Improving the surface characteristics of Ti-6Al-4V and Timetal 834 using PIRAC nitriding treatments

Despite the popularity of a number of techniques of thermochemical diffusion for titanium, in many cases the surface engineering processes used may not be economically viable options for industry. This work focuses on the application of Powder Immersion Reaction Assisted Coating (PIRAC), a relatively inexpensive nitriding treatment that can provide a remarkable improvement in the surface characteristics of titanium alloys. The aim of this work was to determine whether PIRAC could be successfully applied to Ti-6Al-4V and the high-performance near-α titanium alloy Timetal 834. In order to study the response of these materials to PIRAC nitriding, techniques such as X-ray diffraction, micro-indentation hardness, surface profilometry, optical and electron microscopy, nano-scratch adhesion testing and ball-on-plate reciprocating-sliding wear testing were employed. These techniques highlighted the markedly different response between the two alloys to the PIRAC treatment; namely, that Ti-6Al-4V forms a thick compound layer, while at the same processing temperature and time Timetal834 does not form any appreciable Ti 2 N phase instead forming a nitrogen-diffusion case with a thin TiN compound layer at the surface. This inherent difference in nitridability influences the metallurgical response of each alloy. Despite this, the surfaces of both alloys were still hardened considerably and their tribological performance in dry sliding conditions improved compared to the untreated alloys

DISLOCATION MOBILITY IN ALKALI HALIDE CRYSTALS AT LOW TEMPERATURES

La variation de la vitesse des dislocations avec la contrainte de scission appliquée a été mesurée à basse température dans des cristaux purs de NaCl, LiF et KI. La dépendance en température de la contrainte de scission résolue a été étudiée jusqu'à 4,2 K avec les mêmes cristaux et également avec des cristaux purs de KCl, KBr et RbI. Les résultats obtenus sont discutés brièvement.Dislocation velocity dependences on applied shear stress were measured in pure NaCl, LiF and KI crystals at low temperatures. Temperature dependences of the critical resolved shear stress (down to 4.2 K) of the same crystals and also of pure KCl, KBr and RbI were studied. The results obtained are briefly discussed

First Phase Formation at Interfaces: Effective Heat of Formation Model for Ternary Systems.

51147 Koeln 131196

INFLUENCE OF STRUCTURE DEFECTS ON B1 ⇄ B2 PHASE TRANSFORMATION IN ALKALI HALIDES

L'influence de différents défauts de structure (dislocations produites par déformation plastique, limites de grain, inclusion de composants durs et mous, cassures de séparation, pas de séparation) et de facteurs de géométrie et de taille sur les processus de nucléation et de croissance des phases pendant la transformation de phase à haute pression B1 → B2 a été étudiée dans des mono- et polycristaux de RbI, KI et KBr. La méthode de la cellule de Téflon a été utilisée pour créer une pression hydrostatique dans un appareil piston-cylindre. Une machine de vérification Instron a été utilisée pour le chargement des cellules. Il a été possible d'obtenir la pressurisation avec un intervalle de vitesse large, de déterminer la pression de départ requise pour la transformation directe B1 → B2 (Pd) et pour l'inverse B2 → B1 (Pr), et d'interrompre à tout moment la transition de phase. Des Pd de transformations B1 → B2 plus bas ont été obtenus pour : a) des cristaux minces, b) des poudres fines, c) des coins et des tords, d) des surfaces de monocristaux en cassure fraîche, et e) des polycristaux avec inclusions de composants mous. L'influence des autres défauts de structure a été moins prononcée. L'hystérésis la plus forte (l'existence à des pressions plus faibles de phase B2 métastable formée à haute pression) a été observée dans des polycristaux à inclusions de composants durs. La plus faible a été observée dans des poudres fines.Influence of various structure defects : dislocations introduced by plastic déformation, grain boundaries, inclusion of hard and soft components, cleavage cracks, cleavage steps and of geometrical and size factors on nucleation and growth processes of phases during B1 → B2 high pressure phase transformations in RbI, KI and KBr single and polycrystals was studied. Teflon cell method was used to create hydrostatic pressure in piston-cylinder apparatus. Instron testing machine has been used for cell loading. It was possible to obtain pressurization with a wide range of rates, to determine the starting pressure required for direct B1 → B2 (Pd) and the reverse B2 → B1 (Pr) transformations and to interrupt the phase transition in any of its stages. Lower Pd for B1 → B2 transformations were obtained for : a) thin crystals, b) fine powders, c) corners and edges, d) fresh cleavage surfaces of single crystals and e) polycrystals with soft component inclusions. The influence of other structure defects was less pronounced. Highest hysteresis (existance of metastable high pressure phase B2 at lower pressures) has been observed in polycrystals with hard component inclusions, the lowest in fine powders

PHOTOPLASTIC EFFECT IN CdTe

L'influence de la déformation plastique, des différents traitements thermiques, et du dopage sur les paramètres de l'effet photoplastique (PPE) ont été étudiées pour le CdTe. Un modèle de l'effet PPE du CdTe est discuté.The influence of plastic deformation, of various heat treatments and of doping on the photoplastic effect (PPE) in CdTe was studied. A model of the PPE in CdTe is discussed

Vancomycin release from biodegradable βTCP-FeAg nanocomposites

•High strength vancomycin loaded biodegradable βTCP-FeAg nanocomposites.•Nanocomposites were obtained by attrition milling followed by cold sintering.•Lower Ag and higher vancomycin content results in lower density of nanocomposites.•Nanocomposites retained >50% strength in bending after 28 days of degradation.•Steady release of vancomycin was observed with ≥90% release after 14 days. High energy attrition milled biodegradable βTCP-30(FeAg) (vol%) nanocomposite powders loaded with 1–10 wt% vancomycin (VH) were high pressure consolidated at room temperature/cold sintered to densities ≥90% of theoretical. Specimens exhibit high strength in bending being considerably higher than that of cold sintered VH loaded βTCP-40PLA. A desired steady release of VH in Tris buffer solution was observed, with >90% of VH released from specimens of all compositions after 14 days of immersion, with retention of more than 50% strength in bending. Ag containing specimens shows faster release profile than βTCP-Fe composite