剪切力作用下螺位错的运动

利用分子动力学方法研究了金属钨中螺位错在剪切力作用下的运动特性.根据弹性理论在BCC晶体中形成位错线沿<111>的螺位错,在合适的边界条件下获得平衡态的位错结构.发现位错由{110}平面沿<112>方向三个呈对称的皱褶组成.对平衡态结构施加剪切力,发现剪力很小时,位错核心不动,核心形状有畸变;当剪力增大到一定程度时位错开始运动.位错运动后,剪切力较小时,核心呈“之”字形运动;在较大剪力下,位错开始阶段呈“之”字形运动,一段距离后主要沿[211]方向作直线运动.位错运动的速度随着剪切力的增加而增大.

High density dislocations enhance creep ageing response and mechanical properties in 2195 alloy sheet

The creep strain of conventionally treated 2195 alloy is very low,increasing the difficulty of manufacturing Al-Cu-Li alloy sheet parts by creep age forming.Therefore,finding a solution to improve the creep formability of Al-Cu-Li alloy is vital.A thorough comparison of the effects of cryo-deformation and ambient temperature large pre-deformation(LPD)on the creep ageing response in the 2195 alloy sheet at 160℃with different stresses has been made.The evolution of dislocations and precipitates during creep ageing of LPD alloys are revealed by X-ray diffraction and transmission electron microscopy.High-quality 2195 alloy sheet largely pre-deformed by 80%without edge-cracking is obtained by cryo-rolling at liquid nitrogen temperature,while severe edge-cracking occurs during room temperature rolling.The creep formability and strength of the 2195 alloy are both enhanced by introducing pre-existing dislocations with a density over 1.4×10^(15)m^(−2).At 160℃and 150 MPa,creep strain and creep-aged strength generally increases by 4−6 times and 30−50 MPa in the LPD sample,respectively,compared to conventional T3 alloy counterpart.The elongation of creep-aged LPD sample is low but remains relevant for application.The high-density dislocations,though existing in the form of dislocation tangles,promote the formation of refined T1 precipitates with a uniform dispersion.

Influence of Cr addition on microstructure of a 5% Re-containing single crystal nickel-based superalloy

Based on a 5% （mass fraction） Re-containing single crystal nickel-based superalloy with 3% （mass fraction） Cr, the microstructural variation with Cr addition was investigated. The experimental results show that segregation of alloying elements was enhanced in as-cast microstructure with Cr addition; and the volume fraction of eutectic is increased. However, the solidus and liquidus temperatures are remarkably reduced. With the increase of Cr content, the average γ＇ size and volume fraction are decreased in the fully heat treated microstructure. X-ray diffraction results indicate that γ/γ＇ lattice misfit becomes more negative. According to the energy dispersive spectroscopy （EDS） results, Cr is mainly distributed in the γ matrix; and more y-forming elements, such as Re and W, enter the γ matrix, while the γ/γ＇ partition ratio of Cr is inversely decreased.

添加镁对低碳钢的凝固组织影响

为了提高低碳钢方坯内部质量，通过一些试验，采用小尺寸钢锭研究了添加镁对碳含量为0．1％的低碳钢凝固组织影响。同时也用FE-SEM观察钢锭中形成的夹杂物，完成了有关氧化物和氮化物的几种热力学分析。向钢中添加镁可增加等轴晶的比例，特别是在钛含量为0．2％～0．25％的低碳钢中有明显影响，其可导致TiN的结晶直至凝固结束。假定在不含钛钢中添加镁促进等轴晶结晶的影响主要归因于MgO或MgO·A12O3形核的作用，然而，与含钛钢相比，其增加等轴晶的比例较少。显然，对于TiN结晶来说，MgO也能有效作为反应试剂导致促进8-Fe和等轴结晶的异相形核。通过向低碳含钛钢中添加镁证实了MgO和TiN的共同作用。通过添加钙，当向钢中添加镁时，假定由于镁的加入导致的促进作用减少了液态氧化物并且降低了全氧，因此，固态MgO或固态MgO·Al2O3的结晶数量减少。证明了平面错合度是评价相对异相形核能力的有用指数。

A Psychoanalytic Insight Into Blanche in A Streetcar Named Desire Psychic Strength From Defense Mechanism

This paper attempts to analyze Blanche＇s psyche in relation to her employing defense mechanism to restore her mental health and herself in A Streetcar Named Desire （1947） by the American playwright Tennessee Williams. It focuses on her replacing reality with fantastic embodiments or illusion. She has taken unacceptable impulses into acceptable forms by unconsciously blocking the impulses such as superego and thereby reducing agony for the earlier traumatic experiences left indelible marks on her mind, and anxiety for survival. Her anxiety becomes too overwhelming that her ego urgently employs defense mechanisms to protect her. With her new hopes and dreams she desires to replace the highly stressful loss. Under mental and social stress, her illusion and her falsification of reality nevertheless became unable to overcome recurring trauma-causing situation in reality and her healing process thereby leaving her on the verge of extinction.

The influence of temperature on stacking fault energy in Fe-based alloys

Temperature has great influence on the stacking fault energy (SFE). Both SFE and dγ 0/dT for Fe-based alloys containing substitutional or interstitial atoms increase with increasing temperature. Based on the thermodynamic model of SFE, the equation $\frac{{d\gamma _0 }}{{dT}} = \frac{{d\gamma ^{ch} }}{{dT}} + \frac{{d\gamma ^{se\user1{g}} }}{{dT}} + \frac{{d\gamma ^{MG} }}{{dT}}$ and those expressions for three items involved are established. The calculatedγ 0/dT is generally consistent with the experimental. The influence of chemical free energy on the temperature dependence of SFE is almost constant, and is obviously stronger than that of magnetic and segregation contributions. The magnetic transition and the segregation of alloying elements at stacking faults cause a decrease in SFE of the alloys when temperature increases; that is, dγ MG/dT<0 and dγ seg/dT<0. Meanwhile, such an influence decreases with increasing temperature, except for the dγ seg/dT} of Fe?Mn?Si alloys. With these results, the experimental phenomena that the SFE of Fe-based alloys is not zero at the thermo-dynamically equilibrated temperature (T 0) of the λ and ε phases and they are positive both atT>T 0 andT<T 0 can be reasonably explained.