مجله مواد نوین
سال چهاردهم شماره 2 (پیاپی 52، تابستان 1402)

Titanium boride and titanium carbide are the most important ceramic particles to reinforce titanium-molybdenum alloys. If an external reinforcement with an exothermic reaction causes the production of those reinforcements, the heat of reaction can promote the diffusion of molybdenum in the Matrix.

In this research, Ti–10 wt.% Mo–1.5 wt.% B4C composite samples was consolidated in a SPS machine following cold uniaxial precompaction by applying maximum 10 MPa and then SPSed in vacuum below 1 Pa at 1150, 1300 and 1450°C with 50°C/min heating rate under 20 MPa pressure. Subsequently at each sintering temperature the applied pressure was increased to 50 MPa and process continued for 5 and 10 min. Microstructural changes, physical and mechanical properties as well as phase analysis of produced composites were evaluated.

Totally, with rising sintering temperature and time, the density increases. Only at 1450°C for 10 min, a slight decrease in density was observed. Similarly, the mechanical properties improved. Actually, increasing sintering temperature influences the progress of the titanium-boron carbide reaction and the decreasing porosity greater than time. Here, not only increasing sintering temperature and time but also the heat of exothermic reaction encourages the diffusion of molybdenum to matrix and lead to better homogenization, consequently.  Under similar elaborated arrangement, also achieving improved mechanical properties is more accessible.

In recent years, extensive studies have been conducted on severe plastic deformation based on suitable processes for sheets and solid materials. Considering the limitations in some properties and crucial applications of titanium metal, these methods are considered intriguing avenues for enhancing the efficiency of this practical metal. Therefore, efforts have been made to investigate and develop effective severe plastic deformation processes for producing titanium samples. Severe plastic deformation is widely recognized as the primary method for producing ultrafine and nanostructured materials with high strength and hardness. This study focuses on exploring the most recent methods in this family suitable for producing nanostructured titanium samples with ultrafine grains. Furthermore, the study assesses the impact of several key severe plastic deformation methods on titanium properties, comparing them based on the advantages and disadvantages of these methods from both processing and property perspectives.

In this regard, in recent years, severe plastic deformation methods have been introduced and extensively studied. In this research, by examining and reviewing the latest studies related to the advantages and disadvantages of threemethodssimple shear extrusion, accumulative roll bonding, and equal channel angular pressing, the following results have been obtained :
All past research indicates that these three methods have a significant and positive impact on the mechanical properties of titanium metal. These positive effects show an increasing acceleration up to a certain number of passes and then reach a saturation point.
Temperature, speed, and appropriate processing are three fundamental and important factors concerning severe plastic deformation of titanium metal.
Some studies suggest that pure titanium metal can also be processed at room temperature using methods of severe plastic deformation.
The frequency of using these methods in relation to titanium metal and its alloys includes methods such as ECAP, accumulative roll bonding, and simple shear extrusion, respectively.
A noticeable weakness in most studies conducted on processed titanium using severe plastic deformation methods is the lack of investigation into the biocompatibility properties of titanium concurrently with its mechanical properties after the process.
6. It can be almost stated that in none of the studies conducted on severe plastic deformation methods, a specific industrial output has been introduced, and it remains at the level of research work.

Due to the increase in population and industrial activities, the demand for clean water has increased. On the other hand, the amount of fresh water has decreased; As a result, wastewater treatment, including municipal and industrial wastewater, has become very necessary. One of the wastewater treatment methods is the Advanced Oxidation Process (AOP). This research used the advanced oxidation process using the photo-catalyst based on modified activated carbon to treat municipal wastewater in Yasouj City. Activated carbon was prepared from the walnut shell using the chemical activation method and then modified by a composite of ZnO and SnO2 nanoparticles and used as a photo-catalyst in the designed reactor for wastewater treatment. The results of FTIR, XRD, and EDX analyses confirmed the presence of ZnO/SnO2 nanoparticles on the modified activated carbon surface. Due to the coating of these nanoparticles on the surface of the activated carbon and inside its pores, the specific surface area of the modified activated carbon is greatly reduced compared to the activated carbon. The results of the DRS analysis show the low band gap of the synthesized photocatalyst and its applicability in the presence of visible light. To optimize the effect of the parameters, the central composite design method was used to design the experiment. The results showed that the maximum amount of COD reduction of 97.41% has been achieved at a pH of 3, the amount of photocatalyst of 1.25 g/L, and the duration of light irradiation of 45 minutes.

The thermal spraying method with the aim of increasing the working life of steel parts is one of the most important solutions in surface engineering to solve the problem of wear.

In this research, NiCrBSi and NiCrBSi-MoS2 coatings were applied on 304 stainless steel by thermal spraying, and then the wear behavior was evaluated at ambient temperature and 500 degrees. Phase investigations were done by X-ray diffraction test. The chemical composition of the coatings was checked with the help of energy dispersive spectrometer analysis. Porosity was investigated with the help of optical microscope and scanning electron microscope images. The hardness of the samples was measured using a microhardness test. In order to check the adhesion and tribological behavior of the coatings, VDI3198 and ASTM-G99 pin-on-disk tests were used, respectively, and finally, the wear mechanism was evaluated using SEM images and EDS analysis of the wear surfaces of the samples.

Phase analysis (XRD) and chemical composition (EDS) showed that the coating has an amorphous and crystalline phase and the most important phases of the coating are nickel-gamma, carbide and boride. Porosity measurement results with the help of image analysis software showed higher porosity of NiCrBSi-MoS2 coating. The results of hardness measurement from the cross-section of the samples indicated an increase in the hardness of the substrate in the presence of coatings, and the addition of MoS2 particles decreased the hardness of the NiCrBSi coating. The coating with MoS2 has better adhesive behavior due to its crystalline structure and better plastic deformation ability. The tribological results indicated the superiority of the NiCrBSi-MoS2 coating due to the appropriate ability of plastic deformation as well as the intrinsic lubrication property (based on the crystal structure) in this test. It was found that at ambient temperature, the samples mainly had lamellar wear mechanism, and at high temperature, oxidation wear as a secondary mechanism helped to destroy the surface.

The addition of MoS2 to NiCrBSi coating caused more porosity, more roughness, less hardness and better wear behavior of the coating. The addition of MoS2 to the coating improved the wear resistance of the coating at high temperature.

Titanium and Hydroxyapatite (HA) are widely used in various industries, especially medicine and implants. The friction stir welding process (FSP) is one of the best methods for the fabrication of Ti/HA surface composites.

This research specifically examines the effect of pin shape in FSP on the microstructure and mechanical properties of Ti/HA surface composites. Process parameters including pin shape (triangular, square, and conical pins), speeds of 1150 and 1250 rpm, and traverse speeds of 30 and 45 mm/min were used. Characterization of Ti/HA surface composites was performed with the help of FESEM, X-ray diffraction analysis, energy dispersive spectrometer (EDS) analysis, and tensile test.

The results of the microstructure investigation showed that the triangular pin could not enter HA powder in the titanium substrate. At a higher rotational speed, fusion occurs to a greater extent in square and conical pins, reducing defects such as holes and cracks. The ultimate tensile strength values for the square pin with traverse speeds of 30 and 45 mm/min were 772 and 605 MPa, respectively. For the conical pin with traverse speeds of 30 and 45 mm/min, they were 894 and 747 MPa, respectively. Therefore, it was found that the ultimate tensile strength decreases with increasing traverse speed in both square and conical pins. Additionally, the ultimate tensile strength is always higher in samples processed with a conical pin than a square pin. These results show that process parameters significantly affect the mechanical properties of the specimens.

In this study, the influence of intercritical annealing heat treatment on the quenching and partitioning (Q&P) of ferrite-bainite-martensite multiphase in high-silicon low-alloy DIN 1.5025 steel was investigated. Initially, a normalization heat treatment process involving austenitization at 900°C for 5 minutes followed by air cooling to room temperature was conducted to achieve homogeneous and uniform initial ferritic-pearlitic microstructures for all of the specimens. Subsequently, the Q&P heat treatment cycles comprising partial austenitization in the intercritical austenite-ferrite region at 775°C for 60 minutes, followed by quenching in a molten salt bath of partitioning at temperatures of 250, 300, and 350°C for various durations of 2, 5, 15, 30, and 60 minutes were performed. Optical microscopy (OM) and field-emission scanning electron microscopy (FE-SEM) observations, standard tensile tests, and hardness measurements were employed to evaluate the microstructural changes in relation to the mechanical properties of the specimens. The results demonstrate that the presence of ferrite phase during partial austenitization in the intercritical austenite-ferrite region enriches austenite with carbon, reduces the martensite start temperature (Ms), promotes the formation of fine bainite crystals, and consequently leads to unconventional continuous yield behavior in the specimens. A partitioning heat treatment time of 30 minutes in the molten salt bath at 350°C induces the formation of multiphase microstructures containing a mixture of ferrite-bainite-martensite microphases, along with optimizing the formability and tensile strength properties to values of 16% and 1350 MPa, respectively.