مجله مهندسی ساخت و تولید ایران
سال نهم شماره 6 (شهریور 1401)

Some modern alloys, such as high entropy alloys (HEAs), are rapidly emerging due to their wide range of properties and applications. HEAs can be prepared from many metallurgical operations, but mechanical alloying is one of the simplest, most economical, and popular due to the increase in solid solubility, nanocrystalline structure, greater homogeneity, and performing the process at room temperature. The most suitable methods are considered. The method of synthesis of this category of alloys in this research is mechanical alloying, and using thermodynamic relations, the product of mechanical alloying has been validated. Milled products and solid solution phases, identified and by scanning electron microscope, the distribution of elements at different points is shown by MAP images. Also, XRD analysis in all stages of mechanical alloying up to 50 hours using liquid process controller shows that alloying is continuous in 20 hours. The crystal size was calculated using Scherer's relationship and the measured lattice strain was estimated to be 5 nm and 1.9%, respectively.

Open cell structures are architectural cell structures with a determined periodic geometry that can be designed parametrically based on mathematical models or simulations of nature. The silkworm cocoon can be used as a natural structure to design open structure cells. The silk cocoon consists of a hierarchical structure with multiple functions, which have evolved over millions of years to create optimal conditions for metamorphosis and preserving the life of the insect against Predators. In this article, inspired by the infinite loop structure used by silkworms in making cocoons, open cell structures were designed to investigate mechanical properties. For this purpose, based on Maxwell's formula in the design of rod open cell structures, different samples consisting of straight rods or infinity ring structures with different parameters were made using FDM 3D printing method. After manufacturing the parts, the axial tensile stress test was performed on the samples. The obtained results showed that the cell structures designed based on the rings used in the silkworm cocoon are non-isotropic single layers. Although the infinite cell structures have a lower tensile modulus and strength, the larger elastic strain and the gradual process of failure, and as a result, the conversion of the tensile modulus to bending in this structure, is considered one of their important advantages, which are used in various applications such as building sandwich panels that bear the duty They don't have the burden, they can be noticed.

The applicability of the diffusion brazing technique for joining Nimonic105 superalloy using a BNi-2 interlayer was assessed. The phases formed during the brazing process in the isothermally solidified zone (ISZ), athermally solidified zone (ASZ) and diffusion affected zone (DAZ) were studied. The formation of Ni-Cr-Mo boride precipitates in DAZ was determined in this region. The ISZ was a precipitation-free zone, mainly consisting of gamma solid solution. ASZ contains the matrix solid solution of gamma-nickel, Ni-rich boride, and Cr-rich boride and Cr-rich intermetallic compounds. The investigation confirms higher bonding time (60 and 240 min) led to a more uniform hardness profile across the joint and a more homogenous interface region via dissolution of intermetallic phases. The highest shear strength and ductility of the brazed joint can be up to 92.2 MPa and 19%, respectively for the bonding time of 60 min. This high strength and ductility can be attributed to the control of formation of deleterious intermetallic compounds in ASZ and at the same time limited time for grain growth.

Mechanical properties of engineering components are of importance in medical and industrial applications. Ultrasonic nondestructive testing is one of the most effective methods for assessing the elastic properties of materials. The purpose of this paper is to evaluate the elastic properties of components made by fused filament fabrication (FFF) additive manufacturing process by using ultrasonic waves. This is accomplished by fabricating a test specimen with a predetermined geometry from PLA polymer by FFF process. The ultrasonic wave velocity is then measured in this test specimen along different directions. The elastic coefficients of the specimen are then calculated from the measured wave velocities by assuming orthotropic structure for the specimen. The engineering elastic coefficients, such as Young's modulus, Poisson's ratio, and shear modulus are also found by inversing the elastic tensor. Considering that some of the measured elastic constants of this material were almost identical, the hexagonal that was simpler than orthotropic. Based on the results, it can be concluded that the sample has hexagonal anisotropy. The tensile testing results obtained from tensile samples made from the same material were compared with ultrasonic test results and were in agreement. Other acoustic properties of this material such as sound attenuation and acoustic impedance were also measured and discussed. It is concluded that the ultrasonic method is very efficient in measuring the elastic properties of polymer components manufactured by FFF process and can be used for determination of changes in elastic properties of the material due to variations in the process parameters.

NiTiHf high temperature shape memory alloys are highly popular for high temperature industrial applications due to their high transformation temperature, thermal stability and lower cost. However, they have weaker shape memory properties than NiTi binary alloys. The solution to this problem is to increase the strength of the alloy in order to prevent plastic deformation caused by slipping. Thermomechanical treatment is a method to improve the recovery strain. In this research, the Ni50Ti40Hf10 shape memory alloy was cast by vacuum arc melting and then the hot tensile test was performed on the samples with a strain rate of 0.01 s-1 at 800, 900, 1000 and 1100 C, also specimens were hot- rolled at 1000 C with a reduction of thicknesses by 10, 15, 20 and 30%. To determine the amount of recovery strain and recovery ratio by bending test strains of 2.6 to 6 were applied to the samples. The results of the hot tensile test showed that the temperature of 1000 C is acceptable for hot rolling due to the suitable ductility of the alloy. The maximum recovery strain in the cast sample was 5.7 with a recovery ratio of 88%. By applying 10% of hot rolling, the recovery strain and recovery ratio increased to 5.8 and 92 respectively, while after 20% of rolling, these values increased to 5.9 and 94. The formation of uniform and coaxial grains in the microstructure of the samples indicated the occurrence of dynamic recrystallization, which led to an increase in the recovery strain.

Metal matrix composites (MMCs) have higher modulus of elasticity, toughness and ductility than base metal and are widely used in many different industries. These materials have excellent properties such as light weight, high resistance to weight ratio, high specific hardness, high thermal conductivity and good abrasion resistance. Due to the high hardness, machining of these materials by conventional machining processes is very difficult. Electrical discharge machining (EDM) is an advanced machining process can be used to machining metal matrix composite. Experiments related to the present study were modeled using Design Of Experiments (DOE) and Response Surface Methodology (RSM) and the effect of parameters of discharge current intensity, pulse on time and pulse off time in the machining process of electric discharge machining of AZ91 alloy metal matrix composite Magnesium reinforced with 5% silicon carbide powdered particles has been studied and optimized on the material removal rate and surface roughness of the workpiece. The discharge peak current is the only factor affecting the material removal rate and the highest material removal rate can be achieved at pulse on time 300 µs, discharge peak current 17.5 A and pulse off time 40 µs as much as 542 mg/min. the parameters of pulse on time, discharge peak current and Interaction effect of pulse on time and discharge peak current are the factors affecting the surface roughness of the workpiece. The minimum surface roughness of the work piece is 9.55 µm in the pulse on time 100 µs and discharge peak current 5 A.