COMPRESSION TESTING OF QUASI-CRYSTALLINE MATERIALS

Mechanical compression tests were applied to a few alloys, either truly quasicrystalline or made of approximant, crystalline phases with large unit cells. Al-Cu-Co-Si,Al Cu Fe Cr Si-(B) and Al-Cu-Fe-(B) alloys are brittle materials at low temperature but they show high plasticity at temperatures beyond 625-650-degrees-C. In Al63Cu17.5Co17.5Si2, more than 30% of volumic porosity was found in the samples after compression testings at T > 700-degrees-C or after heating and cooling from T > 700-degrees-C with a rate 5-degrees-C min-1. The implication of pore formation in the high plastic behaviour is pointed out. For the Al-Cu-Fe-Cr-Si alloys, the prismatic single crystals show signs of anisotropic mechanical properties along the tenfold and twofold directions, respectively. Small amounts of boron addition modifies the structure of the Al-Cu-Fe-Cr-Si and Al-Cu-Fe alloys and markedly enhances the fracture strength of the materials. The structural modifications are discussed.