Microstructural development and mechanical properties of drop tube atomized binary Al-Fe and ternary Al-Fe-Si alloys

The effect of nonequilibrium solidification on the microstructural development and mechanical properties of Al-2.85 wt% Fe, Al-3.9 wt% Fe, and Al-4.1 wt% Fe-1.9 wt% Fe alloys was studied using a 6.5 m drop tube. Spherical particles with diameters ranging between 850 µm and 38 µm were obtained with the corresponding estimated cooling rates between 155 K s-1 and 20,000 K s-1, respectively. The spherical samples were examined using OM and SEM to understand the microstructural evolution, while XRD and TEM were employed for phase identification. Furthermore, microhardness testing was performed to observe the effect of rapid solidification on the mechanical properties of the alloys. For drop tube atomized Al-2.85 wt% Fe alloys whose diameter were ranging between 850 µm and 53 µm, XRD analysis showed that while α-Al, Al6Fe, Al13Fe4 were formed in all samples, Al5Fe2 was observed in samples with a diameter smaller than 150 µm. SEM and OM results have revealed that samples with a diameter larger than 300 µm had three regions with distinct morphologies: microcellular, dendritic with lamellar interdendritic eutectic, and rod-like eutectic region, which disappeared with decreasing sample size. TEM result has shown that while the interdendritic lamellar eutectic is Al-Al13Fe4, rod-like eutectic is Al-Al6Fe eutectics. Using EDX, Fe content in α-Al has been found to be rising from 0.37 wt% Fe to 1.105 wt% Fe with decreasing sample size. As a result, the volume fraction of the eutectic measured to be decreasing from 49.7 vol.% to 26.7 vol.% with increasing cooling rate. Microhardness has increased from 55.3 HV0.01 to 66.5 HV0.01 for ≥850 µm and ≤75 µm droplets, respectively. Drop tube atomized Al-3.9 wt% Fe alloy was sieved into 9 different sieve fractions ranging between 850+ µm and 38 µm. In large samples (d > 212 µm), large proeutectic Al13Fe4 surrounded by α-Al, dendritic α-Al with interdendritic lamellar eutectic, lamellar eutectic, and rod-like eutectic was observed. The proeutectic Al13Fe4 vanished with decreasing sample size. Featureless Y-shaped structures, which are the first phase to nucleate in the droplet, have emerged in samples with diameters smaller than 212 µm. The solidification in the droplet has proceeded with the formation of divorced eutectic, microcellular α-Al, dendritic α-Al with lamellar interdendritic eutectic and rod-like eutectic. SEM and OM showed that these Y-shaped structures are fragmented. Y-shaped was found to be an internally connected sheet-like morphology by employing serial sectioning. Y-shaped has been revealed to be composed of nano-sized needle-like and spherical precipitates by using TEM. AlmFe was formed in the Y-shaped region. The microhardness has increased 50 HV0.01 to 83 HV0.01 for 850+ µm and 53≤d≤38 µm droplets, respectively. Drop tube atomized Al-4.1 wt% Fe-1.9 wt% Si samples with diameters ranging between 850-53 µm were analysed. XRD results have revealed that there are only two phases: α-Al and Al8Fe2Si regardless of sample size. Microstructural analysis has shown dendritic α-Al with interdendritic lamellar eutectic in large samples (d > 300 µm). However, with decreasing sample size, angular nucleation zone has started to emerge in the microstructure. The fraction of samples with such angular nucleation zone has increased with decreasing sample size. EDX analysis from this zone has depicted that while the Fe content is identical to that of the melt, Si content was found to be around 1 wt% Si regardless of sample size. In addition to the angular nucleation zone, propeller-like structures and Y-shaped structures have been observed in fine samples (d < 106 µm). The formation of propeller-like structures indicates that the growth mechanism of angular structure has changed from faceted growth to continuous growth. TEM analysis from the angular region has depicted the formation of clusters of faceted Al8Fe2Si formed due to solid-state decomposition. The microhardness of the samples has improved from 72 HV0.01 to 90 HV0.01 for between 850-150 µm samples, respectively. However, a further decrease in sample size has resulted in the microhardness from 90 HV0.01 to 80 HV0.01 for 150-53 µm. drop tub

Droplet Dynamics Under Extreme Ambient Conditions

This open access book presents the main results of the Collaborative Research Center SFB-TRR 75, which spanned the period from 2010 to 2022. Scientists from a variety of disciplines, ranging from thermodynamics, fluid mechanics, and electrical engineering to chemistry, mathematics, computer science, and visualization, worked together toward the overarching goal of SFB-TRR 75, to gain a deep physical understanding of fundamental droplet processes, especially those that occur under extreme ambient conditions. These are, for example, near critical thermodynamic conditions, processes at very low temperatures, under the influence of strong electric fields, or in situations with extreme gradients of boundary conditions. The fundamental understanding is a prerequisite for the prediction and optimisation of engineering systems with droplets and sprays, as well as for the prediction of droplet-related phenomena in nature. The book includes results from experimental investigations as well as new analytical and numerical descriptions on different spatial and temporal scales. The contents of the book have been organised according to methodological fundamentals, phenomena associated with free single drops, drop clusters and sprays, and drop and spray phenomena involving wall interactions

Droplet Dynamics Under Extreme Ambient Conditions

This open access book presents the main results of the Collaborative Research Center SFB-TRR 75, which spanned the period from 2010 to 2022. Scientists from a variety of disciplines, ranging from thermodynamics, fluid mechanics, and electrical engineering to chemistry, mathematics, computer science, and visualization, worked together toward the overarching goal of SFB-TRR 75, to gain a deep physical understanding of fundamental droplet processes, especially those that occur under extreme ambient conditions. These are, for example, near critical thermodynamic conditions, processes at very low temperatures, under the influence of strong electric fields, or in situations with extreme gradients of boundary conditions. The fundamental understanding is a prerequisite for the prediction and optimisation of engineering systems with droplets and sprays, as well as for the prediction of droplet-related phenomena in nature. The book includes results from experimental investigations as well as new analytical and numerical descriptions on different spatial and temporal scales. The contents of the book have been organised according to methodological fundamentals, phenomena associated with free single drops, drop clusters and sprays, and drop and spray phenomena involving wall interactions

Materials Research in Microgravity 2012

Reducing gravitational effects such as thermal and solutal buoyancy enables investigation of a large range of different phenomena in materials science. The Symposium on Materials Research in Microgravity involved 6 sessions composed of 39 presentations and 14 posters with contributions from more than 14 countries. The sessions concentrated on four different categories of topics related to ongoing reduced-gravity research. Highlights from this symposium will be featured in the September 2012 issue of JOM. The TMS Materials Processing and Manufacturing Division, Process Technology and Modeling Committee and Solidification Committee sponsored the symposium

Microgravity science and applications program tasks, 1991 revision

Presented here is a compilation of the active research tasks for FY 1991 sponsored by the Microgravity Science and Applications Division of the NASA Office of Space Science and Applications. The purpose is to provide an overview of the program scope for managers and scientists in industry, university, and government communities. Included is an introductory description of the program, the strategy and overall goal, identification of the organizational structures and the people involved, and a description of each. The tasks are grouped into several categories: electronic materials; solidification of metals, alloys, and composites; fluids, interfaces, and transport; biotechnology; combustion science; glasses and ceramics; experimental technology, instrumentation, and facilities; and Physical and Chemistry Experiments (PACE). The tasks cover both the ground based and flight programs

A Microfluidic Approach to Investigate the Contact Force Needed for Successful Contact-Mediated Nucleation

Emulsions with crystalline dispersed phase fractions are becoming increasingly important in the pharmaceutical, chemical, and life science industries. They can be produced by using two-stage melt emulsification processes. The completeness of the crystallization step is of particular importance as it influences the properties, quality, and shelf life of the products. Subcooled, liquid droplets in agitated vessels may contact an already crystallized particle, leading to so-called contact-mediated nucleation (CMN). Energetically, CMN is a more favorable mechanism than spontaneous nucleation. The CMN happens regularly because melt emulsions are stirred during production and storage. It is assumed that three main factors influence the efficiency of CNM, those being collision frequency, contact time, and contact force. Not all contacts lead to successful nucleation of the liquid droplet, therefore, we used microfluidic experiments with inline measurements of the differential pressure to investigate the minimum contact force needed for successful nucleation. Numerical simulations were performed to support the experimental data obtained. We were able to show that the minimum contact force needed for CMN increases with increasing surfactant concentration in the aqueous phase

Automobile air bag inflation system using pressurized carbon dioxide

A novel air bag inflator based on the evaporation ofliquefied carbon dioxide was developed. A detailed qualitative model wasestablished on the basis of an extensive experimental study. An integratedquantitative model of this inflator was constructed. The system was studied by discharging the inflatorinto a tank and measuring pressure and temperature evolution (0-50 ms). Thedispersion of the two-phase spray duringinflation was investigated by high-speed cinematography. The optimal storage pressure of the liquid CO2was found to be 2000 psig (at 22 °C). Two distinct inflator behaviors wereidentified. First, at conditions corresponding to an initial entropy below the critical point, atwo-phase evaporating spray was ejected from the inflator into the tank. Second, at an initial entropy above thecritical point, the inflationsequence constituted the expansion of a real gas without a significant phase transformation. The minimal flow section in thenozzle was found to control the dynamicsof this new inflator. To prevent the formation of solid CO2during inflation, small amounts of organic liquids were added to the inflator. A significant increase in tanktemperature was observed, resultingin a profound improvement in performance. An explanation for the influence of organic liquids was developed based ona \u27layered evaporation model\u27. The qualitative model was based on the interactionof the flashing process with thetwo-phase outflow from the inflator. This interaction was manifested in twodifferent waves, namely a forerunnerand an evaporation wave which controlled the evacuation of the two-phase mixture from the inflator. The latterwas predominantly dispersed accordingto classical atomization mechanisms. The generated droplets evaporated partially by consuming their own internal energyand by interacting with tank gases. The characteristics of the condensate were evaluated by a detailedthermodynamic analysis. The quantitative description of the inflatorinvolved the development of a transientone-dimensional, two-fluid model. Preliminary simulations show excellent agreement with the expected results. The tank modelwas formulated on the basis of an empiricalcorrelation for the atomization process, coupled with a simple droplet evaporation model, followed by a model for themixing of real gases

Hydrodynamics of Supercooled Drops Encountering Solidification at Various Moments of Impact

Icing of surfaces is a hazard to numerous technical applications like aircraft, wind turbines, ships and power lines exposed to cold environments. Ice accretion on crucial parts can lead to significant decrease in efficiency, unpredictable limitation of function or complete failure. Particularly threatening icing scenarios often involve the impact of supercooled large water drops. Being in an initially meta-stable liquid state, their solidification exhibits a dynamic stage involving fast propagation of dendrites in their bulk. The interaction of dendrites with the fluid flow of a drop impact represents a complex problem which is to date not fully understood. This dissertation is devoted to gaining insight into the underlying physics of the impact of a supercooled large drop onto a cold solid surface superimposed by an impinging cold air flow. Focus lies on the onset of solidification at various times of the impact which relates to different stages of an ice layer growing on a surface. For experimental investigations, an icing wind tunnel was designed, built and commissioned in the course of this thesis. It facilitates experiments of single supercooled large drops of different sizes impacting onto solid surfaces with controlled variation of drop temperature, impact velocity and speed of the superimposing air flow. Investigations involve the impact of supercooled liquid drops which develop a corona splash upon impact. The splash extent and remaining fluid on the surface is connected to an existing theoretical model considering the onset of splashing. A superimposed air flow entails a deformation of the drops before impact which is incorporated in the splashing model and also in a semi-empirical approach, aiming for estimation of the maximum spreading diameter. Moreover, the impact of drops on a flat ice surface is investigated, which is characterized by an early onset of freezing. A vital influence of the fluid supercooling, i.e. the dendrite propagation velocity, is quantified and a modified model for estimation of the spreading diameter of the frozen drop is introduced. Furthermore, the impact of drops experiencing nucleation before impact is investigated. The impact behaviour of such partially frozen drops has never been investigated before and the adaption of a plasticity flow model enabled the quantification of rheological properties of this mixed phase. The findings of this work contribute to a deeper understanding of the physics involved in the fluid flow and its interaction with the dynamic solidification arising upon impact of single supercooled drops. The adapted models, empirical approaches and quantified properties can ultimately be employed to improve numerical models aimed at the prediction of ice accretion on technical surface

Research Reports: 1997 NASA/ASEE Summer Faculty Fellowship Program

For the 33rd consecutive year, a NASA/ASEE Summer Faculty Fellowship Program was conducted at the Marshall Space Flight Center (MSFC). The program was conducted by the University of Alabama in Huntsville and MSFC during the period June 2, 1997 through August 8, 1997. Operated under the auspices of the American Society for Engineering Education, the MSFC program was sponsored by the Higher Education Branch, Education Division, NASA Headquarters, Washington, D.C. The basic objectives of the program, which are in the 34th year of operation nationally, are: (1) to further the professional knowledge of qualified engineering and science faculty members; (2) to stimulate an exchange of ideas between participants and NASA; (3) to enrich and refresh the research and teaching activities of the participants' institutions; and (4) to contribute to the research objectives of the NASA centers. The Faculty Fellows spent 10 weeks at MSFC engaged in a research project compatible with their interests and background and worked in collaboration with a NASA/MSFC colleague. This document is a compilation of Fellows' reports on their research during the summer of 1997. The University of Alabama in Huntsville presents the Co-Directors' report on the administrative operations of the program. Further information can be obtained by contacting any of the editors

Performance characterisation of metal additives in paraffin wax hybrid rocket fuel grains.

Masters Degree. University of KwaZulu-Natal, Durban.The Aerospace Systems Research Group (ASReG) at the University of KwaZulu Natal is actively developing sounding rockets in the Phoenix Hybrid Sounding Rocket Programme, for use by the South African scientific community. These sub-orbital launch vehicles use nitrous oxide and paraffin wax as propellants. While paraffin wax offers large performance gains over typical polymeric fuels, due to its high regression rate, further performance gains can be achieved via the use of metal additives such as aluminium powder. The main advantage of using additives such as aluminium is the ability to create a smaller, more compact launch vehicle. This is due to a decrease in the optimal oxidiser-to-fuel ratio brought about by metallisation, which increases overall propellant density. Theoretically, an added advantage is the higher heat of combustion as a result of aluminium combustion. This added heat further increases the regression rate of the solid fuel grain. In order to realise these performance gains, various challenges need to be overcome. Some of these include delayed combustion due to the alumina layer that naturally coats the aluminium particles, slag formation and nozzle erosion. In this study, a laboratory scale hybrid rocket motor was developed to test aluminised paraffin wax fuel grains via a series of hot fire tests. A nitrous oxide feed system was developed, as well as a computer program and associated electronics to control the system remotely and capture data from an array of sensor equipment. Due to time constraints placed on the project, only pure paraffin wax and fuel grains comprising 40 % aluminium by mass were tested. Using specific impulse and characteristic velocity as performance metrics, preliminary data shows little to no gain in performance with aluminised fuel grains due to incomplete combustion of the aluminium. Substantial erosion of the copper nozzles that were used in the aluminium grain tests, due to localised melting, was also noted. Large amounts of aluminium and alumina slag was also found on the nozzles converging face. In order to seek maximum performance gains from aluminium as an additive, it was recommended that the particle size be reduced and stripped of its oxide layer before addition into the solid fuel grain. This will ensure more complete and rapid combustion of the particles before being ejected from the combustion chamber