Including Powder Metallurgy Research Articles

Fabrication, Processing, Properties, and Applications of Closed-Cell Aluminum Foams: A Review.

Closed-cell aluminum foams have many excellent properties, such as low density, high specific strength, great energy absorption, good sound absorption, electromagnetic shielding, heat and flame insulation, etc. As a new kind of material, closed-cell aluminum foams have been used in lightweight structures, traffic collision protections, sound absorption walls, building decorations, and many other places. In this paper, the recent progress of closed-cell aluminum foams, on fabrication techniques, including the melt foaming method, gas injection foaming method, and powder metallurgy foaming method, and on processing techniques, including powder metallurgy foaming process, two-step foaming process, cast foaming process, gas injection foaming process, mold pressing process, and integral foaming process, are summarized. Properties and applications of closed-cell aluminum foams are discussed based on the mechanical properties and physical properties separately. Special focuses are made on the newly developed cast-forming process for complex 3D parts and the improvement of mechanical properties by the development of small pore size foam fabrication and modification of cell wall microstructures.

High-Temperature Solid Lubricants and Self-Lubricating Composites: A Critical Review

Solid lubricants are described as solid materials of intentionally introduced or in situ formed on contact surfaces in relative motion for the purpose of lowering friction and wear and providing protection from damage. Solid lubricants and advanced self-lubricating materials are widely used in modern industries, especially in aerospace, aviation, automotive, metallurgy, materials forming, and machining industries, and have attracted great interest in lubrication applications under very severe circumstances such as elevated temperatures, heavy loads, ultrahigh vacuum, extreme radiation, strong oxidation, and chemical reactivity environments. Many efforts have been made to develop self-lubricating composites by a variety of material preparation techniques, which include powder metallurgy, physical/chemical vapor depositions, thermal spraying, electrodeposition, laser cladding, and additive manufacturing. Although several reviews on the development of high-temperature solid lubricants have been published, most of them only focus on a type of material, a specific process, or application. In this paper, a comprehensive review is provided to present the state-of-the-art progress in solid lubricants, self-lubricating composites/coatings, and their effective functions that can be used over a wide variety of environmental conditions, especially at elevated temperatures. The solid lubricants considered include representative soft metals, layered structure materials (e.g., graphite, hexagonal boron nitride, transition metallic dichalcogenides, MAX phase), chemically stable fluorides, binary or ternary metallic oxides, especially alkaline earth chromates, and sulfates, and synergistic effects from these solid lubricants. This paper also provides new insights into design considerations of environmental adaptive solid lubrication, and the challenges and potential breakthroughs are further highlighted for high-temperature solid lubrication applications.

A simple procedure to produce bio-mimic brick-and-mortar microstructure in commercially pure Ti

The extremely high fracture toughness of nacre is known to arise from its brick-and-mortar microstructure and has inspired the development of metals, metallic glasses and composites with similar bio-mimic microstructures. Although various approaches have been proposed to produce materials with a brick-and-mortar microstructure, including powder metallurgy, electro deposition, spray deposition, etc., the production of large-scale samples remains to be a challenge. In this research, we present a simple way to produce large samples of commercially pure Ti with a brick-and-mortar microstructure, which includes a pre-heat-treatment followed by deformation in the single-phase temperature region and subsequent annealing. EBSD characterization shows a layered microstructure in the produced samples resembling a brick-and-mortar structure.

Fundamentally New Composite Materials of Fast Reactors Made on the Basis of Nanotechnology

The main goal of the work is to identify the advantages of fast reactors when using nanotechnology in the manufacture of core materials. The research methods are based on the adaptation of known technologies (including powder metallurgy) to the design of fast reactors and on the numerical simulation of physical processes carried out using computer programs for the analysis of emergency conditions of fast reactors (including anticipated transient without scram - ATWS). The results of the research show that the use of structural materials based on steels hardened by nanooxides in combination with fundamentally new types of fuel based on composite materials can significantly improve the safety of nuclear technics. Sintered mixtures of ceramic microgranules (oxide, nitride) and nanoadditives of metallic beryllium or uranium are considered as nuclear fuel. Such composite nuclear fuel improves reactor safety and power. The following types of composite fuel were analyzed: mixed oxide with additives of a beryllium or uranium nanopowder, mixed mononitride with additives of a beryllium or uranium nanopowder. Most preferably, a ceramic-metal pellet fuel based on mononitride microgranules and uranium metal nanopowder. The use of such fuel (with a volume fraction of metallic uranium up to 20%) significantly increases the safety of the reactor, combining the advantages of metal and ceramics and completely neutralizing their disadvantages. The proposed materials are of practical importance in the development of new concepts of nuclear technics, in the transition to large-scale nuclear power and high-power reactors. The use of a new cermet-based composite fuel increases the power of the reactor and significantly increases the safety of the reactor.

Effect of pH Values and Microstructures on Corrosion Behavior of Ag-25Cu Alloys in NaCl Acidic Solutions

The effect of pH values and microstructures on the corrosion behavior of one coarse grained and two nanocrystalline Ag-25Cu alloys prepared by three kinds of methods including powder metallurgy (PM), liquid phase reduction (LPR), and mechanical alloying (MA) was investigated in NaCl acidic solutions. The corrosion rates slightly increase in the range of pH values from 7 to 5, but evidently when the pH values are less than 5. Furthermore, the corrosion rates increase after the nanocrystallizations and the nanocrystalline LPR Ag-25Cu alloy corrodes faster than the nanocrystalline MA Ag-25Cu alloy. All three Ag-25Cu alloys produce the passive phenomena and the passive films belong to n-type semiconductors. The passive current densities decrease in the order of PM Ag-25Cu, LPR Ag-25Cu, and MA Ag-25Cu alloys.

Size-Dependent Structural Properties of a High-Nb TiAl Alloy Powder.

TiAl-based alloys are promising light weight structural materials for high temperature applications in the field of aerospace. Recently, fabrication technologies starting from powders including powder metallurgy and additive manufacturing have been developed to overcome the difficulties in the processing, machining and shaping of TiAl-based alloys. Spherical alloy powders with different particle size distributions are usually used in these fabrication techniques. The purpose of this study is to reveal the size-dependent structural properties of a high-Nb TiAl powder for these fabrication technologies starting from powders. A high-Nb TiAl pre-alloyed powder with nominal composition of Ti-48Al-2Cr-8Nb (at. %) was prepared by the electrode induction melting gas atomization (EIGA) method. The phase structure and morphology of the as-atomized powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The size-dependent structural changes of the as-atomized powders with different sizes were studied by differential scanning calorimetry (DSC) and in situ high temperature XRD. It was found that with decreasing the powder size, the content of the γ-TiAl phase decreases and the α2-Ti3Al phase increases. The α2-Ti3Al to γ-TiAl phase transformation was found in the temperature range of 600–770 °C. Based on the present work, the structural characteristics of TiAl powders are strongly dependent on their particle size, which should be considered in optimizing the process parameters of TiAl alloys fabricated from powders.

Recent progress in Mg-Li matrix composites

Abstract Mg-Li matrix composites are one of the ideal structural materials in the fields of aerospace and military due to their high specific strength and stiffness, good damping and wear resistance, and small thermal expansion coefficient. The preparation technologies of Mg-Li matrix composites including powder metallurgy, pressure infiltration, stir-casting, foil metallurgy, and in-situ synthesis were introduced, and their advantages and disadvantages were compared. The common matrix alloys and reinforcements for Mg-Li matrix composites as well as the structure and performance of typical composites were mainly summarized. Then the interface chemistry between matrix and reinforcement was briefly reviewed. Finally, some problems existing at present and the possible solutions were discussed.

Fabrication and Properties of γ-TiAl Sheet Materials: A Review

γ-TiAl alloys have attractive properties such as low density, high creep resistance, high modulus, good oxidation and burn resistance. The main concern for the fabrication and use of TiAl alloys is the low deformability at room and high temperatures. Alloying and processing have been developed during the last three decades to improve the high-temperature deformability. Fabrication methods have been developed, including powder metallurgy and ingot metallurgy, to provide sheet materials for aerospace applications. This paper reviews the current status of TiAl sheet materials in terms of fabrication methods, microstructural control and mechanical properties. Future challenges and opportunities are also discussed.

Principles and Baseline Knowledge of Functionally Graded Aluminium Matrix Materials (FGAMMs): Fabrication Techniques and Applications

This paper discusses the main Functionally Graded Materials (FGMs) and their bulk fabrication techniques, their development, principles and applications. The fabrication processes considered include powder metallurgy (PM), sintering, squeeze casting, infiltration process, compocasting, centrifugal casting, stir casting, material prototyping. The paper provides an overview of the FGM processing parameters including reinforcement particles size and volume %, temperature, pressure (for PM), and stirrer and mould rotational speeds (for stir and centrifugal casting processes respectively). The paper notes that the FGMs are widely used in the following sectors: automotive, medical, aerospace, aviation, nuclear energy, renewable energy, chemical, engineering, optics electronics etc.

Development of non-eroding rocket nozzle throat for ultra-high temperature environment

The powder processing methods including powder metallurgy (P/M) and powder injection molding (PIM) techniques for tungsten (W)–rhenium (Re) were employed to produce a W–Re rocket nozzle. The composition of W–Re was determined by 25wt.% of Re to avoid the formatting brittle sigma (σ) phase. The samples for analysis of the densification behavior on sintering were prepared by die pressing and cold isostatic pressing (CIP). The feedstock for the PIM process was produced by mixing the W–25wt.% Re powder and binder system based on a wax-polymer with an optimum solid loading through the twin-extruder mixer. The injection molded specimens were debound to extract and decompose the binders via the solvent and thermal debindings. The debound samples were sintered in a hydrogen atmosphere. After sintering, hot isostatic pressing (HIP) was carried out in an argon atmosphere to enhance the density.The dilatometry experiments were performed to analyze and predict a densification behavior during sintering. The master sintering curve (MSC) model was used to characterize the densification behavior with a minimal set of preliminary experiments. The mechanical properties were evaluated through microstructure and chemical composition measured by EDX–SEM and X-ray diffraction (XRD).Finally, the eroding test was conducted using the W–25wt.% Re rocket nozzle produced by PIM under the high temperature. After carrying out erosion tests, the erosion rate, hardness and microstructure were evaluated.

Nanotechnology for copper and copper alloys

This article surveys and analyzes the literature data on nanotechnologies for copper and copper alloys. It describes the main methods used to obtain nanomaterials, including powder metallurgy, crystallization from the liquid state with a controlled rate of cooling, intensive plastic deformation, dispersion hardening, and dispersion strengthening with internal oxidation. Preference is given to nanophase materials in the discussion.

Gradient Nickel – Alumina Composite Coatings

Particle reinforced metal matrix composite (MMC) coatings have been developed due to property combinations such as increased hardness, high creep/fatigue resistance as well as superior wear and oxidation resistance. MMC coatings can be produced by various techniques, which include powder metallurgy (plasma spray and HVOF processes), liquid metal processes and electrodeposition. This paper presents the development of the electrodeposition process to obtain nickel-alumina composites. The process conditions were optimized and based on these gradient nickel-alumina composites were prepared. Microstructural characterization and hardness determinations were carried out. The effect of process parameters on the amount and distribution of alumina particles as well as morphology of the deposits with and without alumina gradients are presented and discussed.

News from the European powder metallurgy association: Epma marks its tenth anniversary under conditions of increasing globalization of powder metallurgy

EPMA notes increasing shipments of West European powder metallurgy products in 1998 compared with 1988. Growth has been particularly strong in Germany, Switzerland, Austria, and Spain. This is closely connected with the growth of automobile production. Problems of automobile construction, including powder metallurgy, were considered at a special EPMA seminar on 29 May 1999. The powder metallurgy specialists noted that there is a clear tendency towards globalization of automobile producing companies and their suppliers, including powder metallurgy manufacturers. For further development of European powder metallurgy the following are necessary: to be in closer touch with customers; to have a critical mass for research and development in order to promote cutting edge technology, design, and engineering; a global presence and a leading market share, giving financial strength; the capability to design and supply systems; coordination of European demands for automobile parts with those in America; a decrease in the prices of high-quality powders for producing high-strength and dense parts; attainment of more competitiveness of powder metallurgy production technology as in joining and processing technologies.

Commercial processing of metal matrix composites

Discontinuously reinforced metal matrix composites are a class of materials that exhibit a blending of properties of the reinforcement and the matrix. The reinforcement can be ultra-high strength whiskers, short or chopped fibers or particles. Each of the reinforcements has property or cost attributes that dictate its use in a given situation. Commercial producers have concentrated on composites with particulate reinforcement because of cost issues. These composites have been made by a number of manufacturing techniques. These include powder metallurgy, casting and spray deposition. The technique that has consistently produced higher property composites has been powder metallurgy. This paper concentrates on the commercial production of metal matrix composites. There have been many laboratory scale manufacturing methods developed for creating metal matrix composites. These will not be addressed in this paper. Recent work in this area has focused upon refining techniques that offer lower cost manufacturing. Scale-up of facilities to produce vacuum–hot pressed composite billets has been completed with the help of DOD funds through a Defense Production Act Title III program. Several companies have been working with a cold isostatic pressing–vacuum sintering process (CIP–sinter), to produce lower cost billet stock. In July 1996, the Alyn Corporation used private capitol to put in a scaled-up CIP–sinter facility. This paper will review the recent test data generated from aluminum composites made by the CIP–sinter manufacture method. These data will be compared with data generated by the Title III program that represent state-of-the-art processing. This comparison will demonstrate that both manufacturing methods produce composites with similar properties.

Interfacial reactions in SiC p/Al composite fabricated by pressureless infiltration

Metal matrix composites (MMCs) reinforced by ceramic phases have been fabricated by various techniques including powder metallurgy, casting, etc. Recently Lanxide corporation developed the DIMOX and PRIMEX processes for fabricating ceramic- and metal-matrix composites, respectively. The PRIMEX process is an innovative technique for fabricating MMCs by the spontaneous infiltration of molten AL alloy containing Mg into a ceramic filler or preform under nitrogen atmosphere in pressureless state without the aid of vacuum or externally applied pressure. Although there were many patents on MMC fabrication by the above pressureless infiltration technique, however, few works on the resulting microstructures and their effects on mechanical properties were reported. Thus, in this study, the effects on interfacial reactions occurring during the fabrication of SiC{sub p}AL composite by the pressureless infiltration technique on microstructures and hardness have been investigated.

Processing of molybdenum disilicide

Inspection of the scientific literature reveals that intermetallic compounds have, in recent years, attracted considerable interest as a result of their unique elevated temperature characteristics. Among the wide range of intermetallic compounds that are actively being studied, MoSi2 has been singled out as a result of its unique combination of properties, which include an excellent oxidation resistance, a high modulus of elasticity, and an elevated melting point (2030°C). In view of this interest, the present work was undertaken with the objective of providing the reader with a comprehensive review of the mechanical and oxidation behaviour of MoSi2, paying particular attention to the synergism between processing and microstructure. Accordingly, synthesis techniques, including powder metallurgy, self-propagating hightemperature synthesis, spray processing, solid-state displacement reactions, and exothermic dispersion, are critically reviewed and discussed. In addition, recent efforts aimed at using MoSi2 as a matrix material in metal-matrix composites are also critically reviewed and discussed.

Strain-life fatigue characteristics of wrought aluminum sheet: Chernenkoff, R.A., Krause, A.R. and Davies, R.G. Proc. Conf. Light Metals Processing and Applications, Quebec City, Quebec, Canada, 29 Aug.-1 Sept. 1993, pp. 655–665

Approximately 70% of aluminum produced globally is cast and fabricated into wrought alloy products by processes that are briefly described. These alloys are divided into two groups depending on whether or not they respond to heat treatment. The mechanical properties of the non-heat-treatable alloys are controlled by work hardening and annealing, whereas the heat-treatable groups are strengthened by age hardening. Temper designations are listed and described. Compositions and tensile properties of many of the commercial alloys are summarized in tables and their individual characteristics are discussed in some detail. Joining processes involving arc welding, friction stir welding, laser welding, brazing, diffusion bonding, and soldering are described. Attention is then directed to the commercial applications of the wrought aluminum alloys in the aerospace, automotive, shipping, packaging, and building industries. Reference is also made to lighter weight lithium-containing alloys that are finding structural applications in modern aircraft. Other more specialized topics include powder metallurgy products, aluminum alloy bearings, superplastic alloys, and aluminum-ion storage batteries.

Range-pair-counting fatigue gage: Nagase, Y., Sawaki, Y. and Yoshida, H. Exp. Mech. (Sept. 1993) 33 (3), 242–248

Approximately 70% of aluminum produced globally is cast and fabricated into wrought alloy products by processes that are briefly described. These alloys are divided into two groups depending on whether or not they respond to heat treatment. The mechanical properties of the non-heat-treatable alloys are controlled by work hardening and annealing, whereas the heat-treatable groups are strengthened by age hardening. Temper designations are listed and described. Compositions and tensile properties of many of the commercial alloys are summarized in tables and their individual characteristics are discussed in some detail. Joining processes involving arc welding, friction stir welding, laser welding, brazing, diffusion bonding, and soldering are described. Attention is then directed to the commercial applications of the wrought aluminum alloys in the aerospace, automotive, shipping, packaging, and building industries. Reference is also made to lighter weight lithium-containing alloys that are finding structural applications in modern aircraft. Other more specialized topics include powder metallurgy products, aluminum alloy bearings, superplastic alloys, and aluminum-ion storage batteries.

Degree of dispersion and morphology of the products of thermal decomposition of ferrous formate

One of the methods of obtaining highly dispersed powders of metals and their oxides is thermal decomposition ofthe carboxylates of metals in the solid phase [i]. An analysis of presently existing publications on thermal decomposition of these compounds, including of ferrous formateFe(HCOO)2~ indicates that investigators have revealed particular interest in studying the kinetic characteristics of the decomposition process. Insufficient attention has been devoted to the interrelationships of the degree of dispersion, the morphological characteristics, and the physicochemical properties of the condensed products formed to the kinetic parameters of the decomposition process although these questions become fundamental in the light of further practical use of such products in technology including powder metallurgy, diffusion welding, catalysis, and systems for recording and transmitting information [2-6].

Inco speciality powder products for the 1990's

When Dr. Ludwig Mond co-discovered the carbonyl process with Carl Langer in 1889, he could scarcely have envisaged that 100 years later, one of the most elegant of chemical reactions known to man would form the basis of nickel refining as performed at Inco's advanced refinery in Clydach. During a recent MPR visit to the refinery situated in the Swansea valley, South Wales, it was noted that the present plant, constructed in the late 1960's, admirably conveys the vision of the original discovery, producing speciality Ni powders and pellets by the carbonyl process for a variety of applications including powder metallurgy. This article traces the history of the carbonyl process and its commercialisation at Clydach, and highlights Inco's development of 'Speciality Powder Products' for the 1990's.