W.Y. Jang

Damping mechanism and application of Fe-Mn based alloys

Abstract The damping mechanism and its application in Fe-Mn based high damping alloys are studied in this work. The mechanism of damping capacity is proposed by correlating it with the microstructure, which is varied through changes in grain size. The Fe-Mn based alloys are successfully applied as a part of a stone cutter, reducing the noise by 10–25 dB.

Mechanical Properties and Microstructure Observation with Grain Refinement in CuZnAl Alloy

A small amount of misch metal was added to CuZnAl alloy in order to study the effect of grain refinement and mechanical properties, phase transformation behavior and stabilization of martensite. It was found that the addition of misch metal was very effective for reducing the grain size. The coarse grains over 1000 μm have been refined to the size of 30 μm by the addition of 0.43wt% misch metal. The grain size of thermo-mechanically treated alloys was barely affected by cold working. The fracture strength and ductility have been significantly increased with the increase of misch metal content when tensile test is carried out below Mf temperature. Also, the fracture strength has been more increased in the case of post-quench ageing treatment than the direct quench ageing treatment. The fracture mode has been changed from transgranular brittle fracture to ductile fracture with void formation and coalescence by the addition of misch metal.

Improvement of Actuating Properties of a SMA Coil Spring by Change in Coil Orientation

The present authors have invented a new method of changing coil orientation of a coil spring. The major merit of coil orientation change for SMA are reduction of space and control of two way shape memory effect. For instance, when a coil is heated above Af temperature with a load, the coil contracts. There is unrecovered strain which is attributed to elastic deformation by the load. The elastic strain can be eliminated by changing coil orientation. By removing elastic strain, the necessary space can be reduced. Besides generation and control of two way shape memory effect is presented using the reverse of coil orientation.

Effect of Aging and Microstructure on Mechanical Rolling CuAlNi Shape Memory Alloy

CuAlNi shape memory alloy with Cu-13.5Al-4.5Ni(wt%) composition was prepared by cross-rolling method and the aging effect, phase transformation characteristics, microstructural variation were investigated. Transformation temperature was greatly increased in aged specimens at 250°C. Transformation temperature was not changed after the second reversed transformation, and Ms point was same in most specimens with third reversed transformation cycle. The variation of Ms point was not seen with aging at 100°C, but it was decreased with aging at 250°C. Transformation temperatures appear to be constant, to an measurable extent, in specimens prepared by both hotrolling and cross-rolling at 900°C. Plate shaped-specimen with the thickness of about 1mm was prepared by cross-rolling treatment at 350°C. The transformation temperatures did not change after the second transformation-reverse transformation cycling, and specially transformation start temperature was the same in most specimens experiencing third thermal cycle and thereafter. Undesirable tweed-like structure was observed in 250°C-aged specimen after a cross-rolling at 350°C. On aging the specimen prepared by cross-rolling, G.P zone was formed easier than that of γ2 phase. This phase was transformed to plate-like θ phase during aging.

New SMA Actuator with High Energy Efficiency and Quick Response

The main drawbacks of SMA actuators are a slow response and a waste of electric power. The power should be continuously supplied for SMA elements to remain in the austenite state until the actuator begins to move to the other position. The problems are more serious when batteries and thick SMA elements are used. We develop a new SMA actuator which consumes little energy and responds very quickly. The actuator consists of a specially designed bias spring structure, and two SMA elements which exert the force in opposite direction to each other. The bias spring, unlike a common spring which has one stable position, has two stable positions. A SMA1, for instance, contracts on heating by electricity, the actuator takes one stable configuration. No further power supply is necessary to maintain the stable position, providing enough time for the SMA1 to cool. When the other SMA2 is heated, it contracts with enough force to move the bias spring and to expand the already-cooled SMA1. Power supply stops immediately after the actuator takes the other stable configuration, causing power saving and quick response.

The Behavior of Phase Transformation Characteristics and Ageing on Alloying Method of CuZnAl Shape Memory Alloy

The effect of transformation temperature and phase transformation characteristics by alloying method of CuZnAl shape memory alloy with a small of misch metal and Zr contents were investigated. The addition of misch metal and Zr was very effective for reducing the grain size. After solution treatment, the specimens were post-quench aged or step quenched at 373K to 623K for variation of hardness value. It was found that the hardness value was very increased at 473K and 523K. The fracture mode has been changed from trans granular brittle fracture to ductile fracture with void formation and coalescence by the addition of misch metal and Zr. Ageing of the β-phase decreased the Ms temperature, but that of the martensite phase increases the As temperature. The change in As temperature with post-quench aging can be attributed to recovery of order in the β-phase.

The influence of Ti and Ni additions and thermal cycling on the martensitic transformation in Cu-Zr alloys

The effects of Ti and Ni additions and thermal cycling on the martensitic transformation were investigated in Cu50Zr50-X, Cu50Zr50-XTiX and Cu50-XZr50NiX alloys by calorimetry. The Ms temperatures strongly decreased upon substitution of Ti for Zr, while it increased upon substitution of Ni for Cu in binary Cu50Zr50 alloys. When the alloys were thermally cycled, the transformadon hysteresis in all the alloys became wider, Ms decreases and As increases. With increasing number of cycles, the heat flow measured during the forward and reverse transformadon is reduced and the martensitic transformation with wide hysteresis disappears while another type of martensidc transformadon appears. Ms temperatures of this second transformadon are -10.2°, -34.9° and -15.5° in Cu50Zr50, Cu50Zr48.1 Ti1.9 and Cu47 7Zr50 2Ni2.1 alloys, respectively. This new type of martensitic transformation has small hysteresis(δT≈≡10°) and the transformation temperatures of it remain constant during cycling.