Thermal protection layers

Thermal protection layers in space technology can be used among other things for re-entry technologies (see chapter 5.2.2) or for the thermal insulation of rocket engines. In a research project of the Fraunhofer Institute IWS, the technical university Dresden and the company Astrium, na-

nostructured heat-insulating layers for combustion chambers of cryogenic Thermal protection lay cooled H2/O2 engines, as typically used for Ariane rockets, were develo- ers for rocket engines ped and tested under relevant conditions. Concerning heat-insulating layers in rocket engines, high demands are made with regard to temperature stability, strain tolerance and adhesion strength. The manufacturing process must allow to produce an interior coating of the relevant components, exhibit high precision and reproducibility, as well as ensure a small temperature loading of the substrate material (Gawlitza 2002).

As a solution for this, the PLD (pulse laser deposition) procedure allows to combine laser ablation and laser evaporation and thus to obtain a broad layer thickness range (from 1 nm to 100 pm). The PLD procedure ensures low temperatures during deposition and a multiplicity of target materials can be used. Thus gradient layers with different functionality can be produced (adhesion layers, effect layers, sealing layers etc.), which can be adjusted to the respective load profile.

The principle of the interior wall coating by means of PLD procedures, a schematic layer structure and a REM image of a cross section of a heat-insulating layer manufactured with PLD are represented in the illustration 13. Present development activities concentrate among other things on the interior coating of ceramic combustion chamber structures (CMCs) with high temperature-stable corrosion protection layers.

Tafgei

Sub¬ętrat

Sub¬ętrat

sealing: amorphous ZrO2

^ effect layer -columnar ZrO, sealing: amorphous ZrO2

^ effect layer -columnar ZrO, amorphous ZrO2 Metallic adhesion layer Cu-substrate amorphous ZrO2 Metallic adhesion layer Cu-substrate

Illustration 13: PLD-process for the production of nanostructured heat-insulating layer for combustion chambers in rocket engines, above: principle of interior wall coating with PLD process; below: schematic layer structure and REM image of a heat-insulating layer manufactured with PLD (source: FhG-IWS)

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