Liquid phase sintering (LPS) is a process for forming high performance, multiple-phase components from powders. It involves sintering under conditions where solid grains coexist with a wetting liquid. Many variants of LPS are applied to a wide range of engineering materials. Example applications for this technology are found in automobile engine connecting rods and high-speed metal cutting inserts. Scientific advances in understanding LPS began in the 1950s. The resulting quantitative process models are now embedded in computer simulations to enable predictions of the sintered component dimensions, microstructure, and properties. However, there are remaining areas in need of research attention. This LPS review, based on over 2,500 publications, outlines what happens when mixed powders are heated to the LPS temperature, with a focus on the densification and microstructure evolution events.

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Review: liquid phase sintering

(Vol. 1, part of 2 vols set) Size: 22x14cm., Contents: Chapter I. Tension and Compression within the Elastic Limit II. Analysis of Stress and Strain III. Bending Moment and Shearing Force IV. Stresses in Laterally Loaded Symmetrical beams V. Deflection of Laterally Loaded Symmetrical Beams VI. Statically Indeterminate Problems in Bending VII. Symmetrical Beams of Variable Cross Section-Beams of Two Materials VIII. Bending of Beams in a plane which is not a Plane of Symmetry IX. Combined Bending and Axial Load Theory of Columns X. Torsion and Combined Bending and Torsion XI. Strain Energy and Impact XII. Curved Bars Appendix A: Moments of Inertia of Plane Areas Appendix B. Tables of Structural Shapes Author Index Subject Index. ISBN:8123910304 xiv+442 Yr. of Pub.reprint 2004Paper Back

Strength of materials ..

IEEE Standard on Piezoelectricity

Humans have a myriad of sensory receptors in different sense organs that form the five traditionally recognized senses of sight, hearing, smell, taste, and touch. These receptors detect diverse stimuli originating from the world and turn them into brain-interpretable electrical impulses for sensory cognitive processing, enabling us to communicate and socialize. Developments in biologically inspired electronics have led to the demonstration of a wide range of electronic sensors in all five traditional categories, with the potential to impact a broad spectrum of applications. Here, recent advances in bioinspired electronics that can function as potential artificial sensory systems, including prosthesis and humanoid robots are reviewed. The mechanisms and demonstrations in mimicking biological sensory systems are individually discussed and the remaining future challenges that must be solved for their versatile use are analyzed. Recent progress in bioinspired electronic sensors shows that the five traditional senses are successfully mimicked using novel electronic components and the performance regarding sensitivity, selectivity, and accuracy have improved to levels that outperform human sensory organs. Finally, neural interfacing techniques for connecting artificial sensors to the brain are discussed.

Bioinspired Electronics for Artificial Sensory Systems

The invention relates to a high-pressure gas-discharge lamp, having at least one gastight fused press-seal (61, 62) between a glasslike material and molybdenum, wherein the molybdenum in the fused press-seal (61, 62) is at least partly exposed to an oxidizing environment and at least that part of the molybdenum (5) that is exposed to the oxidizing environment is covered with a coating, and the coating comprises at least one oxide from among Fethe invention relates to a high-pressure gas-discharge lamp,having at least one gastight fused press-seal between a glasslike material and molybdenum,wherein the molybdenum in the fused press-seal is at least partly exposed to an oxidizing environment and at least that part of the molybdenum that is exposed to the oxidizing environment is covered with a coating, and the coating comprises at least one oxide from among Fe2O3, Ta2O5, Nb2O5, Al2O3, SiO2, TiO2, ZrO2, HfO2, and/or one nitride from among TiN, ZrN, HfN, AlN, BN, and/or one carbide from among TiC, ZrC, HfC, VC, NbC, TaC, B4C.

High-pressure gas-discharge lamp

Dimensional precision is one of the prime concerns in forming net-shape bodies by liquid phase sintering. The factors that lead to densification can also cause distortion, leaving a narrow processing window in which to achieve densification without distortion. This paper reports the effect of heating rate on liquid phase sintering of W–Ni–Fe heavy alloys. Heavy alloys with compositions of 83, 88, and 93 wt.% W, balance Ni–Fe in the ratio 7:3, were sintered at heating rates of 1, 5, 10, and 15 °C/min. Over this range, heating rate did not have a significant effect on densification nor distortion. Critical values of contiguity and connectivity were identified that separate distortion from shape preservation. The grain size distributions produced by different heating rates are self-similar. A previously proposed cumulative intercept grain size distribution function gives a good fit to the grain size data. The mean grain growth rate constant is 2.8 μm3/s. The grain growth rate constant varies inversely with the volume fraction of liquid to the 2/3 power.

Heating rate effects on microstructural properties of liquid phase sintered tungsten heavy alloys

This paper aims to correlate the densification and distortion behaviors of liquid-phase sintered 80W-14Ni-6Cu and 80W-14Ni-6Fe heavy alloys with the melting characteristics of the Ni-Cu and Ni-Fe matrices. Differential thermal analysis (DTA) of die-pressed compacts reveals that the melting range of the Ni-Cu matrix is extended from 1235°C to 1453°C by the in situ alloying between elemental Cu and Ni powders, whereas the melting of the Ni-Fe matrix is limited to a narrow temperature range between 1464°C and 1480°C. Dilatometry and furnace sintering tests show that densification due to liquid-phase sintering of 80W-14Ni-6Cu starts at 1287°C and proceeds at a low rate to 1450°C, where full densification without distortion is achieved. In contrast, densification due to liquid-phase sintering of 80W-14Ni-6Fe occurs at a very high rate above 1475°C, and full density can be obtained at 1500°C. For both alloy compacts, distortion is induced by prolonging the sintering time or elevating the sintering temperature after full densification. Crack-like voids develop in the 80W-14Ni-6Cu compact to accommodate the gravity-induced distortion, while spherical pores are dominantly formed in the 80W-14Ni-6Fe compact as a result of water vapor entrapment.

Comparison of densification and distortion behaviors of W-Ni-Cu and W-Ni-Fe heavy alloys in liquid-phase sintering

The characteristics of densification and distortion of a 80W–14Ni–6Cu alloy during liquid-phase sintering (LPS) were investigated in relation to the liquid-phase formation. By means of differential thermal analysis (DTA), the melting process of the Ni–Cu matrix in a die-pressed compact was examined and compared with that in a loose powder mixture. It was revealed that enhanced inter-diffusion and in situ alloying occur between the tightly compacted elemental Cu and Ni powders during heating, leading to an extended temperature range for Ni–Cu liquid formation. Dilatometry and furnace sintering tests showed that the early melting of the Ni–Cu matrix results in an onset of liquid-phase sintering at a lower temperature with die compaction. Full densification of the compact, together with satisfactory microstructure, can be achieved prior to full melting of the Ni–Cu matrix. Distortion is delayed until the end of liquid-phase formation.

Ravi Bollina

Papers

Heating rate effects on microstructural properties of liquid phase sintered tungsten heavy alloys

Comparison of densification and distortion behaviors of W-Ni-Cu and W-Ni-Fe heavy alloys in liquid-phase sintering

Characteristics of densification and distortion of Ni–Cu liquid-phase sintered tungsten heavy alloy

Effect of nanopowder ratio in bimodal powder mixture on powder injection molding

Critical use of video-imaging to rationalize computer sintering simulation models