Materials Science Forum Vol. 690

Abstract: This research paper presents a new possibility for the connection of metal sheets and fibre reinforced plastics (FRPs) through a cold metal transfer welding process. Small metal projections (pins) are welded onto metal surfaces by introduction of additional filler wire. These provide the possibility for building up a fixation with composites through fibre-friendly form-closure and co-curing. Results of tensile loaded double-lap shear geometries are presented for three types of pin geometries. The hybrid joints will be characterized and compared in terms of maximum reaction force and failure history. Joints with cylindrical and spiky pins inside show a certain load transfer capability, where ultimate bearing load and post failure behaviour have a high dependence on the quality of the co-cured adhesive bonding and the bending characteristics of the pins. Joints with spherical ending pins show twice as high ultimate bearing loads at a much more distinctive joint expansion.

Abstract: In this study, we focused on the effect of alloying elements (Fe, Mo, and Al) on the consolidation and mechanical properties of Ti compacts. The elemental blended powders is manufactured by spark plasma sintering. The effects of amount of alloying elements and sintering temperature on the relative density and tensile properties of Ti compacts were investigated. The addition of β-stabilizing elements (Fe and Mo) was found significantly improve the densification of Ti compacts, where the sintered density ratio of Ti-5 wt.% Mo specimen was higher than 99.9 %, and Ti-5 wt.% Fe specimen was higher than 99.0 %. On the other hand, addition of Al as α-stabilizing element showed the sintered density rate of Ti-5 wt.% Al specimen was higher than 99.9 %. The tensile property for sintered Ti-5 wt.% Mo specimens had the highest elongation of 16 %. It will be discussed the microstructures and tensile property of the compacts.

Abstract: A special thermomechanical process has been developed in order to improve the homogeneity of the microstructure and mechanical properties of Ti-6Al-4V alloy bar with a diameter of 450 mm for aerospace application. This study has investigated microstructure and mechanical properties on the large diameter bar. It has been found that the heavy section of the bar has uniform microstructure and mechanical properties, which can meet the specifications for Ti-6Al-4V alloy bar with a diameter of 300 mm, and ultrasonic inspection can meet the specification of ASM 2631 class A.

Abstract: The as cast Ti6Al4V, obtained after investment casting with yttria stabilized zirconia face-coat, was chemically milled using a mixture of hydrofluoric acid and nitric acid. This process removed completely the alpha-case layer. Lower hardness and almost no oxygen contamination are revealed after microhardness measurement, Energy dispersive X-ray and X-ray diffraction analysis. The hydrofluoric acid/nitric acid ratio, pickled Ti6Al4V surface, pickling efficiency, pickling rate, immersion time and solution temperature are discussed.

Abstract: Machining titanium is challenging due to its low thermal conductivity which results in very high temperatures at the tool/workpiece interface and in addition there is a tendency for titanium to react with most cutting materials, resulting in surface and subsurface deformation in the workpiece. This paper investigates the relationship between vibration and surface deformation that occurs while machining commercially pure titanium and Ti6Al4V alloy materials under both wet and dry machining conditions. The results have demonstrated that vibration monitoring (normalised peak frequency amplitude) can be used as a predictive tool for optimising the surface quality of the machined workpiece. Twinning plays a prominent role in the subsurface of the machined Grade 2 material.

Abstract: Threshold stress intensity factor for stress corrosion cracking (K_ISCC) of AZ91D magnesium alloy in a simulated physiological environment has been determined using circumferential notch tensile (CNT) technique. Fracture surfaces of the tested specimens were analysed using scanning electron microscopy (SEM) in order to examine the features for SCC.

Abstract: In addition to the use as light weight construction material, magnesium alloys are also very suitable for future orthopaedic and traumatology applications. Common permanent implant materials such as titanium or stainless steel still suffer from stress shielding problems, causing bone resorption and implant loosening. In contrast, magnesium alloys provide elastic moduli and strengths matching those of cortical bone. In order to support osseointegration and vascularisation, an open porous surface structure of an Mg-implant is advantageous. The powder metallurgical processing route of Mg-alloys enables the generation of such parts. Powder blends with different sintering behaviour were produced via mixing pure Mg-powder with different Ca containing master alloy powders (MAP). As a result, sintering of these Mg alloy powders and blends became feasible. Sintered parts were investigated in view of shrinkage, porosity, grain size using SEM, EDX and XRD. In addition, compression tests were performed revealing ultimate compression strength up to 328 MPa, plastic compressibility of 22 % and compressive yield strength up to 90 MPa. Hence, the PM-route enables the production of parts with mechanical properties matching those of cortical bone.

Abstract: The moderate corrosion rate exhibits by Mg-RE alloys make it candidate material for biodegradable implant. Owing to the operating environment, implants are subjected to stochastic cyclic load and chemical condition. The alloys response to the subjected condition determines its degree of applicability. This work studies the cyclic deformation of newly developed Mg10GdxNd alloys both in air and under corrosive environment. The corrosion fatigue test was carried out in Ringer-Acetate solution and was evaluated using mechanical hysteresis and pH-value measurements. The microstructural changes in correlation to the deformation parameters and fracture surfaces were characterized using SEM. Results show that alloying Mg10Gd with Neodymium improved its fatigue live both in air and corrosive medium. Chilled casted Mg10Gd and Mg10GdxNd were found to undergo brittle fracture in both media. Loading in Ringer-Acetate was found to reduce the fatigue life of the investigated alloys due to the interaction of corrosion and fatigue processes on the microstructure of the alloys. EDX analysis suggests that the improved fatigue life observed on the Mg10GdxNd is connected to the new ternary Mg-Gd-Nd phase observed in the microstructure.