Papers by Author: Wen Ru Zhao

Abstract: NiMnCoIn alloys are new-type magnetic shape memory alloys (MSMAs) in which a reversible magnetic-field-induced phase transformation was observed. They are ideal candidates of materials used in actuators and sensors. The polycrystalline NiMnCoIn alloys are generally brittle so that they can not be easily deformed into the shape applicable to actuators and sensors until now. In the present paper, the influence of hot deformation on the microstructure of Ni₄₅Co₅ Mn_36.7In_13.3 alloy was studied. The experimental results showed that second phase was observed after deformation at high temperature between 800~900 °C and at strain rate lower than 4×10^-3s^-1. The content of Co of second phase was higher than the matrix alloy, while the content of In was lower than the matrix alloy. It was determined by TEM measurements as γ phase with fcc structure which was popular in NiFeGa and NiMnGaCo alloys. It is possible to improve the ductility of Ni₄₅Co₅Mn_36.7In_13.3 alloy by control of amount and distribution of γ phase by hot deformation.

Abstract: In recent years, there has been an increasing interest in magnetic shape memory alloys (MSMAs) due to their unique ability to produce very large output strains and rapid response frequency. NiMnCoIn is a new-type MSMAs in which a reversible magnetic-field-induced phase transformation is observed. The microstructural evolution in the process of dynamic recrystallization in polycrystalline Ni45Co5Mn36.7In13.3 was studied in the present paper. The experimental results showed that the high deformation temperature and slow strain rate were necessary to achieve perfect dynamic-recrystallizing microstructure in Ni45Co5Mn36.7In13.3 alloy. Precipitates with two sizes were observed. The content of Co in precipitates was higher than that in the matrix alloy, while the content of In was lower than that in the matrix alloy.