Применение МКЭ для анализа сварных конструкций с дефектами типа трещин

В данной работе исследован нелинейный процесс деформирования сварных конструкций с трещиноподобными дефектами. В качестве основного параметра используется энергетический J-интеграл и эквивалентная пластическая деформация. Величину J-интеграла для элемента конструкции с трещиной можно определить численными методами, например методом конечных элементов. Автоматизированный анализ изделий с трещиноподобными дефектами осуществлялся с использованием программного комплекса ANSYS и программного комплекса CRACK, разработанным в Карагандинском государственном техническом университете (КарГТУ)

Qualifizieren des Laserstrahl-Auftragschweißens von BLISKs aus Nickel- und Titanbasislegierungen

The subject of this dissertation is the development and improvement of Laser Metal Deposition (LMD) with regard to repair of BLISKs out of Nickel and Titanium base alloys. Defect and oxidation free LMD of Nickel and Titanium base alloys is guaranteed by use of new developed powder and shielding gas nozzles which generate a suitable local gas shielding. Therefore the process can be carried out without using an inert gas chamber. The accessibility of the complex shaped BLISK is guaranteed by the compact designs of the powder and shielding gas nozzles. The suitable process parameters for LMD of Nickel and Titanium base alloys and the suitable process layouts (build-up strategies) are developed on simple rectangular geometries and HCF test samples. The static and dynamic mechanical properties are determined in tensile and HCF tests by use of tensile and HCF test samples manufactured from the geometries mentioned above. Directly after LMD the macro structure of Inconel 718 is isotropic and the mechanical properties are correlating with an annealed forged raw material. By stress relieving static and dynamic mechanical properties are achievable which correlate with a completely heat treated forged raw material. Directly after LMD the macro structures of the Titanium base alloys Ti-17 und Ti-6Al-4V is anisotropic due to the epitactical growth of the columnar grains. The static mechanical properties are strongly depending on the load direction compared with the growth direction of the columnar grains. By a complete heat treatment of LMD Ti-17 static mechanical properties are achievable which correlate with a completely heat treated forged raw material due to an achieved recrystallization. Due to micro bonding defects and micro porosity the achievable dynamic mechanical properties are not fulfilling the specifications. By stress relieving static and dynamic mechanical properties are achievable for LMD Ti-6Al-4V which correlate with a completely heat treated forged raw material. Suitable process layouts and parameters are determined carrying out a systematic variation of build-up strategies and parameters. Defect and oxidation free repairs of the three case studies FOD on the leading edge, wear on the tip and erosion of the complete blade are verified on mock-ups. The transferability of the process layouts and parameters determined on mock-ups to the real OEM parts is estimated to be uncritical in case of geometrical affinity. In case of significant deviations between the geometries to be cladded on the mock-ups compared with the real OEM part a new determination of suitable process layouts and parameters must be carried out due to changed heat conduction conditions. The amount of OEM parts is limited. Therefore the geometrical affinity between OEM part and mock-up is important for an efficient process development. By implementation of a closed-centre process chain and new developed LMD specific macros which guarantee the conversion of the developed process layouts and parameters into NC commands, the process is realized on two OEM parts. To avoid undercuts and to relocate critical areas of higher porosity into areas to be milled tabs are used. A strong necessity is the digitizing of the blade to be reconditioned by LMD and the digitizing of a blade ready for use to calculate the volume to be built-up and due to deviations between the CAD data for manufacture and the geometry of the blade after service and / or manufacture

Increased wear and oxidation resistance of titanium aluminide alloys by laser cladding

A process layout for laser cladding of layers on substrates of titanium aluminides using state-of-the-art and modified (additions of Si and TiB2) TiAl alloys is presented. The process involves a preheating of the samples to reduce thermal stresses and cladding in an inert gas atmosphere with an oxygen content lower than 30 ppm. These conditions lead to crack free layers and low surface oxidation. Microstructure and hardness of the layers are investigated. The abrasive wear resistance of the cladded layers in comparison to the base material is tested with promising results. Finally results of the oxidation behavior are shown and prove the increased performance of modified TiAl layers in comparison to the base material