Advanced Materials Research Vols. 264-265

Abstract: This work investigated the thermal fatigue behavior of Inconel-738LC material deposited thermal barrier coating by Vacuum Plasma Spray(VPS). The Inconel-738LC material which is widely used as a turbine parts is a CoNi-based superalloy with CoNiCrAlY bond coating and ZrO2-8wt%Y2O3 ceramic top coating. The microstructure of coating layer was analyzed by SEM/EDS and XRD. Thermal fatigue tests were performed using compact tension specimens at 550°C, 750°C, 950°C with the load frequency of 10Hz. The fatigue crack growth behavior was characterized depending on number of cycles. The crack growth rate was found to be greater at lower frequency and higher temperature.

Abstract: The possibility of forming a TiN dispersed composite layer on steel was studied by preplacement of titanium powder on steel surface and melting under TIG (Tungsten inert gas) torch in a reactive environment. The surface melting of preplaced 1.8 mg/mm2 Ti powder was performed under TIG torch with energy inputs of 324,378 and 432 J/mm in a pure nitrogen environment. With these melting conditions, the powder layer along with a thin layer of the substrate melted and produced a melt pool of around 1mm thickness. The resolidified melt layer consisted of dispersion of TiN dendrites in ferrite matrix and thus a composite of TiN in ferrite is created on the steel surface. The concentration of dendrite population was found to be higher nearer the melt surface compared to the deeper depth. A maximum surface hardness of about 2000 Hv was developed at the surface when glazed with an energy input of 432 J/mm and the hardness decreased gradually away from the surface. The hardness development is directly related to the concentration of TiN dendrites.

Abstract: In order to modify surface structure titanium powder was preplaced on steel surface and melted under TIG (tungsten inert gas) torch in a pure nitrogen environment which formed a resolidified layer of around 1 mm thickness. The preplaced titanium powder content was varied between 1.3 and 1.8 mg/mm2 and melting was conducted with energy inputs of 324 J/mm to 540 J/mm. The modified surface layer was analyzed in terms of microstructure, hardness, surface defects such as cracks and pores. The resolidified layer consisted of dispersion of TiN, Ti2N and TiN.88 dendrites in a ferrite matrix containing titanium. The modified layer showed some defects when melting were performed with low energy inputs. A maximum surface hardness of around 2000 Hv was developed in most of the tracks and this hardness corresponds to high concentration of TiN dendrites within the modified layer.

Abstract: The formation of hard surface layer on steel provides a protective coating against wear, thermal loads and corrosion. In the present work a hard composite layer is formed on steel surfaces by preplacement of titanium powder and melted under nitrogen environment. Surface melting was conducted using TIG torch with different energy inputs. The microstructure and the morphology of the melt tracks were investigated using SEM and X-ray diffraction. The in-situ melting of titanium powder in nitrogen atmosphere produced dendritic microstructure of titanium nitride. The melt layer contained dispersed TiN, Ti2N dendrites highly populated at the surface compared to the deeper melt and gave a maximum surface hardness of around 1927 Hv. The wear property of the melt track was investigated using pin-on-disk tribometer at room temperature. The modified surface layer gave a low friction value of 0.12 and wear rate of 0.007895 ×10-4 compared to 1.648 × 10-4 mm3/N/m for the uncoated steel surface.

Abstract: In this study an attempt has been made to produce titanium-aluminium dispersed hard nitride layer on mild steel surfaces by preplacement of 50 % Ti and 50 % Al powder mixture and then melting with TIG torch under nitrogen environment. Parameter such as heat input of the torch was varied between 540, 608 and 675 J/mm and its effect on the resolidified melt pool was studied. Glazing under all energy inputs produced more than 1mm thick resolidified clad layer. The microstructural analysis revealed the clad layer with dispersion of dendrites of Ti-Al nitrides and Ti- Al intermetallic in ferrite matrix. The concentration of dendrites were found to be maximum near the surface and decreased at deeper depths.The maximum hardness of the modified surface layer was found to be 900 Hv compared to180 Hv of the mild steel substrate.

Abstract: Nanocrystalline diamond (NCD) films on titanium alloys are of importance for tribology and biomedical implants. However, due to the different thermal expansion coefficients of the two materials, the complex nature of the interlayer formed during diamond deposition, and the difficulty in achieving high nucleation density, it is difficult to deposit adherent NCD films on titanium and its alloys. The aim of this research work is to successfully produce smooth, low roughness and well adherent NCD film on a pure Ti substrate by bias enhanced nucleation (BEN) process using microwave plasma chemical vapor deposition (MWPCVD) method. The friction coefficient was estimated to be around 0.06 in dry air using ball on disk tribometer with reciprocating sliding against a cemented carbide ball of 10 mm diameter at a high contact load of 20 N in dry air. The friction coefficient of bare Ti was between 0.55-06.

Abstract: A three dimensional FE modeling of the laser surface modification is presented. The design capabilities of the ANSYS (11) software were employed for this purpose. The model calculates the dimensions of melting zone and heat affected zone. Model simulations are compared with experimental results that showed very good agreement. A one dimensional model in V.B language was presented too. The model based on conduction of heat in one dimension neglecting the other losses of heat. The results of VISUAL BASIC were compared with experimental results which showed a very good agreement. The two methods were compared with each other to showing which method have a good prediction compared with experimental results in calculating of fusion zone and heat affected zone "HAZ".

Abstract: The application of powder mixed dielectric to improve the efficiency of electrical discharge machining (EDM) has been acknowledged extensively. However, the study of micro-size powder suspension in micro-EDM field is still limited. In this research, nano and micro size powder of MoS2 were used as catalyst agent. Powder suspension in different size was able to provide significant improvement in material removal rate and surface quality to increase the efficiency in μ- EDM processes.

Abstract: The particle behaviour in a heat treatment fluidised bed was studied by the analysis of particle images taken with a high speed CCD digital video camera. The comparison of particle dynamics was performed for the fluidised beds without part, with single part and with multi-parts. The results show that there are significant differences in particle behaviours both in different beds and at different locations of part surfaces. The total and radiative heat transfer coefficients at different surfaces of a metallic part in a fluidised bed were measured by a heat transfer probe developed in the present work. The structure of the probe was optimized with numerical simulation of energy conservation for measuring the heat transfer coefficient of 150-600 W/m2K. The relationship between the particle dynamics and the heat transfer was analysed to form the basis for future more rational designs of fluidised beds as well as for improved quality control.

Abstract: The electrodeposition of tin from Tin (II) Methane Sulfonate (MSA) with varying concentration in air and water stable 1-Butyl-1-Methylpyrrolidinium Trifluoro-Methanesulfonate, (BMPOTF) ionic liquid at room temperature was studied. Cyclic Voltammetry served to characterize theelectrochemical behavior of tin reduction and oxidation. The diffusion coefficient of stannous ions in the mixture of BMPOTF ionic liquid and MSA based electrolyte obtained via Randles- Sevcik was approximately 2.11X 10-7 cm2/s. Electroplating on copper panel was conducted under different current densities to determine BMPOTF based tin plating solution current efficiency. Mixture of BMPOTF and MSA based tin plating solution gave current efficiency as high as 99.9%. The deposit morphology of the mixture BMPOTF and MSA based tin coated substrates was observed by using EDX and SEM. A dense, fine and polygonal grain structure was obtained.