Previous work has shown that the processing of aluminium alloys by Selective Laser Melting (SLM) is challenging, with fully dense components only being produced at high laser powers (minimum 330 W). The high laser power requirement for these parts is a problem as it is higher than that available in many SLM machines. Attempts to produce dense components by combining lower power and slow laser scanning speeds create a large melt pool that is difficult to control, leading to balling of the melted material and possible damage to the powder distribution system. Even when processing is carried out successfully, the laser scan speed, which has to be slower than 150 mm/s, increases build time and hence manufacturing costs. This thesis considers the changes that can be made to the SLM process to reduce the laser power required and to increase the laser scanning rates, while still producing components with a relative density approaching 100%. It also considers why aluminium and its alloys are much more difficult to process than stainless steels and commercially pure titanium. One reason for the difficulties in SLM of aluminium was the flowability of aluminium, which led to the redesign of the powder deposition mechanism of the SLM machines that were used. The major challenge for processing aluminium and its alloys was found to be oxidation due to the presence of oxygen within the build chamber. This formed thin oxide films on both the solid and molten materials. Examination of manufactured parts showed that when processing at laser power of 100 W the oxide films were broken between successive build layers due to Marangoni forces stirring the melt pool, but that walls of oxide were present between tracks within the same layer. As these films occurred in pairs one from each track, pores were formed in between creating open porosity.

The automotive industry is constantly looking for improvements in materials and processes in order to try and reduce the weight of their vehicles to improve fuel efficiency. While improvements in aluminium alloys and ultra high strength steels can assist in light-weighting improvements have been relatively incremental in recent years. Titanium on the other hand has a superior strength-to-weight and corrosion resistance to both steels and aluminium alloys. There have been small scale demonstrations of titanium in road vehicles but major barrier for titanium's introduction into the mass production automotive market is its cost. The introduction of cost effective solid state extraction routes for titanium from its ores or oxides (Metalysis FFC, Cristal Metals, CSIRO TiRO™ and others) has renewed research interest in the cost reduction of titanium. These processes in particular produce powders directly from the extraction cells, which requires a low cost powder consolidation method for a true step change in the economics of the resultant titanium products. Standard solid state consolidation methods tend to rely on batch processes and require multiple steps to produce a fully dense product. The severe plastic deformation that occurs within the Conform process has the potential to solve these problems and provide a truly cost effective thermomechanical processing for titanium particulates. Even though Conform has been around since the 1970s and primarily used to extrude aluminium and copper based alloys significant development has been slowed by a lack of understanding of the thermomechanical behaviour material within the process. Work presented in this thesis demonstrates the successful extrusion of grade 2 hydride-dehydride (HDH) titanium powder through the Conform process to obtain a fully dense rod product with a fine grain size. A finite element model has also been produced in order to demonstrate the evolution of certain microstructural features in the extruded titanium wire. The models are extended to help predict a general titanium powder processing window for continuous extrusion machines.

Magnetron sputter deposition with single target materials was used to produce amorphous and crystalline Ti-A1-(Cr) alloy coatings on a Ti-50Al substrate. The following coatings were studied: Ti-50Al-10Cr, Ti-53Al-15Cr, Ti-50Al-20Cr and Ti-48Al. The microstructures of the coatings were studied in the as deposited condition and after devitrification and heat treatment. A random distribution of nano-precipitates was formed in amorphous as-deposited coatings. Columnar features were present when the as-received deposit had crystallised during sputter deposition. If crystallization occurred during deposition, a columnar microstructure formed with the columnar fibres being parallel to the deposition direction. For the Ti-50Al-10Cr and Ti-53Al-15Cr deposits, the crystalline domains consisted of lamellar gamma // alpha, i.e. the crystalline deposits had a gamma // alpha texture. The alpha → alpha transformation occurred during deposition. Phase competition in the alloys was studied by combining thermodynamic modelling and transformation kinetics. At 1173K, the Ti-50Al-10Cr alloy transformed to a two-phase microstructure, consisting of the gamma and C14 Ti(Al, Cr)2 phases. The Ti-53Al-15Cr alloy transformed to a three-phase microstructure, consisting of the gamma, tau and the C14 Laves phase. The gamma and tau phases were mixed finely, with gamma // tau. The Ti-50Al-20Cr alloy transformed to a two-phase microstructure, consisting of the gamma and the Cl4 Laves phase. No orientation relationship between the gamma and the C14 Laves phase was observed. Phase evolution studies at lower temperatures in the range 773K to 973K indicated that for the amorphous Ti-48Al alloy, the phase transformation path is: the amorphous phase → alpha → gamma + alpha/alpha2. A fine lamellar structure was formed, with gamma being the dominant phase. For the Ti-50Al-20Cr alloy, the phase transformation path was: the amorphous phase → gamma → gamma + Ti(Al, Cr)2. The experimental observations and the modelling results have clearly suggested a tendency of amorphous phase stabilisation via Cr addition. Thermodynamic modelling also indicated that the driving force for amorphous alloy formation is not much less than that for the precipitation of disordered solution phases. Kinetically, the amorphous phase formation during sputter deposition is related to the suppression of surface diffusion at low substrate temperatures. The temperature processing window for ordered phase formation in the Ti-Al(-Cr) alloys during magnetron sputter deposition was evaluated by the effective diffusion distance. Time dependent nucleation calculations showed that in the Ti-48Al amorphous alloy, it would be kinetically easier to precipitate the alpha phase than the gamma phase. In the case of the Ti-50Al-20Cr alloy, the gamma phase forms in preference of alpha, which is consistent with experimental observations. Diffusion phenomena at the coating/substrate interface and the oxidisation of the coatings were also studied. The experimental Cr diffusion profiles and the simulations for the Ti-Al-Cr coatings and the Ti-50Al substrate indicated that diffusion at 1173K is reasonably slow. The Ti-50Al-10Cr, Ti-53Al-15Cr and the Ti-50Al-20Cr coatings could form protective oxide scales at 1173K. When a columnar structure was present in the crystalline deposit, cracking of the coating was observed when the coating was subject to thermal cycling from elevated temperatures. It is concluded that if cracking of the coatings was to be avoided, amorphous deposits should be preferred.

by Roger J. Camrass. / Bibliography: p.98. / Prepared under Grant NSF-ENG75-14103. Originally presented as the author's thesis, (M.S.) in the M.I.T. Dept. of Electrical Engineering and Computer Science, 1976.

by Robert C. Meton. / Bibliography: leaves [33]-[34].

The continued interest in the use of magnesium alloys for new applications demand the successful production of high quality wrought alloys. Magnesium Elektron seek to reliably produce high quality alloy billets by the DC casting method combined with ultrasonic inspection. The main objectives of this study are to characterize the defects which are currently found in the material and to understand the ability of the ultrasonic inspection technique currently employed to detect the defects. This study began by locating defects using the ultrasonic inspection method which were then characterised using X-ray Computed Tomography (XCT) 3D imaging technique. Attempts were then made to understand and simulate the mechanisms by which the defects form during the casting process. The simulations were used to investigate the flow patterns during casting and the growth kinetics of the intermetallic phase. The initial phase of this research established that the defects found comprised of an entrained oxide film entangled with an abundance of intermetallic phase particles. These defects were found to be present in the size range of 0.5 – 5 mm, and were deleterious to the materials mechanical properties. Greater understanding of the ultrasonic inspection process was achieved and informed improvements to assisting the production of high quality feedstock. Simulation of the formation of the defects indicated that there was a region in which the oxide films could form and be free to enter into the final cast product. Simulation of the growth of the intermetallic particles demonstrated that precipitation from the liquid occurs in the mould during which particles are carried by the melt flow and experiences a complex thermal history. The combination of the two phases was established to be due to entanglement of the oxide and particles which when combined will settle out of the melt as a single defect. Improved filtering and melt handling methods were recommended to eliminate the defects and reliably produce high quality alloys.

This dissertation presents a critical analysis of literary texts that recount fully or briefly the life and legend of King Numa Pompilius. Focusing on the 'Golden Age', it comprises the Numan accounts of Cicero, Livy, Dionysius of Halicarnassus and Ovid. These authors lived at a time when Rome was trying to reconcile for herself and for her subjects the price of her military world domination with the belief in her foreordained supremacy. This reconciliation was to be achieved by a reacquaintance with the Roman ancestral values whose observance had merited Rome her dominion and whose neglect had driven the state to civil war. The question of Roman national identity is at the heart of the Numan accounts of the chosen prose-writers. In his portrayal of Numa, who combines the civilizing virtues of classical Athens with native Roman virtue, Cicero offers a rebuttal for Greek critics who questioned Rome's supremacy because of her lack of civilizing virtues. Livy investigates the leading causes of Rome's world domination and identifies the national values and institutions that many generations of leaders forged. Numa is one such leader, having established laws, religious rite and a peaceful way of life. Dionysius represents Numa as the Greek ideal of kingship in order to establish for the Greek world the excellence of the Roman national identity founded on Greek virtue. The Numan accounts of Livy and Dionysius, composed in Augustus' principate, do not draw direct parallels between Numa and Augustus, although the narration sometimes suggests a special relevance to Augustan rule. Finally, Ovid, the only poet, recounting traditional Numan tales, offers analogies and allegories of certain Augustan ideas and measures that may be seen to flatter the ruler.

The corrosion performance of Al-Cu and Al-Mg alloys with and without Li additions have been investigated. These include; AA2024-T3, AA2099-T8E77 (coarse and fine grain structure), AA5083-T351, spray formed Al-Mg-Li and spray formed Al-Mg-Li-Cu-Zn alloy. Atmospheric corrosion was investigated for up to 12 months of exposure in a rural-urban environment, prolonged immersion testing in 3.5 wt.% NaCl for up to 96 hr s and potentiodynamic polarisation in 3.5 wt.% NaCl were examined. This was to answer whether Li additions, spray forming and grain size impacted on the corrosion resistance. Atmospheric exposure showed Al2(CO3)3, NOx, SOx and NaCl compounds being deposited. Cathodic intermetallic compounds (Fe, Si, Mn and Cu rich) were shown to be associated with pitting corrosion, whereas anodic intermetallic compounds (Mg rich) offered sacrificial protection to the matrix. The Al-Cu alloys showed more corrosion compared to the Al-Mg alloys in all three corrosion investigations. The Al-Cu alloys showed pitting corrosion and intergranular corrosion, compared to primarily pitting corrosion on the Al-Mg alloys. AA2024-T3 developed a weakened, friable layer on the surface, consisting of a network of intergranular corrosion and numerous shallow pits. The Al-Cu-Li alloys also showed intergranular corrosion and pitting corrosion, but also developed selective grain dissolution, leading to extensive sub-surface cavities. This showed that Li additions in the Al-Cu alloys was detrimental and was primarily associated with the T type phases likely to be; T1 phase (Al2CuLi). Li additions in the Al-Mg alloys did not show any measurable improvement or reduction in corrosion resistance. Spray forming also did not appear to improve the corrosion resistance. Grain size in turn was shown to impact on corrosion resistance, with the general consensus being that finer grains offer increased corrosion resistances. Al-Cu alloys showed fine grain structures developed easy path propagation for intergranular corrosion, whereas fine grain structures on Al-Mg alloys promoted increased corrosion resistance.

No description available.

In der Arbeit werden spezielle Kupferlote im MIG- und Laserlötverfahren an Stählen mit unterschiedlichem Festigkeitsverhalten untersucht. Die Ergebnisse sollen dazu beitragen, den Lötprozess durch den Einsatz spezieller Kupferbasislote zu optimieren und durch reduzierten Energieeintrag ein homogeneres Eigenschaftsfeld im Bereich der Fügestelle zu erzeugen. Den Verarbeitern dieser Werkstoffe soll die Möglichkeit gegeben werden, diese Werkstoffe rationeller und mit höherer Effektivität zu verarbeiten. Im Ergebnis der Arbeit sollen Verbesserungen der Eigenschaften der Lötnähte erzielt werden, die besonders in der Dünnblechverarbeitung mit Schwerpunkt Karosseriebau Anwendung finden. Wesentliche Ziele sind die Erhöhung der Festigkeitseigenschaften, eine Erhöhung der Fügegeschwindigkeit, die Verbesserung des Phosphatierungsverhaltens sowie eine Reduzierung der eingebrachten Wärmeenergie. Die Vielfältigkeit dieser Anforderungen macht es notwendig, die Versuche sowohl im Laser- als auch im MIG-Lötverfahren durchzuführen. Die Lötverfahren werden in der Praxis für unterschiedliche Anforderungen innerhalb der Karosserie eingesetzt. Das Fügen von hochfesten Strukturelementen oder Außenhautbauteilen erfordert in Abhängigkeit von den Anforderungen die Verwendung ausgewählter Zusatzwerkstoffe. Die Vielfältigkeit der Werkstoffe und der Anforderungen spiegelt sich in den Untersuchungen der vorliegenden Arbeit wieder. Für weitergehende Untersuchungen, speziell im hochfesten Blechbereich, soll die Arbeit entsprechende Grundlagen bieten. Als Vorlage für die Erarbeitung von experimentellen und theoretischen Methodiken der Prozessbetrachtung werden neben typischen Kupferloten neu entwickelte Lotlegierungen verwendet. Bei der Betrachtung der Kupferlegierungen werden die unterschiedlichen Einflüsse auf den Fügeprozess definiert und beschrieben. Es wird festgestellt, dass niedrig schmelzende Lote mit ausgewählter Legierungszusammensetzung im Gegensatz zu Eisenbasis-Schweißdrähten einen geringeren negativen Einfluss auf das Gefüge der Bleche im Nahtbereich ausüben. Um die thermische Beanspruchung, besonders in der Wärmeeinflusszone, während des Fügeprozesses gering zu halten, kann zusätzlich eine geeignete Stromquellentechnik zum Einsatz kommen. Mit Hilfe des „kalten“ Lichtbogens ist es möglich, die eingebrachte Streckenenergie weiter zu reduzieren. Faktoren, die den Energieeintrag beeinflussen, werden in der vorliegenden Arbeit in experimentellen und theoretischen Untersuchungen hinsichtlich ihrer Wirkung auf das Festigkeitsverhalten betrachtet. Es werden durch geeignete Legierungskombinationen die Einflüsse auf die Steigerung der Lötgeschwindigkeit und auf eine Verbesserung des Phosphatierungsverhaltens untersucht. Die Ergebnisse dieser Untersuchungen liefern die Informations- und Beweisbasis für die erarbeiteten Legierungssysteme und ermöglichen es, den optimierten Lötprozess an hochfesten Stahlblechen wissenschaftlich zu betrachten. Die Auswertung der wissenschaftlichen Experimente, dargestellt in den angefügten ausführlichen Tabellen, stellen die Zusammenhänge zwischen der Legierungsauswahl und der eingebrachten Streckenenergie dar. Die Erkenntnisse aus der vorliegenden Arbeit sollen für das Fügen von hochfesten Blechen die Entscheidung über die Auswahl geeigneter Zusatzwerkstoffe erleichtern. Die Ergebnisse der theoretischen Untersuchungen anhand mathematischer Modelle zur Beschreibung der physikalischen Prozesse der Wärmezufuhr durch Verwendung eines ausgewählten Lotes in Kombination mit geeigneter Stromquellentechnologie sind die Grundlage für die Optimierung des Lötprozesses. Die vorgeschlagenen Modelle zur Entwicklung und Optimierung von Lichtbogenlötprozessen mit neu entwickelten Lotlegierungen wurde im Rahmen der vorgelegten Arbeit an realen Blechqualitäten angewendet und überprüft. In den Ergebnissen hat sich bestätigt, dass die Verwendung spezieller Kupferlote zu verbesserten Verarbeitungseigenschaften führen, und damit Konzepte zum wirtschaftlich verbesserten Fügen angeboten werden.:Inhalt 1. Einleitung. Kritische Bewertung der Literatur und Problemanalyse. 11 Perspektiven 1.1. Bedeutung des Lichtbogenlötens an höherfesten Stahlblechen 11 1.2. Entwicklungsstand bei höherfesten Dünnblechen und geeigneten 12 Lotwerkstoffen 1.3. Lichtbogenlöten an höherfesten Stahlblechen und Verfahrensgrenzen 15 2. Wissenschaftliche Problemstellung und Lösungsmöglichkeiten 16 2.1. Problemdarstellung 17 2.1.1. Problematik hochfester Grundwerkstoff 18 2.1.2. Löten vs. Schweißen 18 2.2. Lösungsstrategien und angestrebte Lösungswege 20 3. Theoretische Herleitung eines Mehrphasenmodells auf Kupferbasis 22 mit erhöhten Festigkeitseigenschaften 3.1. Voraussetzungen für die Legierungsbildung in Kupfer 22 3.2. Einfluss wesentlicher Legierungselemente auf die Eigenschaften von 26 Kupferlegierungen 3.2.1. Silizium 26 3.2.2. Aluminium 28 3.2.3. Mangan, Nickel, Zinn, Silber, Mikrolegierungselemente 29 3.3. Ermittlung optimierter Legierungen 30 3.4. Gieß- und ziehtechnische Einschränkungen 33 4. Versuchsdurchführung und Untersuchungsmethoden 34 4.1. Laserlöten 34 4.1.1. Grundwerkstoffe 34 4.1.2. Lote 34 4.1.3. Versuchsaufbau 36 4.1.4. Festlegung der Prozessdaten 37 4.1.5. Versuchsdurchführung 39 4.1.5.1. Bördelnaht DX54D+Z100 39 4.1.5.2. Überlappnaht DX54D+Z100 / HC180BD 40 4.1.5.3. Ermittlung der Benetzungswinkel bei unterschiedlichen 41 Lötgeschwindigkeiten 4.1.5.4. Korrosionsverhalten 43 4.2. MIG-Löten 44 4.2.1. Grundwerkstoffe 44 4.2.2. Lote 44 4.2.3. Versuchsaufbau 45 4.2.4. Messdatenerfassung 47 4.2.5. Versuchsdurchführung 48 4.2.5.1. Überlappnaht 22MnB5+AS 48 4.2.5.2. Überlappnaht HCT780XD Z70 (DP 800), HCT690T Z100 (TRIP700) 49 4.2.5.3. Ermittlung der Benetzungswinkel 49 4.2.5.4. Untersuchung des Wärmeeintrages 50 4.2.5.5. Phosphatierungsverhalten 51 5. Versuchsauswertung 52 5.1. Laserlöten 52 5.1.1. Visuelle Prüfung 52 5.1.1.1. Bördelnaht DX54D+Z100 52 5.1.1.2. Überlappnaht DX54D+Z100 / HC180BD 55 5.1.2. Statische Zugversuche 56 5.1.2.1. Bördelnaht DX54D+Z100 57 5.1.2.2. Überlappnaht DX54D+Z100 / HC180BD 58 5.1.3. Mikroskopische Untersuchungen 60 5.1.3.1. Bördelnaht DX54D+Z100 60 5.1.3.2. Überlappnaht DX54D+Z100 / HC180BD 63 5.1.4. Benetzungsverhalten 65 5.1.5. Beurteilung des Korrosionsverhaltens 67 5.2. MIG-Löten 69 5.2.1. Visuelle Prüfung 69 5.2.1.1. Überlappnaht 22MnB5+AS 69 5.2.1.2. Überlappnaht HCT780XD Z70 (DP 800), HCT690T Z100 (TRIP700) 71 5.2.2. Statische Zugversuche 73 5.2.2.1. Überlappnaht 22MnB5+AS 73 5.2.2.2. Überlappnaht HCT780XD Z70 (DP 800), HCT690T Z100 (TRIP700) 75 5.2.3. Härteverläufe 80 5.2.3.1. Überlappnaht 22MnB5+AS 80 5.2.3.2. Überlappnaht HCT780XD Z70 (DP 800), HCT690T Z100 (TRIP700) 82 5.2.4. Mikroskopische Untersuchungen 83 5.2.4.1. Überlappnaht 22MnB5+AS 83 5.2.4.2. Überlappnaht HCT780XD Z70 (DP 800), HCT690T Z100 (TRIP700) 86 5.2.5. Benetzungsverhalten 87 5.2.6. Schutzgas 89 5.2.7. Thermische Untersuchung 90 5.2.8. Phosphatierungsverhalten 92 6. Betrachtung von Optimierungskriterien 94 6.1. Werkstofftechnische Betrachtungen 95 6.1.1. Legierungssysteme 95 6.1.2. Einfluss von Oberflächenbeschichtungen 96 6.1.3. Streckenenergiebetrachtungen 96 6.2. Betrachtung des Einflusses von Nahtgeometrie, Schutzgas und 96 Gerätetechnik 6.2.1. Nahtgeometrie 96 6.2.2. Gerätetechnik 97 7. Übertragung der Ergebnisse auf andere hochfeste Stähle 97 8. Erprobung unter seriennahen Bedingungen 99 9. Zusammenfassung und Ausblick 101 10. Anhang 104