TY - THES

T1 - Mechanical behaviour and microstructure of low alloy content Ti-Al-Mn alloys

AU - Pühringer, Thomas

N1 - embargoed until null

PY - 2008

Y1 - 2008

N2 - This work was part of a project developing a process to produce titanium sheets via a powder route at lower costs. One of the ideas of this project was to use powders with low contaminants found in titanium ores. In a conventional titanium production route vacuum arc remelting is needed to remove these contaminants which seriously contributes to the product costs. This work studies the potential of the use of contaminants as useful alloying elements. Six different lean Ti-Al-Mn alloys with and without addition of iron were studied. The influence of chemical composition in combination with two different heat treatments on microstructure and mechanical behaviour was examined. Samples were heat treated in an alpha+beta region at 800°C and in a full beta region at 1000°C, both for one hour and water quenched. Shear punch test was utilized to assess mechanical properties. Microstructures were characterised by using X-ray diffraction, optical, scanning and transmission electron microscopy. The heat treatment in the alpha+beta region resulted for most alloys in microstructures with equiaxed globular alpha grains and beta grains at grain boundaries or triple points. Omega phase was discovered finely dispersed in every form of beta phase. The heat treatment in the full beta region produced in combination with water quenching mostly martensitic microstructures. Alloys heat treated at 1000°C showed in general lower ductility and lower strength than alloys heat treated 800°C. Overall Ti-1.5Mn was found to be the most ductile and Ti-1.5Al the strongest alloy both after heat treatment at 800°C. Manganese seems to make alloys more ductile due to increasing of beta phase fraction and aluminium seems to strengthen due to solid solution strengthening and decreasing of beta phase fraction. The highest potential for further development has Ti-0.75Mn-0.75Al-0.3Fe offering a valuable combination of high ductility and high strength.

AB - This work was part of a project developing a process to produce titanium sheets via a powder route at lower costs. One of the ideas of this project was to use powders with low contaminants found in titanium ores. In a conventional titanium production route vacuum arc remelting is needed to remove these contaminants which seriously contributes to the product costs. This work studies the potential of the use of contaminants as useful alloying elements. Six different lean Ti-Al-Mn alloys with and without addition of iron were studied. The influence of chemical composition in combination with two different heat treatments on microstructure and mechanical behaviour was examined. Samples were heat treated in an alpha+beta region at 800°C and in a full beta region at 1000°C, both for one hour and water quenched. Shear punch test was utilized to assess mechanical properties. Microstructures were characterised by using X-ray diffraction, optical, scanning and transmission electron microscopy. The heat treatment in the alpha+beta region resulted for most alloys in microstructures with equiaxed globular alpha grains and beta grains at grain boundaries or triple points. Omega phase was discovered finely dispersed in every form of beta phase. The heat treatment in the full beta region produced in combination with water quenching mostly martensitic microstructures. Alloys heat treated at 1000°C showed in general lower ductility and lower strength than alloys heat treated 800°C. Overall Ti-1.5Mn was found to be the most ductile and Ti-1.5Al the strongest alloy both after heat treatment at 800°C. Manganese seems to make alloys more ductile due to increasing of beta phase fraction and aluminium seems to strengthen due to solid solution strengthening and decreasing of beta phase fraction. The highest potential for further development has Ti-0.75Mn-0.75Al-0.3Fe offering a valuable combination of high ductility and high strength.

KW - Ti-Al-Mn niedriglegiert Alpha-

KW - Beta-

KW - Omega-Phase Gefüge mechanische Eigenschaften Wärmebehandlung

KW - Ti-Al-Mn lean alloy alpha

KW - beta

KW - omega phase microstructure mechanical properties heat treatment

M3 - Diploma Thesis

ER -