@phdthesis{Soyama2014, author = {Soyama, Juliano}, title = {Development of creep resistant titanium aluminide alloys for the Metal Injection Moulding process}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-31610}, school = {BTU Cottbus - Senftenberg}, year = {2014}, abstract = {Titanium aluminides show great technological potential due to their light weight and excellent creep resistance. Their utilisation thus offers a potential to decrease fuel consumption and simultaneously improve the performance of components subjected to stress at high temperatures. However, shaping of titanium aluminides is still a very challenging and costly task considering their brittleness and the sensitivity on chemical composition. Therefore powder metallurgy near-net shape manufacturing techniques are very attractive to decrease material waste and reduce overall processing costs. This research work was focused on the preparation, characterisation and optimisation of creep resistant titanium aluminides for the Metal Injection Moulding (MIM) process. Considering the little information available regarding processing of titanium aluminides by MIM, this work had firstly the goal of assessing the creep behaviour of a reference titanium aluminide alloy. Secondly, alloy variations with compositions based on the reference material were designed with the objective of improving the creep resistance, especially concerning primary creep. The basic strengthening mechanisms applied involved the addition of slow diffusing elements and elements that cause precipitation of hard particles. The specimens were prepared by using pre-alloyed powder and mixtures of a master alloy (pre-alloyed) and elemental powders. Consequently, a great deal of effort was spent in the characterisation of the sintering behaviour in order to achieve reliable test pieces. Even though both methods can deliver sound specimens, the pre-alloyed powder approach led to the best results in terms of residual porosity and microstructural homogeneity. The mechanical testing results indicate that processing of titanium aluminides by MIM is feasible and acceptable creep properties can be achieved with the proper sintering parameters. Even though the ductility at room temperature was considerably limited due to the residual porosity and high amounts of impurities intrinsic to the MIM process, alloys developed within this study showed improved primary creep resistance in the high stress - high temperature regime. In particular alloy variations containing additions of Mo, Si and Gd led to a considerable improvement of the primary creep resistance in comparison to the reference material at 800°C - 350 MPa loading.}, subject = {Titanium Aluminides; Creep; Metal Injection Moulding; Metallpulverspritzguss; Kriechen; Titanaluminide; Titanaluminide; Kriechen; Metallpulver; Spritzgießen}, language = {en} } @phdthesis{Deplanque2007, author = {D{\´e}planque, Sylvain}, title = {Lifetime prediction for solder die-attach in power applications by means of primary and secondary creep}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-4275}, school = {BTU Cottbus - Senftenberg}, year = {2007}, abstract = {The objective of this thesis was to accurately check and improve the models existing for eutectic solder alloys used in simulation tools. Creep deformation,which is the most important deformation mode of solders, of two solder alloys, the widely used eutectic SnPb and the environmentally friendly alternative solder alloy SnAgCu was tested. It was shown that it is necessary to model two different stages of this high temperature induced mechanism: To improve the current material definition, primary creep must be implemented in the FE-software in addition to the existing secondary creep models. This thesis shows how it is possible to test creep behaviour under cyclic loading conditions with a test specimen of novel design. So, primary creep was observed and reoccurs cyclically under such test conditions. Furthermore, steady state creep is also always observed. A Constitutive equation combining both primary and secondary creep was given and verified. This model was implemented in FE-code Ansys, and after performing different kinds of simulation, the necessity of simulating primary creep was demonstrated. In order to achieve reliability information by FE-simulation of solder die attach, the creep-fatigue behaviour with the mean of crack propagation must be modeled. Various kinds of chips on copper substrate (power-transistors) were thermally tested, and different methods were used to investigate crack propagation. These methods were scanning acoustic microscopy and microstructure analysis by optical microscopy. The influence of damage on thermal behaviour (i.e. the thermal resistance of the device) was also assessed. These results were compared with the simulation results in order to build a lifetime prediction model based on crack propagation analysis.}, subject = {Legierung; L{\"o}ten; Kriechen; Kriechen; L{\"o}tstelle; Rissfortschritt; Lebensdauer; Leistungselektronik; Creep; Solder joint; Crack propagation; Lifetime; Power electronic}, language = {en} }