In this paper, the internal friction (IF) signal of some NiTiCu-Y based samples was analyzed by the isothermal method together with the model of Delorme and Gobin and three main IF components were identified: the transient term, IFTR, the intrinsic term, IFINT, and the phase transition term, IFPT. It was found that IFTR follows the path of the phase transition and it helps in the estimation of the martensite finishing temperatures. Besides, IFINT is useful in the evaluation of the finishing transition temperatures in isothermal condition. Finally, by the study of the internal friction of austenite and martensite single phases, it was found that IFPT exponentially grows with Yttrium content. (C) 2016 Elsevier B.V. All rights reserved.