بهنام لطفی

In the present paper, in order to improve the high temperature oxidation resistance of 316 AISI stainless steel, claddings of ER446 and ER446 + 4 wt. % Al filler wires were deposited on this steel using GTAW process. The chemical composition, phase types and microstructure of the claddings were determined by light microscopy (OM), electron microscopy (FESEM-EDS) and X-ray diffraction (XRD). The oxidation behavior of the cladded samples was evaluated and compared using isothermal oxidation test in air (at 1000 °C) and air + 1.5% SO2 (at 800 °C) environments. The adhesion of the interface between the claddings and the substrate was measured by shear strength test before and after oxidation according to ASTM A264 standard. Microstructural observations from the cross section showed that both claddings had excellent adhesion to the substrate and no cavities and discontinuities were observed in the interface between the claddings and the substrate. The results of shear strength test showed that both claddings before and after high temperature oxidation have higher shear strength than the minimum value specified (140 MPa) in the ASTM A264 standard. l Evaluation of the oxidation behavior of the base metal before and after the exert of the coating showed that the claddings (especially with present 4% Al) strongly reduced the oxidation rate (improving the oxidation resistance) in both oxidizing environments. In the early stages of oxidation, chemical reactions at the interface between the oxide scale and the metal controlled the oxidation reaction, and after primarily stages until the end of examination, the diffusion and transfer of oxygen and aggressive ions through the oxide scale toward the interface controlled the oxidation process. It was found that the oxidation kinetics of both claddings follow the parabollic law of oxidation and the cladding containing 4% Al had a constant oxidation rate (kp) 16 times lower than the coating without aluminum. The results showed that the presence of SO2 gas increased the oxidation rate of both claddings.

In this study, in situ Al-Al3Ni-TiC surface composite was successfully fabricated by friction stir processing (FSP) of AA1050 alloy. For this purpose mechanically alloyed Ni-Ti-C powder mixture prepared by high energy milling for a total duration of 20h, was inserted into Al substrate. Microstructure, microhardness and wear behavior of the composites obtained from 2 and 6 FSP passes were evaluated. Microstructural examinations of MAed powder and composite were performed using an optical microscope (OM) and scanning electron microscope (SEM) equipped with microprobe elemental analysis. The results of the experiments showed that in situ reaction occurred between MAed powder and matrix during friction stir processing and resulted in the formation and distribution of Al3Ni and TiC compounds in the matrix. Al3Ni and TiC compounds increased the hardness and improved the wear resistance of in situ composites.The hardness of the composite obtained from 6 FSP passes (70 HV) increased about 280% compared to the base metal (≈25 HV). The composite obtained from 2 FSP passes showed non-uniform hardness due to incomplete reaction and inhomogeneous distribution of powder particles. The dominant wear mechanisms were identified as abrasive wear and adhesive wear for the base metal and composite obtained from 2 FSP passes, and abrasive wear for the composite obtained from 6 FSP passes.

The purpose of this study was the co-electrodeposition of boron carbide (B4C) hard particles and tungsten sulfide (WS2) lubricant particles on copper substrate and produce Ni-B4C-WS2 nanocomposite coatings. Hardness and tribological behavior of nanocomposite coatings were also investigated. Field emission electron microscopy (FESEM) was used to study the microstructure of coatings and hardness and tribological behavior, were evaluated by microhardness and pin-on-disk tests respectively. The results showed that hybrid nanocomposite coating is more fine-grained than other coatings, and have a better distribution of boron carbide and tungsten sulfide particles. The hardness of hybrid coating was obtained 461 vickers, which was much higher than that of the other two coatings. The lowest weight loss after wear test at slide distance of 800 m was obtained in 1 mg hybrid coating which was much lower than other two coatings. Also, the lowest friction coefficient for the hybrid coating was 0.53.

"hookah use" is one of the forms of tobacco use that is currently spreading rapidly in society, especially among young people. The hookah is a very challenging topic for the health of the community due to its inherent disadvantages and the fact that it facilitates people to bring other tobacco products, such as cigarettes and even opiates and drugs. In this research, the Social factors of young tendency towards hookah use were investigated with Merton's theory of deviations, Sutherland's differential association theory and risky behavior theory. To test the hypothesis of the research, descriptive and explanatory survey method with Researcher-made questionnaire has been used in which about 200 17 to 35 year old youth who use hookah are selected as the statistical population In the year 2018. The sample was selected from District 11 of Tehran due to the high density of hookahs shops in this section. Also Cronbach's Alpha for questionnaire is 0.756 and This amount for “contact with friends” indicator 0.640, “Religious Commitment” 0.846, “leisure time spend” 0.608 and for “hookah use” is 0.765. The findings indicate there is significant relationship between age and Employment with hookah use. Also there is indirect relationship between “religious affiliation” (mean= 63.4 & r=0.26) and “spending leisure time” (mean= 50.8 & r=0.39) with “hookah use” (mean= 72.8); but direct relationship between “contact with friends” (mean= 65 & r=0.41) with hookah use. In other words base on the regression analysis resaults most important factor for youth Tendency to hookah use is relationship with hookah users friends (0.391). Also weakness of practical adherence to religious norms (0.272) increase youth tendency to hookah use. Also decrease of leisure time and appropriate hobbies (0.308) will increase youth tendency to hookah use. The total explanation of the dependent variable is 0.461. Finally should be said that the prevalence of hookah use is a result of various social factors and this need to inform families and their supervisory role as well as the long-term policies of the relevant institutions.

The aim of this research was the production of in-situ Al-Al3Ti composite on the surface of Al1050 alloy, using friction stir processing with reactive mechanically alloyed Al-Ti powder. Al-Al3Ti was fabricated with different rotational speeds and FSP passes. the primary Al-Ti powder was mechanically alloyed for different durations and suitable time for achieve a fine lamellar and uniform structure was determined. microstructral evaluations were implemented by optical microscopy (OM) and scanning electron microscopy (SEM). X-ray diffractometery (XRD) was used for phase identification and differential scanning calorimertry (DSC) was used to study the thermal behavior of powder during heating.Vickers micro hardness test and tensile test were used to evaluate mechanical properties of the base metal and FSPed samples. using mechanically alloyed Al-Ti particle led to the enhancement of hardness by 2.5 times, tensile strength by 3.4 times. meanwhile increasing the number of passes to 4, improved the reaction of Al3Ti formation in Al matrix. Improved the distribution of in-situ particles in the matrix caused better mechanical properties. Evaluation of the fracture surfaces indicated ductile fracture for all specimens.

Friction stir processing (FSP) was used as a cladding method for the fabrication of a AA2024 clad layer on a AA1050 sheet. Crossover multi pass FSP with 50% overlap was considered as the cladding method. Effects of the number of FSP passes and post heat treatment on the microstructure and properties of clad layers were evaluated. Microstructural evolutions during the FSP and heat treatment were investigated by field emission scanning electron microscopy (FESEM). The results showed that a defect free clad layer and a uniform metallurgical interface between the clad layer and base material can be achieved by the FSP. Moreover, clad layers exhibited higher hardness values in comparison to the base material. T4 Heat treatment of the FSPed samples resulted in comparatively high hardness values after natural aging. The highest hardness value of about 160 HV was achieved after heat treatment of the sample obtained from 3 intersecting FSP passes. Tensile strength of clad layers increased to 317 MPa after three intersecting FSP passes, compared to about 70 MPa of Al substrate.