Effect of thermal cycling on mechanical and microstructural properties of heat-treated Ti-6Al-4V alloy

Titanium (Ti-6Al-4V) is an α+β phase-field alloy utilized in many industries due to its high strength-to-weight ratio and near-net shaping capability. Solution treated & aging, and stress relief annealing processes were performed on the samples to increase the strength and % of elongation. The heat-treated samples then thermally cycled for 500 cycles, 1000 cycles, and 1500 cycles to evaluate the microhardness and tensile properties. The presence of martensite and α2 precipitates in the thermally cycled samples was confirmed by scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). In this investigation, at 1000 thermal cycles, all specimens show improvement in both hardness and strength when compared within the cycles. Solution-treated and aging (STA), stress relief annealing (SRA), and without any heat-treatment (WHT) processes have their highest hardness values recorded for 1000 thermal cycles, and the values are 471 HV0.5, 381 HV0.5, and 374.6HV0.5, respectively. For the SRA process, ultimate tensile strength (UTS) of 925 MPa and yield strength (YS) of 896 MPa have resulted in 1000 cycles. Similarly, at 1000 thermal cycle WHT processed samples yielded UTS of 920 MPa and YS of 885 MPa. STA process samples that are heat-treated for 1000 thermal cycles have better strength properties than SRA and WHT and had a UTS of 1530MPa and YS of 1420MPa. From a ductility point of view, a maximum elongation of 29% for the STA process has resulted. Compared to forged titanium alloy (base metal), an increase of 31% elongation and 41% ultimate tensile strength for solution treated and aging process at 1000 cycles has resulted in this investigation.

Evaluation of an ivermectin-based attractive targeted sugar bait (ATSB) against Aedes aegypti in Tanzania.

Background The control of vector borne arboviral diseases such as Dengue is mainly achieved by reducing human-vector contact and controlling the vectors through source reduction and environmental management. These measures are constrained by labour intensity, insecticide resistance and pro-active community participation. The current study intended to develop and test an ivermectin-based attractive-targeted sugar bait (ATSB) against Aedes aegypti. Methods The 48hour lethal concentration (LC90) of ivermectin against Ae. aegypti was determined through serial dilution experiment where five 30cm x 30cm x 30cm cages were set; into each, a 10% sugar solution treated with ivermectin were introduced. 40 Ae. aegypti were released into each cage and observed for mortality after 4, 8, 24 and 48 hours. The ivermectin-based ATSB was evaluated in a semi field system where ATSB and attractive sugar bait (ASB) were deployed into each compartment of the semi field and 100 female Ae. aegypti were released every day and recaptured the next day through human land catch and Bio-gent sentinel trap. The developed and semi-field tested ATSB was further tested in the field by deploying them in garages. Results The ivermectin 48hr LC90 of male and female Ae. aegypti was found to be 0.03% w/v. In the semi field system, the ATSB significantly reduced a free-flying population of Ae. aegypti within 24 hours (incidence rate ratio (IRR) = 0.62; [95% confidence interval (95%CI); 0.54-0.70] and p-value < 0.001). However, in the field, the ATSBs required the addition of yeast as a carbon dioxide source to efficiently attract Ae. aegypti mosquitoes to feed. Conclusion Ivermectin is an active ingredient that can be used in an ATSB for Ae. aegypti depopulation. However, further research is needed to improve the developed and tested ATSB to compete with natural sources of sugar in a natural environment.

Microstructural Evolution and Electrochemical Behavior of Solution Treated, Hot Rolled and Aged MgDyZnZr Alloy

In order to develop a potential route to fabricate plates and clips for orthopedic applications, a Mg–3.4Dy–0.2Zn–0.4Zr (wt.%) alloy was produced and analyzed in different conditions: solution treated at 525 °C for 3 h, hot rolled and hot rolled and aged at 250 °C. The aging behavior of the rolled alloy was investigated during isothermal aging at 250 °C, and a significant peak was observed at 10 h. The electrochemical behavior was evaluated in 0.9 wt.% NaCl solution at 37 ± 0.5 °C by potentiodynamic polarization and electrochemical impedance spectroscopy. The 525 °C-3 h and hot rolled specimens exhibited corrosion rates of 2.0 and 1.7 mm/year, respectively. The hot rolled and aged at 250 °C for 10 h specimen presented a grain size of 11.8 ± 1.7 μm with an intense macrotexture of the basal {0002} plane, hardness of 73 ± 3 HV and higher impedance modulus and obtained the highest corrosion resistance with a corrosion rate of 0.9 mm/year.

Microstructure and Hardness of AlMg3 Alloy Subjected to Ultrasonic Upsetting

This study was conducted to study the effect ultrasonic vibrations on the evolution of the microstructure and hardness of the AlMg3 aluminum alloy in a solution treated condition. To understand the process physics in this article, after the deformation the microstructures of the samples before and after deformation were analyzed by the light and electron microscopy, including the electron backscatter diffraction (EBSD) analysis. The result evidently shows that the ultrasonic-assisted deformation has a meaningful influence on the grain refinement – the application of the USV enhances the formation of deformation bands and new sub-grains. This resulted in a certain hardness enhancement.

Shape Memory Properties and Microstructure of New Iron-Based FeNiCoAlTiNb Shape Memory Alloys

The shape memory properties and microstructure of Fe41Ni28Co17Al11.5(Ti+Nb)2.5 (at.%) cold-rolled alloys were studied at the first time using the values reported in constant stress thermal cycling experiments in a three-point bending test. Thermo-magnetization curves of 97% cold-rolled and solution-treated sample aged at 600 °C for 24, 48 and 72 h showed evidence of the martensitic transformation, and the transformation temperatures increased their values from 24 to 72 h. The alloy cold-rolled to 97% and then solution-treated at 1277 °C for 1 h showed that most grains were aligned near <100> in the rolling direction in the recrystallization texture. The intensity of texture was 13.54, and an average grain size was around 400 μm. The sample aged at 600 °C for 48 h showed fully recoverable strain up to 1.6% at 200 MPa stress level in the three-point bending test. However, the experimental recoverable strain values were lower than the theoretical values, possibly due to the small volume fraction of low angle grain boundary, the formation of brittle grain boundary precipitates, and a grain boundary constraint lower than the expected intensity of texture in the samples.

Starch-glyceryl monostearate edible coatings formulated with sodium benzoate control postharvest citrus diseases caused by Penicillium digitatum and Penicillium italicum

The curative antifungal activity of edible composite coatings (ECs) based on pregelatinized potato starch-glyceryl monostearate (PPS-GMS) formulated with or without sodium benzoate (SB) to control green mould (caused by Penicillium digitatum) and blue mould (P. italicum) was assessed on ‘Orri’ mandarins, ‘Valencia’ oranges and ‘Fino’ lemons. These fruit were artificially inoculated with P. digitatum or P. italicum, treated by immersion in coating emulsions and compared to uncoated control fruit immersed in water and fruit immersed in 2% SB (w/v) aqueous solution. Treated fruit were then stored at either 20°C or commercial low temperature (5°C for mandarins and oranges, 12°C for lemons). Coatings without SB did not exhibit antifungal activity, whereas coatings containing 2% SB reduced incidence and severity of green and blue moulds, in comparison to the controls, on all citrus species and in all storage conditions, without differing from the aplication of 2% SB alone. For example, incidence reduction on ‘Fino’ lemons was from 99 to 0% after 7 d at 20°C, and from 99 to 30% after 2 weeks at 12°C. None of the treatments was phytotoxic. These results indicate that applications of SB as antifungal ingredient of PPS-GMS based ECs is a promising non-polluting alternative to control Penicillium postharvest decay of citrus, and these ECs are effective substitutes for conventional waxes amended with synthetic fungicides.

Influence of Solution Treatment Time on Precipitation Behavior and Mechanical Properties of Mg-2.0Nd-2.0Sm-0.4Zn-0.4Zr Alloy

The effect of solution treatment time on the microstructure and mechanical properties of aged the Mg-2.0Nd-2.0Sm-0.4Zn-0.4Zr (wt.%) alloy were investigated to give full play to the performance of the alloy. As the solution treatment time increased from 2 h to 12 h at 788 K, the grain size of the solution-treated alloy significantly increased, and the network-like β-Mg12(Nd, Sm, Zn) phase gradually dissolved into the α-Mg matrix. It should be noted that no obvious residual β phase can be observed when the solution treatment time was more than 8 h. After the solution-treated alloy was further aged at 473 K for 18 h, a large number of nanoscale precipitates were observed in the α-Mg matrix. The solution treatment time was 2 h, the α-Mg matrix mainly consisted of spherical-shaped and basal plate-shaped precipitates. Upon the increase of solution treatment time to 8 h, the key strengthening phases transformed from spherical-shaped precipitates and basal plate-shaped precipitates to prismatic plate-shaped β′ precipitates. The orientation relationship between β′ precipitates and α-Mg matrix was (1¯10)β′ // (11¯00)α and [112]β′ // the [224¯3]α. Further increasing of solution treatment time from 8 h to 12 h, the key strengthening phases mainly were still β′ precipitates. The solution treatment of aged alloy was carried out at 788 K for 8 h, which achieved optimal ultimate tensile strength (UTS) of 261 ± 4.1 MPa, yield strength (YS) of 154 ± 1.5 MPa, and elongation of 5.8 ± 0.1%, respectively.

Numerical and experimental investigations on the effect of target thickness and solution treatment on the ballistic behaviour of AA7075 thick plates

The influence of target thickness and solution treatment on the ballistic behaviour of AA7075 targets has been investigated by both numerical and experimental methods. In numerical simulation, the target thickness was varied from 19 to 26 mm and an Ogive nose shaped projectile of 7.62 mm diameter with inlet velocities ranging between 800–875 m/s was considered. In order to justify the numerical observations, high velocity ballistic experiments were conducted on AA7075-T651 and the solution treated plates of various thicknesses (12, 16, 18, 20, 22 and 25 mm). For this experimental study, a deformable form projectile with dimensions of 7.62 × 51 mm and an inlet velocity of 850 ± 20 m/s was used. Microstructures of ballistic test samples were analysed using an optical microscope. Numerical analysis using ABAQUS predicted the minimum thickness required to resist complete penetration to be 20 mm in the case of AA7075 plates in the T651 condition, while experimental results showed it to be 21 mm. In the case of AA7075 solution treated plates, numerical simulation analysis predicted the minimum required plate thickness to resist complete penetration to be 24 mm, while the experimental results showed it to be 23 mm. Post ballistic microstructure analysis revealed that there was no change in the microstructure in the AA7075-T651 condition plates. Solution treated plates showed deformation of grains nearer to the impact region with the formation of adiabatic shear bands. In the case of the T651 plate, the mode of fracture was brittle, resulting in splinters, whereas it was petalling in the case of the solution-treated plates. The numerically predicted depth of penetration on both targets was reasonably close to experimental results with an average of 4% error.