Corrosion-resistant analogue of Hadfield steel

The concept of alloying austenitic steels with carbon + nitrogen is used for the development of a corrosion-resistant austenitic CrMn steel having an impact wear resistance close to that of the Hadfield steel. A higher stabilization of the austenitic phase by C + N, as compared to carbon or nitrogen alone, is substantiated by ab initio calculation of the electron structure, measurements of the concentration of free electrons and calculations of the phase equilibrium. Based on these results, the compositions (mass%) Cr18Mn18C0.34N0.61 and Cr18Mn18C0.49N0.58 were melted and tested along with Hadfield steel Mn12C1.2. Mechanical tests have shown that, as compared to the Hadfield steel, the experimental steels possess a higher strength, plasticity, hardness and the same resistance to impact wear. TEM studies of the surface layer after impact treatment revealed a mixture of the amorphous phase, nanocrystals and fine-twinned austenite. At the same time, using Mössbauer spectroscopy of conversion electrons, the ferromagnetic ordering was found in the surface layer of up to 10 μm in depth, which is the sign of the strain-induced martensitic phase. The hypothesis of a transition from the low-spin to the high-spin state of the iron atoms within the thin twins in austenite was proposed in order to interpret the discrepancy between TEM and Mössbauer studies. Potentiodynamic measurements and immersion tests show that the CrMnCN steels possess a significantly higher pitting potential and resistance to general corrosion in comparison with Hadfield steel.     

Synthesis and dielectric properties of Sr0.6 − x Ba0.4Na2x Nb2O6 solid solutions

We have prepared Sr_{0.6 ? x} Ba_0.4Na_2x Nb₂O₆ (0 ≤ 2x ≤ 0.3) solid solutions with the tetragonal tungsten bronze (TTB) structure, investigated the sequence of phase changes involved, and determined the lattice parameters of the solid solutions. The electrical properties of polycrystalline samples have been studied in broad frequency and temperature ranges. The results indicate that an increase in sodium content, accompanied by a reduction in the concentration of vacancies on the A site of the TTB structure, reduces the rate of dielectric relaxation.     

A distance PLC programming course employing a remote laboratory based on a flexible manufacturing cell

The increasing necessity of engineers capable of handling the problems of the industry and able to face the technical challenges they will encounter in their professional career is boosting the teaching methods based on projects and real applications. The Center of Technological Innovation in Static Converters and Drives, Technical University of Catalonia (CITCEA-UPC) group, Barcelona, Spain, has introduced such learning methods applied to the automation field in a course taught for the electrical engineering degree and in some postgraduate workshops, making the laboratory platforms available through the Internet in order to allow the use of such practices in e-learning-based courses. The learning method is based on a flexible manufacturing cell, resulting from the collaboration between the CITCEA-UPC and Schneider Electric and its Training Center. The problem proposed to the students is the automation of such a cell with commercial programmable logic controllers (PLCs). The experience has proved to be positive, and the students have valued it accordingly.     

Development of geothermal power engineering in Russia and abroad

World data on using geothermal heat in different technologies are generalized. Current achievements in the development of domestic geothermal power technologies and the creation of geothermal power plants are presented. Main trends in the development of heat and electricity supply on the basis of geothermal sources in Russia and abroad are shown.     

Confined acoustic phonons in ultrathin SOI layers

We try to reproduce experimental mobility curves in ultrathin silicon-on-insulator inversion layers using a Monte Carlo simulator and a bulk model for the electron scattering with acoustic phonons. While it is possible to reproduce the experimental behavior for the thicker samples, the electron mobility is strongly overestimated when the thinnest samples are considered. The mobility curves for the thinnest samples can be reproduced using the same model if the deformation potential parameter increases as the silicon thickness decreases. This fact shows that acoustic phonons are also confined in ultrathin silicon on insulator layers. We then study confined phonons in single and three layer structures in order to give a physical motivation to the increase of acoustic phonon scattering rate for in ultrathin silicon layers.     

ArcFVS: An integration of a Geographic Information System and Forest Vegetation Simulator

This paper presents the design and implementation of an integrated application program called ArcFVS that links the Forest Vegetation Simulator (FVS) and a Geographic Information System (GIS) to realize spatial selection of input files and graphic display of modeling output. Data for testing and running the model came from the U.S. Forest Service’s Forest Inventory and Analysis (FIA) Database and were also collected in field surveys in north-central Indiana. ArcFVS 1.0 is designed using the ArcGIS software from the Environmental Systems Research Institute (ESRI) and the Visual Basic for Applications (VBA) programming environment to manipulate ESRI’s ArcObjects. The resulting product offers custom functions as commands in a new menu or as tools on a new toolbar. They are used to: select spatially or by attribute the forest plots to be projected by FVS, create the FVS input files for the selected plots and display in a geospatial environment different types of FVS output (text output files, tables with variables of interest and visualization image files). Advantages of ArcFVS 1.0 include the new GIS capabilities, enhanced format translation functions and the standardized programming environment.     

A continuous-wave hybrid AlGaInAs-silicon evanescent laser

We report a novel laser architecture, the hybrid silicon evanescent laser (SEL), that utilizes offset AlGaInAs quantum wells (QWs) bonded to a silicon waveguide. The silicon waveguide is fabricated on a silicon-on-insulator wafer using a complimentary metal-oxide-semiconductor-compatible process, and is subsequently bonded with the AlGaInAs QW structure using low temperature O/sub 2/ plasma-assisted wafer bonding. The optical mode in the SEL is predominantly confined in the passive silicon waveguide and evanescently couples into the III-V active region providing optical gain. The SEL lases continuous wave (CW) at 1568 nm with a threshold of 23 mW. The maximum temperature for CW operation is 60/spl deg/C. The maximum single-sided fiber-coupled CW output power at room temperature is 4.5 mW.     

Comment on "From the summation-by-parts algorithm to Pi"

Comments on the paper by Mosig (IEEE Antennas and Propagation Magazine, vol.47, p.38-40, 2005 December). The paper by Mosig discussed acceleration of convergence of series. Without commenting on either the validity or efficiency of his method, the present author would like to draw attention to an existing method, published long ago by D. Shanks (1955). Briefly stated, this method takes a sequence and defines partial sums, which is described in this paper.     

Microstructure and refining performance of an Al−5Ti−0.25C refiner before and after equal-channel angular pressing

Refining experiments were conducted to evaluate the grain refining performance of an Al−5Ti−0.25C refiner before and after equal-channel angular pressing (ECAP) with the use of a high-purity Al. The results show that the Al−5Ti−0.25C refiner has remarkable and stable grain refining performance when the holding times are within 5 to 30 minutes and the melt temperatures are within 1003 to 1073 K. Furthermore, some Al−5Ti−0.25C refiner samples were subjected to severe plastic deformation by using the ECAP technique at 298 K. It was found that Al₃Ti and TiC particles were significantly fragmented and their mean sizes were decreased to 10 and 1.08 μm, respectively, and the Al−5Ti−0.25C refiner appeared to have a double grain refining effect in comparison with that of before ECAP. It is also testified that the Vickers microhardness (Hv) value of the pure Al samples refined by the Al−5Ti−0.25C refiner after ECAP processing has a significant increment than that of before ECAP processing. It is concluded that the Al−5Ti−0.25C refiner with ECAP technique has a very useful practical application in refining industrial Al alloys. ZUOGUI ZHANG, formerly Master's Student, the Key Laboratory of Liquid Structure and Heredity of Material, Ministry of Education, Shandong University, Jinan 250061, People's Republic of China     

Microstructure and yield strength of UDIMET 720LI alloyed with Co-16.9 Wt Pct Ti

We proposed a new method for developing Ni-base turbine disc alloy for application at temperatures above 700 °C by mixing a Ni-base superalloy U720LI with a two-phase alloy Co-16.9 wt pct Ti in various contents. The microstructure and phase stability of the alloys were analyzed using an optical microscope, a scanning electron microscope, energy-dispersive spectroscopy, and an X-ray diffractometer. The yield strength was studied by compression tests at temperatures ranging from 25 °C to 1200 °C. The results show that all the alloys had a dendritic structure. Ni₃Ti (η) phase was formed in the interdendritic region in the alloys with the addition of Co-16.9 wt pct Ti, and its volume fraction increased with the increase in the addition of Co-16.9 wt pct Ti. The results of exposure at 750 °C show that the addition of Co-16.9 wt pct Ti to U720LI had a great effect on suppressing the formation of σ phase due to the reduced Cr content in the γ matrix. Compared to U720LI, the alloys with the addition of Co-16.9 wt pct Ti possessed higher yield strength. The solid-solution strengthening of γ and γ′ and higher volume fraction of γ′ were assumed to cause this strength increase.