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The formation and phase transformation mechanism of eta and sigma phases in three experimental polycrystalline superalloys were studied. It was shown that a high (Ti + Al) content in the alloys would favor the formation of eta and alpha phases in the interdendritic region. Different as-cast microstructures resulted in different phase transformation processes during heat treatment and thermal exposure. Influence of eta and sigma phase on tensile properties had been investigated as well. The tensile properties of the alloys were sensitive to gamma' volume fraction of the alloys, as well as morphologies of eta and sigma phases in the interdendritic area. Formation of plate-like eta phase had negative impact on the low and intermediate temperature tensile properties of the polycrystalline superalloy. (c) 2009 Elsevier B.V. All rights reserved.