Anomalous influence of polarity in sink EDM of titanium alloys

An anodic tool polarity is generally adopted in sink electrical discharge machining (EDM) to maximize material removal relative to tool wear. Sink EDM of Ti and Ti6Al4V is however atypical in that these materials necessitate a cathodic tool polarity. Adding to the intrigue is γ-TiAl, which machines better under the conventional anodic polarity. This research focused on clarifying the phenomena behind this interesting behavior by investigating removal mechanisms over a range of relevant process conditions. The anomaly is demonstrated to arise from the polarity-dependent nature and extent of TiC formation on the work surface, which significantly affects material removal.     

Atomistic studies of stress effects on self-interstitial diffusion in α-titanium*

The diffusion anisotropy of intrinsic point defects is an important factor governing the behavior of the HCP metals bombarded by energetic particles. The effects of stress on the diffusion and its anisotropy, although known to be important, have not been well understood. In this paper, we use a combination of molecular dynamics and molecular statics methods to investigate energy states of a self-interstitial in α-titanium, a typical HCP metal. Our calculation shows that the most stable configuration of the self-interstitial is the basal-split dumbbell configuration on the basal plane. Compression along the [0001] or the [1ˉ100] directions leads to an insignificant change in the migration energies, while compression along the [11ˉ20] direction leads to a larger migration energy. A significant change of the diffusion anisotropy is observed when a uni-axial compressive stress of 200 MPa is applied along the [11ˉ20] direction. Similar stress along the other two directions does not produce substantial changes of the anisotropy. We also show that an applied hydrostatic stress can significantly change the diffusion anisotropy of HCP metals and alloys. Thus, under irradiation, a hydrostatic stress can produce a significant creep-like deformation (i.e., with a deviatoric strain rate) through a stress-dependent change of the growth rate. This revised version was published online in June 2006 with corrections to the Cover Date.     

工业纯钛和00Cr25Ni22Mo2N不锈钢的钝化与再钝化性能

用恒电位划伤电极法及再钝化动力学参数ｉ０、β、Ｑｐ值对工业纯钛和００Ｃｒ２５Ｎｉ２２Ｍｏ２Ｎ不锈钢的钝化与再钝化性能进行了评价。在Ｈ２ＳＯ４溶液中的实验结果表明，两种材料再钝化初期电流密度衰减规律都符合单指数函数关系：ｉ（ｔ）＝ｉ０ｅｘｐ（－βｔ），并指出工业纯钛的钝化、再钝化性能优于００Ｃｒ２５Ｎｉ２２Ｍｏ２Ｎ不锈钢。     

近年来国内钛光度分析的进展

综述了近十年来国内钢铁、合金等中钛的光度测定方法．分别从普通光度法、荧光光度法、动力学光度法和多组份光度法四个方面加以介绍，参考文献１０２篇．     

光控石墨炉原子吸收光谱法测定钛的研究

研究了钛原子吸收光谱的两个基本问题：钛吸收线的特征和钛原子的生成和消失．考察了石墨管的基质材料、灰化温度、原子化温度、升温技术和基体效应的影响．建立了全热解石墨管、Ca（NO3）2－NH4F混合基体改进剂，光控快速升温石墨炉原子吸收光谱测定钛的方法，特征质量为39pg/0.0044A。     

Modeling the high strain rate behavior of titanium undergoing ballistic impact and penetration

Titanium is an important candidate in the search for lighter weight armors. Increasingly, it is being considered as a replacement for steel components. It is also an important component in the application of ceramics to armor systems, especially in armor modules that are capable of defeating kinetic energy penetrators while sustaining little or no penetration of the ceramic element. The best alloy available today for ballistic applications is Ti-6Al-4V, an aerospace grade titanium alloy. The principal deterrent to widespread use of this alloy as an armor material is cost, and a significant portion of the cost is in processing. Consequently, the U.S. Army Research Laboratory undertook a program to study a particular lower cost processing technique [1].

The objectives of this work are to characterize the low-cost titanium alloy by generating constants for the Johnson-Cook (JC) and Zerilli-Armstrong (ZA) strength models, and to use and compare these two models in simulations of ballistic experiments. High strain rate strength data for the low-cost titanium alloy are used to generate parameters for the two models. The approach to fitting the JC parameters follows one previously used successfully to model 2-in thick rolled homogeneous armor (RHA) [2]. The approach to fitting the ZA parameters is based on a method described by Gray et al. [3]. The resulting model parameters are used in the shock physics code CTH [4] to model a Ti-6Al-4V penetrator penetrating a Ti-6Al-4V semi-infinite block at impact velocities up to 2,000 m/s. Similar experiments are performed, and the predictions of the two models are compared to each other and to the experimental results.     

新试剂2-(2''''-苯并噻唑偶氮)-1,8-二羟基-3,6-萘二磺酸与钛(Ⅳ)和 CTMAB 形成三元络合物显色反应的研究

在阳离子表面活性剂ＣＴＭＡＢ存在下，２－（２′－苯并噻唑偶氮）－１，８－二羟基－３，６－苯二磺酸与钛（Ⅳ）在ｐＨ３．５～４．５范围内发生高灵敏的显色反应，形成一种蓝色的三元胶束络合物，其最大吸收波长位于６５０ｎｍ，表观摩尔吸光系数ε＝１．２２×１０５·Ｌ·ｃｍ－１。络合物中钛（Ⅳ）与显色剂的组成比为１：２，钛含量在０～８．０μｇ／２５ｍＬ范围内符从比尔定律。间用于铝合金中微量钛的测定，结果满意。     

Ohmic contacts to n-type GaN

Ohmic contacts to n-GaN using Ag, Au, TiN, Au/Ti, Au/Mo/Ti, and Au/Si/Ti have been studied. The Fermi level of GaN appears to be unpinned, and metals and compounds with work functions less than the electron affinity resulted in ohmic contacts. Reactively sputter deposited TiN was ohmic as deposited. However, Au/Ti, Au/Mo/Ti, and Au/Si/Ti required heat treatments to form ohmic contacts, with the best being an RTA at 900°C. Ag and Au were shown to diffuse across the GaN surface at T>500°C; therefore, they are unstable, poor ohmic contact metallizations as single metals. The other contact schemes were thermally stable up to 500°C for times of 30 min.     

高压氮气中自蔓延燃烧合成氮化钛

利用钛粉在高压氮气中的自蔓延燃烧合成（ＳＨＳ），制备了含氮量较高的ＴｉＮ，研究了反应物的松装密度、氮气压的改变与稀释剂的加入对燃烧波蔓延速率和产物转化率的影响，还观察到燃烧方式的改变。     

CL-5209萃淋树脂分离铀、二安替比林甲烷光度法测定八氧化三铀中微量钛

文章介绍了用CL-5209萃淋树脂分离铀、二安替比林甲烷光度法测定八氧化三铀中微量钛的方法研究。该法选择性高、形成的络合物稳定性好。方法的相对标准偏差为±3%,回收率为100～104%。在含0～20μg钛的范围内,服从朗伯-比耳定律。