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Influence of Heat Treatments on Microstructure of Electron Beam Additive Manufactured Ti-6Al-4V Alloy
Damir Skuhala, 2020, master's thesis

Abstract: Additive manufacturing of metallic parts is increasing in popularity and starting to emerge as a new competitive manufacturing process. Printed structures from Ti-6Al-4V titanium alloy, produced by electron beam additive manufacturing (EBAM), possess columnar prior β grains and layer bands, alongside an ultrafine lamellar microstructure, which is prone to low ductility and thus requiring thermal post-processing. Several heat treatments were performed in α + β and β field, in one or multiple stages. The results showed that bi-lamellar microstructure can be obtained, and that selection of annealing temperature and cooling rate determines the morphology, thickness, and distribution of both primary and secondary α features. Mechanical properties were evaluated on three selected heat treatments. Annealing of the As-built condition was performed at 710°C (HT1) and 870°C (HT2), resulting in lamellar microstructure with basketweave morphology. In two-stage heat treatment (HT3), the temperature in the first stage has exceeded β transus, while in the second, annealing was performed again at 870°C. The microstructure was characterized as a mixture of lamellar and bi-lamellar with large α colonies inside the rearranged prior β grains. Air cooling was performed in all HT from the final annealing stage. Strength and hardness have decreased with increasingly coarser microstructural features, while fracture toughness was improved, except in HT1, where the decrease in the fracture toughness was mainly attributed to reduced intrinsic toughening. As-built and HT1 conditions were effected by microstructural texture, causing inconsistent fracture morphology, reduced crack roughness and scattering in results. The influence of texture was decreased by coarser microstructure in HT2, while crack tortuosity was increased. Very unpredictable fracture behaviour was observed in HT3 due to large α colonies, as their orientation determines the areas of ductile or cleavage crack propagation.
Keywords: Titanium alloys, Ti-6Al-4V, additive manufacturing, EBAM, heat treatments, microstructural optimization, mechanical properties, fracture toughness
Published: 11.05.2020; Views: 502; Downloads: 141
.pdf Full text (25,14 MB)

Vibracijsko utrujanje nosilca alternatorja
Damir Skuhala, 2017, undergraduate thesis

Abstract: V diplomskem delu je predstavljen numeričen preračun dobe trajanja nosilca alternatorja. Nosilec obremenjujejo vibracije motorja, ki so dinamične narave in ga vibracijsko utrujajo. Predstavljen je izvor vibracij v motorju z notranjim zgorevanjem ter njihov matematični zapis. Statične obremenitve nosilca pri obratovanju alternatorja so izračunane analitično. Izvedene so statična in modalna analiza, analiza harmoničnega vzbujanja ter analiza vibracijskega utrujanja v frekvenčni domeni po metodi končnih elementov. Na podlagi pridobljenih rezultatov je nosilec analiziran, pri čemer je ugotovljeno, da doseže območje trajne trdnosti s faktorjem varnosti 2,978.
Keywords: vibracije, vibracijsko utrujanje, dimenzioniranje na dobo trajanja, numerične simulacije
Published: 11.09.2017; Views: 743; Downloads: 176
.pdf Full text (3,87 MB)

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