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Metallic Ti–Co binary coatings were fabricated on titanium alloy (Ti–6Al–4V) substrate by laser surface cladding technique using a continuous wave RofinSinar 4 kW Nd: YAG laser. The influence of laser power on microstructure, hardness and tribological performance of Ti–Co laser clad coatings on titanium alloy (Ti–6Al–4V) was examined. Laser powers of 750 and 900 W were varied with constant scan speed of 1.2 m/min. A beam size of 3 mm and argon shield gas flow rate of 1.2 L/min were set as the operating laser parameters. Phase identification and morphological studies of the coatings were carried out using X-ray diffractometry (XRD) and scanning electron microscopy (SEM), respectively. Based on the results of laser process optimisation, it was observed that both laser powers produced clad coatings with good metallurgical bond with no cracks or pores in the coatings. With respect to the substrate (Ti–6Al–4V), the microstructure, hardness and friction/wear behaviour of Ti–Co coatings on Ti–6Al–4V substrate were enhanced obviously. [ABSTRACT FROM PUBLISHER]

The hourglass-shaped specimen, which is commonly used for axial fatigue testing, cannot be easily fabricated by metal injection moulding. Consequently, this work aimed at evaluating the performance of an alternative specimen (dog bone geometry) for fatigue characterisation. Additionally, an effort towards the assessment of the fatigue damage with specimens fatigued until halflife was made. The alloy used in this study, serving as an example for the test validation, was Ti–6Al–4V. The feasibility of using the specimens for fatigue testing was confirmed with a narrow scatterband, however, only in the range of 105 cycles. The crack initiation sites were always found on the surface associated with quasi cleavage facets. Specimens fatigued until halflife showed a decrease in ductility in conventional tensile testing; nonetheless, the ultimate tensile strength remained unchanged. [ABSTRACT FROM AUTHOR]

We describe here the combined efforts of engineering and biological sciences as a systemic approach to fundamentally elucidate osteoblast functions in functionally graded Ti-6Al-4 V mesh structures in relation to uniform/monolithic mesh arrays. First, the interconnecting porous architecture of functionally graded mesh arrays was conducive to cellular functions including attachment, proliferation, and mineralization. The underlying reason is that the graded fabricated structure with cells seeded from the large pore size side provided a channel for efficient transfer of nutrients to other end of the structure (small pore size), leading to the generation of mineralized extracellular matrix by differentiating pre-osteoblasts. Second, a comparative and parametric study indicated that gradient mesh structure had a pronounced effect on cell adhesion and mineralization, and strongly influenced the proliferation phase. High intensity and near-uniform distribution of proteins (actin and vinculin) on struts of the gradient mesh structure (cells seeded from large pore side) implied signal transduction during cell adhesion and was responsible for superior cellular activity, in comparison to the uniform mesh structure and non-porous titanium alloy. Cells adhered to the mesh struts by forming a sheet, bridging the pores through numerous cytoplasmic extensions, in the case of porous mesh structures. Intercellular interaction in porous structures provided a pathway for cells to communicate and mature to a differentiated phenotype. Furthermore, the capability of cells to migrate through the interconnecting porous architecture on mesh structures led to colonization of the entire structure. Cells were embedded layer-by-layer in the extracellular matrix as the matrix mineralized. The outcomes of the study are expected to address challenges associated with the treatment of segmental bone defects and bone-remodeling through favorable modulation of cellular response. Moreover, the study provides a foundation for a new branch of functionally graded materials with interconnected porous architecture. [ABSTRACT FROM AUTHOR]

For the production of complex shaped titanium parts huge advances have been made by powder metallurgy (P/M) during the last years. However, when it comes to miniaturized parts with intricate inner structures like closed channels without entrapped powder and high aspect ratios conventional P/M methods are stretched to their limits. To remedy this shortcoming, Fraunhofer IFAM Dresden uses 3D screen printing, a modified screen printing process based on a powder-binder mixture which is printed layer-by-layer to the desired shape followed by debinding and a conventional sintering step. Especially for small parts a productivity of several million parts per year is achievable. The objective of this work is to demonstrate the possibility to manufacture complex designs based on titanium including thin walls down to 120 μm. Therefore, pre-alloyed gas atomized Ti-6Al-4V powder was used. Analysis of part accuracy, resulting porosity, impurity level and mechanical properties were performed. [ABSTRACT FROM AUTHOR]

Powder preform forging is a technology that comprises the preparation of near net shape preforms through powder metallurgy and a subsequent hot forging in order to obtain the desired final shape. In this work, two Ti-6Al-4V powder preforms were sintered through spark plasma sintering (SPS) and then hot compressed in a horizontal dilatometer. Varying the temperature of the process, two full density preforms having different microstructures were produced: sintering at 950°C, a plate-like α was obtained, whereas sintering at 1050°C, an acicular α was obtained. The behaviour of the preforms under hot forging has been studied through hot compression tests carried out in a quenching and deformation dilatometer in a range of temperature and strain rates typically used in hot forging this alloy (850-1050°C, 0·01-1 s-1). Hot workability has been evaluated by measuring the stresses required for deformation and by analysing both the stress-strain curves recorded during testing and the microstructures after deformation. The main microstructural phenomena occurring during hot compression were individuated. The best conditions for the hot forging operation of SPS preform are temperatures above β transus, where the materials are deformed in a regime of dynamic recrystallisation, at every strain rate. [ABSTRACT FROM AUTHOR]

Low cost resistance butt welds between a similar Ti–6Al–4V alloy couple have been fabricated using a Gleeble thermomechanical simulator. The optimisation of the key bonding parameters (pressure, time, temperature and environment) required to produce high quality joints with near parent properties is discussed. Metallographic sections, chemical composition and microhardness traverses across the bond line are presented. The mechanical response of the bonds was assessed under monotonic tensile loading conditions. The suitability of this solid state diffusion technique for the fabrication of engineering components is discussed. [ABSTRACT FROM AUTHOR]