Search Results for refractory metal alloys

The refractory metals include niobium, tantalum, molybdenum, tungsten, and rhenium. They are readily degraded by oxidizing environments at moderately low temperatures. Protective coating systems have been developed, mostly for niobium alloys, to permit their use in high-temperature oxidizing aerospace applications. This article discusses the properties, processing, applications, and classes of refractory metals and its alloys, namely molybdenum, tungsten, niobium, tantalum and rhenium. It also provides an outline of the coating processes used to improve their oxidation resistance.

All refractory metals, except osmium and iridium, have the highest melting temperatures and lowest vapor pressures of all metals. This article discusses the commercial applications, and production procedures of refractory metals and alloys. These procedures include fabrication, machining, forming, cleaning, joining, and coatings. The article also presents information on, and specifications for, the following metals and their alloys: niobium, tantalum, molybdenum, tungsten, rhenium, and refractory metal fiber-reinforced composites. It discusses the processes involved in their production, their mechanical properties, physical properties, thermal properties, electrical properties, chemical properties, applications, and corrosion resistance.

This article discusses special metallurgical considerations during the fusion welding of refractory metal alloys. These considerations are: microstructure, interstitial impurities, and welding conditions that are considered during the fusion welding of refractory metal alloys, including tantalum, niobium, rhenium, molybdenum, and tungsten. Refractory metal alloys are discussed in the order of decreasing weldability: tantalum, niobium, rhenium, molybdenum, and tungsten.

This article describes various procedures used in the metallographic preparation of niobium, tantalum, molybdenum, and tungsten alloys. It provides information on sectioning, grinding, mounting, polishing, and electrolytic etching as well as alternate procedures that have been used on refractory metals. The article presents and analyzes several micrographs, provides etchant formulas for various materials, and discusses the unique characteristics of rhenium and its alloys.

This article addresses surface cleaning, finishing, and coating operations that have proven to be effective for molybdenum, tungsten, tantalum, and niobium. It describes standard procedures for abrasive blasting, molten caustic processing, acid cleaning, pickling, and solvent and electrolytic cleaning as well as mechanical grinding and finishing. The article also provides information on common plating and coating methods, including electroplating, anodizing, and oxidation-resistant coatings.

The residual porosity in sintered refractory metal ingots is usually eliminated by different densification processes, such as thermomechanical processes. This article focuses on thermomechanical processing of tungsten, molybdenum, and tantalum. It provides an overview of liquid-phase sintering of tungsten heavy alloys and describes the infiltration of tungsten and molybdenum for attaining full density. The article concludes by providing information on hot isostatic pressing of refractory metal alloys to full density.

This article focuses on the selection, properties, and applications of powder metallurgy refractory metals and their alloys, including tungsten, molybdenum, tantalum, niobium, and rhenium.

This article provides a discussion on filler metal selection, brazing procedures, and brazing equipment for brazing refractory metals. These include molybdenum, tungsten, niobium, and tantalum, and reactive metals. Commercially pure and alpha titanium alloys, alpha-beta alloys, zirconium alloys, and beryllium alloys are some reactive metals discussed in the article.

Ultrasonic welding (USW) is effectively used to join both similar and dissimilar metals with lap-joint welds. This article describes procedure considerations for the ultrasonic welding of specific material types. It reviews difficult-to-weld alloys, such as carbon and low-alloy steels, high-strength steels, and stainless steel, and provides information on the applications of weldable alloys such as aluminum alloys and copper alloys. The article concludes with a discussion on welding of dissimilar metal (nonferrous-to-nonferrous) combinations and its applications.

This article describes the formability and surface contamination of the refractory metals such as niobium, tantalum, molybdenum, tungsten, and titanium-zirconium-molybdenum alloys. It reviews the factors that affect mechanical properties and formability during rolling and heat treatment. The effect of temperature on the formability of refractory metals is discussed. The article provides a description of the forming methods of sheet and preformed blanks using refractory metals. It also discusses the types of lubricants, including oils, soaps, waxes, silicones, graphite, and molybdenum disulphide, used in the forming of refractory metals.

Refractory metals are typically processed from powders into ingots that are subsequently swaged into round bars or rolled into plates. Secondary operations are required to fabricate more complex refractory metal components. This article discusses two such secondary operations, namely, machining and joining processes for tungsten, tungsten heavy alloys, molybdenum, tantalum, niobium, and rhenium components. It describes the various types of metal joining processes, including mechanical fastening, brazing, and welding.

This article discusses surface engineering of nonferrous metals including aluminum and aluminum alloys, copper and copper alloys, magnesium alloys, nickel and nickel alloys, titanium and titanium alloys, zirconium and hafnium, zinc alloys, and refractory metals and alloys. It describes various techniques to improve functional surface properties and enhance the appearance of product forms. The article discusses various cleaning and finishing techniques such as abrasive blast cleaning, polishing and buffing, barrel burnishing, chemical cleaning, pickling, etching and bright dipping, electrochemical cleaning, mechanical cleaning, and mass finishing. It also examines coating processes such as plating, anodizing, chemical conversion coating, and thermal spray, and concludes with a discussion on oxidation-resistant coatings for refractory metals.

Electrical contacts are made of elemental metals, composites, or alloys that are made by the melt-cast method or manufactured by powder metallurgy (PM) processes. PM facilitates combinations of metals that ordinarily cannot be achieved by alloying. This article describes the processing, properties, and performance of electrical contacts based on PM or hybrid composite technologies with refractory metals and compounds. These metals and compounds include tungsten, molybdenum, carbide-based composites, and silver-base composites. The article explains composite manufacturing methods, namely, PM methods, internal oxidation, and hybrid consolidation. The availability of the refractory metals and compounds in various product forms are also reviewed.

Characteristics of stainless steel that affect its formability include yield strength, tensile strength, and ductility, in addition to the effect of work hardening on these properties. This article discusses the forming process of stainless steel, heat-resistant alloys and refractory metals, detailing the major aspects of forming, including formability, lubrication, and forming methods and tools. The effect of factors such as alloy condition, cold reduction, forming direction (in the case of heat-resistant alloys) and temperature (in the case of refractory metals) on formability is also discussed.

The melting process often includes refining and treating the metal. The choice of which type of melting to use depends on a number of factors: type of alloy being melted, the local cost of electric power, and local environmental regulations. This article discusses the principles, furnace types, charging practices of metal melting methods, namely induction melting, cupola melting, arc melting, crucible melting, reaction melting, and vacuum melting, and the refractories and charging practice of reverberatory furnaces. Molten metal treatment of steels and aluminum also is discussed in the article.

Refractory metals are extracted from ore concentrates or scrap, processed into intermediate chemicals, and then reduced to metal, usually in powder form. This article discusses the raw materials needed and the processing steps for producing pure and alloyed refractory metal powders. The effects of processing conditions on the physical and chemical properties of tungsten, molybdenum, tantalum, niobium, and rhenium powders are reviewed.

Heat treating of stainless steel produces changes in physical condition, mechanical properties, and residual stress level and restores maximum corrosion resistance when that property has been adversely affected by previous fabrication or heating. This article focuses on annealing of different types of stainless steels such as austenitic, ferritic, duplex, martensitic, and precipitation-hardening, and on the heat treatment of superalloys and refractory metals. It discusses the recommended procedures for solution annealing, austenite conditioning, transformation cooling, and age tempering of precipitation-hardening stainless steels. The article also lists general recommendations for the annealing temperatures of tantalum, niobium, molybdenum, tungsten, and their alloys.

Electron-beam welding (EBW) can produce deep, narrow, and almost parallel-sided welds with low total heat input and relatively narrow heat-affected zones in a wide variety of common and exotic metals. This article discusses the joint configurations and shrinkage stresses encountered in various joint designs for electron-beam welding, as well as special joints and welds including multiple-pass welds, tangent-tube welds, three-piece welds, and multiple-tier welds. It provides a comparison of medium vacuum EBW with high-vacuum EBW. Scanning is a method of checking the run-out between the beam spot and the joint to be welded. The article describes various scanning techniques for welding dissimilar metals and provides information on the application of electron-beam wire-feed process for repairs. It concludes with a discussion on EBW of heat-resistant alloys, refractory metals, aluminum alloys, titanium alloys, copper and copper alloys, magnesium alloys, and beryllium.