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International audience; We report the role of ultrasonic shot-peening (SP) and laser-shock peening (LSP) on the insertion of atmospheric nitrogen during high temperature oxidation of pure titanium and the improvement of its oxidation resistance. Ion Beam analysis showed that for short oxidation durations, a layer of Ti 2 N is formed at the oxide-metal interface. However, only the LSP treatment leads to the formation of a long-term stable nitrogen-rich layer which acts as a barrier for the diffusion of oxygen. This explains the efficiency of the LSP treatment to reduce the oxidation of Ti and prevent embrittlement.

Das Verbundstrahlen stellt ein neu entwickeltes Verfahren auf Basis des Mikrostrahlens dar. Durch die Erweiterung einer Mikrostrahlanlage um eine Heizeinheit ist es möglich, keramische Strahlpartikel mehrere Mikrometer in ein Grundmaterial einzubringen. Die Eindringtiefe ist dabei von unterschiedlichen Prozessparametern, wie Materialpaarung, Temperatur, Strahldruck und Bearbeitungsanzahl abhängig. In der vorliegenden Arbeit wird der Zusammenhang zwischen den Prozessparametern, der sich ausbildenden Mikrostruktur und den daraus resultierenden Eigenschaften beschrieben. Mikroskopische Untersuchungen zeigen, dass sich durch das vielfache Auftreffen der Keramikpartikel eine Hügel-Tal-Struktur ausbildet. Weiterhin führt der mehrfache Aufprall zu einem Fragmentieren der Keramikpartikel. Diese werden vor allem in den Tälern der Oberflächenstruktur vorgefunden. Durch Prozesstemperaturen nahe dem Schmelzpunkt des Grundmaterials ist es möglich, die Fragmente der Keramikpartikel bis zu einer Tiefe von 40 μm in Aluminiumwerkstoffe einzubringen. Analytische Modelle aus den Bereichen des Strahlverschleißes und der Ballistik berechnen ähnliche Eindringtiefen. Detaillierte Untersuchungen der Mikrostruktur mittels Röntgendiffraktometrie (XRD) und Transmissionselektronenmikroskopie (TEM) zeigen, dass die ehemals mikrometergroßen Strahlpartikel bis hin zu nanoskaligen Partikeln zerbrechen. Weiterhin weisen die Partikel durch den massiven Aufprall eine erhebliche Defektdichte auf. Die quasi-statischen Eigenschaften werden nur geringfügig durch das Verbundstrahlen beeinflusst und sind nahezu unabhängig von den Prozessparametern. Die eingebrachten Partikel und die gesteigerte Rauheit der Oberfläche nach dem Verbundstrahlprozess führt bei Wechselbiegeversuchen zu einer geringfügigen Reduktion der Langzeitfestigkeit. Den größten Einfluss hat die verbundgestrahlte Oberfläche bei tribologischer Belastung. Die harte und raue Oberfläche erhöht den Reibungskoeffizient unter Schwing-Reib-Verschleiß, steigert aber den Widerstand gegen Abrasion erheblich.

International audience; Improving the high temperature (HT) resistance of titanium alloys is currently a technological challenge for extending their use in aerospace engines. Ti-Beta-21S is a metastable $\beta$ titanium alloy specifically designed for high temperature applications up to 593 °C. We report the effect of a surface treatment by laser-shock peening (LSP) on the high temperature behavior of Ti-Beta-21S in order to increase further its maximum service temperature. The oxidation kinetics at 700 °C for duration up to 3000 h showed that the LSP treatment increases the oxidation resistance of Ti-Beta-21S. The effects of the LSP treatment on the alloy microstructure, its evolution at high temperature and the diffusion of light atmospheric elements (oxygen and nitrogen) are also reported.

Mechanical surface treatments based on repeated impacts are known to create a graded strengthening in-depth by the means of severe plastic deformation. However microstructural evolution mechanisms leading local progressive grain refinement and the resulting surface mechanical hardening are not yet fully understood. It is shown in this paper that micro-percussion testing represents an interesting case scenario to emulate conventional treatments such as shot peening and better characterize microstructural changes at local and global scales. For this technique, every impact is made at the same position by a rigid conical indenter, controlling the number, angle and velocity of each impact. The main issue of this work is as follows: (i) to describe the transformed microstructures by the means of SEM microscopy and EBSD mapping; (ii) to quantify the mechanical gradient in-depth using the micro-pillar compression testing; and (iii) to converge both descriptions to understand the mechanisms involved on the strengthening of refined structures. This coupled experimental analysis would reveal the influence of different strengthening effects as the Hall-Petch effect or the dislocation hardening. This investigation is carried out in pure α-iron. Keywords: Micro-pillar compression, Micro-percussion, Shot peening, Hammering, EBSD, Hall-Petch effect, Dislocation density, Mechanical surface treatments

The mechanical surface treatments confer better local mechanical properties against wear or fatigue service conditions. In the case of impact-based treatments, the material is exposed to repeated mechanical loadings, producing a severe plastic deformation in the near-surface. It leads to a local and progressive refinement of the microstructure into the affected zone, commonly known as Tribologically Transformed Surface (TTS). For this project, two mechanical surface treatments are used in a model material (pure α-iron): (i) shot-peening and (ii) micro-percussion.The resulting surfaces are characterized by a mechanical property gradient in-depth as a consequence of the microstructural transformation over a few tens of microns. Nowadays, it is well-known that this rise of local mechanical properties could improve the service lifetime of materials. However, a simple micro-hardness test is not quite enough to quantify precisely the engendered variation of mechanical properties and understand the influence of several microstructural effects. For this purpose, two micro-mechanical tests are considered: (i) nano-indentation and (ii) in situ micro-pillar compression.The main issue of this work is to characterize the mechanically-induced transformed surfaces and correlate the mechanical properties gradients with the local microstructural evolutions. Indeed, three main goals are considered: (i) quantify the mechanical and microstructural gradients induced by the surface treatments (shot-peening and micro-percussion), (ii) correlate the results obtained by the means of both mechanical tests (nano-indentation and micro-pillar compression) and finally (iii) investigate the influence of several microstructural effects related with the graded strengthening of hyper-deformed surfaces., Dans l’industrie, les traitements mécaniques de surface métalliques permettent d’améliorer les conditions de service des pièces mécaniques. Les effets de contact de ces types de procédés engendrent une forte déformation plastique du matériau et par conséquent une transformation microstructurale en sous-surface. Cette transformation se manifeste dans le raffinement progressif de la microstructure dans une couche de quelques dizaines de micromètres. Celle-ci est souvent dénommé "surface tribologiquement transformée" (en anglais : Tribologically Transformed Surface - TTS). Une telle transformation microstructurale conduit à une augmentation des propriétés mécaniques en extrême surface et rend le matériau plus résistant aux conditions de frottement, usure et fatigue.Dans le cadre de cette étude, deux procédures de transformation microstructurale ont été employées sur un matériau modèle : le fer-α. Pour la première technique (grenaillage), la surface est impactée de façon répétitive avec des billes métalliques projetées à grande vitesse. Concernant la deuxième méthode (micro-percussion), la surface est impactée répétitivement à un endroit précis avec un indenteur conique rigide.L’objet de ce projet se centre sur trois aspects principaux : (i) déterminer les gradients mécaniques et microstructuraux induits sur les deux types de surfaces transformées (grenaillage et micro-percussion), (ii) établir un lien quantitatif entre les mesures faites par deux types d’essais micromécaniques (nano-indentation et micro-compression de piliers) et (iii) mettre en évidence les effets microstructuraux impliqués (taille de grain, densité de dislocations, etc...) dans l’augmentation des propriétés mécaniques par hyper-déformation de surfaces.

Mechanical surface treatments such as Shot Peening (SP) and Deep Cold Rolling (DCR) are being used to introduce Compressive Residual Stress (CRS) at the surface and subsurface layers of aerospace components, respectively. This paper investigates the feasibility of a combined introduction of both the surface and sub-surface compressive residual stress on Ti6Al4V material through a successive application of the two aforementioned processes, one after the other. CRS profiles between individual processes were compared to that of combination of processes to validate the feasibility. It was found out that shot peening introduces surface compressive residual stress into the already deep cold rolled sample, resulting in both surface and sub-surface compressive residual stresses in the material. However the drawback of such a combination would be the increased surface roughness after shot peening a deep cold rolled sample which can be critical especially in compressor components. Hence, a new technology, Vibro-Peening (VP) may be used as an alternative to SP to introduce surface stress at reduced roughness. ispartof: IOP Conference Series: Materials Science and Engineering vol:157 issue:1 ispartof: 2nd International Conference on Mechanical Engineering and Automation Science (ICMEAS) location:Singapore: SINGAPORE date:13 Oct - 15 Oct 2016 status: published

Artigo em acesso restrito. Two experimental methods to characterize the mechanical behavior of work-hardened surface layers of metallic materials, induced by mechanical surface treatments, are described and discussed. The study was conducted using two steels with different mechanical properties, subjected to a similar shot-peening treatment. To characterize the elastic–plastic behavior of the surface layers affected by shot-peening, the X-ray diffraction assisted four-point bending method (XRDABM) and the normalized hardness variation method (NHVM) were applied. The results were compared and discussed taking into account the advantages and disadvantages of both methods. Similar yield strength values of the treated surfaces were found by both proposed methods. Taking into account their measuring characteristics, these can be considered complementary methods.

The main objective of this study was to evaluate the influence of mechanical surface treatments for excess glass removal on the fracture toughness of a glass infiltrated zirconia toughened alumina "GI-ZTA" disks (In-Ceram® Zirconia). The GI-ZTA disks were submitted to three different mechanical surface treatments after glass infiltration (grinding, sandblasting and grinding/sandblasting/annealing). Fracture toughness was evaluated through indentation fracture (IF) test. Reliability of tests results was accessed through Weibull statistics. Results: Indentation fracture tests (IF) of GI-ZTA disks have shown that grinding was the surface treatment that presented the lowest K Ic and reliability. An annealing treatment after grinding and sandblasting promoted an increase in K Ic, mainly due to monoclinic-tetragonal reverse transformation recovering the tetragonal zirconia lost during the different mechanical surface treatments. The highest K Ic values were observed after sandblasting and grinding/sandblasting/annealing. Significance: The proposed mechanical surface treatments played an important role on the metastability of tetragonal zirconia and strongly influenced the mechanical performance of GI-ZTA. Kruskhall-Wallis test indicated that K Ic values of the three mechanical surface treatments were statistically distinct.