جستجوی مقالات مرتبط با کلیدواژه « Severe Plastic Deformation » در نشریات گروه « فنی و مهندسی »

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.

Pure copper pipes have various applications in industries. It is necessary to improve their mechanical properties. The main strengthening mechanism in this case is severe plastic deformation in order to achieve ultrafine-grain microstructure. In this research, the deformation method of tube cyclic extrusion-compression (TCEC) was used. The design of punch and mould was performed by Solidwork and Mo40 steel was used for manufacture of both mould and punch. Then, the pure copper tube at ambient temperature and 750 °C deformed in one pass. Investigation of microstructural evaluation and hardness measurement on the cross-sectional surface and side surface of the pipe showed that in the case of cold TCECed pipe, the microstructure of the cross-section is slightly fine-grain and compared to the raw sample, a substantial hardness improvement (60%) was achieved. In the microstructure, orientation of grains and material flow were also observed in the direction of extrusion. In the hot SPD treatment, the cross-sectional area of ​​the sample significantly was fine-grained and the hardness of this part increased considerably by about 93% compared to the raw sample.

In the present study, the effect of thermal treatment on the corrosion behavior and microstructure changes of two-layer stainless-304-Cu sheet steel sheets after the explosive welding process has been investigated. Explosive welding has been done in parallel with an explosive layer of 46 and 63 µm and a stop distance of 2-3 mm. After explosive welding, the heat treatment process was carried out at 350 and 450 ° C for 8 and 16 hours. Explosive welding with an explosive load and variable stop distance. From the results of the electrochemical impedance test, it can be seen that the n number in the heat treatment sample at 350 ° C and 8 hours is less than the heat treatment sample at 450 ° C and 8 hours, and as a result, the corrosion current in the heat treatment sample The temperature is 350 ° C and the time is 8 hours, which reduces the load transfer resistance. By comparing the heat treatment samples at 350 ° C and 8 hours and the heat treatment at 450 ° C and the time of 8 hours with varying aniline temperature, the annealing time is constant and the heat treatment sample at 450 ° C and time 8 The hour with more annealing temperature has a value of n (0.80), followed by heat treatment at 350 ° C and 8 hours (n = 0.66), due to annealing temperature and reduced energy storage In the chapter.

Due to the compatibility of Magnesium with the body, it is a suitable material for making biodegradable stents, although its mechanical properties are not desirable for stent application. Accordingly, lately, microstructure and mechanical properties of magnesium have been improved using various methods, including Severe Plastic Deformation (SPD). Many SPD methods have been introduced for the fabrication of ultrafine grain tubes until now, and the process of Tubular Channel Angular Pressing (TCAP) is the most effective one. In this research, by optimally designing the geometrical parameters of the trapezoidal channel, the process force in TCAP has been reduced, and for the first time, magnesium tubes with a thickness of 1 mm have been processed using this process. At the beginning of the research, using the finite element model, the process was simulated in Abaqus software, and the effect of the geometric parameters on the process force was investigated. To investigate the performance of the process with optimal geometric parameters, magnesium tubes with an outer diameter of 5 mm and a thickness of 1 mm were processed at a temperature of 200°C in three passes. The results of metallographic, microhardness, and tensile tests show that the TCAP process with trapezoidal geometry and optimal geometrical parameters is a suitable process for modifying the microstructure and improving the mechanical properties of magnesium tubes with a thickness of one millimeter. The values of yield strength and ultimate strength in the second pass are 1.6 and 1.26 times the initial sample, respectively, and have reached 60 and 92 MPa. The average grain size and hardness have reached from 200 µm and 30 HV in the initial sample to 3 µm and 40 HV after the third pass, respectively. The ductility and strength of processed samples have improved compared to the initial sample.

In present study, an improved severe plastic deformation process named improved tube cyclic expansion extrusion process has been introduced. The idea of this process is taken from the conventional tube cyclic expansion extrusion process, and in this novel process, it is tried to solve some important problems of the conventional process. Improved tube cyclic expansion extrusion process is capable of severe plastic deforming and improving microstructure and mechanical properties of tubular components. Also, this process can be considered for producing relatively long tubes. For this purpose, the improved tube cyclic expansion extrusion process was successfully performed on AZ91 magnesium alloy tubes, up to two passes. Then, the microstructure evolution and the mechanical properties improvement were scrutinized. The results showed that the microstructure and mechanical properties were improved considerably. In this way, after two passes of this process, an ultrafine grained (UFG) microstructure was formed, and the values of ultimate strength (UTS), hardness (Hv) and ductility (EL%) became 3.6, 1.83 and 1.8 times higher, respectively. Also, the comparison of the results of the improved tube cyclic expansion extrusion process with those of the conventional tube cyclic expansion extrusion process indicated that ultimate strength and hardness of the improved process were near to those of the conventional process, but the value of elongation to failure of the improved process is considerably higher than the value of the conventional process. This can be considered as one of the important advantages of the improved process over the conventional process.

In this study, Tube cyclic Extrusion Compression (TCEC) process was performed on copper pipes at ambient and 200°C (dynamic recrystallization activation threshold temperature) and the effect of process temperature on microstructure and mechanical properties were investigated. The results showed that by applying TCEC at ambient temperature, an equiaxed crystalline structure with an average grain size of 370 nm was obtained while by increasing the forming temperature to 200°C, the equiaxed grains with average size of 720 nm resulted. Applying the TCEC process at ambient temperature on a copper tube, increased its yield strength from 116 to 242 MPa and its average hardness from 69.2 to 101.4 Vickers while at the forming temperature of 200°C, the yield and ultimate strength were about 217 and 225 MPa, respectively, and the average hardness value was about 86.8 Vickers. Therefore, performing TCEC process at 200 °C on copper reduced the strength by 10% and increased the elongation to fracture by 21% compared to the cold forming state.

Crack nucleation mechanisms, its growth, and the determination of critical failure parameters are of industrial importance. Therefore, it is inevitable to study the mechanical behavior of cracked materials under applied load during severe plastic deformation. The present study studied the mode I fracture behavior, mechanical properties, and microstructure characterization of the 6061 aluminum alloy fabricated by friction stir processing (FSP). For this purpose, a milling machine made a perfect stirring zone to perform the FSP method with the specific non-consumable tool. According to the tensile test results, the yield and ultimate tensile strength of the FSP-processed sample have increased by 39% and 37%, respectively. Based on the three-point bending test, the fracture toughness of the processed aluminum was calculated as 10.86 MPa√m, which shows a 14.3% improvement compared to the as-received annealed state. Eventually, the average grain size of the annealed and processed samples was measured as 35 and 15, respectively, which indicated a 57% reduction in the aluminum grain size after FSP. Note that this grain refinement is associated with improved strength and toughness.

One of the main methods for strengthening and increasing the hardness of the materials is the use of the severe plastic deformation (SPD) processes. Equal channel angular pressing (ECAP) method is one of the SPD methods. Two challenging issues including (1) the very high required punching force, and (2) the deflection of the punch restrict the application of the method in industry. In this paper, a new design of ECAP process is proposed, which in addition to reducing the punching force, eliminates the deflection problem. The main purpose of this paper is to investigate the effect of the process parameters including process temperature (100- 200-300) ° C, lubrication (dry and graphite) and the number of ECAP passes (1-2-3) on the hardness of 7075 aluminum material and determining their optimal levels. The Taguchi design is used for design of experiment and the S/N ratio is used to find the optimal levels of the parameters and to maximize the hardness of the material. Based on the analysis of the variance, the process temperature and the number of ECAP passes have the greatest effect on the hardness of the post ECAP samples. However, the lubrication condition has not a significant effect on the hardness of the post ECAP samples in all temperatures.

In the present study, in addition to reviewing the severe plastic deformation (SPD) processes and their mechanisms in the microstructural evolution, previous researches on the corrosion behavior of various metallic materials that have undergone SPD are investigated. Grain size, as an important metallurgical parameter, affects a broad range of mechanical, chemical, physical and electrochemical properties of metallic materials. As mostly reported, the reduction in grain size is in line with a considerable improvement in the mentioned properties. In recent years, SPD methods have been nominated as an ideal way to reach nano- and ultrafine-grains. Among the mentioned properties, the corrosion performance of ultrafine-grained materials produced by SPD methods is still controversial for researchers. The purpose of this study is to review the SPD methods, the mechanism of grain refinement during them, and their effects on the corrosion behavior of various metals and engineering alloys such as steels, aluminum, titanium, copper, and magnesium.