细晶Al-5356合金在低应变速率下基于高分辨率应变测量的“异常瞬时蠕变”(英文)

极低应变速率下(<10-10s-1)的瞬时蠕变仍然未知。由于应变分辨率低(～10-6),传统的单轴拉伸/压缩等蠕变测试技术并不能满足此蠕变区的测试要求。采用具有高应变分辨率的螺旋弹簧蠕变试验法,研究Al-5356合金在温度范围为0.4Tm^0.8Tm(Tm为熔点的绝对温度)、应变速率小于10-10s-1的瞬时蠕变行为。采用透射电子显微镜研究蠕变微观组织以揭示极低应变速率下的瞬时蠕变机制。实验结果首次显示了一些异常蠕变行为:"高温强化"(T>Tp,Tp为发生相变的温度,Tp=0.58Tm)或"中温弱化"(0.4Tm<T≤Tp)和"双正常型蠕变"(蠕变曲线包含两次加工硬化阶段(T=Tp))。试样经中温(0.58Tm)蠕变后(1×10-4),微观组织中发现有大量等间隔割阶的塞积位错和从晶界发射的弧形位错。当温度高于523K时,β-Al3Mg2相溶解引起固溶Mg量增加,因此,异常蠕变行为可能归因于蠕变过程中相转变引起的固溶强化的差异。

纯铜在低温和极低应变速率下的初始蠕变和粘弹性回复（英文）

采用高应变分辨率的螺旋弹簧蠕变试验法,研究晶粒尺寸d_g为40μm纯铜在低温(T<T_m,T_m为纯铜的熔点)和应变速率小于1×10^(-10) s^(-1)条件下的蠕变和粘弹性回复行为。采用基于蠕变曲线尺度因子的数据解析法,代替传统基于外推的稳态蠕变速率的蠕变数据解析法。结果表明:纯铜低温、低应力初始蠕变行为可由幂律蠕变方程描述,因为幂律蠕变方程初始参数不随蠕变时间改变而变化;粘弹性应变为弹性应变的1/6;粘弹性应变速率的对数和粘弹性应变的对数呈线性关系(斜率为1)。因此,纯铜低温、低应力蠕变可能由三维位错网的收缩机制控制。

Effect of lower bainite/martensite/retained austenite triplex microstructure on the mechanical properties of a low-carbon steel with quenching and partitioning process

We present a study concerning Fe-0. 176C-1.31Si-1.58Mn-0.26Al-0.3Cr （wt%） steel subjected to a quenching and partitioning （Q＆P） process. The results of scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and tensile tests demon- strate that the microstructures primarily consist of lath martensite, retained austenite, lower bainite （LB）, and a small amount of tempered martensite; moreover, few twin austenite grains were observed. In the microstrucmre, three types of retained austenite with different sizes and morphologies were observed： blocky retained austenite （-300 nm in width）, film-like retained austenite （80-120 nm in width）, and ul- tra-fine film-like retained austenite （30-40 nm in width）. Because of the effect of the retained austenite/martensite/LB triplex microstructure, the specimens prepared using different quenching temperatures exhibit high ultimate tensile strength and yield strength. Furthermore, the strength effect of LB can partially counteract the decreasing strength effect of martensite. The formation of LB substantially reduces the amount of retained austenite. Analyses of the retained austenite and the amount of blocky retained austenite indicated that the carbon content is critical to the total elongation of Q＆P steel.

Microstructural evolution and mechanical properties of a low-carbon quenching and partitioning steel after partial and full austenitization

In this work, low-carbon steel specimens were subjected to the quenching and partitioning process after being partially or fully austenitized to investigate their microstructural evolution and mechanical properties. According to the results of scanning electron microscopy and transmission electron microscopy observations, X-ray diffraction analysis, and tensile tests, upper bainite or tempered martensite appears successively in the microstructure with increasing austenitization temperature or increasing partitioning time. In the partially austenitized specimens, the retained austenite grains are carbon-enriched twice during the heat treatment, which can significantly stabilize the phases at room temperature. Furthermore, after partial austenitization, the specimen exhibits excellent elongation, with a maximum elongation of 37.1%. By contrast, after full austenitization, the specimens exhibit good ultimate tensile strength and high yield strength. In the case of a specimen with a yield strength of 969 MPa, the maximum value of the ultimate tensile strength reaches 1222 MPa. During the partitioning process, carbon partitioning and carbon homogenization within austenite affect interface migration. In addition, the volume fraction and grain size of retained austenite observed in the final microstructure will also be affected.

高氮高铬铁素体耐热钢的开发

我们研制了新一代高氮铁素体耐热钢，评估了这些钢在高温下的微观组织和力学性能。在4．0MPa气压下，应用加压熔炼方法，在没有气孔形成的条件下，将0．3％的N成功地加入到铁素体钢中。在高氮铁素体耐热钢的板条马氏体结构中存在几种氮化物。富氮粗大的颗粒经分析鉴定是结晶的MN。根据V含量，细小的VN或Cr羽颗粒在马氏体晶界（如原始奥氏体晶界、晶包边界、晶团边界和板条边界）上析出来。高氮钢的马氏体组织舍有多级微观结构，这些微观结构包括马氏体板条、团、包和原始奥氏体晶粒。这些马氏体结构象传统碳素钢一样，遵循Kurdjumov—Sachs关系。试验钢的蠕变强度，虽然比92^#钢低，但可以与91^#钢比美。为了进一步提高钢的强度，除了氮化物之外，还需要其它析出物。