Influence of process factors on shape memory effect of CuZnAl alloys

Thermal cycle training of CuZnAl shape memory alloys with differenttransformation temperatures was carried out. The influence of different pre-strains, heat treatmentsand media on the shape memory effect(SME) of CuZnAl alloys with different transformationtemperatures was studied by means of scanning electron microscopy(SEM) and X-raydiffractometry(XRD). Experimental results show that despite respective variation in heat treatment,medium and cycling number, the recover}'' rate always decreases as pre-strain increases. The declineis obvious when pre-strain is less than 2.6 percent but not so sharp when pre-strain exceeds 2.6percent. Larger pre-strain results in more than one slip system and causes intercutting of themartensite strips among martensitic variants, then leads to the decline of SME. The SME of alloyswith transformation temperatures below 347 K is larger than that of alloys beyond 361 K by 20percent - 40 percent. The recovery rate of two-step aged alloy is higher than that of step-quenchedalloy by 20 percent - 25 percent. During thermal cycling, the recovery rate in oil is better thanthat in water.

First Cycle Effect of Polycrystalline CuZnAl Shape Memory Alloy during Thermal-Mechanical Cycling

The thermal-mechanical (T-M) cycles at constant strain of a polycrystalline CuZnAl alloy have been studied in the. present work. In-situ optical microscopic observations have been made to reveal the features of the phase transitions during T-M cycling. The variation of stress-temperature (S-T) curves and electrical resistance-temperature (R-T) curves accompanying with T-M cycling have been measured by tensile test and electrical resistance measurements. It has been found that the polycrystalline CuZnAl alloy shows apparent morphology changes and properties variations in the first cycle during T-M cycling which is called the first cycle effect in the present work. The stable transformation procedure in the T-M cycle is: martensiteparent phase +residual acicular martensite. This residual martensite possesses the character of stress-induced martensite.

Damping performance of Cu-Zn-Al shape memory alloys in engineering structures

The stress strain curves of two CuZnAl shape memory alloys which have the martensitic transformation temperatures of 50 ℃ and -10 ℃ respectively, were measured by using electronic material tester after treated by different heat-treatment conditions. The results show that the area enclosed by hysteresis loop of the CuZnAl shape memory alloy in martensitic state is much larger than that of the alloy in austenitic state with super-elasticity at room temperature. Therefore, the former has better vibration attenuation effect. After being oil-quenched, water-quenched, and step-quenched, the CuZnAl alloy takes on more stable shape memory effect,better super-plasticity and superelasticity (pseudoelasticity). A CuZnAl shape memory alloy damper was designed, produced and installed to a 2-layer frame structure. In addition, the vibration experiments were made by dynamic data collecting analysis meter. The velocity of vibration attenuation of frame structure with CuZnAl shape memory alloy damper is much faster than that without it. And with the help of CuZnAl shape memory alloy damper, the attenuation period reduces to 1/10 of the original.

DRY SLIDING WEAR OF Cu-BASED SHAPE MEMORY ALLOY

The wear of Cu-based CuZnAl shape memory alloys under dry sliding against steel was found to be plasticity-dominated,with adhesion and delamination being the two main mecha- nisms.Adhesion was found to be accompanied by metal transfer.TEM observation on tensile test of thin foil showed that the stress-induced martensitic transformation occurred from β-phase in the vicinity of pre-existing microcracks.The blunt effect of crack tips may be proposed to explain the wear of CuZnAl shape memory alloy due to preferential orientation reaction of variants in martensite and stress-induced martensitic transformation in β-phase.