نشریه مهندسی متالورژی و مواد
سال سی و چهارم شماره 4 (زمستان 1402)

In the present work we report the development of carbon nanotube reinforced copper-zinc alloy nanocomposites. The carbon nanotubes were used in both uncoated and nickel coated conditions to reinforce copper matrix. The nanocomposites with different carbon nanotubes (0.25 to 1.0) weight percentage were developed using a combination of ultrasonication, ball milling and sintering processes. The developed nanocomposites were subjected to microstructural characterization using scanning and transmission electron microscopes to observe the dispersion of carbon nanotubes. The effect of carbon nanotubes on friction and wear properties of copper nanocomposites were studied using pin on disc testing rig as per ASTM G99 standard. The coefficient of friction of both 1 wt% uncoated and nickel coated carbon nanotubes reinforced nanocomposites was found when compared to copper-zinc alloy. Similarly the wear rate of nanocomposites were found to decrease with the incoporation of carbon nanotubes. The low coefficient of friction and wear rate were attributed to uniform dispersion of carbon nanotubes and formation of carbonaceous layer on the surface of nanocomposites during dry sliding wear.

In this research, silicon carbide (SiC) powder with a particle size of 30 to 45 micrometers and an irregular morphology was used for coating in an electroless nickel bath. The effect of particle surface roughening parameters in an acidic solution and electroless process time on uniformity and thickness of Ni-P coating on the SiC particles was investigated. SiC(Ni)-70vol.%Co blended powder was coated on simple carbon steel substrates by high-velocity oxy-fuel (HVOF) and atmospheric plasma spraying (APS) processes. The composite powder was obtained from the mechanical blending of cobalt powder with coated silicon carbide SiC(Ni) powder. The microstructure and morphology of powder particles and corresponding coatings were investigated by scanning electron microscopy (SEM). The results showed that the surface preparation of SiC powder by roughening the particles with HF/NaF solution and electroless time of 5 minutes led to the formation of a continuous and uniform Ni-P coating with a thickness of 1-3 micrometers on the SiC particles. Electroless nickel coating during thermal spraying by HVOF protected SiC particles against decomposition and oxidation and as a carrier led to the placement and distribution of SiC in SiC(Ni)-Co composite coating. In the APS process, due to the very high temperature of the plasma jet and thermal decomposition, SiC particles was insignificantly contributed to the coating microstructure. The micro-hardness of two mentioned coatings was measured as 570±40 and 460±30 HV0.3, respectively, and this difference was due to the effect of the significant distribution of SiC in the HVOF coating.

Cu-Mn mixed metal oxide nanoparticles were synthesized using the solution combustion method with using glycine as the fuel. Various ratios of fuel to oxidizer and different molar percentages of Cu and Mn cations were considered as variables in this system for investigation. Then, the effect of the aforementioned changes on the crystallization of the phases of the final product and the change in the crystallite size of the particles were evaluated. In the next step, the physical and chemical characteristics of the final products were carefully evaluated using using both X-ray diffraction (XRD) and scanning electron microscope (SEM). The results obtained from XRD and FE-SEM analyses, the simultaneous effect of changes in the ratio of fuel to oxidizer and the molar percentage of metal cations on the composition of phases, the morphology of the constituent particles, and the crystallite size of the particles were investigated. Also, the use of glycine fuel led to the synthesis of solid solutions of CuMn2O4 and CuMnO2 without needing furnaces or expensive equipment. By increasing the molar percentage of Mn in the fuel-to-oxidizer ratio (1), the porosity and pore size increased. Furthermore, calculations confirmed the smallest crystallite size at this fuel-to-oxidizer ratio.

The main purpose of the present study is to apply micro-spark oxidation coating on AZ31 alloy to improve corrosion resistance, bioactivity and biocompatibility of this alloy. The results of the electrochemical impedance test show the improved corrosion resistance of the AZ31 alloy. X-ray diffraction (XRD), transmission electron microscopy (TEM), infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and elemental analysis by X-ray energy (EDS) tests were used to examine the samples. Body simulation fluid (SBF) test was used to evaluate the ability to form apatite on the samples. The results show that the formation of an apatite layer on the surface of the samples can be considered as a measure of bioactivity. Be the right choice for bone implants In the 19th century, at the same time as the Industrial Revolution, the use of metals as implants in the body was developed. The first use of metal implants in the body to repair broken bones was reported. Metal implants are widely used in orthopedic surgery in both temporary and permanent forms. Today, metals have wider applications in orthopedic and dental surgeries. Only a small number of them are biocompatible and are used as implants. Among these magnesium metals and their alloys due to their close properties to bone, release of magnesium ions into bone and its biodegradability. In the simulated body environment, it has been widely considered as temporary implants in medical and orthopedic applications.

Considering the application of conductive polymer composites with segregated structure in electronics and aerospace industries, there is important to investigate their mechanical properties. In this research, High Density Polyethylene (HDPE), Carbon Black (CB) as conductive phase and Low Density Polyethylene (LDPE) were used as reinforcing phase to make composite. For Sample preparation first, mechanical mixing and hot pressing was selected. The conductivity of the samples was measured to ensure the formation of segregated structure. The results showed that the conductivity in composites with segregated structure has more conductivity than the polymer matrix and composites with random distribution.Analysis of microscopic images also confirmed the results of electrical conductivity. carbon black compeletely covered the surface of HDPE granuls.Besides, the mechanical properties was performed by tensile strength test. The addition of CB phase alone improved the yield strength and Young's modulus, while the addition of 0.5% CB had no effect on the improvement.

Knowing the behavior of hot deformation and microstructure changes of API-5CT-L80 alloy steel is of great importance in the production of oil and gas industry pipes. For this purpose, in this research, the thermomechanical behavior of this steel was investigated by isothermal hot compression test in the temperature range of 1173 to 1373 K and strain rates of 0.001 to 1 s-1 s. The experimental results showed that the hot deformation behavior of steel is a softening behavior caused by the dynamic recrystallization phenomenon that in some conditions, the material shows complex behavior in the form of multi-peaked curves. The results of the microstructural investigation showed that with the increase in the deformation temperature, the formed grains have a larger size compared to the low temperature state, and more martensite phases are formed, which are more elongated martensite blades compared to the phases formed at low temperatures. The effect of strain rate was also significant like the effect of temperature because the rate of deformation had an inverse effect on grain growth, so recrystallized grains have enough time to grow at low strain rates. At high strain rates, the pearlite phases appeared more polygonal, and very small nucleation were observed in the austenitic boundaries of the ferrite and Wiedmannstein phase, which did not have enough time to grow, and at high strain rates, the martensite blades also tend to thin.