Mikrostruktura a textura titanu připraveného přáškovou metalurgií

Komerčně čistý titan byl připraven jako objemový materiál pomocí práškové metalurgie, konkrétně pomocí kryogenního mletí a sintrování elektrickým prou- dem, s cílem připravit ultrajemnozrnný materiál se zvýšenou pevností. Mikro- struktura prášků po mletí byla detailně zkoumána pomocí transmisního EBSD - nové metody, která umožnila první přímé pozorování textury uvnitř částic. Tato textura je podobná textuře po válcování díky podobnosti deformačních mecha- nismů. V prášku byla pozorována zrna s velikostí pod 100 nm. Vliv parametrů sintrování na vlastnosti materiálu byl studován pomocí skeno- vací elektronové mikroskopie včetně EBSD, rentgenové difrakce a pomocí měření mikrotvrdosti. Byl odhalen kompromisní vztah mezi porozitou a velikostí zrna - zcela neporézní materiál s ultrajemnozrnnou strukturou není možné připravit. Zvýšený obsah kyslíku je hlavním faktorem přispívajícím ke zpevnění materiálu, zatímco porozita má značně nepříznivý vliv na mechanické vlastnosti. Textura prášku byla za- chována i v sintrovaném materiálu. Možnost stabilizace ultrajemnozrnné struktury mechanickým legováním Ti s oxi- dem ytritým byla studována se smíšenými výsledky. Stabilizace byla úspěšná,...Bulk commercially pure titanium was prepared by powder metallurgy, namely by cryogenic milling and spark plasma sintering, with aim to produce ultra-fine grained material with enhanced strength. The microstructure of milled powders was investigated in detail by a novel method called transmission EBSD, which allowed the first direct observation of texture within the powder particles. This texture is similar to rolling texture, because of the similar nature of the defor- mation during milling. Microstructure observations revealed grains with the size under 100 nm. The influence of sintering parameters on material properties were studied by scan- ning electron microscopy including EBSD, X-ray diffraction and by microhardness measurements. The trade-off relationship between porosity and grain size was identified, fully dense material with ultra-fine grained microstructure could not be produced. Increased oxygen content was identified as a main strengthening factor, while porosity has significant deteriorating effect on mechanical properties. The texture of powder was retained in the bulk material. The possibility of stabilizing the microstructure by mechanical alloying of Ti with yttrium oxide nanoparticles was investigated with mixed results. The stabiliza- tion was successful, but several issues...Katedra fyziky materiálůDepartment of Physics of MaterialsMatematicko-fyzikální fakultaFaculty of Mathematics and Physic

Prášková metalurgie hybridních materiálů pro pokročilé aplikace

Prášková metalurgie hybridních materiálů pro pokročilé aplikace Sintrování elektrickým proudem (FAST) je univerzální metoda pro kompaktizaci prášků, která ohřívá materiál pomocí procházejícího elektrického proudu. Běžně se používá pro sintrování kovových materiálů, ovšem většinou s využitím předslitin jako výchozích prášků. Cílem disertační práce je prozkoumat možnosti metody FAST pro sintrování kompozitních materiálů a pro přípravu slitin z elementárních prášků v následujících oblastech: 1. Příprava strukturovaných kompozitů 2. Kompaktizace a precipitační žíhání v rámci jednoho sintrovacího cyklu (in-situ žíhání) 3. Rychlé prototypování slitin ze směsi elementárních prášků 4. Efektivní experimentální meření víceprvkových fázových diagramů Byl vyroben strukturovaný kompozit Al6061 + Ti-6Al-4V, kvůli malým rozměrům mřížky však došlo k problémům s pronikáním prášku dovnitř. Mechanické zkoušky tak bylo možno provést pouze pomocí tříbodového ohybu. Nevyžíhaný kompozit dosáhl větší pevnosti než nevyžíhaná slitina Al6061 bez výztuže, ale ve vyžíhaném stavu došlo k brzkému lomu. Pro výrobu strukturovaných kompozitů se metoda FAST nezdá jako příliš vhodná. Z elementárních prášků byla vyrobena slitina Ti-5Al-5V-5Mo-3Cr ve formě dlouhé, plně kompaktní tyče. Celý proces...Powder Metallurgy of Hybrid Materials for Advanced Applications The field-assisted sintering technology (FAST) is a versatile powder consolidation method, which uses electrical current for rapid heating of the sintered material. It is routinely used for sintering of various metallic materials, but mostly with preal- loyed powders as a feedstock. The aim of the thesis is to explore the capabilities of FAST for sintering of composite materials and for using blended elemental powders as a raw material in following areas: 1. Manufacturing of architectured composites 2. Consolidation and ageing in a single processing run (in-situ ageing) 3. Rapid alloy prototyping using blended elemental powders 4. High-throughput experimental investigations of multicomponent phase dia- grams Al6061 + Ti-6Al-4V architectured composite was produced, but issues with the pow- der penetration into the lattice have arisen due to the small lattice dimensions. Me- chanical properties could have been assessed by a three-point bending only. The composite has shown improved strength over the plain, unannealed Al6061 matrix, but a premature fracture when the Al matrix was aged properly. Using FAST was found to be inconvenient for architectured composite manufacturing. A long, fully dense rod was manufactured from the Ti-5Al-5V-5Mo-3Cr...Katedra fyziky materiálůDepartment of Physics of MaterialsMatematicko-fyzikální fakultaFaculty of Mathematics and Physic

Titanium and titanium alloys prepared by cryogenic milling

Ultra-fine grained materials are presently thoroughly investigated due to their enhanced mechanical properties. Cryogenic milling is one of the severe plastic deformation methods, which allow production of these materials. Titanium powder was processed by cryogenic milling in liquid nitrogen and argon and consequently consolidated via spark plasma sintering method. In this work, the influence of milling conditions (liquid nitrogen vs. liquid argon, material of balls, duration and speed of milling, usage of stearic acid) on size and shape of powder particles, contamination and mechanical properties was investigated. Particle size reduction was generally not observed, while their morphology changed significantly. Using liquid nitrogen as a cooling medium leads to strong contamination of prepared material and consequently to its hardening and embrittlement. Stearic acid supresses cold welding of particles during milling and enhances its efficiency. It is possible to eliminate stearic acid from powder by cleaning in acetone before sintering, to prevent contamination of processed material. Microhardness increased, depending on milling efficiency (in liquid argon), from original 178 HV to 200-300 HV range. Increase of yield and ultimate stength was observed in compression tests while maintaining ductility...

Cryogenic Milling of Titanium Powder

Ti Grade 2 was prepared by cryogenic attritor milling in liquid nitrogen and liquid argon. Two types of milling balls were used—stainless steel balls and heavy tungsten carbide balls. The effect of processing parameters on particle size and morphology, contamination of powder and its microhardness was investigated. Milling in liquid nitrogen was not feasible due to excessive contamination by nitrogen. Minor reduction of particle size and significant alterations in particle morphology depended on type of milling balls and application of stearic acid as processing control agent. Heavily deformed ultra-fine grained (UFG) internal microstructure of powder particles was observed by the method of “transmission Kikuchi diffraction”

Powder Metallurgy of Hybrid Materials for Advanced Applications

Powder Metallurgy of Hybrid Materials for Advanced Applications The field-assisted sintering technology (FAST) is a versatile powder consolidation method, which uses electrical current for rapid heating of the sintered material. It is routinely used for sintering of various metallic materials, but mostly with preal- loyed powders as a feedstock. The aim of the thesis is to explore the capabilities of FAST for sintering of composite materials and for using blended elemental powders as a raw material in following areas: 1. Manufacturing of architectured composites 2. Consolidation and ageing in a single processing run (in-situ ageing) 3. Rapid alloy prototyping using blended elemental powders 4. High-throughput experimental investigations of multicomponent phase dia- grams Al6061 + Ti-6Al-4V architectured composite was produced, but issues with the pow- der penetration into the lattice have arisen due to the small lattice dimensions. Me- chanical properties could have been assessed by a three-point bending only. The composite has shown improved strength over the plain, unannealed Al6061 matrix, but a premature fracture when the Al matrix was aged properly. Using FAST was found to be inconvenient for architectured composite manufacturing. A long, fully dense rod was manufactured from the Ti-5Al-5V-5Mo-3Cr..

Microstructure and Texture of Titanium Prepared by Powder Metallurgy

Bulk commercially pure titanium was prepared by powder metallurgy, namely by cryogenic milling and spark plasma sintering, with aim to produce ultra-fine grained material with enhanced strength. The microstructure of milled powders was investigated in detail by a novel method called transmission EBSD, which allowed the first direct observation of texture within the powder particles. This texture is similar to rolling texture, because of the similar nature of the defor- mation during milling. Microstructure observations revealed grains with the size under 100 nm. The influence of sintering parameters on material properties were studied by scan- ning electron microscopy including EBSD, X-ray diffraction and by microhardness measurements. The trade-off relationship between porosity and grain size was identified, fully dense material with ultra-fine grained microstructure could not be produced. Increased oxygen content was identified as a main strengthening factor, while porosity has significant deteriorating effect on mechanical properties. The texture of powder was retained in the bulk material. The possibility of stabilizing the microstructure by mechanical alloying of Ti with yttrium oxide nanoparticles was investigated with mixed results. The stabiliza- tion was successful, but several issues..

Analysis of university students needs on the mobile telephone market

Import 15/12/2009Prezenční116 - Katedra marketingu a obchoduNeuveden

Microstructure and texture in cryomilled and spark plasma sintered Ti Grade 2

Titanium (Grade 2) was processed by cryogenic milling and subsequently sintered by spark plasma sintering (SPS) method with the aim of creating and preserving the ultra-fine grained (UFG, < 1 μm) microstructure. Microstructural investigation was performed after both cryogenic milling and spark plasma sintering. An advanced technique of transmission Kikuchi diffraction (TKD) was used to characterize the individual milled powder particles. Investigations of milled powders showed significant grain refinement down to 50 nm after milling in liquid argon with tungsten carbide balls. We assume that this is the equilibrium grain size resulting from the balance of deformation, recovery and dynamic recrystallization. A texture, resembling the rolling texture in Ti, was also found in the milled particles, which can be explained by the nature of deformation during milling. UFG microstructure was not maintained after sintering, with the mean grain size of 2.6 μm. Although the grains are completely recrystallized, a texture, similar to the powder texture, was also found in these samples as a result of packing of the powder particles and the nature of the recrystallization process (continuous static recrystallization)

Microstructure and texture in cryomilled and spark plasma sintered Ti Grade 2

Titanium (Grade 2) was processed by cryogenic milling and subsequently sintered by spark plasma sintering (SPS) method with the aim of creating and preserving the ultra-fine grained (UFG, < 1 μm) microstructure. Microstructural investigation was performed after both cryogenic milling and spark plasma sintering. An advanced technique of transmission Kikuchi diffraction (TKD) was used to characterize the individual milled powder particles. Investigations of milled powders showed significant grain refinement down to 50 nm after milling in liquid argon with tungsten carbide balls. We assume that this is the equilibrium grain size resulting from the balance of deformation, recovery and dynamic recrystallization. A texture, resembling the rolling texture in Ti, was also found in the milled particles, which can be explained by the nature of deformation during milling. UFG microstructure was not maintained after sintering, with the mean grain size of 2.6 μm. Although the grains are completely recrystallized, a texture, similar to the powder texture, was also found in these samples as a result of packing of the powder particles and the nature of the recrystallization process (continuous static recrystallization)