Fatigue behaviour of AZ31 and AZ61 magnesium alloys after corrosion degradation

Dizertační práce je zaměřená na hodnocení vlivu korozní expozice v 5% solné mlze na únavové chování slitin AZ31 a AZ61 vyrobených metodou squeeze casting. V práci je hodnocena mikrostruktura a základní mechanické vlastnosti slitin, u slitiny AZ61 je provedena optimalizace tepelného zpracování na základě mikrostrukturních a mechanických charakteristik. U všech tří typů materiálu pak byla hodnocena hloubka korozního napadení, rychlost a mechanismus koroze. Na únavových zkušebních tělesech po korozní expozici 480 a 1000 hodin byl hodnocen vliv koroze na únavové chování jednotlivých slitin srovnáním s daty získanými na hladkých zkušebních tělesech. Na hladkých únavových zkušebních tělesech i tělesech po korozní expozici byla provedena fraktografická analýza. Na závěr byl zhodnocen vliv množství a způsobu vyloučení hliníku na korozní a únavové chování testovaných slitin.Dissertation thesis is focused on evaluation of influence of exposure in 5% salt fog on fatigue behavior of AZ31 and AZ61 magnesium alloy fabricated by squeeze casting method. Microstructure and mechanical properties of experimental materials have been evaluated. The AZ61 alloy was solution heat treated after prior optimization of the heat treatment process based on microstructural characteristics and mechanical properties. Depths of corrosion damage, corrosion rate and mechanism of corrosion of all three experimental alloys have been evaluated. Influence of prior corrosion exposure for 480 and 1000 hours on fatigue behavior of experimental materials was evaluated. Obtained data were compared with data obtained using smooth test specimens. Fractographic analysis was carried out on both smooth and precorroded specimens. Furthermore, influence of aluminium on corrosion and fatigue behavior of tested alloys was defined.

Determination of Mechanical Properties and Structural Evaluation of the Alloy AZ31 with Different Content of Calcium

V této bakalářské práci jsou porovnávány mechanické vlastnosti hořčíkové slitiny AZ31 s rozdílným obsahem vápníku. Jednotlivé vzorky jsou bez Ca, s 0,5hm%, 1hm% a 2hm% Ca. Práce obsahuje údaje o chemickém složení jednotlivých vzorků, fotografie jejich mikrostruktury, výsledky tahových zkoušek a měření tvrdosti. Slitiny s obsahem 1hm% a 2hm% Ca byly tepelně zpracovány pro porovnání se vzorky ve výchozím stavu.Mechanical properties of magnesium alloy AZ31 with different content of calcium were compared in this bachelor thesis. Specimens contain 0,5 wt%, 1 wt%, 2 wt% Ca and one of them was free of calcium. Specimens with 1 wt% and 2 wt% of calcium were heat treated to match them up with as fabricated alloy. The thesis presents information about chemical composition and resultes of tensile and hardness tests. Microstructures of alloys recorded on the light microscopy pictures are included as well.

Fatigue properties of magnesium alloy AZ31 after corrosion degradation

Předmětem této diplomové práce je hodnocení cyklické odezvy a únavového chování hořčíkové slitiny AZ31 v základním stavu a po korozní degradaci v mlze neutrálního 5% roztoku NaCl po dobu 480 a 1000 hodin. V práci je hodnocena mikrostruktura, základní mechanické vlastnosti a únavové chování experimentálního materiálu v základním stavu. U materiálu po korozní degradaci je hodnocen vzhled a hloubka lokálního korozního napadení a dále také mechanismus koroze. Na únavových zkušebních tělesech po korozi 480 a 1000 hodin byl hodnocen vliv korozní degradace na cyklickou plasticitu a únavové chování slitiny AZ31 v nízkocyklové i vysokocyklové oblasti. Na závěr byl hodnocen vliv lokálního korozního napadení na iniciaci únavových trhlin.The present study is focussed on assessment of cyclic deformation response and fatigue behaviour of bare and precorroded AZ31 magnesium alloys. Corrosion degradation was carried out in a salt spray fog (5% solution of sodium chloride) for 480 and 1000 hrs. Microstructure, mechanical properties, low- and high-cycle fatigue behaviour of experimental material in as-cast condition has been evaluated. Furthermore, the corrosion behaviour of material has been investigated. The fatigue tests have been performed using precorroded specimens to assess influence of corrosion degradation on cyclic deformation response and on low- and high-cycle fatigue behaviour. Influence of local corrosion degradation on initiation of fatigue cracks has been studied.

Synthesis of wollastonite powder and manufacturing of porous scaffolds for multiple applications

Wollastonite (CaSiO3) is gaining attention due to its attractive properties, which can be used in a wide field of industries, i.e., thermal insulation; catalysis; filters and water purification; reinforcement phase in composites; and more recently, in orthopaedics. The additive manufacturing method has been used to process various materials in order to obtain diverse shaped-structures with controlled porosity. The aim of the present work is to establish an easy synthesis and processing of wollastonite powder to elaborate porous structures via robocasting technique. An injectable paste that serves as an ink was developed to build up cylindrical structures of 10 mm in diameter and 10 mm in height, using a tip of 410 μm. The cylinders were 3D-printed following two different arrangement patterns, named as honeycomb and rectilinear infills. In the same way, two pore sizes of 350 and 500 μm were produced. The final structures were evaluated in terms of their porosity, shape and size of pores by scanning electron microscopy and compression test. The purity of the wollastonite bodies was evaluated by X-ray diffraction. Moreover, preliminary studies were carried out on the final consolidated porous scaffolds showing its potential use in catalysis, water purification and/or orthopaedics

Chemical stability of tricalcium phosphate - iron composite during spark plasma sintering

Tricalcium phosphate (Ca3(PO4)2, TCP) is a wide-used ceramic as a bone filler material due to its good osteoconductivity property. Nevertheless, its poor mechanical properties does not allow its use for load-bearing applications. Therefore, the option of improving its strength and toughness by adding a Biocompatible metallic component is a promising alternative to overcome this drawback, leading to the fabrication of improved bone implants. The present work is focused on defining the thermal stability of alpha-TCP (-TCP) when it is sintered together with iron (Fe) by spark plasma sintering. The results showed the thermal stability of the composite with no degradation or oxidation in the ceramic or metal phase. A clear advantage from the TCP-Fe composites respect others, such as hydroxyapatite-titanium, is the complete retention of the TCP due to the less reactivity with iron respect titanium. Furthermore, the allotropic phase transformation from alpha to beta-TCP polymorph was reduced by sintering at 900 °C. However, also the densification of the material was impaired at this temperature. It is expected that spark plasma sintering allows the fabrication of TCP-Fe composites free of secondary phases that compromise the mechanical strength of the material

Interpenetrated Magnesium–Tricalcium Phosphate Composite: Manufacture, Characterization and In Vitro Degradation Test

Magnesium and calcium phosphates composites are promising biomaterials to create biodegradable load-bearing implants for bone regeneration. The present investigation is focused on the design of an interpenetrated magnesium–tricalcium phosphate (Mg–TCP) composite and its evaluation under immersion test. In the study, TCP porous preforms were fabricated by robocasting to have a prefect control of porosity and pore size and later infiltrated with pure commercial Mg through current-assisted metal infiltration (CAMI) technique. The microstructure, composition, distribution of phases and degradation of the composite under physiological simulated conditions were analysed by scanning electron microscopy, elemental chemical analysis and X-ray diffraction. The results revealed that robocast TCP preforms were full infiltrated by magnesium through CAMI, even small pores below 2 lm have been filled with Mg, giving to the composite a good interpenetration. The degradation rate of the Mg–TCP composite displays lower value compared to the one of pure Mg during the first 24 h of immersion test.Magnesium and calcium phosphates composites are promising biomaterials to create biodegradable load-bearing implants for bone regeneration. The present investigation is focused on the design of an interpenetrated magnesium–tricalcium phosphate (Mg–TCP) composite and its evaluation under immersion test. In the study, TCP porous preforms were fabricated by robocasting to have a prefect control of porosity and pore size and later infiltrated with pure commercial Mg through current-assisted metal infiltration (CAMI) technique. The microstructure, composition, distribution of phases and degradation of the composite under physiological simulated conditions were analysed by scanning electron microscopy, elemental chemical analysis and X-ray diffraction. The results revealed that robocast TCP preforms were full infiltrated by magnesium through CAMI, even small pores below 2 lm have been filled with Mg, giving to the composite a good interpenetration. The degradation rate of the Mg–TCP composite displays lower value compared to the one of pure Mg during the first 24 h of immersion test

Effect of Laser Parameters on Processing of Biodegradable Magnesium Alloy WE43 via Selective Laser Melting Method

The global aim of the theme of magnesium alloy processing by the selective laser melting technology is to enable printing of replacements into the human body. By combining the advantages of WE43 magnesium alloy and additive manufacturing, it is possible to print support structures that have very similar properties to human bones. However, printing magnesium alloy parts is very difficult, and the printing strategies are still under development. Knowledge of weld deposit behaviour is needed to design a complex printing strategy and still missing. The main aim of the manuscript is the find a stable process window and identify the dependence of the weld deposit shape and properties on the laser power and scanning speed. The range of the tested parameters was 100–400 W and 100–800 mm/s for laser power and scanning speed. The profilometry and light microscopy were used to verify the continuity and shape evaluation. The microhardness and EDX analysis were used for the detailed view of the weld deposit. The manuscript specifies the weld deposit dimensions, their changes depending on laser power and scanning speed, and the continuity of the weld tracks. The stable weld deposits are made by the energy density of 5.5–12 J/mm2. Thin walls were also created by layering welds to determine the surface roughness scattering (Ra 35–60) for various settings of laser power and scanning speed