Y. Huo
,
Y. Chen
,
X. Zu and M. Tu( Department of Metal Materials
,
Sichuan University
,
Chengdu 610065
,
China)( Department of Metal Materials
,
Sichuan University
,
Chengdu 610065
,
China)( Department of Metal Materials
,
Sichuan University
,
Chengdu 610065
,
China)( Department of Physics
,
Sichuan University
,
Chengdu 610065
,
China)
金属学报(英文版)
In this paper, a theoretical model was presented to simulate the stress-strain hysteresis and the inner hysteretic behaviors, which were observed for polycrystalline Ni-Ti and Cu-based shape memory alloys (SMAs) at various temperatures. It was assumed that the stress-strum hysteresis of the grains of a polycrystalline sample of SMAs was relatively simple and easy to be calculated. The texture of the sample was characterized by a distribution function, which could be obtained from the experiments. Thercfore,the model provided a means to simulate and, for the first time, to predict the stressstrain hysteresis at different loading temperatures for polycrystalline SMAs.
关键词:
shape memory alloys (SMAs); hysteresis; mathematical modeling of phase transition
Y.H.Wen 1)
,
N.Li 1)
,
Y.G.Xu 1)
,
M.J.Tu 1)
,
P.Q.Li 2)
,
Y.L.Liu 2) and Y.L.Ma 2) 1) Department of Materials Shaping and Controlling Engineering
,
Sichuan University
,
Chengdu 610065
,
China 2) Xi'an Petroleum Pipe Research Institute
,
Xi'an 710065
,
China
金属学报(英文版)
The effects of quenching temperature on shape memory effect and microstructure of Fe 18Mn 5Si 8Cr 4Ni shape memory alloy have been studied. The results show that both the shape recovery ratio and the recovery strain increased as quenching temperature increased, the amount of stress induced ε martensite in the process of cold work decreased with the increase of quenching temperature, the shape recovery ratio and the recovery strain reached maximum at 650℃, and then decreased rapidly with the further increase of quenching temperature,the stress induced ε martensite wholly disappeared at 1023K. But when the quenching temperature is higher than 1023K, the further increase of quenching temperature had little effect on shape recovery ratio, the amount and size of thermal induced ε martensite would increased with the further increase in quenching temperature. The shape memory effect can be improved by the moderate amount of pre exist ε martensite in the matrix before deforming.
关键词:
shape memory alloy
,
null
,
null
Q.A. Li
,
H.Q. Mo
,
Y.Z. Huo
,
G. Sang
,
Y.F. Chen
,
M.G. Han
,
Y.G. Chen and M.J. Tu Department of Metal Materials
,
Sichuan University
,
Chengdu 610065
,
China
金属学报(英文版)
In this paper,a simulation model for the temperature field in the solidification process and microstructure distribution is presented. Then, the result of simulation for the final microstructure distribution is compared with experiment using 10-Kg ingot of MlNi3.55Al0.3Mn0.4CO0.75 (Ml: Lanthanum-rich Mischmetal) hydrogen stor- age alloy cast in a mould, which agrees with the experiment well. Finally, in order to obtain the expected as-cast microstructure distribution of 15-Kg ingot of MlNi3.55Al0.3Mn0.4Co0.75 alloy, the size of Cu mould is optimized using the model described. The optimized mould is then made and the alloy is cast in it, the expected as-cast microstructure distribution is obtained.
关键词:
hydrogen storage alloy
,
null
,
null
,
null
M Liu
,
XM Zhang
,
M.Z. Liu
,
X.M. Mengand Y Y Li(Institute of Metal Research
,
Chinese Academy of Sciences
,
Shenyang 110015
,
China)(Metal Material Department
,
Sichuan Union University
,
Chengdu 610065
,
China)
金属学报(英文版)
In this paper by means of TEM and HREM, we found that the presence of r-phase plays the most important role in enabling two way shape memory effect (TWME) to be obtained by the stabilization of stress induced martensite variants (SSIM). This idea is different from the traditional suggestion that strain fields developed by dislocation produced TWME. With prolonged isothermal ageing time, the bainitic tronsforma-tion product α1 precipitated, the amount of γ-phase increased, while the martensite was retained and became less ondered. These factors all reduced TWME. During age-ing, the stacking faults in bainitic product α1 disappeared, which indicated that the bainitic product α1 is a sub-equilibrium phase. The interfaces of α-plates also lost straightness step by step, some plates twisted, bronched and overlapped. Its formation is irreversible in tnorphology and reduces the quantities of martensite. Although the precipitation of r may stabilize some martensite or oppose its growth,α may hinder nucleation of martensite. Thus, it was considered that α-plates were the worst de- stroyed element. These suggestions agreed well with our performance test results in that the transformation temperntures and the amount of TWME changed in the same way with prolonged ageing, firstly increasing and then decreasing after reaching an optimal maximum value.
关键词:
precipitate
,
null
,
null
,
null
M Liu
,
X.M Zhang
,
M.Z. Liuand R.S. Liu(Metal Material Department
,
Sichuan Union University
,
Chengdu 610065
,
China) (Institute of Metal Research
,
Chinese Academy of Sciences
,
Shenyang 110015
,
China)
金属学报(英文版)
In this paper, an in situ metallographic video system was used to study the morphology in Cu-Zn-Al shape memory alloy (SMA) during thermal cycling phase tmnsforma-tion. There are seven different types of martensite morphology in Cu-Zn-Al SMA,i.e. plate, spean bamboo, noose, round-spot, line and dot-like martensites. During transformation and inverse-transformation, the thermoelastic martensites were rising and falling, growing and shrinking, splitting and merping. The growth patterns of thermoelastic martensite were divided into three types: fast growing, very slow ex-pansion and uniform automatic growth. Automatic growth appeared when ageing at a temperature below Ms. The result, for the first time, coofirmed Olson and Cohen,s suggestion that thermoelastic martensite may be automatically grown when ageing be-low Ms. With increasing numbers of thermal cycling, both the memory recovery ratio (% )and memory recoverp degradation (%) degraded logarithmically. The degrada-tion was steep in the initial stage and then became more and more gradual in the middle and the final stages caused by the stabilisation of martensite. In the initial stage, vacancies assumed the controlling role, while dislocations took the major role in other stages. The martensite transformation caused the intedeces to become bent and blurmd, but with increasing cycling numbers, the movements of interface had the same degradation effects as the memory recovery ratio curves. Under these conditions, we also found the martensites on one side of the intedece became reorientated and par-allel to the intedece. It was therefore concluded that the movement degradation of the interface and the appearance of bamboo like martensite induced the degradation of two way shape memory effect (TWMP).
关键词:
in situ metallographic video study
,
null
,
null
,
null
