The thermal stability of the icosahedral phase(iphase) inTi45Zr38Ni17alloys is demonstrated. As-cast alloys containing initially only the C14 hexagonal Laves and &agr;-solid-solution phases transformed primarily to the icosahedral phase upon annealing in vacuum for 64 h at 570 °C. This confirms previous evidence fori-phase stability and firmly establishes this quasicrystal as the first nonaluminum stable icosahedral phase. Diffraction data show that this stableiphase is primitive; energy dispersive x-ray spectroscopy measurements place its composition nearTi41.5Zr41.5Ni17.These and other results suggest that the structure of thisiphase is similar to that ofi(AlLiCu). ©1997 American Institute of Physics.