Effect of hydrogen on phase and microstructure of Ti600 alloy

Effects of hydrogen on microstructure characteristics and precipitation behavior have been investigated in Ti600 alloy hydrogenated at 750°C. Due to the precipitation of δ hydride and α″ martensite, X-ray diffraction (XRD) peaks of α phase shifted to lower angles and became broadened. XRD data showed that the addition of hydrogen expanded crystal lattice of α phase and lattice volume increased linearly in the range of 0?C _H?″ martensite and δ hydride. Compared to as-received one, microstructure of hydrogenated Ti600 alloy changed obviously. Equiaxed α phase decreased and even vanished with hydrogen contents increasing. Parallel fine lamellar structure appeared and the colonies were constructed by different orientation. Micro-hardness of hydrogenated Ti600 alloy increased with the increase of hydrogen concentration, and it was considered that interstitial solution strengthening, precipitation of δ hydride, and generation of defects were the major factors.     

Comment on: “Structural,elastic, and thermodynamic properties under pressure of the FeC in the martensitic phase: an ab-initio study”

Recently reported [Chihi T, Bouhemadou A, Bin-Omran S. High Press Res. 2013;33:572] results of density-functional theory calculations for a “martensitic” FeC with allegedly tetragonal body-centered ground state structure are shown to be compatible with a cubic rocksalt structure of that FeC.     

Development of new-generation low-carbon steel: Part II-wear behaviour

A new-generation unalloyed low-carbon steel (containing 0.1?wt.% C) has been recently developed by the research group of the present corresponding author through incomplete austenitisation-based cyclic ice-brine quenching possessing an exceptionally high strength (UTS?=?1.7?GPa) along with elimination of a yield point phenomenon. This is attributed to the evolution of a novel microstructure that consists of fine plate martensite crystals with a dispersion of nano-sized cementite particles and clusters. The present research work is conceived as the Part II of this investigation to establish this new-generation ultrahigh strength low-carbon steel as a unique wear-resistant steel substituting the conventional dual-phase steel along with the readily awaited in-depth correlation between wear mechanism and structural evolution. The wear behaviour of heat-treated steels is investigated against an alumina disc using a pin-on-disc tribometer. The steel subjected to incomplete austenitisation-based cyclic ice-brine quenching exhibits much better wear resistance than conventional dual-phase steel. Dominant microcutting and microploughing abrasion aggravate wear loss, especially at higher load, in dual-phase steel that inherently possesses lower matrix hardness. But, very high-surface hardness is attained in the incomplete austenitisation-based cyclic ice-brine quenched steel by virtue of a significant strain hardening of martensite matrix in between hard nano-sized cementite particles. Besides, the wear rate is not allowed to shoot up even at the highest load through the generation of hard abrasion-resistant tribo-oxide layer of Al₂FeO₄. This envisages an advent of novel wear-resistant steel as a better substitution for the dual-phase steel.     

超弹性形状记忆合金管单向拉伸试验的数值模拟

NiTi形状记忆合金具有很强的超弹性行为,这种超弹性行为是由于材料在应力作用下发生可逆的马氏体相变所引起。最近Sun和Lee^[4]在NiTi形状记忆合金管单向拉伸试验中观测到,应力诱导马氏体相变具有螺旋带状的形貌特征,本文对此作了数值模拟研究。采用包含应变软化效应的三线性本构关系,建立了NiTi形状记忆合金管的三维有限元模型。通过迭代计算,成功地再现了试验中所观察到的螺旋状相变带从形成到长大的全过程。数值计算结果表明,产生这一独特现象的力学机制,在于NiTi形状记忆合金管在拉伸状态下出现的局部变形失稳极其传播。     

Effect of nonlocal elasticity on internal friction peaks observed during martensite transformation

The internal friction associated with martensite is calculated using elastic interaction energy between dislocations and solute atoms in nonlocal elasticity during low temperature aging process. The relaxation strength depends on the lattice parameter of the crystal as well as the temperature and the heating rate. The peak heights increase with increasing lattice parameter. The proposed model can demonstrate more realistically the shape of the change of internal friction versus temperature when nonlocal elasticity is included.     

Electron microscope investigation of small particles

In this review paper some possibilities to investigate small particles (1–1000 nm) with the electron microscope are treated. The transmission electron microscope is a unique tool to obtain information from small particles. This information covers the important area where atomic and bulk properties meet. The emphasis is focused on observations in connection with gas evaporation, adhesion between particles, possible vibration at contact, particle twinning, dynamical effects, martensitic transformation and superlattice crystals.     

Heusler合金Mn2NiGe磁性形状记忆效应的第一性原理预测

运用基于密度泛函理论的第一性原理,对Hg₂CuTi型Mn₂NiGe的四方变形、晶体结构、磁性、电子结构、压力响应等进行了计算.计算结果表明: 1)在由立方结构至四方结构的转变中,在c/a约为1.34处存在一个稳定的马氏体相;2)在奥氏体态和马氏体态下,Mn原子均是Mn₂NiGe总磁矩的主要贡献者,但Mn(A),Mn(B)原子磁矩的值不等且呈反平行耦合,因而Mn₂N 关键词： 第一性原理 磁性形状记忆 四方变形 马氏体相变     

Buckling of a Rod Undergoing Direct or Reverse Martensite Transformation under Compressive Stresses

Analytical solutions of the problem of buckling of a compressed rod made of a shape-memory alloy, which undergoes direct or reverse martensite phase transition under compressive stresses, are obtained with the use of various hypotheses. Specific features of the experimentally observed buckling phenomenon caused by martensite transformations are described. It is found that the hypotheses of continuing phase transition and continuing loading give the minimum critical loads.     

Crystallographic variant selection of martensite during fatigue deformation

Metastable austenitic stainless steels are prone to form deformation-induced martensite under the influence of externally applied stress. Crystallographic variant selection during martensitic transformation of metastable austenite has been investigated thoroughly with respect to the interaction between the applied uniaxial cyclic stress and the resulting accumulated plastic strain during cyclic plastic deformation. The orientation of all the Kurdjomov–Sachs (K-S) variants has been evaluated extensively and compared with the measured orientation of martensite with their corresponding interaction energies by applying the elegant transformation texture model recently developed by Kundu and Bhadeshia. Encouraging correlation between model prediction and experimental data generation for martensite pole figures at many deformed austenite grains has been observed. It has been found that both the applied uniaxial cyclic stress and the accumulated plastic strain are having strong influence on crystallographic variant selection during cyclic plastic deformation. Patel and Cohen’s classical theory can be utilized to predict the crystallographic variant selection, if it is correctly used along with the phenomenological theory of martensite crystallography.     

Fe和Co对Ni2MnGa合金(110)马氏体孪晶界面电子结构的影响

利用密度泛函理论研究了Fe，Co两种合金元素对Ni₂MnGa合金(110)马氏体孪晶界面电子结构的影响. 分别从界面能、偏聚能、磁矩、键序和电子态密度等角度对合金元素在界面处的掺杂效应进行了分析和比较. 计算结果表明，在对界面的钉扎作用上，Co的界面掺杂效应较Fe的掺杂效应强；对于界面磁性的影响，Fe掺杂对界面磁结构的作用比Co掺杂显著. 关键词： 密度泛函理论 孪晶界面 掺杂效应 马氏体