Base Material Compatibility Issues

Establish competitive bid vendor contracts to identify conceptual designs and materials of construction and have vendors initiate small scale coupon fabrication and testing to identify fabrication and material compatibility issues with a focus on braze fin integrity. Identify accelerated testing to ensure braze base metal compatibility and fin and braze interface strength over mission life. 

Ceramic materials are lightweight and have low thermal conductivity. However, at elevated operating temperatures, radiation contributes significantly to the total heat transfer through the ceramic foam, because most ceramics are partially transparent to radiation Thus, the heat transfer would be higher than expected based on ceramic foam s room temperature thermal conductivity alone. Cochran et at concluded that muliite and alumina foams made from spheres had low thermal conductivity values at low temperatures, see Reference 9- 80 Additional potential problems include material compatibility issues and mechanical properties... 

Some factors that may arise include whether the match is being made to solvent or water based material. In certain instances the component cannot be painted in a water based system as is the body of the automobile. This can be a tough issue if the standard is also not created in the same system and has never been tested for that type of technology compatibility. 

The combination with fibres has proved difficult however. Often there are issues with compatibility between bio-resins and fibres (both natural and synthetic), which cause defects in the composite structure and ultimately poorer physical properties. Castor-oil polyurethane was compared with phenolic resins when infused over sisal fibres however, the phenolic resins showed better structural performance when compared with the castor oil-based material [52]. This is not always the case, as some improvements have been made. Soybean oil thermoset polymers were used in a glass/flax hybrid composite resulting in improved mechanical performance [73], Thermoset resins were produced from triglyceride oils with a wide range of properties (tensile modulus 1-2 GPa, glass transition temperature Tg 70-120 °C) and glass- and hemp- fibre composites were manufactured [74,75]. 

While most base materials comply with the RoHS directive, the question of compatibility with lead-free assembly processes is a more complex issue.The material properties that are important for lead-free assembly compatibility include ... 

Probe fouling and corrosion are probably the biggest issues associated with probe optics. These issues have been discussed previously. When corrosion is the problem, it is usually because of a poor material choice or a suitable material compatible with the design of the probe is not available. Some materials are so aggressive that they even slowly attack the very process pipes of which the plant is made. Process applications based on these types of materials normally require the plant operations staff to provide some level of continuous preventive maintenance to the process structure itself, thus refurbishing a probe head or probe optic presents in little additional concern. 

The effects of microstructural phase stability and braze/base metal compatibility over a 20 year life on material properties has not been fully investigated or incorporated into the design for the Ni-base superalioy materials being considered for the recuperator. Hamilton Sundstrand had planned on long term braze sample tests to better address this issue. 

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