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Microstructure and mechanical properties of PM Fe-Cu-Al 2 O 3 alloys
Abstract
The purpose of this study was to investigate the effect of Cu addition on the microstructure and mechanical properties of PM Fe-Cu-Al2O3 alloys produced using hot-pressing method. Copper powder was added to iron powder at 5 wt.%, 10 wt.% and 15 wt.% rates. Production of Fe-Cu-Al2O3 alloys was carried out under pressure of 35 MPa, at 750, 800 and 850C , and for a sintering time of 4 minutes. Microstructure phase composition, relative density, hardness, and transverse rupture strength of the alloys were investigated. Phase composition and microstructure of the alloys were characterised by optical microscopy, X-ray diffraction and scanning electron microscope (SEM-EDS) techniques. The transverse rupture strength (TRS) of the samples was assessed by means of a three-point bending test. Hardness of Fe-Cu-Al2O3 alloys changed between 57 HB and 110 HB depending on the amount of Cu and sintering temperature. Results show that the TRS of the alloys decreased together with the increase in the amount of copper, while it increased with increasing sintering temperature.
Cu-TiC composites have been produced by powder metallurgy technique. Mixtures of Cu–TiC powders corresponding to weight fractions of 1, 3, 5, 10 and 15 wt.% TiC were hot-pressed for 4 min at 700 °C under an applied pressure of 50 MPa. The transverse rupture strength (TRS) of the composites was evaluated by a three-point bending test. SEM were used to analyze the resulting fracture surfaces from the bending test. The TRS decreased rapidly in the 0-5 wt.% TiC contents, while it decreased slowly in the 5-15 wt.% TiC contents. SEM results showed that with the increase in the addition of titanium carbide to copper matrix, pores and gaps were present in the structure.
In this work, Alumix 431 (A17xxx) powder was pressed cold (room temperature) and warm (80°C) and its static and dynamic mechanical properties were investigated. Experiments were performed in two stages. In the first stage, cylindrical samples (Ø=15 mm, h=15 mm) were pressed warm and cold under 300-500 MPa pressure with 50 MPa intervals and sintering conditions that give optimum density were determined by sintering under three different sintering medium. In the second stage, tensile and fatigue samples that give the same density with this determined sintering condition were produced and these tests were conducted. In order to obtain the same density with cold and warm pressing in tensile and fatigue samples, 230 and 180 MPa pressure, respectively, was used. Since they have the same density, tensile and fatigue test results that were pressed cold and warm were equal. In addition, microstructures and morphologies of samples were investigated with Light and Scanning Electron Microscope.
The mechanisms of densification during laser ignited reaction sintering of Ni-Al-Cu powder materials were studied. With the addition of Cu, densification of Ni-Al-Cu specimens made of big particles was realized under laser rapid ignition and sintering without signification change of the final products. Filling of the mixture of liquid and disintegrated small grains or particles was regarded as the dominant mechanism for the final densification.
In the production of particle-reinforced metal-matrix composite castings, particle sedimentation during the melting process and particle redistribution during solidification can lead to particle segregation in the as-cast structure, the effects of which, in addition to those of porosity, can be highly detrimental to the properties and quality of the casting. Solidification rate and metal feedability are considered mainly responsible for the two problems. The present work reports on the influence of these factors on the particle distribution and porosity in 359 alloy composites reinforced with SiC and Al2O3 particles. The results show that the microporosity observed in 359/SiC(p) composites is a consequence of pore nucleation at the SiC particle sites and hindered liquid metal flow due to particle clustering; the former is responsible for the skewed porosity distribution profiles typically observed in these composites, similar to the type I distributions observed in A356 alloy. In the 359/Al2O3(p) composite, limited feedability and the wider range or larger particle sizes of the alumina particles result in the bell-shaped porosity profile observed, as well as the larger maximum pore size range (100–180 μm2 against 0–40 μm2 for the SiC(p) composites). The interparticle distance distributions for the SiC(p) composites show that finer dendrite arm spacings (DASs) produce a more uniform distribution of the SiC particles, while higher spacings lead to particle clustering, usually at separations of about 5 μm, the probability increasing with increase in SiC(p) content. In the 359/Al2O3(p) composite, the distribution profile changes from a normal, random distribution to an exponential type as the DAS is increased. Together with the microstructural observations, the distributions indicate that particle pushing is the dominant phenomenon in the SiC(p) composites during solidification, whereas in the Al2O3(p) composite, mechanical trapping of the particles takes place at smaller DASs, that changes to particle pushing at larger spacings.
Copper matrix composites reinforced with 1wt.%, 2wt.%, 3wt.% and 5wt.% SiC particles were fabricated by powder metallurgy method. Cu and Cu–SiC powder mixtures were compacted with a compressive force of 280MPa and sintered in an open atmospheric furnace at 900–950°C for 2h. Within the furnace compacted samples were embedding into the graphite powder. The presence of Cu and SiC components in composites was verified by XRD analysis. Optical and SEM studies showed that Cu–SiC composites have a uniform microstructure in which silicon carbide particles are distributed uniformly in the copper matrix. The results of the study on mechanical and electrical conductivity properties of Cu–SiC composites indicated that with increasing SiC content (wt.%), hardness increased, but relative density and electrical conductivity decreased. The highest electrical conductivity of 98.8% IACS and relative density of 98.2% were obtained for the Cu–1wt.%SiC composite sintered at 900°C and this temperature was defined as the optimum sintering temperature.
We may in time find industry performing a function hitherto associated entirely with scientific societies and universities, if it follows the lead of the Sylvania Electric Products, Inc. which recently sponsored a symposium on the physics of powder metallurgy at Fort Totten in Bayside, Long Island. Walter E. Kingston, manager of Sylvania's Metallurgical Research Laboratories, was the moving spirit of the meeting, which was organized and financially supported by his company independently of any technical society. Kingston assembled a program of twenty?two papers and approximately one hundred and fifty physicists and metallurgists attended.
Sylvania Symposium in late August
The main problem of metal matrix composite (MMC) when submitted to high temperature is the degradation of the reinforcement. Normally, this effect is studied through degradation at the interface of the reinforcement. In this case, the high temperatures produce the formation of intermetallic compounds. Generally, particle or whisker type reinforcements produce an improvement in the mechanical properties. In either case, to do a prediction of this influence through a mathematical model is very difficult and the single utilisation of the rule-of-mixtures is unsuitable for evaluating the effect that a discontinuous reinforcement would produce in these materials, because the different properties involved are very sensitive to the changes that occur in the microstructure during the production of the composite. This paper presents a numerical model to evaluate the Young’s modulus of the MMCs as a function of the sintering temperature. This model is similar to that presented in the rule of mixtures. However, it considers the porosity of the sintered material itself and the diffusion phenomena produced during the sintering of these materials. The suggested model utilises experimental data of the sample sintered in a vacuum at 1120, 1160, 1200, 1230 and 1250°C for periods of 30min. The Young’s modulus was obtained from the tensile curves of stress–strain. The utilised material is constituted of powder particles with size 99.8%
The aim of this research is to investigate the effect of the amount of reinforcement on the properties of Al–Al2O3 composite. Alumina particles were mixed with Aluminum particles in the range of 0–20wt.%. The average particle sizes for the matrix and reinforcement were 30 and 12μm, respectively.The samples were prepared at two levels of sintering temperature for a constant sintering time of 45min. It was illustrated that at high weight fractions of reinforcement, the relative density decreases while the hardness and wear resistance increases.Results show that by increasing the amount of Alumina from 0% to 10%, the hardness increased from 33 to 62 BHN, while the compressive strength was raised from 133 to 273MPa. The addition of alumina decreased the wear rate from 0.0447mm3/m to 0.0262mm3/m.
Although sintering is an essential process in the manufacture of
ceramics and certain metals, as well as several other industrial
operations, until now, no single book has treated both the background
theory and the practical application of this complex and often delicate
procedure. In Sintering Theory and Practice, leading researcher and
materials engineer Randall M. German presents a comprehensive treatment
of this subject that will be of great use to manufacturers and
scientists alike.
This practical guide to sintering considers the fact that while the
bonding process improves strength and other engineering properties of
the compacted material, inappropriate methods of control may lead to
cracking, distortion, and other defects. It provides a working knowledge
of sintering, and shows how to avoid problems while accounting for
variables such as particle size, maximum temperature, time at that
temperature, and other problems that may cause changes in processing.
The book describes the fundamental atomic events that govern the
transformation from particles to solid, covers all forms of the
sintering process, and provides a summary of many actual production
cycles. Building from the ground up, it begins with definitions and
progresses to measurement techniques, easing the transition, especially
for students, into advanced topics such as single-phase solid-state
sintering, microstructure changes, the complications of mixed particles,
and pressure-assisted sintering. German draws on some six thousand
references to provide a coherent and lucid treatment of the subject,
making scientific principles and practical applications accessible to
both students and professionals. In the process, he also points out and
avoids the pitfalls found in various competing theories, concepts, and
mathematical disputes within the field.
A unique opportunity to discover what sintering is all about--both in
theory and in practice
What is sintering? We see the end product of this thermal process all
around us--in manufactured objects from metals, ceramics, polymers, and
many compounds. From a vast professional literature, Sintering Theory
and Practice emerges as the only comprehensive, systematic, and
self-contained volume on the subject.
Covering all aspects of sintering as a processing topic, including
materials, processes, theories, and the overall state of the art, the
book
Offers numerous examples, illustrations, and tables that detail actual
processing cycles, and that stress existing knowledge in the field
Uses the specifics of various consolidation cycles to illustrate the
basics
Leads the reader from the fundamentals to advanced topics, without
getting bogged down in various mathematical disputes over treatments and
measurements
Supports the discussion with critically selected references from
thousands of sources
Examines the sintering behavior of a wide variety of engineered
materials--metals, alloys, oxide ceramics, composites, carbides,
intermetallics, glasses, and polymers
Guides the reader through the sintering processes for several important
industrial materials and demonstrates how to control these processes
effectively and improve present techniques
Provides a helpful reference for specific information on materials,
processing problems, and concepts
For practitioners and researchers in ceramics, powder metallurgy, and
other areas, and for students and faculty in materials science and
engineering, this book provides the know-how and understanding crucial
to many industrial operations, offers many ideas for further research,
and suggests future applications of this important technology.
This book offers an unprecedented opportunity to explore sintering in
both practical and theoretical terms, whether at the lab or in
real-world applications, and to acquire a broad, yet thorough,
understanding of this important technology.
Workability is concerned with the extent to which a material can be deformed in a specific metalworking process without the initiation of cracks. The ductile fracture of components is the most common mode of cracks in any metalworking processes. Workability is the complex technological concept, depends upon the ductility of the material and the details of the process parameters. An experimental research work was preformed for the understanding of the working behaviour of Al–Al2O3 composite under various stress state conditions, namely uniaxial, plane and triaxial stress states. Upsetting of Al–Al2O3 powder metallurgy compacts with various aspect ratios and initial preform densities were carried out and the working behaviour of the powder compacts at various state conditions was computed. The curves plotted for different components such as axial strain vs. formability stress index, relative density vs. axial strain, fracture strain vs. formability stress index and stress ratio parameters vs. axial strain were analyzed, using the true strains induced during upsetting with the consideration of bulging effect.
Residual stresses in a typical industrial green component were determined using neutron diffraction. The measured residual stresses were found to correlate with cross-sectional variations. Residual stress at the edge of the compact in contact with the die wall during compaction reached up to +80 MPa (tension) and −100 MPa (compression).
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Alternative binders of diamond cutting tools
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E. Çelik, Alternative binders of diamond cutting
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