Phase transition and internal friction behaviors in Mn-doped Co-V-Ga shape memory alloys

Shape memory alloys with a high abundance of mobile interfaces exhibit remarkable internal friction () behaviors, which can be utilized for the reduction of noise and vibration. In this study, we systematically investigate the martensitic transformation and internal friction behaviors in the Mn-doped CoVGaMn ( = 0 - 10) polycrystalline alloys. Our findings indicate that using Mn to replace V results in decreased transformation temperatures but increased thermal hysteresis. The addition of Mn enhances magnetic exchange interaction, leading to a gradual enhancement in magnetization difference across martensitic transformation, thereby compromising the transformation entropy change and arresting the martensitic transformation. At a frequency of 0.4 Hz, the intensity of transformation peak is enhanced from 0.124 to 0.178 with increasing the Mn content from 0 to 4.5 %, as a result of deteriorated geometrical compatibility between austenite and martensite due to the addition of Mn. Furthermore, hydrogenation treatments substantially improve both the peak intensity and frequency dependence of peak position for the relaxation-type , demonstrating the great contribution from hydrogen-twin boundary interaction.