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Study on the Deformation Behaviors of Hydrogen Ti-45Al-5Nb-0.8Mo-0.3Y Alloysat High Temperatures

Author: YangDanMei
Tutor: ZongYingYing
School: Harbin Institute of Technology
Course: Materials Processing Engineering
Keywords: TiAl alloys hydrogen-enhanced plasticity mechanical behavior microstructural evolution
CLC: TG146.23
Type: Master's thesis
Year: 2013
Downloads: 37
Quote: 0
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Abstract


TiAl based alloys have low density, good heat resistance, high specific strengthand specific stiffness, high elastic modulus, high temperature creep resistance andoxidation resistance. However, their high room temperature brittleness, lack ofenough ductility, bad workability and wear resistance, and high processing costs limitwidespread application of TiAl based alloys. Improving the TiAl based alloys hotworkability and room temperature properties by hydrogen treatment technology is anew approach to solving above problems. The effects of hydrogen treatment on thehigh temperature deformation behaviors of TiAl based alloys are lack of systematicstudy. Therefore, this paper systematically studied about these aspects.In this paper, microstructures of hydrogenated and unhydrogenated alloys werestudied using X-ray diffraction analysis （XRD）, scanning electron microscope （SEM）and transmission electron microscope （TEM）. The effects of hydrogen on roomtemperature microstructure and substructure were investigated. The microstructuralevolution of hydrogenated and dehydrogenated alloys was discussed. Roomtemperature mechanical properties tests of unhydrogenated, hydrogenated anddehydrogenated alloys were carried out. The results showed that the room temperaturefracture of alloys presented typical cleavage fracture feature; with hydrogen additionincreasing, the room temperature strength and hardness increased, and plasticityreduced. Although the mechanical properties of dehydrogenated alloy had the certainrecovery comparing with the hydrogenated alloys, its plasticity was still poor.The high temperature deformation behaviors of Ti-45Al-5Nb-0.8Mo-0.3Y-xHalloys were mainly studied in this paper. The effects of hydrogen contents,deformation temperatures, strain rates and amounts deformation on high temperaturemechanical properties and microstructural evolution of the alloys were analyzed. Theresults showed that as temperature raised and strain rate reduced, the flow stress ofalloys remarkably dropped. Under the certain deformation conditions, the flow stressof the hydrogenated alloys was lower than that of the unhydrogenated alloys, with alargest drop of28%in term of peak stress. By hydrogenating, plasticity was enhanced,deformation temperature decreased by about100℃, and hot workability wasimproved. In addition, hydrogen-enhanced plasticity mechanism of TiAl based alloys was disclosed by analyzing microstructural evolution of the hydrogenatedTi-45Al-5Nb-0.8Mo-0.3Y alloy in high temperature deformation.Processing maps of Ti-45Al-5Nb-0.8Mo-0.3Y-0.377H was established. Throughanalyzing the processing maps, it was found that the region of38<η<67%could beregarded as safe zone for hot process of hydrogenated alloys, where no cracks werefound in workpiece deformed at temperature ranging from1080℃to1180℃andstrain rate of less than0.01s-1.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metallic materials > Non - ferrous metals and their alloys > Light non-ferrous metals and their alloys > Titanium
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