Examiner/supervisor: Uta Klement, IMS
Opponent: Hannah Karlsson
Thermal spraying is a widespread method for applying coatings on top of a material to enhance, protect or add certain properties. Conventionally, radial loading has been the norm in industry. However, recent studies have shown favorable results when axial loading has been used instead. As the standard has been to use one feedstock, often in powder form, an interesting area to explore is the effect of adding a supplementary feed during the coating process. Thus, this thesis has studied the influence of adding an additional, simultaneously sprayed, suspension feed during the spraying process, hence spraying with a hybrid powder-suspension, in an axial setup. Additionally, the influence of the spray distance on the coating and the effect of adding different amounts of hBN wt% in suspension feed have also been examined. HVAF and APS were the applied coating techniques with NiCr-Cr3C2, Cr2O3, water and hBN used as the feedstocks. Results show that when spraying NiCr-Cr3C2 powder together with either a water or hBN suspension feed in a HVAF setting, more delaminations occur. There are also more rough particles embedded into the coating when a liquid feed has been added to the spraying process. Two different NiCr and CrC phases are produced for all of the NiCr-Cr3C2 containing coatings, a Ni rich phase and a Cr rich phase. All NiCr-Cr3C2 sprayed coatings show a homogeneous distribution of the phases with both fine and globular pores in the coating. Cracks in the different phases can also be seen, especially in the CrC phase. SEM imaging of Cr2O3 sprayed coatings together with a 5% hBN suspension feed in an APS setup, reveals that varying the spray distance between 100 – 130 mm influences the topography and microstructure of the coating. When a shorter distance is applied, bumps on top of the coating are formed with a higher pore content underneath them as well as larger vertical or diagonal cracks in the coating. All Cr2O3 sprayed coatings show a homogeneous distribution with a laminar microstructure containing a mixture of fine and globular pores embedded into the coating. For all hBN sprayed coatings, only small amounts of hBN could be detected by SEM/EDS.
Student project presentation
01 June, 2020, 13:00
01 June, 2020, 14:00