Internal Diameter Coating Processes for Bond Coat (HVOF) and Thermal Barrier Coating (APS) Systems

Abstract

Current developments in different industrial sectors show an increasing demand of thermally sprayed internal diameter (ID) coatings. The most recent research and development is mainly focused on commercial applications such as arc spraying (AS), atmospheric plasma spraying (APS), and plasma transferred wire arc spraying, especially for cylinder liner surfaces. However, efficient HVOF torches are meanwhile available for ID applications as well, but in this field, there is still a lack of scientific research. Especially, the compact design of HVOF-ID and APS-ID spray guns, the need of finer powders, and the internal spray situation leads to new process effects and challenges, which have to be understood in order to achieve high-quality coating properties comparable to outer diameter coatings. Thus, in the present work, the focus is on the ID spraying of bond coats (BC) and thermal barrier coatings (TBC) for high-temperature applications. An HVOF-ID gun with a N 2 injection was used to spray dense BCs (MCrAlY) coatings. The TBCs (YSZ) were sprayed by utilizing an APS-ID torch. Initially, flat steel samples were used as substrates. The morphology and properties of the sprayed ID coating systems were investigated with respect to the combination of different HVOF and APS spray parameter sets. The results of the conducted experiments show that the HVOF-ID spray process with N 2 injection allows to adjust the particle temperatures and speeds within a wide range. CoNiCrAlY bond coats with a porosity from 3.09 to 3.92% were produced. The spray distance was set to 53 mm, which leads to a smallest coatable ID of 133 mm. The porosity of the TBC ranged from 7.2 to 7.3%. The spray distance for the APS-ID process was set to 70 mm, which leads to a smallest coatable ID of 118 mm.

Metal Droplet Deposition: From Foundation to Engineering Manufacturing

“…Tillmann et al prepared conical bonded coatings with porosities of 3.09–3.92% using a high‐velocity oxygen‐fuel (HVOF) gun with N 2 injection. [ 89 ] Verma et al prepared a bonded coating of NiCr and Al 2 O 3 on an aluminum alloy substrate using a thermal‐spray process. They investigated the effect of coating thickness on thermal fatigue.…”

A Critical Review of Coating on AISI 1045 Steel Substrate by High Velocity Oxygen Fuel (HVOF)

“…A minor drawback of AISI 1045 is that, unlike other medium carbon steels, it does not sustain complete hardening except for short parts of up to 60 mm. Surface treatment technologies have been the subject of extensive investigation for decades for AISI 1045 to enhance mechanical properties by thermal spray coating [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16],plasma arc cladding [17],electron beam cladding [18],tungsten inert gas arc cladding [19 22], laser beam cladding [23][24][25][26][27] and other surface modification methods.In order to apply the required coating, the HVOF process employs a mix of heat and kinetic energy to melt and accelerate powder particles. In the production of coatings, combustion and gas dynamics are crucial.…”

Surface Remelting of Mold Inserts Made of NC11 Steel

“…Extending the life of new machine parts is mainly by means of the use of new expensive materials and alloys and their heat treatment [9][10][11][12][13]. Repair of damage or the regeneration of parts of machinery worn as a result of operation usually involves supplementing the damaged area using powder spraying techniques or 3D printing [14][15][16][17][18]. The present authors' experience in the area of the local hardening of alloys with the use of a concentrated heat stream enabled them to advance the conclusion that, with the use of a laser beam, it would be possible to locally alter the microstructure of NC11 steel, increasing its hardness in comparison to the initial material, and thus extending the service life of the mold inserts [19][20][21][22].…”