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Congratulations to Grzegorz Rzepka - Design Engineer on becoming Ph.D. Eng.

Dissertation topic: Development of the microstructure of two-layer connection of turbocharger’s housing made of iron alloys under the influence of thermo-mechanical stresses


Based on the analysis of literature data on the issue of producing a two-layer connection of materials, a research hypothesis was adopted about the possibility of its manufacturing in the turbocharger’s bearing housing during the casting process. The goal was to increase the resistance of its material to fatigue cracking in conditions of increased thermomechanical stresses and elevated temperature.

A numerical simulation process was carried out for the operating conditions of the turbocharger system with a bearing housing with a two-layer connection of heat-resistant materials adopted in the housing flange design. On its basis, a double-layer combination of EN-GJL-250 (liquid state) + GX40CrNiSiNb25-20 (solid state) and EN-GJL-250 (liquid state) + GJS-XSiMo5-1 (solid state) were adopted.

Obtained results of conducted model connection tests and literature data indicated the necessity of introducing the decarbonization process of the surface layer of ductile iron GJS-XSiMo5-1 before the casting process to produce a two-layer connection. The developed decarbonization process ensures a specific value of the difference in carbon content in the materials forming the double-layer connection: EN-GJL-250 (liquid state) + GJS-XSi    Mo5-1 (solid state).

In subsequent research tasks, experimental tests were carried out to produce castings with a two-layer joint with dimensions similar to the bearing housing casting. The conducted tests indicate a change in the width of the transition zone of the two-layer connection depending on the conditions of the casting process (pouring temperature of EN-GJL-250 liquid cast iron, the soaking temperature of the GX40CrNiSiNb25-20 cast steel insert or GJS-XSiMo5-1 cast iron and the value of the mass ratio of solid material and liquid - insert and cast iron).

For the two-layer joints produced in the casting process, tests of mechanical properties - thermal fatigue resistance test and static tensile test - were carried out. The analysis of the research results is the basis for the statement that the obtained strength properties were achieved for the developed conditions of the casting process for the production of a two-layer joint cast iron EN-GJL-250 (liquid state) + cast steel GX40CrNiSiNb25-20 (solid state - insert). The predicted strength properties were not obtained for a two-layer connection: EN-GJL-250 cast iron (liquid state) + GJS-XSiMo5-1 cast iron (solid state - insert).                                                                                             


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