NiTi合金中应力诱导的I/C相变及其界面动力学的研究

在改装了的拉力试验机上,以不同的拉伸速率ε(0.79—18×10^-5s^-1)进行加、卸载试验,并用中间扭摆和四端电位法同时测量了Ni-49at％Ti合金丝在应力诱导I/C相变过程的内耗Q^-1、模量M/M₀、电阻率ρ/ρ₀和应力-应变曲线。研究了应力循环和应变速率的影响。在Q^-1-ε曲线上出现Q^-1峰,而在f²-ε曲线上出现与之相对应的模量极小。内耗峰的高度Q_p^-1和模量亏损值均随ε增大而增大。根据界面动力学模型和内耗的实验数据,计算得应力诱导I/C相变过程界面的动力学关系为V=V^*(△G—△G_R)^m,V^*和m为动力学参数,△G_R为相变过程中运动相界面所受的阻力,计算得△G_R≈1cal/mol。讨论了内耗和模量亏损、软模效应之间的关系。关键词：

THE STUDIES OF STRESS-INDUCED I/C TRANSITION AND INTERFACE DYNAMICS IN NiTi ALLOY

The internal friction (IF) Q^-1, modulus f², electrical resistance R and stress s of superelastic Ni₅₁Ti₄₉ alloy in the process of stress induced incommensurate/commensurate (I/C) transition was measured as a function of strain e by a middle torsion pendulum on a tensile testing machihe modified with a four-terminal potential equipment.The effects of number of stress cycles and strain rate e (in the range of 7×10^-7/s to 1×10^-4/s) were studied. An IF peak and a minimum of modulus were observed respectively in the Q^-1-εand f²-εcurves. The IF peak height Q_p^-1 and modulus defect △M/M increase with an increasing of ε/ω, where ω is angular frequency of measuring. By utilizing an expression obtained from phase interface dynamics and experimental data of Q_p^-1 (as a function of ε/ω and amount of phase transition F), an explicit functional relationship of average I/C phase interface velocity V and effective phase transition driving force △G′= △G - △G_R (where △G_R is resistance) was derived as V =V^*(△G - △C_R)^m, where V^* and m are dynamic parameters an △G_R is a resistance force exerting on the moving interface, which has the order of 1 cal/mol for stress-induced I/C transition of superelastisity NiTi alloy. The relationship between Q^-1 and modulus defect △M/M and soft modulus effect are disussed.