فصلنامه علوم و مهندسی سطح ایران
پیاپی 23 (بهار 1394)

In this paper the waer behaviour of tungesten carbide coated insert in turning Inconel718 has been carried out. In this approach the modeling and experiment as well as wear mechanism map were used to understand the relationship between the cutting conditions and the wear mechanisms. In this research, the WC insert with TiAIN layer was chosen as a cutting tool. The most important variables under study in this work are the cutting velocity, feed rate, tool nose radius, entering angle and turning time. As a result, the recommended machining conditions with minimal wear would be the selection a tool with a radius of 1.6 mm. The results showed that the TiAIN layer acts as a protection against the transfer of elements between the tool and workpiece in mild and transient wear zones. However, with an increase in the cutting velocity and feed rate, i.e. moving in the severe wear zone, the TiA1N layer breaks off the tool surface resulting in a considerable increase in the adhesive wear due to the transfer of such elements in Inconel718 as Nickel, chrome and iron to the flank face.

In this study effect off adding oxide reinforcement YSZ on mechanical properties and wear resistance of CoNiCrAlY/YSZ coating has been investigated. First, for preparing composite powders CoNiCrAlY with 5, 10 and 15% YSZ were mechanical milled 24 hours. The composite coatings and commercial coating were deposited on Inconel 617 substrate with high velocity oxygen – fuel method. The microstructures, wear resistance, mechanical properties and worn surface morphologies of the coatings were comparatively analyzed as well by means of Scanning Electron Microscopy, energy dispersive X-ray analysis, pin-on disc wear test, micro and macro hardness tests. Results show that with increasing YSZ content unmelted particles increased in composite coatings. Adding YSZ to 10%, increase the hardness of composite coatings, but adding more YSZ to 15% increased porosity in coatings which led to decline in hardness. Adding YSZ to CoNiCrAlY coatings has been increased the wear resistance of composite coating, so that 5% YSZ coating with a protective oxide layer on the wear track has shown lowest level of wear rate.

The aim of this study is investigating the effects of plasma nitriding on the bulk mechanical properties, including tensile properties of AISI 316L austenitic stainless steel (in adition to surface properties). In order to reach this goal, the tensile properties of 316L stainless steel have been studied before and after plasma nitriding process. Plasma nitriding process carried out at two constant temperatures of 450 and 500 ºC with gas composition of 75vol.%H2-25vol.%N2 for 5 hours. To evaluate the effect of plasma nitriding process on the tensile properties, a simple tension test was carried out at speed of 5 mm/min. To evaluate the surface hardness, the Vickers microhardness test was used with the indentation loads of 50, 100, 300 and 500 g.f. The microstructural study of the cross section and phase analysis were performed by scanning electron microscope and X-ray diffraction, respectively. Changes in nitrogen concentration in cross section were evaluated by energy dispersive spectroscopy. Results showed that the plasma nitriding process at 450 ºC increased the yield strength from 320 to 340 MPa and tensile strength from 570 to 595 MPa. Moreover, by increasing the temperature from 450 to 500 ºC, yield and tensile strengths were increased to 355 and 610 MPa respectively. The surface hardness enhanced from 230 to almost 1000 HV by plasma nitriding at 450 ºC. By elevating the process temperature from 450 to 500 ºC, hardness was increased to nearly 1250 HV. In overall, plasma nitriding not only improved surface properties but also enhanced bulk properties of AISI316L stainless steel significantly.

Weathering is the main degradation factor of wood surface in open air spaces. Understanding of its mechanism in different woods has a great importance for wood conservation. Regarding to developed application of white poplar wood (Populus alba L.) in open air spaces, structural changes of its biopolymers was studied under accelerated weathering after 300 and 800 hours. Mass losses were measured after weathering levels. Aesthetic properties were assessed by colorimetery. Fourier Transform Infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were applied for investigation of chemical and morphological characteristics respectively. Results showed the intensive aesthetic variations after both levels of weathering. It signified the production of new chromophores and increase of carbonyl groups due to lignin decomposition. Degradation of guaiacyl unit detected more severe compared to syringyl unit of lignin. Cellulose content was decreased after weathering procedures. The degradation had been focused in amorphous cellulose after 300 hours. Mass losses data indicated to leaching of degradation products from the surface of weathered wood samples. Defibrillation and fiber fractures confirmed the decomposition of lignin in middle lamella layer and chain scission of cellulose in cell wall due to weathering effects.

Stellite 6 clad layer containing different contents of TiC particles (0, 10, 20 and 30) was cladded on stainless steel 316 by Gas-Tungsten arc welding (TIG) with DCEN current. Microstructure of clad layers was studied using optical microscopy and scanning electron microscopy (SEM). X-ray diffractometery (XRD) was applied to study the phase evolution and structure of clad layers. Hardness profiles were obtained by microhardness testing. Wear testing was performed by pin on disk method to evaluate the wear resistance of cladded samples, and wear mechanism was investigated by scanning electron microscopy (SEM). According to the results microstructure of clad layers included dendritic cobalt solid solution together with a layer structure containing cobalt solid solution, TiC and small quantities of Co3Ti, CrFe7C0.45, CoCx. Stellite- 20wt.% TiC clad layer showed the maximum wear resistance and hardness among different compositions. Higher and lower amounts of reinforcing particles resulted in the coarsening of cobalt solid solution dendrites and lower hardness values. The dominant wear mechanisms on the surface of clad layers were determined to be abrasive and adhesive mechanisms.

Induced residual stress at the machining processes affects significantly fatigue life of manufactured components. Inconel718 superalloy has been used widely in the different parts of aerospace industries and in the rotary parts of turbines engines because of its unique properties. Therefore, evaluation of undesirable state of the residual stress in finish turning of Inconel718 is so needed. Unfortunately, the effect of machining parameters has not been investigated extensively on residual stress due to the high expenses and several difficulties for measuring residual stress. Thus, the present study has been conducted in order to obviate the mentioned requirement. At first, the residual stress was measured by X-Ray Diffraction (XRD) method. Then, the effect of machining parameters including cutting speed, feed rate, and depth of cut was investigated widely on residual stress using Artificial Neural Network (ANN) trained by Genetic Algorithm (GA). Obtained results showed that, the residual stresses were estimated accurately and finally the most suitable machining parameters were accessed so that the undesirable state of tensile residual stress was reduced in finish machining of Inconel718.

Recently, Ni-Cerium oxide nanocomposite coatings are of great interest and have been successfully used in many applications such as: high oxidation and corrosion resistance films, catalytic and magnetic. Many of these applications require high wear resistance. In this research, the nano-indentation and nano-scratch techniques were used to evaluate the wear properties of Ni-CeO2 nanocomposite coatings. It can be seen from the results that the molar ratio of Ce/Ni in the deposition bath has an important role on the tribological properties of the coatings. It was observed that, by increasing the molar ratio of Ce/Ni from 0 to 0.001 and 0.01, the percent of cerium oxide in the coating increase. The increase in ceria percent in the coating makes an increase in elastic modulus and hardness of the coating and causes decrease in friction coefficient of the coating. Also, by increasing the molar ratio of Ce/Ni from 0.01 to 0.1 and 0.2, the friction coefficient and scratch resistance of the coating, owing to formation of cracks in the coatings, increase and decrease, respectively. So, high scratch and wear resistance coating was formed when the amount of molar ratio of Ce/Ni was 0.01.

The main goal of this study is to investigate the structural and magnetic properties of FePt thin film with respect to the annealing tempreture. The FePt thin films were deposited by RF magnetron sputtering on Corning glass substrates at a room temperature. Base pressure was kept constant at 2 10-7 Torr. The Ar pressure was mTorr. Thin films was sputtered with an rf power supply at 110 W, yelding a rate of 6. After deposition, samples were annealed in the range of 450-650℃ for 30 min. Phase identification of thin films was performed using X-ray diffraction (XRD). With employing SEM, the size and uniformity of grains were studied. The morphology and surface roughness was also determined using an atomic force microscopy (AFM). Moreover magnetic properties of annealed thin films were evaluated using a vibrating sample magnetometer (VSM). XRD results showed that the ordered FePt structure is formed at 450℃ and with an increase in annealing temperature, ordering parameter were enhanced and at 650℃ reaches at its maximum value. On the other hand surface roughness and grain size increased with increasing temperature. The topography of the film consists of two main kinds of grain: those with a needlelike shape and those in form of platelets. According to the hysteresis loops, hard ferromagnetic FePt phase is formed at 550 ℃ due to high order parameter. However the best structural and magnetic properties were obtained at 650℃.

In this paper vertically aligned Multi-walled carbon nanotubes (VA-MWCNTs) have been successfully synthesized by chemical vapor deposition (CVD) using ethanol (C2H5OH) as a carbon source and Co as a catalyst on quartz substrate. The effects of growth time and growth temperature on MWCNT growth were studied in detail. At 45 min growth time, by increasing the growth temperature from 550 oC to 650 oC, the length and density of MWCNTs increase. At 750 oC, MWCNTs become spaghetti-like. The optimum growth conditions were found to be at growth temperature of 650 oC. At 650 oC, by increasing the growth time from 30 min to 75 min, the length of carbon nanotubes increases (from 2μm to 12μm approximately). The morphology and structure of the grown MWCNTs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy techniques.