磨PCD刀具陶瓷结合剂金刚石砂轮的研究

本文研究制备Na2O-B203-Si02-Al203多元系基玻璃料,并配制成低温陶瓷结合剂,研究发现:耐火度为685℃,流动性为110%～130%,线膨胀系数为5.35×10-6℃-1的低温陶瓷结合剂具有优异的性能.制备的陶瓷结合剂金刚石砂轮在725℃烧成后,磨具的抗弯强度和洛氏硬度达到最佳值,分别58.61 MPa和77.9.用其磨削PCD刀片时锋利性好,磨削中间不需修整,砂轮耐用度高.运用扫描电子显微镜(SEM)分析了陶瓷结合剂金刚石磨具的断面形貌、磨削后磨削面形貌,表明结合剂对磨粒黏结牢固,断面组织均匀.     

Examination of superplastic forming combined with diffusion bonding for titanium: Perspective from experience

Superplastic forming (SPF) combined with diffusion bonding (DB) has been used successfully for the fabrication of titanium aerospace hardware. Many of these applications have been for military aircraft, whereby a complex built-up structure has been replaced with monolithic parts. Several methods for applying the two- and four-sheet titanium SPF/DB processes have been devised, including the welding of sheets prior to forming and the use of silk-screened stop-off (yttria) to prevent bonding where it is undesirable. Very little progress has been made in the past few years toward understanding and modeling the SPF/DB process using constitutive equations and data by laboratory testing. Concerns that engineers face in designing for fatigue life, acceptable design loads, and damage tolerance are currently being studied, but the database is very limited. This is a summary of past work found in the literature and forms the foundation for additional research. This paper was presented at the International Symposium on Superplasticity and Superplastic Forming sponsored by the Manufacturing Critical Sector at the ASM International AeroMat 2004 Conference and Exposition, June 8–9, 2004, in Seattle, WA. The symposium was organized by Daniel G. Sanders, The Boeing Company.     

The characteristics of a low-power-consumption plasma jet and ceramic coatings

The effects of the composition of plasma gases (Ar-N₂, Ar-H₂), arc current, and voltage on the temperature and velocity of a low-power (5 kW) plasma torch in the arc field free region has been investigated using an enthalpy probe. Coatings of Al₂O₃-13TiO₂ were deposited under different conditions. The results show that in the Ar-N₂ plasma, the enthalpy, temperature, and velocity change little with arc current and voltage when regulating the nitrogen proportion in the plasma gas. The hardness of the resulting coatings is 800 to 900 kg/mm² HV.300. For Ar-H₂ plasma, however, increases in the H₂ content in the mixture of the gases remarkably enhanced the velocity and heat transfer ability of the plasma jet, with the result that the coatings showed high hardness up to 1200 HV.     

Effect of austenitization on austempering of copper alloyed ductile iron

A ductile iron containing 0.6% copper as the main alloying element was austempered at a fixed austempering temperature of 330 °C for a fixed austempering time of 60 min after austenitization at 850 °C for different austenitization periods of 60, 90, and 120 min. The austempering process was repeated after changing austenitization temperature to 900 °C. The effect of austenitization temperature and time was studied on the carbon content and its distribution in the austenite after austenitization. The effect of austenitization parameters was also studied on austempered microstructure, structural parameters like volume fraction of austenite, X _γ , carbon content C _γ , and X _γ C _γ , and bainitic ferrite needle size, d _α after austempering. The average carbon content of austenite increases linearly with austenitization time and reaches a saturation level. Higher austenitization temperature results in higher carbon content of austenite. As regards the austempered structure, the lowering austenitization temperature causes significant refinement and more uniform distribution of austempered structure, and a decrease in the volume fraction of retained austenite.     

Influence of the Workpiece Stiffness on the Electromagnetic Sheet Metal Forming Process into Dies

Electromagnetic sheet metal forming is a high speed forming process using pulsed magnetic fields to form metals with high electrical conductivity such as aluminum. Thereby, workpiece velocities of more than 300 m/s are achievable, which can cause difficulties when forming into a die. The kinetic energy, which is related to the workpiece velocity, must be dissipated in a short time slot when the workpiece hits the die; otherwise undesired effects, for example rebound can occur. One possibility to handle this shortcoming is to locally increase the stiffness of the workpiece. A modal analysis is carried out in order to determine the stiffness of specific regions of the workpiece so that an estimation concerning the feasibility of the desired geometry is possible in advance without doing cost and time consuming experiments. Thereby, the desired geometry of the workpiece will be fractionized in significant sectors. This approach has to define the internal force variables acting on the cutting edge, which are required to constrain the numerical model. Finally, a method will be developed with the objective of calculating the stiffness of each sector. The numerical results will be verified by experiments. This article was presented at Materials Science & Technology 2006, Innovations in Metal Forming symposium held in Cincinnati, OH, October 15-19, 2006.     

Thermal analysis of laser surface transformation hardening—optimization of process parameters

This paper deals with the optimization of process parameters for maximum productivity (given by the product of scanning velocity and cross feed) in laser transformation hardening. The process parameters considered are laser beam power, P; laser beam diameter, D_b; and the heat intensity distribution, namely, normal, bimodal, or uniform. A thermal analysis of the laser surface transformation hardening of gears was conducted (based on Jaeger’s classical moving heat source method) by considering the laser beam as a moving plane (disc) heat source to establish the temperature rise distribution in the workpiece (gear) of finite width. In a recent investigation [Int. J. Heat Mass Transfer 44 (2001) 2845], the authors considered the case of a heat source with a pseudo-Gaussian (or normal) distribution of heat intensity. The analytical results were compared with the experimental results published in the literature. In laser heat treatment of steel, it is generally considered preferable to use a wider heat intensity distribution, such as uniform or bimodal, for it enables more uniform case hardening depth. In this paper, this model is extended to cover bimodal and uniform distributions and compared with the normal distribution. Scanning velocities for no surface melting and for a case hardening depth of 0.1 mm were determined for surface transformation hardening of AISI 1036 (EN 8) steel for a range of laser beam powers, P, laser beam diameters, D_b, and various heat intensity distributions. Since diffusion during the heat treatment (surface transformation hardening) process is a time dependent phenomenon, based on the literature review, an interaction time of 15 ms was taken as a basis. It is hoped that laser industry with adequate facilities available can validate the thermal analysis and subsequent optimization presented in this paper.     

钻杆环缝数控自动焊机

研制的钻杆环缝数控自动机焊为全自动的数控焊机。用于钻杆与两端法兰的内外共4条环缝的焊接。工件的上料、定位、夹紧、内外焊枪的到位、内外焊枪的焊接、自动排列焊道各层各道的焊接工艺参数的改变等均能自动进行。不同管径和不同壁厚采用的各种焊接参数都可在人机界面上预置。采用富氩混合气体保护焊工艺方法，焊缝美观，性能优良，几乎没有飞溅。经大量的生产实践证明该钻杆环缝数控自动焊机焊接质量好，生产效率高。     

Copper-nickel superalloys as inert alloy anodes for aluminum electrolysis

The superalloys Cu-Ni-Al, Cu-Ni-Fe, and Cu-Ni-Cr were studied as anodes for aluminum electrolysis. The alloys were tested for corrosion in acidic electrolyte molten salt and for oxidation in both air and oxygen. The results showed that the Cu-Ni-Al anodes possess excellent resistance to oxidation and corrosion, and the oxidation rates of Cu-Ni-Fe and Cu-Ni-Al anodes were slower than those of pure copper or nickel. During electrolysis, the cell voltage of the Cu-Ni-Al anode was affected most by the concentration of alumina in cryolite molten salt. The Cu-Ni-Fe anode exhibited corrosion resistance in electrolyte molten salt. Comparatively, the Cu-Ni-Cr anode showed poor resistance to oxidation and corrosion. The testing found that further study is warranted on the use of Cu-Ni-Al and Cu-Ni-Fe as inert alloy anodes. For more information, contact Zhongning Shi, Northeastern University, School of Materials and Metallurgy, WenhuiRoad No. 3, Shenynag, Liaoning 110004 China; e-mail znshi@163.com     

Properties of Induction Plasma Sprayed Iron Based Nanostructured Alloy Coatings for Metal Based Thermal Barrier Coatings

Metal-based thermal barrier coatings (MBTBCs) have been produced using high frequency induction plasma spraying (IPS) of iron-based nanostructured alloy powders. The study of MBTBCs has been initiated to challenge issues associated with current TBC materials such as difficult prediction of their “in-service” lifetime. Reliability of TBCs is an important aspect besides the economical consideration. Therefore, the study of MBTBCs, which should posses higher toughness than the current TBC materials, has been initiated to challenge the mechanical problems of ceramic-based TBCs (CBTBCs) to create a new generation of TBCs. The thermal diffusivity (TD) (α) properties of the MBTBCs were measured using a laser flash method, and density (ρ) and specific heat (C _p) of the MBTBCs were also measured for their thermal conductivity (k) calculation (k = αρ C _p).     

Advances in fabricating superplastically formed and diffusion bonded components for aerospace structures

Superplastic forming and diffusion bonding (SPF/DB) production hardware is being fabricated today for aerospace applications. Metal tooling is being used to bring the titanium sheets into contact so diffusion bonding can occur. However, due to material sheet and tooling tolerances, good bond quality is difficult to achieve over large areas. A better method for achieving DB is to use “stop-off” inside sealed sheets of titanium, which constitutes a pack, and then the pack is bonded using external gas pressure. A good method for heating the pack for this process is to use induction heating. Components using “stop-off” that were diffusion bonded first and then superplastically formed have shown much better bond quality than components that were produced using matched metal tooling. This type of tooling has been successful at bonding small areas as long as the exerted pressure is concentrated on the area where bonding is required. Finite element modeling is providing weight effect solutions for titanium SPF/DB aerospace structures. This paper was presented at the International Symposium on Superplasticity and Superplastic Forming, sponsored by the Manufacturing Critical Sector at the ASM International AeroMat 2004 Conference and Exposition, June 8–9, 2004, in Seattle, WA. The symposium was organized by Daniel G. Sanders, The Boeing Company.