Solid State Phenomena Vol. 212

Abstract: The principle and the potential of an incremental bulk metal forming method is presented in the paper. It can be used for manufacturing of the specific aircraft integral panels in a form of ribbed parts with high surface/thickness ratio. A unique laboratory device has been developed to investigate the effect of process parameters on the material flow and the press load. It utilizes tooling consisting of working rolls, a die and a punch that is divided into a number of segments. The results of preliminary numerical simulations proved that the presented forming method offers significant advantages in comparison with conventional forging.

Abstract: mpact of complex modification and filtration during pouring into moulds on durability has been evaluated in this study in conditions of high-temperature creep of castings made from nickel superalloy IN-713C post production rejects. The conditions of initiation and propagation of cracks in the specimens were analysed with consideration of morphological properties of material macro-, micro-and substructure. It has been demonstrated that in conditions of high-temperature creep at temperature 980°C with stress σ =150 MPa creep resistance of the IN-713C superalloy increases significantly with the increase of macrograin size. Creep resistance of specimens made of coarse grain material was significantly higher than the resistance of fine grain material.

Abstract: The subject matter of the paper is the quantitative evaluation of gaseous and shrinkage porosity in the turbine blades using quantitative metallography methods. The research material consisted of blades with a polycrystalline structure made of IN 713C superalloys. Three different shell mould systems were used during the investment casting: shell A - typical industrial shell mould system and used in this work as the reference; shell B – similar to version A, but SiC grit was applied as back-up stucco; shell C – entirely SiC shell mould system. The blades of superalloy IN-713C cast into the wholly SiC shell mould system have revealed much lower porosity as compared to the blades cast into the typical industrial shell mould system.

Abstract: Mechanical working manufacturing methods of nickel alloys used conventionally strips and blanks need to solve many problems concerning high strength material forming which is characteristic limited plasticity. The production pressed elements of vehicle constructions and aircraft engine elements requires the high quality drawpieces since these are essential for safety. They are also the main structural components. Conventional methods of mechanical working such as pressing can be used in quantity production of the above mentioned elements and their production can also be cost-effective. Forming nickel alloys generates a lot of technological wastes resulting from back-springing effects determining the most appropriate pressure in the process of pressing. Failure holes in the process of bulging as well as cracking of drawpieces in the process of deep drawing. The heterogeneous mechanical properties distribution on thin sheet blanks made of Inconel alloy, which is different than material quality certificate shows, produces also a lot of manufacturing problems. These problems are usually solved by production engineers in the following way: dividing the production of ready drawpieces into a bigger number of simple blank profiling operations, shallow pressing, using a rubber punch for pressing or hydroforming. Complex drawpieces shapes are quite often made of several parts which are next welded. In the case of presented tube a tubular diffuser made of Inconel 718 alloy blank and cone made of Inconel 625. However the process of forming high strength materials like nickel alloys requires the application bigger forming forces than in the same kind of conventional formable steel processes. Tools get jammed quite often in the process and high force presses of 10 MN or more need to be used so is very expensive. The aspect of cold mechanical forming discussed materials has been a particular interest. The researches based on precise evaluation mechanical properties and technological plasticity of the selected materials in basic mechanical and technological tests as well as in FEM numerical simulation (finite elements method). The material models applied to simulation contain the pointed out experimentally the mechanical characteristics of Inconel alloys. The thin sheets blanks made of 0,9 mm thick Inconel 718 alloy and 0,45 mm thick Inconel 625 alloy blanks have been examined. The possibilities of using numerical simulations for solving the problems of selecting or modifying the pressing technology and hydroforming that type materials as well as forecasting the results of forming processes have been also presented. The evaluation of drawability of thin sheets blanks made of Inconel 718 and 625 alloys has also been discussed in the paper.

Abstract: Root causes of premature breakage of the bolts fastening the connection members of shut-off valves in valve chests for secondary superheated steam. The experiments showed that the cracking of bolts had been caused by the process of accelerated creeping under high tensile stresses. The obtained results may constitute the basis for formulation of operating guidelines and recommendations, resulting in extended life of the components under consideration.