DAMPING PROPERTIES OF MARTENSITE AND MARTENSITIC TRANSFORMATION IN CuZnAl ALLOYS

The internal friction of alloys in martensite state is believed to be an M/M interface one, which can be explained by an expression deduced from the theory of dislocation internal fric- tion.The internal friction during martensitic transformation consists of two parts,including those of the M/M interface and of the phase transformation.The latter is further composed of two portions,the major one produced by reverse martensitic transformation and the other from stress-induced martensite.It was also found that the degradation of damping properties of the CuZnAl alloys is related to the dislocation,which is introduced from the exciting pro- cess,and tends to be of stable value after certain excitements.

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.

ENFLUENCE OF DEFORMATION AT MARTENSITE STATE ON SHAPE RECOVERY IN CuZnAl MEMORY ALLOYS

An investigation of the influence of deformation on shape recovery has been put forward in Cu-Zn-Al shape memory alloys.Starting at a model of the re-orientation of martensitic va- riants,the principle and essentiality of the influence of the amount of pre-deformation ε on shape recovery rate η is elucidated.

CuZnAl Shape Memory Alloy Refined with Composite Rare Earths La+Ce

The effects of composite rare earths La+Ce on properties of CuZnAl shape memory alloys were studied bymetallograph examination, tensile and bending tests, electric resistivity measurements, EDS and SEM. The test resultsshow that the grain size of CuZnAl shape memory alloys could be diminished effectively and the mechanical propertiesimproved obviously by the addition of composite rare earths La+Ce (La: Ce=1: 1). Meanwhile, the excellent shapememory properties remained unchanged. The results of microanalyses indicate that the composite rare earths were segregated at grain boundaries and impeded the grain growth, leading to the improvement of the mechanical properties ofCuZnAl alloys. If the amount of composite rare earths La+Ce was greater than 0. 10%, the shape memorial propertiesbecame poor.

Isothermal Aging Kinetics in CuZnAl Shape Memory Alloy

Isothermal aging behaviours of a CuZnAl shape memory alloy have been investigated by means of dilatometry.The length of the specimens during isothermal aging from 190 to 280℃ increases with the aging time at each temperature.The isothermal aging kinetics fits in Avrami equation and the time exponent n decreases with the increase in aging temperature.The apparent activation energy for the isothermal aging process was measured to be 109.0kJ/mol,which is about equal to that of a relaxation internal friction peak at about 200℃ (f≈1 Hz) in the alloy.

FINE STRUCTURE VARIATION OF 18R MARTENSITE UNDER DEFORMATION IN POLYCRYSTALLINE CuZnAl AI JOY

The transmission electron microscopy has been used to investigate the fine structure variation of 18R martensite under deformation in a polycrvstalline CuZnAl shape memory alloys.It has been found that the strain is gabined by the reorientation of martensite variants in the ini- tial deformation stage.In addition to the result of optical microscopy studies,however,the reorientation is often incomplete and the interfaces among the prior variants still remain.A lot of twins will appear in martensite under enormous deformation,and the twin plane is(001) phane of martensite lattice.The dislocations has also been observed in some regions.In this case,the martensite will lose its thermoelasticitv and the shape memory effect will be damaged.

INFLUENCE OF GRAIN SIZE AND ORDERING DEGREE OF PARENT PHASE ON SME IN A CuZnAl ALLOY CONTAINING BORON

The influence of grain size and ordering degree of the parent phase on the shape memory re- covery in a Cu-25.62Zn-3.97Al-0.0018B(wt-%)memory alloy is investigated.A mathematical relationship is set up between the recovery ratio and ordering degree,probabili- ty of atoms at their ordered sites,grain size,the thickness of the grain boundary affected re- gions,the stress during deformation,as well as the critical shear stress.Shape memory effect reaches a maximum with varying grain size and increases linearly with increasing ordering parameter,which agrees well with experimental results.

Relationship between Relaxation Internal Friction Peak at about 200℃(f≈1Hz)and Bainitic Transformation In a CuZnAl Alloy

The present investigation showed that the re- laxation peak at about 200℃ (f≈1Hz) was related to bainitic transformation in a CuZnAl alloy.The peak decreased when bainite precipitated.The activation energy of the peak was the same as the apparent activation energy of bainitic transforma- tion.According to the relations between the peak and the bainitic transformation,the mechanism of the peak has been discussed.

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.

Influence of α Phase on Shape Memory Effect and Superelasticity of CuZnAI Alloy

The influence of a small amount of α phase in β′ matrix on shape memory effect and superelasticity of CuZnAl shape memory alloy has been studied systematically.It has been found that transformation temperature can be adjusted in a large scale by controlling the amount of α phase, meanwhile,shape memory effect and superelasticity do not decrease obviously when there exists a small amount of α phase.Based on the optical and trans- mission electron microscopy observation,the influ- ence of α phase on shape memory effect and superelasticity has been discussed.

Internal Friction in a Shape Memory Alloy Cu-Zn-Al under Equilibrium Condition

1. Introduction CuZnAl shape memory alloys have beenextensively studied as a new type of material.Dejonghe[1]et al. firstly reported theirresults on the internal friction (IF) of CuZnAlalloys in 1975. Later, some researchershave done much work on internal friction.But most of them were concerned withphase transformation internal frictionof martensite and reverse martensite andfew of them were about internal friction

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.