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

Preliminary evaluation of artemisinin–cholesterol conjugates as potential drugs for the treatment of intractable forms of malaria and tuberculosis

To evaluate the feasibility of developing drugs that may be active against both malaria and tuberculosis (TB) by using in part putative cholesterol transporters in the causative pathogens and through enhancement of passive diffusion in granulomatous TB, artemisinin–cholesterol conjugates were synthesized by connecting the component molecules through various linkers. The compounds were screened in vitro against Plasmodium falciparum (Pf) and Mycobacterium tuberculosis (Mtb). Antimalarial activities (IC50) against Pf drug‐sensitive NF54, and drug‐resistant K1 and W2 strains ranged from 0.03–2.6, 0.03–1.9, and 0.02–1.7 μm. Although the compounds are less active than the precursor artemisinin derivatives, the cholesterol moiety renders the compounds relatively insoluble in the culture medium, and variation in solubilities among the different compounds may reflect in the range of efficacies observed. Activities against Mtb H37Rv were assessed using a standardized colony‐forming unit (CFU) assay after 24 h pretreatment of cultures with each of the compounds. Percentage inhibition ranged from 3–38 % and 18–52 % at 10 and 80 μm, respectively. Thus, in contrast to the comparator drug artemether, the conjugates display enhanced activities. The immediate aims include the preparation of conjugates with enhanced aqueous solubilities, assays against malaria and TB in vivo, and for TB, assays using an infected macrophage model and assessment of granuloma influx.The South African Medical Research Council (MRC) with funds from the National Treasury under its Economic Competitiveness and Support Package. The South African National Research Foundation (NRF) is thanked for financial support to R.K.H. (NRF UIDs 90682 and 98934). H.N.W., F.S., J.F.W., D.D.N., and R.K.H. also thank the North‐West University for financial support.https://onlinelibrary.wiley.com/journal/18607187hj2019Biochemistr