A comparative study of oxygen pick-up of TiHDH powder during press and sinter and loose sintering processing

Abstract: Press and sinter is considered to be the most cost effective powder metallurgy process for producing parts. However, loose powder sintering shows to be a more promising cost effective powder metallurgy process as it entails pouring powder into a mould followed by sintering. The differences in their behaviour with respect to densification, maintaining dimensional stability and their oxidation behaviours determine the choice of their industrial applicability. Titanium has a high affinity for oxygen which in turn makes it difficult to process components from powder. It also affects the mechanical properties of products significantly; particularly in applications where ductility is imperative. The focus of this study was therefore to evaluate the oxygen pick-up of the two cost effective powder metallurgy processes (press and sinter and loose sintering). A 100 Mesh TiHDH powder was used for sintering. Sintering was performed at 1500°C for 4 hours. The oxygen contents of the green and sintered compacts were then compared. High oxygen contents were observed in tap density powder and pressed samples. The loosely sintered components showed high oxygen pick-up after sintering while oxygen pickup decreased with increasing pressure in pressed samples. These results show that press and sinter is advantageous over loose sintering where oxygen control is critical

Advances, gaps and way forward in provision of climate services over the Greater Horn of Africa

The Greater Horn of Africa is prone to extreme climatic conditions, thus, making climate services increasingly important in supporting decision-making processes across a range of climate sensitive sectors. This study aims to provide a comprehensive review of the recent advances, gaps and challenges in the provision of climate services over the region, for each of the components of the Global Framework for Climate Services. The study explores various milestones that have been achieved toward climate service delivery. The achievements include improvement of station network coverage, and enhancing the capacity of member states to utilize various tools in data analysis and generate routine climate products. The advancement in science, and availability of High-Performance Computing has made it possible for forecast information to be provided from nowcasting to seasonal timescales. Moreover, operationalizing of the objective forecasting method for monthly and seasonal forecasts has made it possible to translate tercile forecasts for applications models. Additionally, innovative approaches to user engagement through co-production, communication channels, user-friendly interfaces, and dissemination of climate information have also been developed. Despite the significant progress that has been made in the provision of climate services, there are still many challenges and gaps that need to be overcome in order to ensure that these services are effectively meeting the needs of users. The research of the science underpinning climate variability, capacity building and stakeholder engagement, as well as improved data management and quality control processes are some of the gaps that exist over the region. Additionally, communication and dissemination of climate information, including timely warnings and risk communication, require improvement to reach diverse user groups effectively. Addressing these challenges will require strengthened partnerships, increased investment in capacity building, enhanced collaboration between the climate information producers and stakeholders, and the development of user-friendly climate products. Bridging these gaps will foster greater resilience to climate-related hazards and disasters in the Greater Horn of Africa and support sustainable development in the region

A comparison of the microstructures, thermal and mechanical properties of pressed and sintered TieCu, TieNi and TieCueNi alloys intended for dental applications

The effect of Ni and Cu on the a/b phase transformation temperature, possible retention of the b-phase, and mechanical properties of Ti, Tie13Cu, Tie4.5Ni and Tie13Cue4.5Ni (compositions in wt. %) alloys were investigated. The alloys were developed using the conventional uniaxial cold press and sintering technique. The thermal properties of the sintered alloys were traced by the differential scanning calorimetry (DSC) analysis. The x-ray diffraction (XRD) and electron backscatter diffraction (EBSD) analysis determined phase composition, crystal structures and grain orientations. It has emerged that the Ti e13Cu and Tie13Cue4.5Ni retained the b-Ti phase. The mechanical properties were evaluated under tension with Tie13Cu and Tie4.5Ni possessing high ultimate tensile strength (UTS) and percentage elongation (%El) than the Tie13Cu-4.5Ni alloy. Although all the alloys have revealed the presence of porosity, its effect on mechanical properties was more on the Tie13Cue4.5Ni alloy. While the mechanical properties of Tie13Cu-4.5Ni alloy were inferior due to extensive porosity, those of Ti, Tie13Cu and Ti e4.5Ni allow them to be classified as Type 3 and Type 4 dental alloys, respectively, proving that the conventional powder metallurgy process has potential to be used as a processing technique for TieCubased dental alloys

Interfacial Reaction During High Energy Ball Milling Dispersion of Carbon Nanotubes into Ti6Al4V

The unique thermal and mechanical properties of carbon nanotubes (CNTs) have made them choice reinforcements for metal matrix composites (MMCs). However, there still remains a critical challenge in achieving homogeneous dispersion of CNTs in metallic matrices. Although high energy ball milling (HEBM) has been reported as an effective method of dispersing CNTs into metal matrices, a careful selection of the milling parameters is important not to compromise the structural integrity of CNTs which may cause interfacial reactions with the matrix. In this study, multi-walled carbon nanotubes (MWCNTs) were purified by annealing in argon and vacuum atmospheres at 1000 and 1800 °C, respectively, for 5 h to remove possible metallic catalyst impurities. Subsequently, 1, 2 and 3 wt.% MWCNTs were dispersed by adapted HEBM into Ti6Al4V alloy metal matrix. Raman spectroscopy (RS), x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray spectrometry and transmission electron microscopy techniques were used to characterize the as-received and annealed MWCNTs, as well as the admixed MWCNT/Ti6Al4V nanocomposite powders. The experimental results showed that vacuum annealing successfully eliminated retained nickel (Ni) catalysts from MWCNTs, while the adapted HEBM method achieved a relative homogeneous dispersion of MWCNTs into the Ti6Al4V matrix and helped to control interfacial reactions between defective MWCNTs and the metal matrix