Self-Propagating High-Temperature Synthesis in Mechanoactivated Compositions

The main results on the effect of preliminary mechanoactivation of the reaction mixture on the regularities and parameters of self-propagating high-temperature synthesis are presented.     

Estimation of the Maximum Transverse Size of Multilayer Bimetallic Films for Self-Propagating High-Temperature Synthesis for the Ni/Al Structure as an Example

Technical Physics - Self-propagating high-temperature synthesis (solid-flame combustion) is simulated based on a layered model in which the product is formed between the layers of initial reactants...     

High-Temperature Characteristics of Ti/Al/Ni/Au Ohmic Contacts to n-GaN

We present the high-temperature characteristics of Ti/Al/Ni/Au（15 nm/220 nm/40 nm/50 nm） multiplayer contacts to n-type GaN （Nd = 3.7 × 10^17 cm^-3, Nd = 3.0 × 10^18 cm^-3）. The contact resistivity increases with the measurement temperature. Furthermore, the increasing tendency is related to doping concentration. The higher the doped, the slower the contact resistivity with decreasing measurement temperature. Ti/Al/Ni/Au ohmic contact to heavy doping n-GaN takes on better high temperature reliability. According to the analyses of XRD and AES for the n-GaN/Ti/Al/Ni/Au, the Au atoms permeate through the Ni layer which is not thick enough into the AI layer even the Ti layer.     

Atomic Arrangement in B2 FeAl Prepared by Self-Propagated High-Temperature Synthesis at Varying Al Content and Annealing

Atomic arrangement in B2 FeAl prepared by self-propagated high temperature synthesis (SHS) as a function of Al concentration and annealing temperature has been studied by ⁵⁷Fe Mössbauer spectroscopy (MS) and X-ray diffraction (XRD). The increase of B2 FeAl isomer shift (IS) and lattice parameter (a) with Al concentration in the whole concentration range has been detected. This may originate from the formation of Al antisite atoms. Calculation of s-electron populations against number of Al antisites using a cluster approach and MO LCAO method supported this assumption. Annealing resulted in atomic rearrangements both in near-stoichiometric and Al-rich B2 FeAl.     

High-Temperature Gas Extrusion of a Reactive Ni + Al Powder Mixture

Doklady Physics - The results of studying steel cladded intermetallic rods manufactured by means of high-temperature gas extrusion applied for the first time for reactive powder mixtures are...     

六角相硼碳氮化合物的合成研究

 以三聚氰胺和氧化硼为原料,利用真空热处理和高温高压技术,对BCN化合物的形成及结构进行了研究。在真空条件下,原料经1 100 K热处理得到非晶BCN的前驱物,将前驱物在5.0 GPa、1 500 K条件下高温高压热处理30 min,合成出了单相的六角BCN晶体。采用Materials Studio软件的Reflex模块对样品的X射线衍射图谱进行分析,结果表明,得到的样品为纯的六角相,晶格常数为a=0.250 5 nm,c=0.665 9 nm。对样品进行了透射电镜（TEM）分析,得到了样品的形貌和电子衍射,同样证实了样品为六角BCN晶体,晶粒尺寸约200 nm。对样品进行了XPS表征,确定了样品中存在C—C、C—N、C—B、N—B键,表明B、C、N三元素之间达到了原子级化合,样品的组分含量通过EDX进行标定。     

Surface ablation by excimer laser irradiation of Ti and Ti6Al4V alloy

This paper presents the surface microstructure of Ti and Ti6Al4V alloy irradiated with a high output energy XeCl ( = 308 nm) excimer laser. The treatments are carried out on both materials at two beam fluences and the effects of single- and multiple-pulse irradiation are compared. The results of the scanning electron microscopy and of the X-ray diffraction techniques suggest the possible influence of both time-behaviour and energy fluence of the laser pulse on the relative weight of the ablation rate and of the reaction product deposition rate at the sample surface.     

Synthesis of ultrafine titania nano-cages by pulsed laser ablation of Ti/Al alloy in ammonium hydroxide

A simple and versatile strategy is designed to successfully fabricate ultrafine Ti O2nano-cages based on the rapid decomposition reaction between amphoteric hydroxide and ammonia solution by pulsed laser ablation of Ti/Al alloy in liquid. With the ammonia concentration(Vammonia:Vwater, where V is volume) increasing from 1∶10 to1∶4, the diameter and shell thickness of quasi-spherical Ti O2nano-cages substantially decrease from300 and 60 nm to 9.2 and 2.8 nm, respectively. The obtained results have significant implications for obtaining insight into the properties of the Ti O2 porous nano-cages, offering the basis for further fabrication of other nano-cages.     

Fluvio-mechanical resetting of the Al and Ti centres in quartz

ESR dating of fluvial terraces is usually based on the assumption of sunlight resetting of the Al centres in quartz. Very long bleaching times (months of sunlight exposure) are required to reset this centre to a stable, non-zero ESR intensity. Considering that highly light sensitive optically stimulated luminescence (OSL) analyses of fluvial samples often indicate partial bleaching, ESR dating should be extremely difficult. Two samples were analysed, a fluvial sediment from a Chinese river terrace and an Australian granite. Using a Höhnle sunlight simulator, the Ti centres of both samples were completely bleached within 1 to 65 h, while the Al centre required extreme bleaching times to reach stable residual intensities (∼1000 h). As an alternative to light resetting, tumbler experiments were carried out to simulate fluvial action. The samples were treated under OSL sample preparation conditions. After relatively short tumbling times, corresponding to a few km of fluvial transport, both Al- and Ti-centres were partially reset. In a granite sample, the tumbling reduced the intensity of the Al centre more effectively than light exposure.     

Electrical characterization of Al/AlOx/molecule/Ti/Al devices

We report experimental electrical characterization of Al/AlO_x/molecule/Ti/Al planar crossbar devices incorporating Langmuir–Blodgett organic monolayers of eicosanoic acid, fast blue, or chlorophyll-B. Current–voltage and capacitance–voltage measurements on all three molecular device structures exhibited controllable switching hysteresis. Control devices containing no molecules showed no evidence of switching. A model of interface trapped charge mediating electronic transport appears consistent with all of the data. This data illustrates the importance of considering the complete device system (consisting of the molecules, the electrodes, and the interfaces) when analyzing its electrical behavior. PACS 85.65.+h; 73.40.Rw; 73.50.Gr     

Friction and wear behaviour of cp Ti and Ti6Al4V following nitric acid passivation

Nitric acid passivation increases the thickness of the TiO₂ passive film formed at the cp Ti and Ti6Al4V surface. The TiO₂ oxide, which has a lubricating nature, reduces the wear rate. A linear ball-on-disc friction test has been carried out at room temperature in ambient air, NaCl 3% and Ringer's solutions, with a sliding velocity of 4 mm s⁻¹ and a normal load of 1 N. Friction coefficient curves obtained from ball-on-disc wear test, as well as following the optical microscopy observation of ball trace, indicated the presence of periodic phenomenon. One period can be divided into four stages. This can be clearly seen for cp Ti (accommodation stage, creation of wear particles, adherence of particles layer on the alumina ball and ejection of this layer). In order to confirm this observation and understand the chemical interfacial phenomena, open circuit potential (OCP) measurements were carried out in the same time of friction tests.     

Computer simulation of Ti3Al intermetallic cleavage fracture

The decohesion energy and the energy of unstable stacking faults for all cracking planes and dislocation slip systems observed experimentally are calculated using the molecular dynamics method with N-particle atomic potentials. A dimensionless parameter characterizing the brittle behavior of the material is calculated for basis, prism, and pyramid faces in terms of the model elaborated by Kelly et al. and extended by Rice and Thompson. Cleavage in Ti₃Al is due to low decohesion energy values, which facilitates cracking, and high energies of unstable stacking faults, which prevents the formation of a plastic zone and stress relaxation at its vertex.     

High-temperature resistivity of Ti1-X Al X alloys

We have measured the high-temperature resistivities of dilute Ti_1-x Al _x alloys withx0.135 up to 1100 K (2.6 _D , where _D is the Debye temperature). We observe that possesses a strong downward deviation from a linear temperature-dependence at high temperatures (several hundred degrees Kelvin). Eventually, saturates to a constant. This non-Bloch-Grüneisen-like behavior is compared with the predictions of current theories.     

Reaction of evaporated Ti films with large-grained Al substrates

We have studied the reaction kinetics of titanium films on large-grained aluminium substrates during furnace annealing in vacuum for temperatures between 450–550°C. Oxygen was profiled by elastic resonance¹⁶O(, )¹⁶O backscattering. A TiAl₃ aluminide layer always forms at the Ti/Al interface. In addition, a second TiAl₃ layer grows at the free Ti surface when the contamination of the annealing ambient by oxygen-carrying species is reduced during annealing. Otherwise, the nucleation of the second compound layer is inhibited by an oxygen-rich surface layer of the Ti.     

Al3Ti Alloy: Long-Period States and Electronic Structure

Proceeding from ab initio calculations of the electronic structure and the generalized electronic susceptibility, the relationship between the Fermi surface nesting properties and the character of long-period structures in an Al₃Ti alloy is studied. The observed dependence of the long period M on temperature is analyzed.     

Structural investigations of nanocrystalline Ti–Al and Ni by PAC

Nanocrystalline Ti-Al and Ni are investigated on an atomic scale by perturbed γγ-angular correlation spectroscopy in combination with X-ray diffraction. Ti-Al compounds produced by mechanical alloying consist of disordered solid solutions. Annealing of the samples effects a transformation into ordered intermetallic compounds, which is observed via the occurrence of characteristic electric field gradients. The local magnetic properties of nanocrystalline Ni, produced by pulsed electrodeposition, are investigated. Besides the local magnetic field known from polycrystalline Ni, a second component is detected, which is attributed to a magnetic perturbation due to grain boundaries. The width of this magnetic boundary is estimated to 3–4 nm. This revised version was published online in August 2006 with corrections to the Cover Date.