Binary Si-Al Controlled Expansion (CE) Alloys for Use in CTE Mismatch Thermal Stress Reduction Applications

The coefficient of thermal expansion(CTE) mismatch between two bonded components gives rise to stresses proportionate to the change in temperature, therefore CTE is a critical property of materials to be used at extreme temperatures. By using materials with similar CTE values this effect can be minimised. CE alloys have performance benefits over conventional alloys and ceramics typically used for these applications. CE alloys are up to 10% lighter than even pure aluminium, have a high thermal conductivity up to 180W/mK, are electrically conductive, have excellent thermo-mechanical stability from 500°C down to cryogenic temperatures and a tuneable CTE between 5 and 17ppm/°C.

The Si:Al ratio is varied to achieve the range in CTE, the usual embrittlement of high silicon aluminium alloys is avoided by using a rapid solidification method to achieve a fine, isotropic structure, giving the alloys extremely homogenous mechanical and thermal properties.

CTE, thermal conductivity and mechanical properties are measured at cryogenic temperatures to demonstrate the performance of CE-alloys in space and astronomical instruments. These investigations show that CE-Alloys offer a machinable, light-weight, thermally stable, high stiffness alternative to conventional materials. All alloys exhibit good thermal conductibvity at low temperatures and this can be readily enhanced with Au plating for extreme environments.