Defect and Diffusion Forum Vol. 418

Abstract: A single-step of pulsed laser deposition method was used to manufacture (Cu₂O) cuprous oxide nanothin films on Silicone substrates at low growing temperature in this study. The effects of three parameters of pulsed laser energies (800-1200 mJ) was used to explored in order to maximize the structural and morphological quality. (XRD) X-ray diffraction, Scanning electron microscopy with field emission (FESEM), and Atomic force microscopy were used to evaluate the effects of laser pulsed energies on the characteristics of Cu₂O nanofilms (FESEM). When compared to a crystalline silicon surface, the results of AFM show a higher possibility of better absorption and hence lower reflection.

Abstract: Graphite is a versatile material which is also used in various load bearing applications such as thrust bearings and dies for mechanical pressing such as hot pressing. Natural graphite has anisotropic layered structure which reduces its (compressive) strength in axes which are not parallel to c-axis. To increase strength, isotropy is introduced in graphite structure by breaking down its layers and minimizing grain size. We performed an in-depth characterization of relative aniostropy in graphite using pole figure density mapping. Locally available graphite samples were characterized by XRD and pole figures/3-D orientation distribution function (ODF). SEM and hardness testing were also performed to substantiate the pole density method. Results show that it is possible to characterize (qualitative/quantitative) isotropy or lack thereof in graphite by correlating it with the distribution of crystallinity/pole density mapping of (002) poles and 3D ODF figures.

Abstract: Thick seamless pipes of hardenable aluminum alloys demand close geometrical tolerances as well as high quality surface finish which are met by cold drawing after a series of different thermo-mechanical treatments. To meet the requirements of critical applications the final product undergoes stringent quality inspection procedures. State of the art quality assessment can detect even minor isolated defects. The production facilities develop their quality criteria suitable for specific applications. The present study investigated minute defects on the inside surface of thick seamless pipes, proposed mechanism of their formation and suggested the impact of defects on the end use. The root cause analysis was conducted, and measures were suggested to control the defects. Thick extruded seamless aluminum alloy pipes underwent a series of different thermo mechanical treatments; the final dimensions with required tolerances and the surface finish were achieved by adopting a 2-step cold drawing process. Cold drawing generated residual stresses which resulted in the formation of cracks in the material, preferentially at the defects generated during solidification and/or extrusion processes. The final product underwent stringent quality inspection, and the material was rejected if cracks of size 3 mm or larger were detected. The die scratches or notches generated on the inside surface of the pipes, during extrusion are assumed to grow if subjected to high stresses during subsequent processes, e.g. cold working. Observations at high magnification in SEM helped to determine the morphology of cracks. Radiographic testing did not detect any crack in the bulk material. Particles with faceted features indicated the presence of inclusion. Inclusions were detected in the form of strings along the direction of cold drawing. Energy dispersive spectrometry in SEM was used to determine the composition of inclusion detected in the vicinity of cracks. Almost all the inclusions were rich in silicon, iron, calcium along with carbon; it indicated that the inclusions were trapped particles of fluxes, slag, and brick powder. Particles rich in Ca, Na and/or Cl indicated entrapped flux, Fe and Si were mostly coming from aluminum scrap and refractory powder while presence of carbon indicated entrapped extrusion lubricant. Inclusions rich in a large variety of unwanted elements indicated presence of slag particles. Numerical analysis was conducted to develop a model in FEM in which scratches of different depths were introduced and autofrettage pressure was applied to determine the stresses generated according to the established Von Mises Model; the latter was used to establish the yield criteria. Finite Element Modelling concluded that when cold drawing pressure was applied on a pipe with a single notch of depth 0.3mm or three notches of depth 0.1 or greater at different locations the Von Mises stresses approached the yield strength of the pipe.

Abstract: During aircraft startup, abnormal noise was heard at 100-200 RPM and the aircraft was switched off. On detailed inspection, damage and deformation was found inside the starter fairing, intakes and tail pipe. The failure analysis revealed that the damages were due to the engagement of some stock during rotation, which could be an internal engine’s object. The failure of the bearing inner race was subsequent. The fracture features of shaft were similar to the torsional overload; the fracture was started from a notched region. It was also the consequence of internal object damage.

Abstract: One of the prime mechanical properties of any steel is impact strength, which may change dramatically due to the thermal treatments. The present investigation covers the influence of different thermally treated conditions on the impact strength of AISI 1020 steel. The thermal conditions included are: as rolled, oil quenched & tempered, air quenched, normalized and annealed condition. To evaluate the characteristics of the steel in different thermal conditions; optical microscopy, scanning electron microscopy, hardness testing and room temperature impact testing were carried out. Experimental results elaborated the existence of a narrow temperature range (250 ± 50 °C), which may decrease the impact strength drastically, when the steel is heat treated. In this temperature range toughness scavengers i.e., As, S, Sb etc. are precipitated on the grain boundary, which cause the noticeable decrease in impact strength. Optimum impact strength could be achievable where this critical temperature range was avoided.

Abstract: The objective of the present research is to investigate the degradation phenomenon of Polyvinyl Chloride (PVC) cable jacket exposed under accelerated thermally aged at 100°C for 4 days then irradiated under n’s flux of 1.5x 10¹¹ n’s / cm².sec for 1 hr in PARR-2 reactor at PINSTECH. Thermal, mechanical and chemical etc. properties of degraded cable jacket were studied with respect to fresh sample. It was examined that plasticizer content in PVC matrix started to deplete under the effect of temperature which made the matrix more rigid. In addition, the interaction of radiation with polymeric chains weakens the hydrocarbon bonding. The hydrogen and chlorine ions ejected from PVC molecular chains recombine to form hydrogen chloride (HCl) which induces porosity by creating localized pitting. This phenomenon is known as dehydrochlorination which created scissioning in PVC materials. Hence, due to the synergistic effects of temperature and radiation aging, cracks were observed on the outer surface of cable jacket in 2 years equivalent time. This study concludes that cables having PVC insulation are not suitable for long term exposure (i.e. decades) in thermo-irradiation environment.

Abstract: This investigation is aimed to study microstructural heterogeneities raised due to the inherent melt transport phenomenon and their effect on mechanical properties. Modified, Cleaned, and degassed A356 aluminum alloy melt was poured at 704°C in H13 tool steel die, while temperatures of lower die segment, side segment, and upper segment were 368°C, 375°C, and 290°C respectively. Then liquid melt was forged till its complete solidification under pressure using a hydraulic forging press. The liquid forged wheel was subjected to metallurgical investigation of microstructure, mechanical properties, and fractography of tensile test samples at different cross-sections along the protrusion of the wheel. Results conclude gradual variation in accumulation of eutectic Si phase from surface to the center of thickness and from flange to the outer rim region. The elastic properties are not affected by accumulation of the eutectic silicon however, plasticity have adversely affected with decrease in effective ductile cross-section. Also, refinement of primary α-aluminum and modification in the eutectic silicon phase in specific areas of the wheel is observed.

Abstract: Elbow pipes are important pipeline components in hydrocarbon transportation systems, and they were prone to erosive wear by the impact of abrasive particles. A discrete phase modeling (DPM) and numerical simulation of the liquid-sand transportation process was carried out focused on the investigation into the influence of carrier fluid viscosity on erosion distribution of carbon steel 90° elbows. The accuracy of the predicted results was validated by comparison with experimental data. CFD simulations have been carried out by combining DPM to predict the erosion rate and particle impaction regions in carbon steel 90° elbow with a diameter of 50.8 mm. The fluid viscosity is set for 1cP, 5cP, and 15 cP with an inlet velocity of 8 m/s, and the size of sand particles is 200 μm. While the maximum erosion rates enhance with an increase in fluid viscosity, the location of maximum particle impaction has been specified to be adjacent to the outlet for 1 cP and 5 cP carrier fluid viscosity. It is also found that increasing the viscosity does not considerably alter the average erosion rate. Moreover, the increase in carrier fluid viscosity with the same flow velocity influences maximum erosion rate and yields 1.45 times higher erosion rates at 15 cP compared to 5cP and 1cP. This is mainly due to severe sand impaction at the side of the elbow wall.