iman ebrahimzadeh

In this study, the transient liquid phase bonding of St52 plain carbon steel to WC-Co compound using BNi-2 interlayer with a thickness of 50 μm was investigated. For this purpose, samples were bonded at a temperature of 1050 °C and holding times of 1, 15, 30 and 45 min. After the joining process, the microstructure of the bonded samples was examined using a scanning electron microscope equipped with energy-dispersive X-ray spectroscopy. X-ray diffraction analysis was also used to investigate the effects of bonding parameters on the phase transformations of the bonding region. Microhardness and tensile shear tests were also conducted to study the mechanical properties of the bonded samples. Microstructural studies showed that the formation mechanism of the solidification zone in all samples was isothermal solidification mechanism. The results of the investigations showed that the only phase in the isothermal solidification zone was the nickel base solid solution. The maximum hardness in all samples belonged to WC-Co base materials due to the presence of WC particles in it. The maximum tensile-shear strength was related to the sample with bonding time of 30 min. The mode of failure in all samples was a combination of brittle and ductile fracture.

In this research, laser cladding of Stellite 6 on the 35CrMo substrate was done. Various parameters of the laser caldding process were studied and after optimization of the parameters, microstructure and microhardness were evaluated. Characterization of the cladded layer was done by scanning electron microscope, X-ray diffraction, and Vickers microhardness. The results show that the clad track height was dependent on the parameters of the powder feeding rate and the laser scanning speed, and the laser power had the minimal effect. Similarly, the clad track width was controlled by the laser power and laser scanning speed. The clad track dilution was proportional to the laser power and had the greatest impact compared to other parameters. The wetting angle was controlled by three parameters: laser power, laser scanning speed, and powder feeding rate. Laser power of 550 W, powder feeding rate of 0.6 g/s, and laser scanning speed of 10 mm/s were chosen as the optimal parameters. The results showed a good metallurgical bonding between the cladding and the substrate. The microstructure of the single clad track was dense and crack- and pore-free, and due to the thermal and concentration gradient changes during solidification, it consisted of three different areas, including planar, columnar dendritic, and equiaxed dendritic microstructures. A significant improvement in the microhardness of Stellite 6 cladding was observed as compared with the substrate. By increasing the overlapping ratio from 30 to 60%, the dilution rate decreased from 31 to 7%. As a result, the microhardness reached 361 HV in the overlapping ratio of 30% and further to 452 HV in the overlapping ratio of 60%. The overlapping ratio of 60% between adjacent passes created the best results.

WC-Co and St52 were joined using the TLP method. The joining process was carried out at 1050 °C for different times using a BNi-2 interlayer. After the joining process, the microstructure of the bonded samples was examined using a scanning electron microscope equipped with energy-dispersive X-ray spectroscopy. X-ray diffraction analysis was also used to investigate the effects of bonding parameters on the phase transformations of the bonding region. The results of the investigations showed that in the isothermal solidification zone, the Ni-base solid solution phase was observed in all samples. Also, the η phase (Co6W6C) was formed in the diffusion affected zone of the WC-Co base material. The size of the produced zones in the bonding region depended on the time of the bonding process, and with the change in the bonding time, the size of these zones also changed. The hardness profile for all samples had the same trend and the maximum hardness was related to WC-Co base material (around 1100 HV) and the hardness in the isothermal solidification zone was about 380 HV. The maximum shear strength was related to the bonded sample at 30 min, about 320 MPa, which was due to the removal and damping of residual stresses by the isothermal solidification zone. The mode of failure in all samples was brittle-ductile.

Employing lightweight steels in the transportation industry, especially the automotive industry, has received lots of attention in today’s time, and much research has been done to replace the low carbon steel used in the transportation industry with lighter materials. In this regard, in the present study, a new class of lightweight steels called architectured steels involving alternating layered structure of steel and aluminum was produced. In this process cold rolling process was employed to make a connection between a simple low carbon steel and 6061 aluminum alloy. In order to improve the inter-layer connection and properties of the product, the prepared samples were subjected to annealing treatment at different time (30-120 min) and temperatures (400-500° C). Finally, after examining the conditions of different annealing processes, the best cycle to achieve an appropriate combination of strength and ductility was determined. In the end, the best mechanical properties (610 MPa UTS and 16.1% elongation) was obtained in the specimen annealed at 400°C for 90 min.

Age hardening behavior and the related changes were studied to elucidate the hardening mechanism of an Ag–Cu–Pd alloy by Differential Scanning Calorimetry (DSC), hardness test, X-ray diffraction (XRD), scanning electron microscopic (SEM) observations and an energy dispersive spectrometer (EDS). The results showed that the hardness of the alloy was raised to 90% and 68% of its solution state value by isothermal aging at 300 ◦C and 400 ◦C, respectively. However, aging at 500 ◦C led to a decrease in the hardness of the alloy. Moreover, while age hardening at 300 ◦C occurred because of coherency strains between the (111) plane of Ag-rich and the (111) plane of Cu3Pd phases, the mechanism of aging at 400 ◦C was the formation of Cu3Pd superlattice with the L12-type crystal structure. In contrast, reduction of the Cu3Pd phase from the microstructure and formation of the Cu solid solution decreased hardness during aging at 500oC.

Plasma spark sintering is an effective method for producing nanostructured metal materials. In this process, a graphite die is usually used. The limitation of graphite die is using this die at higher pressure of 100 MPa. In this research, the simultaneous effect of the pressure and type of die (graphite die with a pressure of 40 MPa and Inconel die with a pressure of 250 MPa) on the microstructure and the properties of nanostructured silver in the spark plasma sintering process were evaluated. The first nanostructured powder with a 47nm crystallite was transformed into two nanoscale silver pieces using two different dies and pressures. Changes in the crystallite size of the powder and the bulks, the percentage of dislocations and the strain of the nanostructured silver bulks were calculated using the X-ray diffraction results. Microstructure and micro hardness of samples were also investigated using FESEM and micro hardness tests, respectively.The results indicate that the increase in crystallite size was 6% in a specimen prepared with a graphite die and 40 MPa pressure and reduce 53% in a crystallite size of a sample prepared in an Inconel die with a pressure of 250 MPa. The change in the type of mold and the applied pressure has no effect on the density of the bulk samples, but the hardness of the sample in the case of Inconel die conditions is increased by 40% compared to the sample prepared in graphite die.High temperature pressure tests show superplasticity behavior nanostructured silver at high temperature.

Deep sub-zero treatment is a complementary operation performed on all types of tool steels, carbonized and high-speed steels to improve wear resistance and hardness. Among these tool steels, H13 is a hot work tool steel that have an extended application in industry as a hot deforming tool. This paper investigates the wear behavior of deep cryogenic treated H13 hot work steel at operating temperature. Two quench-tempered and quench-subzero-tempered samples are compared. The microstructures of the specimens were determined by scanning electron microscopy, and the structures were determined by X-ray diffraction. Vickers hardness used for determining hardness after each treatment. The wear test was carried out at 250°C (mold temperature on forging of copper base alloys). Finally, the wear surface was examined by scanning electron microscope equipped with EDS analyzer. The results show that the highest hardness was in quench-subzero-tempered condition which is about 26% higher than the quench-tempered in oil conditions. This is due to the formation of fine, dispersed and uniform precipitates and higher martensite percentage in quench-subzero-tempered sample compared to quench-tempered sample. Quench-subzero-temper operation reduced the residual austenite percentage by 10% and improved the wear properties by 36% at 250° C. Examination of wear surfaces indicates the presence of oxidized surfaces adhered to the wear surface in the form of abrasive particles. These oxide levels were lower in quench-subzero-tempered sample than quench-tempered sample.

In this study, a FeAl powder synthesized by mechanical alloying and annealing process was used as a binder to produce WC-FeAl composite. The powders of WC and FeAl were blended with composition of WC-25 vol% FeAl and sintered by spark plasma sintering at 1150℃. The hardness, fracture toughness and wear behavior of sintered WC-FeAl sample was investigated and compared with a commercial WC-Co. Structural evaluation of mixed powder was showed a homogeneous distribution of WC and FeAl which related to particle size of FeAl to be in the range of 50-800 nm. FeAl nanoparticles were able to diffuse faster between WC particles and occupy interparticle spaces among larger particles in the sintering condition; thus resulted to formation of an almost homogeneous structure with densification to near theoretical density. The hardness and fracture toughness of WC-FeAl was 17.90 GPa and 9.1 MPa√m, respectively that this hardness was higher than that of WC-Co (15.7 GPa) and fracture toughness was lower slightly. The results for wear test showed that the specific wear rate of both samples was enhanced with increasing the test temperature from room temperature to 500℃. Furthermore, WC-FeAl showed higher wear resistance than WC-Co at both room and 500℃ temperatures.

The AZ31 magnesium alloy has a significant potential for the aircraft manufacturing industry due to its low density and proper mechanical properties. In this research, the Gas Tungsten Arc Welding (GTAW) process was used by applying pulse current for the AZ31 as-cast alloy joint. The GTAW process is conducted by pulse time, voltage, and equivalent current of 0.5 sec, 12 V, 187.5 A, respectively. Then, the surface of welded joint by the GTAW was improved using friction stir processing (FSP). The effect of FSP on the microstructure and mechanical properties of this joint was examined. Subsequently, the friction stir processing was performed with a tool rotating speed of 1120 rpm, the tool traverse speed of 50 mm/min in two passes behind and on the welding line. The microstructure and fracture sections of the prepared samples were respectively examined by optical microscopy and scanning electron microscopy (SEM). The mechanical behavior of the samples was studied using tensile, micro-hardness and impact tests. According to the results, the microstructure of the welding region of the TIG sample included highly fine homogeneous and coaxial grains. After the friction stir process (FSP), the microstructure transformed into fine and structural grains in the form of a ring-shaped morphology. The FSP resulted in a 23% improvement in the tensile strength of the TIG sample. Also, the impact energy of the welding metal increased by about 37%. In general, the mechanical behavior of the joint was improved after applying the friction stir process.

In this paper, nanostructured CrAlN coatings were deposited onto steel substrates using an industrial cathodic arc physical vapor deposition (Arc-PVD) technique. Field emission scanning electron microscopy (FESEM) was employed to evaluate the microstructure and the phase analysis was carried out using Energy Dispersive Spectroscopy (EDS) and X-ray diffraction (XRD) methods. The XRD patterns were used to determine the crystallographic texture of the coatings and the results showed (222) as the dominant texture. Moreover, it was found that all coatings had nanocrystalline structure with crystallite sizes between 8-18 nm. CrN was found to be the dominant phase in the XRD patterns; addition of aluminum produced CrAlN, leading to shifts of the diffraction peaks. Cr2N and AlN phases were identified by the XRD pattern which can be attributed to the decrease of the nitrogen pressure down below a critical value and the increase in the evaporation of aluminium, respectively. The change in the Al content of the coating and the subsequent displacement of the diffraction lines caused a challenge in the phase identification procedure. Therefore, identifying the existing phases in the coating was not feasible merely by the EXPERT software since CrAlN is not defined in its database; the crystal phase data of the nitride coatings must be used for accurate phase identification.

Aluminum-based alloy composites with high strength and low density can be used in corrosive environments. In this research, the nano-powders of A16061 alloy and A16061/TiB2 composite were synthesized by mechanical alloying (MA) method. Then, A16061 /TiB2 nano-composite bulk samples were prepared at laboratory scale by hot extrusion approach. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) devices were respectively used for measurement of particles and grains, and the polarization test was employed to assess the corrosion behavior of A16061 /TiB2 nano-composites. The grains size of hot extrusion samples were calculated as about 95 nm. Uniform corrosion behavior and pitting of the produced nano samples of MA6061 /1.25 TiB2 have higher corrosion resistance compared to the alloy samples of MA6061.3. The uniform corrosion in the 2MA-Al-6061/1.25TiB2 composite had the lowest rate compared to other samples.The sensitivity of this alloy to pitting corrosion has raised compared to the melting state; however, this sensitivity is less than the alloy made by mechanical alloying method.

In this study, the effect of the heat input on the microstructure and mechanical behavior of the 5456 series aluminum thin sheets in two processes of gas tungsten arc welding (GTAW) and gas metal arc welding of (GMAW) was investigated. For this purpose, the aluminum base metal with a thickness of 0.9 mm, ER5356 as metal filler with a diameter of 1.2 mm and argon gas were used. Microstructure and fracture surface were studied by optical microscopy and scanning electron microscopy respectively. Also, to study the mechanical properties of the joint, the tensile and microhardness tests were used. The results shows that the microstructure of TIG and MIG welding process is coaxially dendrite and dendritic columnar respectively. The microstructure of TIG welded sample was finer than MIG welded sample as a result of lower heat input and lower temperature gradient. This event cause increase in strength and elongation in TIG welded sample compared to MIG welded sample. Also, the fracture surface of TIG sample is consists of the fine dumplings and funnel-shaped cavities, and so the ductile fracture has occurred, but the semi brittle failure was done in the MIG sample.

The performance of components produced by conventional route of a thermo mechanical process and those produced by continuous casting is interesting from different aspects of economy and technology. The performance of products in their service depends on their properties which are strongly influenced by production routes. In the present work the hardness, tensile and tensile-impact behaviors of CuZn40Al1 alloys produced by continuous casting and extrusion were investigated. Micro structural features and fracture surfaces were studied by optical and scanning electron microscopy. Results showed that wrought samples exhibited higher absorbed energy than those of continuous cast samples. Reduction of impact velocity led to a higher absorbed energy in all samples. A systematic and meaningful relationship was observed between micro structural features and mechanical properties such as hardness, yield stress and ultimate tensile strength. Fractography investigations showed that fracture occurred with dimple formation in all cases.