فصلنامه مواد پیشرفته در مهندسی
سال چهل و چهارم شماره 3 (پاییز 1404)

Nickel-titanium alloys have poor hardness and tribological properties. There is a possibility of loosening caused by wear while using these alloys for medical applications such as artificial bone joints. The hardness, wear resistance, and corrosion resistance of the surfaces can be improved by deposition of coatings such as TiN. The study's main objective was to investigate how the deposition atmosphere affects the morphological and microstructural properties and the mechanical and corrosion behavior of the coatings.

This study demonstrates the effective use of the dense plasma focus method to deposit titanium nitride coatings onto nickel-titanium shape memory alloys in various atmospheric conditions. The atmospheres used were (i) 50 vol. % argon and 50 vol. % nitrogen, and (ii) 75 vol. % argon and 25 vol. % nitrogen.

Nitriding process under the above-mentioned conditions increased the hardness of the samples. The average hardness of samples 0.5N2-7 and 0.25N2-7 were obtained to be ~ 459 HV and 410.5 HV, respectively. At a constant distance from the anode to the sample surface, with a decrease in the ratio of nitrogen to the total inlet gas, the sputtering rate in the chamber increases and leads to an increase in the coating thickness. The coating thickness of samples 0.5N2-7 and 0.25N2-7 were obtained to be 0.91 µm and 1.75 µm, respectively.

Scanning electron microscope images of the coating surfaces indicated that the nitriding process in the 75 vol. % argon and 25 vol. % nitrogen environment was more effective in preventing cracking. Additionally, lowering the nitrogen ratio in the atmosphere led to a higher sputtering rate within the chamber, contributing to an increase in coating thickness and improved corrosion resistance.

Cobalt ferrite nanoparticles have garnered significant attention from researchers owing to their desirable properties and unique performance. Consequently, efforts have been made in recent years to optimize the parameters influencing the properties of the nanoparticles. Accordingly, the aim of the present study is to investigate the effect of calcination temperature on the structural, microstructural, and magnetic properties.

To this end, cobalt ferrite nanoparticles were synthesized with the self-combustion sol-gel method in the presence of the natural additive albumin, and were calcined at four temperatures of 700, 800, 900, and 1000 °C and characterized with X-ray diffraction analysis, field emission scanning electron microscopy, Fourier transform infrared spectroscopy, and vibrating sample magnetometer analysis.

The obtained results showed that at lower temperatures, the Co3O4 as impurity was formed, whereas with increasing calcination temperature to 900 °C, a single-phase spinel crystal structure with an average crystallite size in the range of 21 to 105 nm was obtained. In addition, images revealed that the calcination temperature had a significant influence on the morphology of the synthesized nanoparticles. Furthermore, the spectra clearly confirmed the formation of metal-oxygen bonds. The results also revealed that with changing the calcination temperature, the saturation magnetization and coercivity varied in the ranges of 25.26-45.14 emu/g and 170-743.28 Oe, respectively.

The results show that the optimization of the calcination temperature is greatly effective in enhancing the final properties.

34CrMo4 steel has the ability to increase its strength through quenching and annealing heat treatment due to its moderate carbon content. The aim of the present study is to obtain the optimal annealing temperature in order to achieve optimal structural and mechanical properties, including hardness and burst pressure.

In the present study, 34CrMo4 steel was used as the starting material. After going through the stages of the natural gas tank construction process and performing heat treatment, hardness testing, hydraulic pressure testing, burst pressure testing, and microstructural studies were performed to investigate the microstructural and mechanical properties of the produced tanks.

The results showed that in the annealing temperature range of 505 to 585°C, the hardness decreased from 392 to 310 Brinell and the breaking pressure decreased from 620 to 500 bar. Compared to the national standard (ISIRI 7598), the samples made at temperatures of 505, 525, and 545°C do not meet the standard conditions and the optimum heat treatment temperature is in the range of 565 to 585°C for compressed natural gas tanks.

With increasing tempering temperature, the strength of the material decreases and bursting occurs with less pressure. With increasing annealing temperature, the fracture surfaces will progress from brittle fracture to quasi-brittle and ductile fracture. The annealing temperature range at which optimal mechanical properties will be achieved in accordance with the National Standard 7598 will be between 565-585°C.

The aim of this study is to investigate the effect of addition of mesophase carbon microbeads (MCMB) on the microstructure, mechanical properties, and friction coefficient of MCMB-Cf/SiC composites prepared by spark plasma sintering.

Silicon carbide nanocomposite powder reinforced with 20 wt. % carbon fibers and different percentages of MCMB was prepared. Disk-shaped samples were prepared using spark plasma sintering (SPS). The effect of addition of different percentages of MCMB on the density, friction coefficient, fracture toughness, flexural strength, and microhardness of the samples was investigated.

The results showed that by increasing the MCMB content from 0.1 to 1 wt. %, the density of the sintered samples decreased from 93.1% to 89.8% of the theoretical density due to the higher porosity of this sample. Also, the friction coefficient decreased from 0.54 to 0.48 with increasing MCMB content due to the higher graphite content in higher MCMB weight percent. The hardness of the sintered samples with silicon carbide nanoparticles matrix also increased from 1095 to 1510 Vickers due to the higher density and lower porosity of sample with decreasing MCMB content from 1 to 0.1 wt.%. The fracture toughness and flexural strength of MCMB-Cf/SiC samples increased from 3.47 to 5.96 MPa.m1/2 and 72.9 to 138.7 MPa, respectively.

It was found that the MCMB-Cf/SiC sample containing 1 wt. % of MCMB has the closest properties to the properties of air brake discs. The densities of the SPS-sintered samples containing 1 wt. % of MCMB were obtained as 93.1% of theoretical density. The friction coefficient of these samples was obtained to be 0.48, which had the closest friction coefficient to that required for air brakes (0.4).

The HfCZrCTiC composite is part of the family of ultra-high temperature ceramics used in heat shields for spacecraft, furnace linings, supersonic aircraft components, and nuclear reactor components. The purpose of this research is to investigate the effect of nanocarbon black and silicon on the oxidation resistance of HfCZrCTiC composite.

Four composites, including HfCZrCTiC, HfCZrCTiC containing nano carbon black, HfCZrCTiC containing silicon, and HfCZrCTiC containing nano carbon black and silicon simultaneously were sintered at 2000 °C by spark plasma method. The oxidation process was carried out using differential thermal analysis (DTA) and thermal gravimetry analysis (TGA) at a temperature of 1200 °C. Microstructural evaluation and phase identification were done using a scanning electron microscope and X-ray diffraction.

The results showed that the weight changes for HfZrTi, HfZrTi-C.Bn, HfZrTi-Si and HfZrTi-C.Bn-Si samples were obtained to be 13.5%, 16.9%, 12.9%, and 7%, respectively. In addition, the results of differential thermal analysis (DTA) revealed that in the samples of HfZrTi, HfZrTi-C.Bn, HfZrTi-Si and HfZrTi-C.Bn-Si, the starting temperature of oxidation occurred at 480 °C, 400 °C, 500 °C, and 580 °C, respectively, indicating the lower the starting temperature of oxidation, the higher the weight changes.

It was found that in HfZrTi and HfZrTi-C.Bn samples, the detected phases after oxidation included hafnium oxide, zirconium oxide, and titanium oxide. These phases along with silicon oxide were identified in HfZrTi-Si and HfZrTi-C.Bn-Si samples.

Optimization of vanadium phosphate compounds through the control of synthesis methods plays a key role in enhancing their performance. In this research, the effect of adding cetyltrimethylammonium bromide with different molar percentages relative to the oxidizer (lithium nitrate) on the electrochemical properties of lithium vanadium phosphate cathode was investigated.

The solution combustion synthesis method was used to produce lithium vanadium phosphate samples with two different fuel-to-oxidizer ratios (φ = 0.5 and φ = 1). Cetyltrimethylammonium bromide was used not only as a fuel but also as a carbon source.

Scanning electron microscopy results showed that increasing the fuel-to-oxidizer ratio from 0.5 to 1 led to the formation of spherical particles in the morphology, which improved the electrochemical performance. The lithium vanadium phosphate sample with φ = 1 exhibited superior electrochemical performance, with a specific discharge capacity of 111.17 mAh/g at a current rate of 0.1C and 68 mAh/g at a current rate of 5C. After 150 cycles, the lithium vanadium phosphate sample with φ = 1 maintained a capacity of 79.16 mAh/g at a current rate of 5C.

The findings of this research indicate that the use of cetyltrimethylammonium bromide in the solution combustion synthesis process and the adjustment of the fuel-to-oxidizer ratio can play a significant role in optimizing the structure and improving the electrochemical performance of lithium vanadium phosphate cathode. The results of this study can be utilized in optimizing synthesis processes and developing new materials for next-generation batteries.

Determining the constitutive equations which describe the material flow stress, microstructural investigation, and preparing a processing map are essential for designing and optimizing metals forming. The aim of this paper is to obtain a relationship between stress, strain, temperature, and strain rate for Al-7.5Mg alloy in order to use it in the forming process.

In this study, stress-strain diagrams at four temperatures and three strain rates and friction elimination using experimental and computational methods were used. The activation energy value of hot deformation was calculated in the Arrhenius model. A processing map at strain 0.6 was drawn to establish the relationship between stress, temperature, and strain rate, and the instability region at a specific temperature and strain rate was determined. The metallography examination was performed to study the microstructure of the alloy.

In the Arrhenius model, the activation energy value of hot deformation increased with increasing strain. As the temperature decreased and the strain rate increased, the Zener-Hollomon parameter also increased. The instability region increased with increasing temperature and decreasing strain rate. The metallography test results showed that dynamic recrystallization occurred due to the high magnesium content in this alloy.

In this paper, the Arrhenius model (as a phenomenological model) was correctly extracted using a hot plane strain test on an extruded plate of Al-7.5Mg alloy, and a relationship between stress, temperature, strain, and strain rate was obtained using the constitutive equations and the Arrhenius model.

Some novel alloys, including high-entropy alloys, have gained increasing attention due to their diverse properties and applications. This study aims to investigate the relationship between the magnetic properties and phase transformations of the FeCrCoNiMn high-entropy alloy with the addition of titanium.

The high entropy alloy powder was synthesized by mechanically alloying pure constituent elements in a planetary mill. The synthesized high entropy alloy powder was phase-analyzed using the X-ray diffraction method. Furthermore, phase structure formation was predicted by thermodynamic functions via JMatPro software. The magnetic behavior was analyzed using a vibrating sample magnetometer, and particle morphology was examined using field emission scanning electron microscopy.

The FeCrCoNiMn alloy milled includes a single-phase FCC structure after 40 hours. The presence of Ti in the composition of the alloy created BCC and Laves phase structures. Concurrently, the addition of titanium increased both the coercivity force and saturation magnetization. 

The increase in saturation magnetization is due to the formation of the BCC phase in the FeCrCoNiMnTi alloy, while the BCC phase has a strong exchange interaction between ferromagnetic elements. However, the presence of both the non-magnetic Laves intermetallic phase and interphase boundaries has increased the coercivity force.