échantillons d'alliage Fe10wt%Cr de haute pureté à température ambiante. Les échantillons implantés ont ensuite été recuits à diverses températures entre 600 à 1100°C pour favoriser la précipitation de nano-oxydes, conformément au principe de cette technique. La microscopie électronique à transmission a été utilisée pour caractériser la structure cristallographique et la composition chimique des nano-oxydes formés lors de trois séries d'expériences. Tout d'abord, l'implantation séquentielle d'ions Ti et O a été mise en œuvre. Un recuit ultérieur a révélé qu’il n’y avait pas de précipitation d'oxyde de titane jusqu’à des températures inférieures à 1000°C, mais la présence de nano-oxydes riches en chrome avec une structure hexagonale de type corundum, qui contiennent une certaine quantité de Ti à des températures suffisamment élevées. Ce n’est qu’après le recuit à 1100°C que des nano-oxydes d’un autre type à cœur enrichi en Ti et coquille enrichie en Cr ont également été observés. Deuxièmement, l'implantation séquentielle d’ions Y et O a entraîné la formation à 800°C de nano-oxydes probablement riches en yttrium. Le recuit à 1100°C a favorisé la croissance des particules identifiées comme étant des nano-oxydes d’yttrium avec une coquille enrichie en Cr. Enfin, une implantation ionique séquentielle de deux ions métalliques (Y et Ti) a été réalisée, suivie d'une implantation d’O. L'ordre d'implantation des ions métalliques s'est révélé crucial pour la précipitation de nano-oxydes lors du recuit ultérieur. Lors de la séquence avec une implantation de Ti en premier, une précipitation d'oxyde riche en chrome de structure corundum hexagonale a été observée, très similaire au cas de l'implantation d’ions Ti et O. En revanche, la séquence avec une implantation d’ions Y en premier a produit des nano-oxydes d'yttrium-titane qui possèdent une structure non identifiable. En résumé, l’étude a démontré la faisabilité de la formation de nano-oxydes de Y, Ti et (Y, Ti) par implantation ionique. La thèse présente la caractérisation détaillée de ces nano-oxydes, ainsi que certaines de leurs caractéristiques spécifiques, telles que la présence de relations d'orientation entre les nano-oxydes et la matrice FeCr, qui ont été observées même dans le cas de nano-oxydes de type corundum riches en Cr. Enfin, les résultats obtenus, combinées avec les données de la littérature, sont discutées pour une meilleure compréhension des mécanismes impliqués dans la formation des nano-oxydes dans les aciers ODS. / Oxide Dispersion Strengthened (ODS) steels, that is steels reinforced with a homogeneous distribution of (Y,Ti) oxide nano-particles, are advanced structural materials for nuclear applications. The oxide particles serve as point defect recombination centres and obstacles to dislocation motion thereby improving radiation resistance and high-temperature strength of these steels making them perfect candidate materials for future fusion and fission nuclear reactors. The conventional fabrication of ODS steels is achieved by mechanical alloying followed by thermomechanical heat treatments. This way of ODS steel production seems complicated to understand the physical mechanisms leading to the precipitation of nano-oxide particles. The kinetics of nanoparticle formation can be much better studied using an alternative technique of nanoparticle growth, namely Ion Beam Synthesis (IBS). This approach has many advantages including the precise control of experimental parameters and the ability to de-correlate various factors contributing to precipitation kinetics. A better knowledge gained in this way would be potentially helpful for optimization of ODS steel production routines. In the course of this PhD study, the IBS approach was applied to investigate the co-precipitation of metal (Y and/or Ti) and oxygen ions implanted into a model Fe-Cr alloy with the composition close to those typical for commercial ODS steels. Following the standard IBS schedule, consisting of ion implantation followed by high-temperature heat treatment, ions of Y, Ti and O at low energies were implanted into high-purity Fe10wt%Cr alloy samples at room temperature. The implanted samples were then annealed at various temperatures ranging from 600 to 1100°C to promote the precipitation of nano-oxide particles. A range of Transmission Electron Microscopy techniques were used to characterize the crystallographic structure and chemical composition of the nanoparticles. The study has been performed following three sets of experiments. First of all, the sequential implantation of Ti and O ions was implemented. Subsequent annealing at temperatures below 1000°C revealed that precipitation of titanium oxide was suppressed. Instead, chromium-rich nano-oxide particles with corundum hexagonal structure were found to precipitate. At sufficiently high temperatures these corundum particles were found to contain certain amount of Ti. Only after annealing at the highest temperature of 1100°C, particles of another type with Ti enriched core and Cr enriched shell were additionally fixed. Secondly, sequential Y and O ion implantation resulted in the formation of probable yttrium-rich oxides at 800°C. Annealing at 1100°C promoted their growth to larger sized yttria (Y₂O₃) particles with a Cr enriched shell. Finally, sequential ion implantation of both metal ions (Y and Ti) was performed, followed by O implantation. The order of metal ion implantation has been found to be crucial for subsequent oxide precipitation at the annealing stage. With the Ti implantation first in the sequence, the precipitation of corundum hexagonal chromium-rich oxide was observed, very similar to the case of Ti and O implantation. In contrast, implantation starting with Y produced yttrium-titanium oxide particles with unidentifiable structure. Summing up, the study has demonstrated the feasibility of the formation of Y, Ti and (Y,Ti) oxides by ion implantation. The thesis presents the detailed characterization of the nanoparticles, as well as the discovered specific features of precipitated particles, such as the presence of orientation relationships between the particles and the FeCr matrix, which was observed even for the case of Cr-rich corundum particles. Finally, the implications of the obtained results, in conjunction with the already known data from the existing literature, for the better understanding of the mechanisms involved in the formation of nano-oxide particles in ODS steels are discussed.