Compared to other CMC manufacture procedures, like CVI and LPI/PIP, the LSI process offers significant economic and technological advantages:
The LSI process, well known for the manufacture of C/C-SiC materials and structures, has been transferred to the manufacture of novel, biomorphic SiSiC materials and structural components. Either commercially available, wooden preforms, like medium density fiber boards (MDF), or wood based composites, developed and manufactured at DLR, are used as raw materials. After the pyrolysis of the wooden preforms a highly porous C preform is obtained, which is infiltrated with melted SI in the last process step. Thereby the carbon is converted almost completely to SiC and the remaining porosity is filled with SI leading to a dense SiSiC material. Due to the fact that the shrinkage occurs exclusively during pyrolysis and there is no change in geometry during siliconization, very filigree, complex shaped and even large sized structures can be manufactured in near neat shape technology. Additionally, very complex structures can be realized with a special in situ joining technology.
At DLR, the basis for the reliable and reproducible manufacture of C/C-SiC materials and components is an extensive quality assurance system, consisting of the income inspection of all raw materials, a detailed job traveller for each individual part, the investigation of materials and components as well as the documentation of all relevant process parameters after each manufacturing step. For the investigation and qualification of components, defined test procedures for non-destructive testing (air and water-coupled ultrasonic, computer tomography, lock in thermography, photogrammetry) are available.
Current development focuses on: