Ferromagnetic Ni-Mn-Ga films were fabricated by depositing on MgO （001） substrates at temperatures from 673 K to 923 K. Microstructure, crystal structure, martensitic transformation behavior, and magnetic properties...Ferromagnetic Ni-Mn-Ga films were fabricated by depositing on MgO （001） substrates at temperatures from 673 K to 923 K. Microstructure, crystal structure, martensitic transformation behavior, and magnetic properties of the films were studied. With increasing deposition temperature, the surface morphology of the films transforms from granular to continu- ous. The martensitic transformation temperature is not dependent on deposition temperature; while transformation behavior is affected substantially by deposition temperature. X-ray analysis reveals that the film deposited at 873 K has a 7M marten- site phase, and its magnetization curve provides a typical step-increase, indicating the occurrence of magnetically induced reorientation （MIR）. In situ magnetic domain structure observation on the film deposited at 873 K reflects that the marten- sitic transformation could be divided into two periods： nucleation and growth, in the form of stripe domains. The MIR occurs at the temperature at which martensitic transformation starts, and the switching field increases with the decrease of temperature due to damped thermal activation. The magnetically induced martensitic transformation is related to the difference of magnetization between martensite and austenite. A shift of martensite temperature of dT/dH = 0.43 K/T is observed, consistent with the theoretical value, 0.41 K/T.展开更多
A possible mechanism of all-round shape memory behaviour hy help of a physical model pro- posed by Muller has been ascertained.The all-round shape mernory effect can be due to the fact that stress induced martensite o...A possible mechanism of all-round shape memory behaviour hy help of a physical model pro- posed by Muller has been ascertained.The all-round shape mernory effect can be due to the fact that stress induced martensite of two different orientations is formed during the martensitic transformation in the outer and inner layers of the specimen respectively.展开更多
2Y-PSZ/TRIP steel composites have been sintered by hot-pressing method. Their microstructure and mechanical properties were investigated by means of SEM, TEM, XRD and static tension, split Hopkinson pressure bar metho...2Y-PSZ/TRIP steel composites have been sintered by hot-pressing method. Their microstructure and mechanical properties were investigated by means of SEM, TEM, XRD and static tension, split Hopkinson pressure bar method. The results showed that the strength and elastic modulus of 2Y-PSZ/TRIP steel composites at room temperature decreased with the increase of 2Y-PSZ content. The main reason was that the combining strength was quite weak between the grains of ZrO2. Distortion induced martensite transformation and plasticity during the dynamic loading increased the strength and distortion capability of the composites. The transformation was carried out mainly through twins formation. The shape of martensite induced by distortion was lamellate with substructures of twins. The habit plane was near {259}T with no mid-ridge and no explosion phenomena. The interface was straight between the austenite and martensite induced by distortion. The increase of 2Y-PSZ content, on the one hand, made the composite dynamic flow stress improved. Thereby, the fracture strength was improved. On the other hand, it depressed both the distortion capability and the martensite transformation induced by distortion. This resulted in the decrease of dynamic fracture strength.展开更多
The stress-strain-resistance relations of the Fe-Mn-Si alloys with different Si content have been investigated by measuring strain (ε) and resistance (△ R/R) upon tension synchronously. The results show that the str...The stress-strain-resistance relations of the Fe-Mn-Si alloys with different Si content have been investigated by measuring strain (ε) and resistance (△ R/R) upon tension synchronously. The results show that the strum induced γ→ε martensitic transfor- mation increases the strain sensitivity coeffcient of resistance (K) for the Fe-Mn-Si alloys in plastic region. There is a critical strum where dσ/dε becomes a constant value. Si increases the critical strum. A correlation between the critical strain and shape memory effect (SME) in the Fe-Mn-Si alloys is suggested.展开更多
基金Project supported by the National Key Project of Fundamental Research of China (Grant No.2012CB932304)the National Natural Science Foundation of China (Grant No.50831006)the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘Ferromagnetic Ni-Mn-Ga films were fabricated by depositing on MgO （001） substrates at temperatures from 673 K to 923 K. Microstructure, crystal structure, martensitic transformation behavior, and magnetic properties of the films were studied. With increasing deposition temperature, the surface morphology of the films transforms from granular to continu- ous. The martensitic transformation temperature is not dependent on deposition temperature; while transformation behavior is affected substantially by deposition temperature. X-ray analysis reveals that the film deposited at 873 K has a 7M marten- site phase, and its magnetization curve provides a typical step-increase, indicating the occurrence of magnetically induced reorientation （MIR）. In situ magnetic domain structure observation on the film deposited at 873 K reflects that the marten- sitic transformation could be divided into two periods： nucleation and growth, in the form of stripe domains. The MIR occurs at the temperature at which martensitic transformation starts, and the switching field increases with the decrease of temperature due to damped thermal activation. The magnetically induced martensitic transformation is related to the difference of magnetization between martensite and austenite. A shift of martensite temperature of dT/dH = 0.43 K/T is observed, consistent with the theoretical value, 0.41 K/T.
文摘A possible mechanism of all-round shape memory behaviour hy help of a physical model pro- posed by Muller has been ascertained.The all-round shape mernory effect can be due to the fact that stress induced martensite of two different orientations is formed during the martensitic transformation in the outer and inner layers of the specimen respectively.
文摘2Y-PSZ/TRIP steel composites have been sintered by hot-pressing method. Their microstructure and mechanical properties were investigated by means of SEM, TEM, XRD and static tension, split Hopkinson pressure bar method. The results showed that the strength and elastic modulus of 2Y-PSZ/TRIP steel composites at room temperature decreased with the increase of 2Y-PSZ content. The main reason was that the combining strength was quite weak between the grains of ZrO2. Distortion induced martensite transformation and plasticity during the dynamic loading increased the strength and distortion capability of the composites. The transformation was carried out mainly through twins formation. The shape of martensite induced by distortion was lamellate with substructures of twins. The habit plane was near {259}T with no mid-ridge and no explosion phenomena. The interface was straight between the austenite and martensite induced by distortion. The increase of 2Y-PSZ content, on the one hand, made the composite dynamic flow stress improved. Thereby, the fracture strength was improved. On the other hand, it depressed both the distortion capability and the martensite transformation induced by distortion. This resulted in the decrease of dynamic fracture strength.
文摘The stress-strain-resistance relations of the Fe-Mn-Si alloys with different Si content have been investigated by measuring strain (ε) and resistance (△ R/R) upon tension synchronously. The results show that the strum induced γ→ε martensitic transfor- mation increases the strain sensitivity coeffcient of resistance (K) for the Fe-Mn-Si alloys in plastic region. There is a critical strum where dσ/dε becomes a constant value. Si increases the critical strum. A correlation between the critical strain and shape memory effect (SME) in the Fe-Mn-Si alloys is suggested.
