جستجوی مقالات مرتبط با کلیدواژه « Mechanical Properties » در نشریات گروه « مواد و متالورژی »

In this research, the effect of heating rate on non-isothermal aging behavior of AA2024 aluminum ‎alloy matrix composite reinforced with nickel aluminide has been studied. Nickel aluminide was ‎created in-situ in the AA2024 aluminum alloy matrix and as a result of adding 4.5 wt.% of nickel ‎during composite fabrication. The results showed that the addition of nickel reduces the ‎precipitation ability of the AA2024 aluminum alloy during non-isothermal heat treatment despite ‎the formation of nickel aluminide. Also, with the increase of the heating rate, the amount of S-‎Al2CuMg precipitates formed in the microstructure decreases during non-isothermal aging. By ‎increasing the heating rate, the maximum hardness is reduced during aging heat treatment and is ‎obtained at higher temperatures. Non-isothermal aging of AA2024 aluminum alloy matrix ‎composite reinforced with nickel aluminide at a heating rate of 5°C/min led to an increase in ‎hardness and ultimate tensile strength by 17 and 22%, respectively, compared to the AA2024 ‎aluminum alloy matrix.‎

In this study, the effects of friction stir welding (FSW) parameters on the properties of dissimilar joints formed between 5083 aluminum alloys and 316L austenitic stainless steel, with a thickness of 4 mm, are investigated. The tool speed is varied in the range of 16 to 25 mm/min, while the tool rotation speed is maintained at a constant value of 250 rpm. To examine the microstructure of different weld regions, both optical and scanning electron microscopes are employed. To assess the mechanical properties, hardness and tensile tests are conducted. The results shows the formation of a composite region characterized by steel reinforcement particles dispersed within an aluminum matrix. At the steel-aluminum interface, a single layer of discontinuous intermetallic composition with a thickness of approximately 2 micrometers is observed. Notably, when the rotation speed is set to 250 rpm and the tool speed is 16 mm/min, a tensile strength of 298 MPa and ductility of 26% (93% of the tensile strength and 50% of the ductility of the 5083 aluminum alloy) are achieved.

The present study focuses on optimizing the mechanical properties and microstructure of laser welding in Haynes 25 (L-605) cobalt-based superalloy. Initially, the influence of laser welding variables such as laser power, pulse frequency, welding speed, and pulse width on the mechanical and metallurgical properties of the weld joints is investigated. By examining the welding variables, the values of G (thermal gradient) and R (cooling rate) are calculated, and their ratio (G/R) and cooling rate (G×R), which predominantly affect the solidification microstructure, are determined. The structural correlation with the mechanical properties resulting from welding is examined.  In this research, it is considered to obtain the welding variables to create a high percentage of the structure in the form of equiaxed dendrite. Microstructural analysis reveals the growth of equiaxed grains and dendritic structures in the weld zone. The high cooling rate in the weld pool leads to dendritic solidification starting from columnar dendrites at the weld walls and ending in equiaxed dendrites at the center of the weld. The microhardness value in the weld zone is HV 328, which is very close to the microhardness of the base material. The tensile strength of the weld samples reaches about 93% to 94% of the base metal tensile strength. Tensile testing of the weld samples indicates a ductile-brittle fracture. Examination of the scanning electron microscope confirms the presence of dimples, intergranular cracks, and microvoids in the fracture zone.

The proximity of elastomers to fuel leads to fuel absorption and swelling. The solubility coefficient plays a role as an effective factor in the absorption of fuel by rubber and the swelling phenomenon. Inflation is a phenomenon of control penetration; which depends on the chemical nature of the polymer and solvent. The solubility coefficient of tetralin fuel was calculated ( ) using four methods the equilibrium swelling diagram, volumetric mass, light refractive index and enthalpy of evaporation. The presence of fuel exposed to the rubber leads to negative effects on its properties and causes a decrease in properties and a reduction in the useful life of the rubber part. By increasing the difference between the solubility coefficient of the fuel and the rubber, the swelling decreases and consequently reduces the loss of the properties of the rubber mixture. The NBR compound with filler swollen in tetralin fuel, a decrease in tension properties equal to 67%, strength 59% and for NBR compound non-filler decrease of tension 76% and strain 77% has been observed. Also, it has observed the energy of break for NBR compound with filler swollen 83% and NBR compound non-filler 88%.

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.

This study aims to compare the effect of graphite content (0–5 wt.%) on the mechanical and ‎tribological properties of aluminum matrix nanocomposites. The bulk samples were prepared ‎by the mechanical milling/hot pressing (temperature 420 °C/ pressure 400 MPa/ time 1h) ‎process. According to the obtained results in this work, the addition of graphite to an ‎aluminum matrix significantly improves the wear properties of aluminum (wear rate and ‎coefficient of friction). The best wear performance was obtained with the sample containing ‎‎5wt.% graphite, which showed a 62% reduction in the wear rate and a 2.5-fold reduction in ‎coefficient of friction compared to the unreinforced aluminum sample. Although increasing ‎the amount of graphite in the range of 0-5 wt.% leads to a continuous improvement in the ‎wear behavior of the composite material, it results in a simultaneous deterioration of the ‎mechanical properties (hardness and compressive strength) and the density of the Aluminum- ‎Graphite composites.‎

Silicon nitride ceramics are materials with excellent mechanical, dielectric and thermal properties which with such properties is one of the main candidates for use in high temperature environments. In this study, the effect of sintering temperature on microstructure control and densification and optimization of mechanical and dielectric properties of silicon nitride ceramics prepared by hot pressing at different temperatures of 1500 °C, 1600 °C, 1700 °C and 1800 °C has been investigated. Scanning electron microscopy and X-ray diffraction have been used to study the microstructure and analysis of the formed phases, respectively. According to the X-ray diffraction pattern and the Gazara-Mesier relationship, in the sintered samples at 1600 °C and 1700 °C, all alpha phases were converted to beta, and in the sintered samples at 1500 °C, the conversion rate was 95.45%. Is. The results show that increasing the sintering temperature from 1500˚C to 1800˚C leads to larger rod-shaped grains and achieves dual microstructure and the average grain diameter has increased from 0.7 µm to 1.34 µm. sintered specimen at 1500 °C, with the lowest average diameter (0.7 µm) among other specimens, has the highest flexural strength of 550 ± 9.5 Mpa. Is By increasing the average grain size and decreasing the α/β phase ratio due to the increase in fusion temperature, the mean dielectric constant and tangent of the sample loss increased from 4.5 to 9.2 and from 0.099 to 0.22, respectively

In this research, the effect of dual curing agent TDI:DDI with different ratios on properties such as mechanical strength, elongation percentage, elastic modulus, hardness, burning rate and pressure exponent (n) has been investigated. Dimeryl diisocyanate (DDI) is a diisocyanate with long carbon chain, high molecular weight, low toxicity and low reactivity. In order to investigate the effect of the TDI: DDI double curing agent on propellant properties, five propellant formulations with the same loading rate and R value were produced and the prepared samples were tested for mechanical properties and burning rate. The results of the tensile test on the seventh day of the propellant curing process showed that with the increase in the ratio of DDI to TDI in the propellant formulation, the amount of elongation increases, the tensile strength decreases and the modulus decreases with the passage of time. The results of the burning rate test showed that with the increase in the ratio of DDI to TDI in the propellant formulation, the burning rate decreases. Comparing the propellants with different ratios of dual TDI:DDI curing agents with the propellant that is the only TDI curing agent, shows that as the amount of DDI in the formula increases, the pressure exponent (n) will decrease.