METALLURGICAL ENGINEERING
Year:2015 | Volume:17 | Issue:56 |Papers Count:8

In this paper, the slurry based method has been used to produce the Al-CNT nanocomposite accompanying the suitable protection of CNTs. For this purpose, the carboxyl functionalized CNTs and Al@PVA powder were mixed in water environment after adding the SDS surfactant and diluted nitritic acid for controlling the PH. Consequently, the hydrogen bonding between the surface agents of constituents and temporary polarity due to the surfactant and acid hydrolyzation could lead to stabillazation of suspention at PH=5 and the final composite powder was settled in beaker without any external force or physical stress and it is absoloutely obtained from chemical reaction. The chemical analyze of initial materials in each step was performed by IR and Raman experiments and the microstructure of initial materials and final nanocomposite has been studied through SEM and FE-SEM, respectively.

In this investigation, the role of the structural anisotropy due to cold rolling on the distortion value of hot work tool steel employing in moulding before and after the hardening heat treatment was studied. For the hardening treatment, was used a step martempering process. Distortion amount was calculated by flatness factor in 3 states; after machining, after stress relief treatment and after martempering. For purpose of the consideration of the anisotropy effect on the steel distortion, dependent on the rolling direction, were prepared samples in 3 geometrical states.Before martempering, the distortion value of samples is very low and negligible. It is also independent on the sampling direction. Thus it is an isotropic characteristic. Results revealed that distortion is induced in the martempered steel. It is also significantly different in various directions of sampling. It is implied that in the hardened steel, distortion is an anisotropic property. The lowest distortion is belonging to sample which is perpendicular to rolled direction.Hardeness measurement shows that this specification is an isotropic property both before and after hardening and is not affected by the geometrical direction of sampling.

Intercritical heat treatment is an important and effective operations on the mechanical properties of steel. This operation is easy and cost-effective ways to achieve the desired mechanical properties such as strength and ductility. In this paper, we investigate the effect of Intercritical heat treatment on fatigue properties of microalloying boron steel. In order to achieve different dual phase microstructures with different amounts of martensite, the temperatures of 730, 750 and 7700c was selected as the Intercritical temperatures and valus of 52, 68 and 88% by volume martensite obtained with the ferrite. To investigate the effect of tempering on fatigue properties, one series of samples were Tampere. The present study shows that the fatigue strength increases with increasing volume fraction of martensite and with tempering the fatigue strength will decrease.

Tube-sheet to tube weld joint is a critical section in shell-tube pressure vessels. The leakage and failure are two common problems that happen in this joint. The tensile residual stresses associated with welding can play a major role in the mentioned problems. In the present study, residual stresses distribution is investigated by Finite Element Method and experimental tests. The joint includes a circumferential fillet weld in one pass by Gas Tungsten Arc Welding process. The thermo-mechanical behavior of the joint is simulated by a 2D axisymmetric model using a subroutine developed in ANSYS software. The thermography Method used to thermal analysis verification and the Whole Drilling Strain Gauge under Post Weld Heat Treatment used to mechanical analysis verification. The numerical and experimental results show that the residual stress as von Mises criteria is about 105 MPa and as stress intensity criteria is about 115 MPa in root of Tube-sheet to tube weld joint. Maximum defference between numerical and experimental results, in thermal analysis and mechanical analysis, is about 11% and 18% respectively.

Application of hydrophobic polymer coatings in protection of historical monuments as well as in anti-fog, anti-frost, anti-bio-fouling and anti corrosion surfaces, has drawn the attention of many researchers in recent years. Reaching this target needs to provide coating with low surface free energy and appropriate surface roughness. Controlling these parameters results in preparing surfaces with surface nature ranged from hydrophobic to superhydrophobic. The present study investigates the role of a surface tension reducing additive based on hydroxyl-functional silicone modified polyacrylate on the surface roughness and wetting behavior of polyurethane coatings. Polyurethane coatings with different amounts of additives were prepared. The coatings were cured at two different temperatures, i.e. ambient and 80 o C. Using atomic force microscope and contact angle measuring device the roughness and surface free energy of the samples were investigated, respectively. The results showed that addition of additive affected the roughness pattern of the surface as well as its chemistry. Furthermore, It was found that the roughness pattern of the coating was also influenced by the curing temperature. The largest contact angle (103o) value was obtained when the coating loaded with 5 mol % of additive was cured at the ambient temperature. These suggest that this sample possesses the optimum chemical properties as well as the most appropriate roughness pattern.

The aim of current research was to examine the texture of annealed Al-7075 alloy that develops during Equalchannel angular pressing (ECAP) in different ECAP routes. After annealing heat treatment, the material was pressed up to 4 passes by route A and BC at room temperature. The effect of copper tube casing on the texture evolution was also investigated. The texture was studied by X-Ray diffractometer in ED-plane as well as TD-plane. The qualitative and quantitative analysis of the texture reveals that the texture of the first pass is relevant to initial texture, but by increasing pass number this dependency disappears and the texture is mainly relevant to processing route. The texture calculation by Labotex software shows that the results in both TD (z) and ED (x) planes are in good agreement and covering the specimens with copper tube causes a decrease in texture strength and microstructure inhomogeneity of the specimens.