Search

An investigation of mechanical properties of Ti6Al4V produced by additive manufacturing (AM) in the as-printed condition have been conducted and compared with wrought alloys. The AM samples were built by Selective Laser Melting (SLM) and Electron Beam Melting (EBM) in 0°, 45° and 90°—relative to horizontal direction. Similarly, the wrought samples were also cut and tested in the same directions relative to the plate rolling direction. The microstructures of the samples were significantly different on all samples. α′ martensite was observed on the SLM, acicular α on EBM and combination of both on the wrought alloy. EBM samples had higher surface roughness (Ra) compared with both SLM and wrought alloy. SLM samples were comparatively harder than wrought alloy and EBM. Tensile strength of the wrought alloy was higher in all directions except for 45°, where SLM samples showed higher strength than both EBM and wrought alloy on that direction. The ductility of the wrought alloy was consistently higher than both SLM and EBM indicated by clear necking feature on the wrought alloy samples. Dimples were observed on all fracture surfaces.

Titanium alloy composites with titanium boride (TiB) discontinuous reinforcement have shown improved performance in terms of strength, stiffness, and hardness. Producing this composite through selective laser melting (SLM) can combine the advantages of freeform design with the ability to produce TiB reinforcement in-situ. In this study, SLM was used to consolidate a pre-alloyed Ti-6Al-4V (Ti64) and amorphous boron (B) powder mixture with the intent of producing 1.5wt% TiB reinforcement in a Ti64 matrix. The processing parameters of laser power and scanning speed were investigated for their effect on the density, microstructures, and hardness of the composite material. The results showed that the boron and Ti64 composite could achieve a density greater than 99.4%. Furthermore, it was found that processing parameters changed the microstructural features of the material. The higher the energy density employed the more homogenous the distribution of boron modified material. Macro features were also observed with laser paths being clearly evident in the subsurface microstructure. Micro-hardness testing and density measurement also showed a corresponding increase with increasing energy density. Maximum hardness of 392.4HV was achieved in the composite compared to 354.2HV in SLM fabricated Ti64.

Selective laser melting (SLM) is an additive manufacturing technique which permits fabrication of three dimensional parts by selectively melting consecutive layers of metallic powder. This allows the production of parts with high geometrical complexity. Titanium alloy Ti-6Al-4V (Ti64) is widely used in industry due to its high strength-to-mass ratio, corrosion resistance and biocompatibility. SLM increases the application range of Ti64 because of its flexibility for prototyping any part and its low material waste. Nitriding is a diffusion-based thermo-chemical treatment for interstitial hardening of the surface of Ti64 alloy products. This study characterized the fatigue behaviour of SLM-produced Ti64 nitrided and annealed bars in as-built and machined surface conditions. The surface of the SLM-produced Ti64 parts after gas nitriding showed high values of micro-hardness up to 550 HV just below the surface. Fatigue testing was performed to assess the materials fatigue strength and fractographic imaging was used to examine fracture surface and nitride layer characteristics. Nitriding was found to reduce the fatigue strength of the samples to a similar level irrespective of being in the as-built or machined condition. The effect of nitriding on crack initiation and growth at various stress levels under fatigue loading was investigated.

Titanium alloys have poor wear performance, with severe adhesive wear and three-body abrasion being dominant mechanisms. To extend the use of titanium to applications demanding better wear properties, modifications can be made to the alloys. This can include the addition of hard particulates or interstitial strengthening, by increasing the oxygen or nitrogen content. The metal additive manufacturing process of selective laser melting (SLM) has been shown to enable manufacture of these modified titanium alloys in situ. In this study, small amounts of boron and titanium dioxide powders were added to Ti-6Al-4V (Ti64) and processed using SLM. To compare wear performance of these modified materials, reciprocating pin on plate tests in brine solution were performed. Increased oxygen content increased the hardness of the material, which reduced wear. The presence of boron increased wear in the short term but reduced the long-term wear rate. Incorporating of oxygen and boron has been shown to improve the saline solution wear properties of Ti64 against silicon nitride.

Time-lapse geophysical technologies, including 4D seismic methods, are key enablers for improved hydrocarbon recovery and more cost-effective field operations. By analyzing differences in multiple geophysical surveys and by integrating those analyses with conventional reservoir monitoring data, time

High-speed cine photography has been applied to an optically-accessed version of a modern 4-valve, pent-roof, SI engine in order to observe the behavior of fuel under cold starting and warm-up conditions. A wall film was formed on the combustion chamber surface in the vicinity of the valves when fuel was supplied by pintle and disk-type injectors. This wall film survived combustion but was drawn into the exhaust system when the exhaust valves opened. The use of an air-blast atomizer avoided the formation of this wall film, but some wetting of the piston was apparent, as it was with the other types of injector.