Study On Damping Capacity And Mechanical Properties Of The Mn-Rich MnNi Based Alloys

The ?Mn based alloys are new functional materials, which get wide attention for their antiferromagnetism, shape memory effect and damping characteristics. As the typical ?Mn based alloys, their antiferromagnetic transition and martensitic transformation would happen in Mn-rich MnNi based alloys under certain conditions,but their structure transformation is complicated. In this research, we studied damping capacity and mechanical properties of the Mn-rich MnNi based alloys by X-ray diffractometer, thermal expansion analysis, differential scanning calorimetry,metallographic observation, internal friction test and mental compression test. Effects on addition of alloy elements and aging treatment have been explored to the alloys.The results show that Mn80Ni20-x Cux(x=0,5,10) alloys have high damping capacity above room temperature and pseudoelasticity at room temperature. High damping is derived from the antiferromagnetic transition and martensite phase transition. Addition of copper reduces antiferromagnetic phase transformation temperature and promotes the occurrence of martensitic transformation. With increment of Cu contents, antiferromagnetic transition internal frition peak closes to or tightly coupled with martensitic transition internal frition peak, which improved the alloys' damping capacity; And the recovery strain increase remarkably under the circle stress, the alloys' pseudoelasticity improves too. Mn80Ni10Cu10 have both excellent damping capacity and pseudoelasticity, with the Q-1 reach 3.6×10-2, the recovery strain reach 5.73%, and the recovery percentage reach 92.12%.Aging treatment has a great influence on Mn80Ni20 alloy's microstructure and properties. Experiment results show that after 3~9 hours of aging at the temperature of 480? then water quenching, martensitic transformation occurred in samples. With extension of aged time, martensitic transformation temperature haven't changed much,but the quantity of martensites increase in alloys, the damping capacity is improved;And the recovery strain increase in compression test, the alloys' pseudoelasticity is greatly improved. After aging 12 hours, ?-Mn phase separates out in the alloy. The?-Mn phase hinders the movement of martensites, and makes the recovery straindimimish. Both of the damping capacity and pseudoelasticity reduce. Mn80Ni20 have both excellent damping capacity and pseudoelasticity when aged 9 hours.Addition of Fe element leads to crystal lattice distortion in the matrix of Mn80Ni10Cu10-x Fex(x=2,4) alloys, and the distortion degree exceed 0.5 percent, the fcc?fct martensitic transformation has been triggered, and antiferromagnetic transformation temperature is reduced markedly. The alloys' damping capacity is sensitive to Fe element. Firstly, the damping capacity is quickly reduced with lattice distortion which is caused by Fe addition, then, antiferromagnetic transition internal frition peak tightly coupled with martensitic transition internal frition peak when Fe content is 4 at. %, the damping capacity increases rapidly.