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A three dimensional distributed heat source model is developed to represent an electronbeam as a heat source based on the electron penetration theory proposed by Kanaya andOkayama [Kanaya and Okayama, J. Phys. D: Appl. Phys., 1972 ]. The fraction of electronenergy absorbed in the substrate is calculated theoretically for the fist time to provide theheating efficiency of the electron beam. Further, the heat source model is applied in thenumerical analysis of micro electron beam welding and the results are compared with thoseof the exponential decay heat source model used previously. The optimum Peclet number ofthe process to be 100 and the beam penetration to be twice that of the maximum meltingdepth as obtained using the Kanaya-Okayama heat source model are similar to the previousfindings using the exponential decay heat source model. However, the predictions of thetemperature field in the solid as a result of microwelding are relatively lower in case ofKanaya-Okayama heat source model because of the differences in the distribution of heatinto the condensed matter. The lower weld surface temperatures in microwelding using theelectron beam suggest less ablation as opposed to the use of laser beams.

The small spot sizes and short residence times involved in microwelding ideally demands the use of extremely high power density heat sources, outside of what is considered the feasible range in welding. The present work explores the use of volumetric heating as a key to enable microwelding at such enhanced heat intensity levels. In this work, the electron beam is represented as a volumetric heat source and a numerical model is developed to obtain the temperature field in a moving heat source problem. The model has been validated against analytical solutions to asymptotic cases. The asymptotic cases include the heat distribution by conduction far from the beam and the temperature field due to negligible conduction under the beam. The effect of weld speed and beam interaction volume is evaluated to propose the optimum conditions of microwelding. Optimality is based on limited heat flow into the material, high controllability, and tolerable maximum temperature of the process. For the choice of AISI 304 material as an example, the optimum welding conditions required to produce a 2.5 micron weld depth are determined in the non-dimensional form of Peclet number 100 and relative beam penetration in the range of 0.8-1.2.

A coupled model of heat transfer and plastic deformation around the pin during Friction Stir Welding (FSW) is presented. The approach pursued is based on asymptotic analysis, along the lines of boundary layer analysis in fluid mechanics, resulting in closed-form expressions of great generality. The resulting expressions predict the correct trends and orders of magnitude for the maximum temperature reached in the process, the thickness of the shear layer, the shear stress around the pin, the torque and the thermal effect of the shoulder. In addition to process predictions, the analysis also yields four significant dimensionless groups, which capture the effect of translation and rotational speed, thickness of shear layer, and contribution from the shoulder to temperature peak. A comparison of the scaling laws obtained with published experimental measurements and numerical simulations show that within the range of validity, the expressions obtained captures the right order of magnitude and trends with no model calibration whatsoever. The available experimental and numerical data was used to calibrate the closed-form predictions resulting in simple and accurate closed form expressions (14% standard deviation from measurements for maximum temperature). The proposed calibrated expressions are accurate for a broad range of materials including aluminum alloys 6061, 2024, 7075, 7050, 5083, mild steel, stainless steel, and titanium. We envision that this model can help metallurgical research on FSW in a similar way that Rosenthal’s solution have helped research on arc welding: by providing relatively simple and accurate approximations of broad validity across alloy systems that can be used to quickly assess problem parameters for models of phase transformations, to generalize observations about defect formation, and to design FSW applications of radically different materials or dimensions than currently known.

With the oil sands holding a large portion of the natural resources industry in Alberta, the protection of mining and transportation equipment operating in this erosive and corrosive environment has become a paramount issue. A wide variety of overlay materials exist but it has been determine that a nickel matrix reinforced with tungsten carbide particles performs the best in this demanding environment. Currently, these overlays are deposited by Plasma Transferred Arc Welding (PTAW) with the nickel and tungsten carbide powders blown into the arc. The formation of tubular wire consumables using a nickel sheath and tungsten carbide powder contained within has provided industry with a promising alternative method to depositing wear resistant nickel tungsten carbide overlays for oil sands and mining operations.

Low-pressure cold spraying was used to deposit aluminum particles (~25 μm diameter) on to low carbon steel, and the particle–particle interactions of the aluminum coating were analyzed. A simplified energy conservation model was developed to estimate the temperature at the interface of the deformed particle during deposition of the powder. The Johnson–Cook model was used to calculate the particle flow stress, which was used to estimate the total energy dissipated via plastic deformation during impact and spreading of the particle. Microstructural analysis was conducted to show that plastic deformation occurred mainly at the interfacial regions of the deformed particles. By coupling microstructural observations of the cold-sprayed particles with the energy conservation model, it was found that the interface between the aluminum particles contained recrystallized ultra-fine and nanocrystalline grain structures that were likely formed at temperatures above 260 °C, but the majority of particles likely achieved interfacial temperatures which were lower than the melting point of aluminum (660 °C). This suggests that local melting is not likely to dominate the inter-particle bonding mechanism, and the resulting interfacial regions contain ultra-fine grain structures, which significantly contribute to the coating hardness.

The influence of tool rotation speed and travel speed during friction stir welding is studied in the case of Al 2024 which contains low melting point phases. When a tool rotation speed of 1600 rev min^-1 is applied with a travel speed of 100 mm min^-1, S-phase (Al₂CuMg) particles in the base material form melted films, promoting the formation of spalling defects comprising subsurface cracks along the trailing edge of the weld below the tool shoulder. Decreasing the tool rotation speed to 400 rev min^-1 prevented formation of the melted films by reducing the peak temperature in the stir zone, and avoided formation of spalling defects. When the travel speed is decreased to 32 mm min^-1 when using 1600 rev min^-1, dissolution of the S-phase occurs and fewer melted films remain in the stir zone. This implies that travel speeds are limited in alloys which contain low melting point phases since these promote cracking defects.

This work presents a method of calculating the martensite fraction of an Fe-alloy, using cooling curve analysis (CCA). It is based on a differential heat balance equation which takes into account only convective exchange with the surroundings. By measuring a T(t) curve of an Fe-alloy and solving numerically the differential heat balance equation the martensite fraction can be calculated. It is found that calculated martensite fraction using this methodology is comparable with results obtained using electron backscattering diffraction (EBDS).

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This study involved mathematical and experimental studies in many different alloy systems and welding parameters that fall in the gouging region weld pool morphology (typically welding currents were higher than 180-220 A and travel speeds were over 3-4 mm/s, varies due to the material type). The mathematical model was based on the physics of the process, which involved the equations of heat transfer with the proper boundary conditions accounting for a thin weld pool, heat input, arc pressure, and plasma gas shear. In experimental studies ASTM A36 structural steel, AISI304 stainless steel, CP aluminum, AA5083 aluminum alloys and CP Titanium (Grade 3) were used. The gouging penetration modeling was provided a reliable scaling law and was validated by experimentally measured penetration depths. The estimation of penetration depth was proven to be valid for five different materials with the bead-on-plate technique.

This paper addresses the renewed need to focus on the physics of welding to realize thefull potential of the latest welding technologies which include fiber and disk lasers, frictionstir welding, and inverter power supplies. The approach to understanding, synthesis,and generalization in other engineering branches is reviewed, highlighting the central role ofhandbook-type solution in the conceptual design stage. It is shown that the multiphysics andmulticoupled aspects of welding exceed the capabilities of other engineering approaches andthe methodology of scaling is proposed as a promising alternative. The application of scalingto friction stir welding is shown through an example in which the maximum temperature inthe metal is generalized into a power law, experimental and numerical data are synthesizedinto a general correction factor, and secondary effects are captured as dimensionless groups.

Typically, standard alloys do not have the wear resistance properties necessary to combat the aggressive abrasive, impact and corrosive conditions prevalent throughout the oil sands mining process. Protective overlays are applied to standard mining equipment and piping systems in order to extend the equipment life and prevent unplanned outages. The choice of overlay materials and deposition methods depend on both the service environment and economic factors. This paper will provide an overview of the types of alloys and composite materials available, the range of application methods employed and the performance benefits observed in the field. Innovative technologies developed for oil sands mining applications will also be outlined.