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A recent subsea failure of two subsea connectors made of UNS S32760, a 25 wt% Cr super duplex stainless steel, led to an extensive root cause failure analysis. The components showed a single longit...

Rapid industrialisation had led to a scarcity of resources. The concept of sustainable manufacturing has emerged to address this scarcity and to minimise environmental degradation. 3D printing also known as additive manufacturing, could potentially reduce material wastage, energy consumption and resulting emissions. A 'techno-eco-efficiency' framework was developed to produce technically, economically, and environmentally feasible centrifugal pump impellers 3D printed using the fused filament fabrication process. Firstly, surface properties, geometric properties, build material properties, static structural and dynamic properties, and the hydraulic performance of impellers were assessed in order to investigate how process parameters, such as infill pattern, infill rate and reinforcement material affect the technical performance. Secondly, the eco-efficiency performance of technically suitable impellers was assessed using environmental life cycle assessment, life cycle costing tools and portfolio analysis. Thus, this 'techno-eco-efficiency' framework was used to achieve sustainable manufacturing and could act as a decision support tool for selecting cost-competitive, environmentally benign, and technically feasible products. Alternatively, it would assist product designers and manufacturers to minimise a trade-off between technical and resulting eco-efficiency performance.

Titanium alloys, due to their biocompatibility and low stiffness, are among the most studied of metallic implant materials. Whereas most titanium-based biomaterials are produced from pre-alloyed powders, in this work the authors have utilised elemental powder to manufacture porous Ti-Nb-Ta-Zr alloys using a powder metallurgy technique based on the pressurised gasinduced expansion of pores. Samples of porous Ti-Nb-Ta-Zr alloy were prepared from a blend of elemental powders sealed into steel cans under a pressurised argon atmosphere. Following this, the pressurised cans were densified by hot isostatic pressing (HIP) at 1100 degreesC and 100 MPa for 4 hours, with cubic specimens from each can being treated in a vacuum furnace (1100, 1225, 1350 degreesC) for 10 hours in order to allow the pressurised pores to expand due to creep of the surrounding metal (foaming). Following this, the phase composition of HIP and foamed samples was characterised by x-ray diffraction (XRD), while microstructure and pore morphology were examined using optical microscopy and scanning electron microscopy. Mechanical testing under compressive loading was carried out at a strain rate of 10-3 s-1. Following HIP, XRD indicated the suppression of peaks related to alpha-Ti while microstructural analysis revealed the particle boundaries to have become diffuse due to the partial dissolution of Nb and Ta, with initial porosity levels being generally less than 3 %. Increasing the foaming temperature led to increases in porosity and proportion of alpha-Ti phase with a resulting decrease in elastic stiffness. These porous materials were concluded to be an attractive candidate for low stiffness biocompatible implant materials.

The characterization of fabricated porous β titanium alloy using powder metallurgy technique from elemental powders, i.e. Ti, Nb, Ta and Zr has been carried out. Those elemental powders were blended and filled in steel container. The container was vacuumed and pressurized with argon gas subsequently. The pressurized container was subjected for hot isostatic pressing (HIP-ing) at temperature of 1100°C under 100 MPa of argon pressure subsequent furnace cooling. The HIP-ed container was cut into cubic shape followed by placing in vacuum furnace at high temperatures of 1100°C and 1125°C for foaming process. While microstructure and hardness examination by electron microscope and Vickers indentation were respectively conducted, chemical composition of the porous alloy was determined using X-ray fluorescence (XRF). Their corrosion behavior was evaluated by using potentiodynamic polarization technique. The result shows that whilst the porosity level and the hardness increased with the increase of foaming temperature, the specimen foamed at the lower temperature exhibited higher pitting and corrosion resistance.

The authors have conducted a preliminary investigation with regard to the potential to manufacture porous titanium alloys for biomedical applications using toxic-free elemental powders, i.e., Ti, Nb, Ta, Zr, in combination with the pressurised gas bubble entrapment method and in contrast to standard processing routes that generally utilise prealloyed powder containing potentially toxic elements. Elemental powder compacts were either hot isostatic pressed (HIP-ed) at 1000°C and then foamed at 1150°C or else HIP-ed at 1100°C and foamed at 1350°C. Porous α + β alloys containing up to 45 vol% of porosity in the size range 20–200 μm were successfully produced, thus highlighting the potential of this manufacturing route. It was expected that further optimisation of the processing route would allow full development of the preferred β-Ti phase (from the point of view of elastic modulus compatibility between implant and bone) with this being the subject of future work by the authors.

A fully age hardened Al-4%CuPl%Mg alloy has been subjected to plain-fatigue and fretting-fatigue and the resulting fracture surfaces compared. Crack initiation in the plain-fatigue sample occurred at cracked inter-metallic inclusions and subsequent crack growth was at 90" to the surface. Crack initiation in the fretting-fatigue sample occurred at the edge of wear scar and subsequent crack growth was at 45" to the surface. Measurement of fatigue striation spacing on the fracture surfaces showed that, for the same applied stress, the initial crack propagation rate was an order of magnitude higher in the fretting-fatigue sample. This accelerated crack propagation rate was maintained until the crack reached a depth of 0.5-1.0 mm; thereafter the growth rate was the same as that in the plain-fatigue sample.

— Fretting fatigue strengths of high strength spring steel (JIS SUP9) and low strength medium carbon steel (JIS S45C) were examined by clamping the contact pads of the same individual materials. The pad contact pressures were kept constant at 60 MPa for SUP9 steel and at 45 MPa for S45C steel. The fretting reduced the fatigue strengths by a factor of about two in both the steels. Cyclic J-integral concepts were successfully employed to predict crack propagation lives using measured data on frictional forces between the fretting pads and the specimens.

Both surface hardening and residual compressive stresses in the surface have beneficial effects in combating fretting-fatigue damage: Shot peening produces both these effects. By applying carefully controlled permanent strains to shot-peened specimens it has been possible to remove the residual compressive stress without affecting the surface work-hardening. The two alloys used in this work have very different work-hardening characteristics, but in both cases it has been shown that removal of the compressive surface stress completely nullifies the effect of shot-peening. It is therefore concluded that surface work-hardening has only a very minor role in improving fretting-fatigue performance.

An Al-4.2%Cu-0.7%Mg-0.7%Si age hardening alloy (2014A) has been shot peened and subjected to plain and fretting fatigue. The shot peening improves both plain and fretting fatigue strengths, and in particular the fretting fatigue strength of the alloy in the fully aged condition is increased by 130%. The improvement in fretting fatigue properties is largely due to the residual compressive stresses induced into the surface by the shot peening process. Surface roughening also has a small beneficial effect but work hardening of the surface does not influence the fretting fatigue properties.