The role of deposition temperature and scanning speed in the functional performance of laser assisted cold sprayed (LACS) coatings

Abstract: The functional performance of laser assisted cold sprayed (LACS) commercially pure ( CP) grade 1 titanium coatings was elucidated in terms of its mechanism of densification, microstructural evolution and corrosion resistance as the deposition temperature and scanning speed were altered by employing optical microscopy (OM) and potentio-dynamic polarization technique. The outcome of this study indicates that the densification mechanism of the coating was mainly influenced by the ratio of the processing temperature (T) and the scanning speed (SS) which is designated as . The attainment of the optimised functional properties of the coatings could be attributed to the thermal shear in the titanium film as well as its solid state inter-particulate consolidation resulting from localised thermal gradient which was induced between the ductile titanium particles and the brittle oxide film covering it at the optimum laser-gas-material interaction obtained at 600oC/10mm/s coupled with the adiabatic shearing of the particles upon impact at the deposition site. It was also established that microstructural porosity and cracks resulted from the increased lifetime of the liquid phase under suboptimal processing conditions which allowed more time for the propellant gas to initiate bubble formation within the coating’s microstructure. In addition, non-optimal parameters failed to attain the most desirable microstructural properties and corrosion resistance for the coatings. Finally, key factors in optimising LACS process parameters in order to achieve fully dense coatings are outlined

Awareness of Selected Information and Communication Technologies for Extension Training on Improved Agricultural Practices Among Extension Agents of Ogun and Oyo States, Nigeria

Over several decades agricultural production in Nigeria has improved through the extension services, coupled with the invention of ICTs in recent time. The application of any ICT gadget would be determined by its awareness and its appropriateness for the intended purpose desired to serve by the user. This study, therefore, assesses awareness of selected ICTs for disseminating agricultural information to farmers by the Extension Agents (EAs) of Ogun and Oyo States, Nigeria. Multistage sampling method was employed to obtain data from 287 EAs with interview schedule and Focus Group Discussion (FGD). Using both descriptive and inferential statistical tools, the paper analyses personal characteristics of the EAs in both States; agricultural crop information disseminated through the selected ICTs and level of awareness of the selected ICTs among the EAs. It was deduced in the study that the EAs and extension agency used different ICTs in disseminating agricultural information to farmers in the areas, though the EAs have different level of awareness on the usage of selected ICTs for such purpose, with GSM-phones ranked 1st (wms=4.76), radio (wms=4.63=2nd), extension bulletins/posters/newsmagazine ranked 3rd (wms=3.74) respectively. The PPMC analysis revealed that age (0.117*), educational level (0.145*) and years of working experience (0.176**) of EAs recorded a significant relationship with awareness level of selected ICTs at both 1% and 5%. The T-test analysis further revealed that a significant difference existed in the awareness level of the selected ICTs among the EAs of Ogun and Oyo States. The study, therefore, recommends the need to encourage the use of other ICT gadgets apart from GSM-phonesthrough adequate awareness on the use and appropriateness of ICTs for disseminating agricultural information to users and also socioeconomic characteristics of the applicants for extension service should be given consideration during recruitment exercise. Keywords: Awareness, ICT, Agriculture, Extension Agent DOI: 10.7176/RHSS/11-10-02 Publication date:May 31st 202

Effect of Energy Density on the Consolidation Mechanism and Microstructural Evolution of Laser Cladded Functionally-Graded Composite Ti-Al System

The engagement of additive manufacturing (AM) technology in developing intermetallic coatings involves additional heat treatment with a view to obtaining desirable microstructure and mechanical properties. This eventually increases the lead time and the manufacturing cost. To address these challenges, this study explores the fabrication of gradient and laminar structures of titanium aluminide (Ti-Al) composite coatings deposited on Ti-6Al-4V substrate via a single step laser cladding (LC). The alterations in microstructural properties, chemical composition and phase analysis of the coatings reinforced with TiC were investigated as a function of laser energy density. Evaluation of the deposited samples reveals that FGM composite clads were fabricated from Ti-Al blended with TiC when LED was set at 17.50 J/mm2 . At the selected LED, a thermo-positive reaction between the constituents’ materials was induced and it resulted in the formation of intermetallic compounds (e.g. Ti2AlC, and 2 matrix phases) with a microhardness more than that of the substrate (Ti-6Al-4V alloy). This study provides new insights on the selection of process parameters for the coating manufacturers while employing low cost- and time-effective LC process for fabricating functional graded Ti-Al coatings.Mechanical Engineerin

Aging Behavior of High-Strength Al Alloy 2618 Produced by Selective Laser Melting

High Si-bearing Al alloys are commonly used in additive manufacturing, but they have moderate mechanical properties. New high-strength compositions are necessary to spread the use of additively manufactured Al parts for heavy-duty structural applications. This work focuses on the microstructure, mechanical behavior, and aging response of an Al alloy 2618 processed by selective laser melting. Calorimetric analysis, electron microscopy, and compression tests were performed in order to correlate the mechanical properties with the peculiar microstructure induced by laser melting and thermal treatment

A study on the laser spatter and the oxidation reactions during selective laser melting of 316L stainless steel, Al-Si10-Mg, and Ti-6Al-4V

The creation of an object by selective laser melting (SLM) occurs by melting contiguous areas of a powder bed according to a corresponding digital model. It is therefore clear that the success of this metal Additive Manufacturing (AM) technology relies on the comprehension of the events that take place during the melting and solidification of the powder bed. This study was designed to understand the generation of the laser spatter that is commonly observed during SLM and the potential effects that the spatter has on the processing of 316L stainless steel, Al-Si10-Mg, and Ti-6Al-4V. With the exception of Ti-6Al-4V, the characterization of the laser spatter revealed the presence of surface oxides enriched in the most volatile alloying elements of the materials. The study will discuss the implication of this finding on the material quality of the built parts