ОБРАЗОВАНИЕ МАРТЕНСИТА 14М В МИКРОКРИСТАЛЛИЧЕСКИХ СПЛАВАХ НА ОСНОВЕ Ni-Al

Abstract

Ni-Al alloys are considered the materials with high-temperature shape memory effect. However, being in coarse-crystalline state, Ni-Al alloys have low ductility. By performing grain refinement, it is possible to improve the alloys ductility. For example, it is possible to use the ultrarapid crystallization on revolving drum. The grain refinement will cause the structure dispersion. In this paper, the authors made an attempt to detect a 14M martensite in Ni-Al alloys - Ni 62,5 Al 37,5 , Ni­­ 64 Al 36 , Ni­­ 65 Al 35 and Ni 56 Al 34 Co 10 (at. %) - produced by melt spinning on the revolving steel drum. Tape samples having thickness of 30 µm and the grain-size of 0,5–4 µm were produced in the result of rapid crystallization. Using the resistometric measurement, the authors determined the temperatures of the direct and the reverse martensitic transformations in all alloys under examination. The authors could determine the martensitic transformation temperatures in Ni­­ 65 Al 35 and Ni 56 Al 34 Co 10 alloys only with the help of rapid heat at the rate of 75 ºС/min, as during the slow heat at the rate of 1–5 ºС/min the maraging with the А 5 В 3 (Ni 5 Al­ 3 ) type phase takes place, which causes the loss of martensitic transformation reversibility. The alloys’ structure is studied with the help of transmission electron microscopy. At room temperature, Ni­­ 62,5 Al 37,5 alloy stays in metastable austenitic condition with B2 lattice and Ni­­ 64 Al 36 , Ni 65 Al 35 and Ni 56 Al 34 Co 10 alloys go through martensitic transformation. The structure in Ni 65 Al 35 and Ni 56 Al 34 Co 10 alloys consists of plate martensite depleted of inner fine-scale twinning, whilst the Ni­­ 64 Al 36 alloy structure consists of thin-plate martensite and retained austenite. According to the microdiffraction data, martensite in three alloys is recognized as martensite with L1 0 lattice. Using the radiographic analysis, the authors determined in Ni­­ 64 Al 36 and Ni­­ 65 Al 35 alloys a small amount of 14M martensite as well as the major martensitic L1 0 phase and the retained austenite.