The reverse transformation has never occurred in a quenched and aged specimen upon heating from room temperature to 320℃ at which the martensite disappears thoroughly.Both B2 9R and DO_318R coexist in step-quenched a...The reverse transformation has never occurred in a quenched and aged specimen upon heating from room temperature to 320℃ at which the martensite disappears thoroughly.Both B2 9R and DO_318R coexist in step-quenched and short-time isothermally treated specimen. As prolonging the isothermal holding,the B29R disappears and DO_318R intensifies. B29R occurs only in specimen quenched and up-quenched immediately to 100—150℃. Rapid quenching from high temperatures will depress the B2→DO_3 ordering but not the A2 →B2 one.A plenty enough concentration of vacancy is a necessary condition of occurrence of B2→DO_3 ordering.The possible mechanism for the stabilization of martensite in a Cu-Zn-Al alloy was also discussed.展开更多
Shape memory alloys can recover the deformed shape due to their superelasticity or shape memory effect. In this study, a novel Cu-Al-Mn-Fe shape memory single crystal is reported. The results show that it has excellen...Shape memory alloys can recover the deformed shape due to their superelasticity or shape memory effect. In this study, a novel Cu-Al-Mn-Fe shape memory single crystal is reported. The results show that it has excellent superelasticity and shape memory effect simultaneously when deformed at room temperature, as well as tunably wide response temperature range with near-zero interval of reverse phase transformation. When deforming one single crystal at room temperature, it not only possesses full superelasticity of 7%, but also tunable shape memory effects up to 8.8 %. The full shape recovery during heating exhibits near-zero response interval and tunably wide response temperature range of 166 K depending on the deformation. The functional characteristics of the alloys result from the controllable reverse phase transformation hinging on the stabilization of stress-induced martensite. This class of Cu-Al-Mn-Fe alloy may be used as both superelastic materials, and shape memory materials with wide working temperature range as high-sensitive detector, driver or sensor.展开更多
Based on uniaxial tensile and plane strain deformation tests, the effects of strain states on the stability of RA （retained austenite） in medium Mn steels, which were subjected to IA （intercritical annealing） and ...Based on uniaxial tensile and plane strain deformation tests, the effects of strain states on the stability of RA （retained austenite） in medium Mn steels, which were subjected to IA （intercritical annealing） and Q＆P （quenching and partitioning） processing, were investigated. The volume fractions of RA before and after deformation were measured at different equivalent strains. The transformation behaviors of RA were also investigated. The stability of RA differed across two different transformation stages at the plane strain state： the stability was much lower in the first stage than in the second stage. For the uniaxial ten sion strain state, the stability of RA corresponded only to a single transformation stage. The main reason was that there were two types of transformations from RA in the medium Mn steel for the plane strain state. One type was that the martensite originated in the strain-induced stacking faults （SISF）. The other type was the strain-induced directly twin martensite at a certain equivalent strain. However, for the uniax- ial tension state, only the strain-induced twin martensite was observed. Dislocation lines and dislocation tangles were also observed in specimens deformed at different strain states. In addition, complex micro- structures of stacking faults and lath-like phases were observed within a grain at the plane strain state.展开更多
Stress induced deformation in A p～ M p and concomitant shape recovery behavior of Cu 13.4Al 4.0Ni single crystals were studied. Abnormal high stress induced deformation exists in A p～ M p under the conditions of eit...Stress induced deformation in A p～ M p and concomitant shape recovery behavior of Cu 13.4Al 4.0Ni single crystals were studied. Abnormal high stress induced deformation exists in A p～ M p under the conditions of either heating with load or cooling with load. The recovered deformation is successively composed of four parts, the recoveries from superelasticity, normal reverse transformation, thermally activated reverse transformation of partially stabilized martensite and reverse transformation of stabilized martensite by over heating. With increasing cycling number, the recovery part from normal reverse transformation decreases, while that from reverse transformation of stabilized martensite by over heating increases, which shows a typical stabilization of martensite.展开更多
文摘The reverse transformation has never occurred in a quenched and aged specimen upon heating from room temperature to 320℃ at which the martensite disappears thoroughly.Both B2 9R and DO_318R coexist in step-quenched and short-time isothermally treated specimen. As prolonging the isothermal holding,the B29R disappears and DO_318R intensifies. B29R occurs only in specimen quenched and up-quenched immediately to 100—150℃. Rapid quenching from high temperatures will depress the B2→DO_3 ordering but not the A2 →B2 one.A plenty enough concentration of vacancy is a necessary condition of occurrence of B2→DO_3 ordering.The possible mechanism for the stabilization of martensite in a Cu-Zn-Al alloy was also discussed.
基金financially supported by the National Natural Science Foundation of China (No. 51971185)the National Key R&D Program of China (No. 2017YFB0702901)。
文摘Shape memory alloys can recover the deformed shape due to their superelasticity or shape memory effect. In this study, a novel Cu-Al-Mn-Fe shape memory single crystal is reported. The results show that it has excellent superelasticity and shape memory effect simultaneously when deformed at room temperature, as well as tunably wide response temperature range with near-zero interval of reverse phase transformation. When deforming one single crystal at room temperature, it not only possesses full superelasticity of 7%, but also tunable shape memory effects up to 8.8 %. The full shape recovery during heating exhibits near-zero response interval and tunably wide response temperature range of 166 K depending on the deformation. The functional characteristics of the alloys result from the controllable reverse phase transformation hinging on the stabilization of stress-induced martensite. This class of Cu-Al-Mn-Fe alloy may be used as both superelastic materials, and shape memory materials with wide working temperature range as high-sensitive detector, driver or sensor.
基金financial support of the State Key Research and Development Program of China(Grant No.2017YFB0304404)
文摘Based on uniaxial tensile and plane strain deformation tests, the effects of strain states on the stability of RA （retained austenite） in medium Mn steels, which were subjected to IA （intercritical annealing） and Q＆P （quenching and partitioning） processing, were investigated. The volume fractions of RA before and after deformation were measured at different equivalent strains. The transformation behaviors of RA were also investigated. The stability of RA differed across two different transformation stages at the plane strain state： the stability was much lower in the first stage than in the second stage. For the uniaxial ten sion strain state, the stability of RA corresponded only to a single transformation stage. The main reason was that there were two types of transformations from RA in the medium Mn steel for the plane strain state. One type was that the martensite originated in the strain-induced stacking faults （SISF）. The other type was the strain-induced directly twin martensite at a certain equivalent strain. However, for the uniax- ial tension state, only the strain-induced twin martensite was observed. Dislocation lines and dislocation tangles were also observed in specimens deformed at different strain states. In addition, complex micro- structures of stacking faults and lath-like phases were observed within a grain at the plane strain state.
文摘Stress induced deformation in A p～ M p and concomitant shape recovery behavior of Cu 13.4Al 4.0Ni single crystals were studied. Abnormal high stress induced deformation exists in A p～ M p under the conditions of either heating with load or cooling with load. The recovered deformation is successively composed of four parts, the recoveries from superelasticity, normal reverse transformation, thermally activated reverse transformation of partially stabilized martensite and reverse transformation of stabilized martensite by over heating. With increasing cycling number, the recovery part from normal reverse transformation decreases, while that from reverse transformation of stabilized martensite by over heating increases, which shows a typical stabilization of martensite.
