Studying Of The Transformation And The Relevant Effects In The Cu-based Shape Memory Alloys

The thermal stability of the Cu-based Shape Memory Alloy(SMA),including the abilities of martensite stabilization resistance, parent phase decomposition resistance and thermal cycling weakening resistance, has been studied by means of electrical resistance vs temperature ( P -T) curve and shape memory effect as well as mechanical properties measurement, X-ray diffraction, TEM / SEM and optical observation. A ways for solving the problem has been put forward. On the basis of it, a new type of Cu-24Al-3Mn alloy, which has high resistance to martensite stabilization, parent phase decomposition and thermal cycling weakening, has been designed. A new type of elasticity-damping composite has been manufactured using the Cu-24Al-3Mn alloy and QBe2 alloy by explosion cladding, and equipped on the new type of xxx-weapon. In addition, Cu-18.4Al-8.7Mn-3.4Zn-0.1Zr alloy, another new type of SMA, with wide transformation hysteresis, good cold-working, high reversibility and low price has been designed. The deformation condition to generate wide transformation hysteresis and high reversibility of the stress-induced martensite in the alloy has been studied. Using this alloy, the wide transformation hysteresis shape memory pipe coupling has been manufactured and applied to the MEILING refrigerator. The results are as follows:1. In order to set a pace for the martensite stabilization effect, the Cu-13Zn-15Al (at%) alloy with high Ms( 200 C) has been studied. The air-quenched martensite structure of the alloy is M18R and its lattice parameters are as follows: a=0.4422nm, b=0.5329nm, c=3.818nm and B= 88.8 . The atoms distribution on the basal plane of the martensite is as follows: I : 15/25 Al +10/25 Cu II :Cu s III: 13/25Zn+ 12/25 Cu. For the air-quenched alloy, the martensite stabilization is easy to occur. The martensite stabilization is accompanied by (1)AS increasing;(2) the electrical resistance of martensite abnormally increasing; (3) the abnormal re-relief phenomenon emerging;(4)the reverse shape memory effect occurring;(5)12lM, 20lm and 04lM, 32lM diffraction pairs of the martensite tending to get closer, the d-value of 0018M diffraction increasing, the martensite parameter aand c increasing, b decreasing, a/b -0.866, the monoclinic angle B- 90 .2. The similarity of macro-effects between the martensite stabilization (items of (2)?(5)) and martensite transformation (B1-M) has been studied. The crystallography model of the martensite stabilization has been established, the nature of the martensite stabilization is the transformation of M18R-N18R which coexists with the character of diffusion and shearing transformation. The tendency of the disordering of the atoms on the basal plane is caused by diffusion, the abnormal re-relief and the reverse shape memory effect are caused by shearing.3. The reversal transformation of the stabilized martensite is studied in details. This process is different from that of the thermoelastic martensite. The latter relies on the movement of the B1/M boundary. The former relies on the orientational re-nucleation and growth of the parent phase in the martensite variants. Although this process is incomplete, it can generate the forward shape memory effect.4. The structure stability of the B1 parent phase in Cu-13Zn-15Al alloy is poor. The B1 parent phase decomposes into B and a phases immediately when it is transformed from the stabilized martensite. This process takes place inside the stabilized martensite variants, and it leads to the heredity of the decomposed structure. The decomposition product re-dissolves into B phase at the higher temperature. But re-dissolving sequence is different for the decomposition product at different place. The decomposition product around the boundaries of the stabilized martensite re-dissolves in the end. The B phase transforms into B1 parent phase and then into martensite during cooling, and the martensite grows along the orientation of former martensite before the decomposed structure heredity disappears. This results...