Search Results for chromizing

Pack cementation is the most widely employed method of diffusion coating. This article briefly reviews pack cementation processes of aluminizing, chromizing, and siliconizing. It contains tables that list typical characteristics of pack cementation processes and commercial applications of pack cementation aluminizing, which is used to improve the performance of steels in high-temperature corrosive environments.

This article describes the widespread use of diffusion coatings for elevated-temperature protection of the turbine components for aircraft engines and gas turbines. The principles of pack diffusion coating, namely, aluminizing, chromizing, and siliconizing, are discussed. The article presents information on the coating formation mechanism of superalloys and explains the steps involved in a typical pack cementation process. It concludes with information on the processing procedures and properties of pack aluminized steels.

This article focuses on the pack-cementation coatings, in particular, halide-activated pack cementation coatings on nickel alloys. It also describes the thermodynamics and kinetics of, and simultaneous deposition of various types of, pack cementation processes. These include pack aluminizing, chromizing, and siliconizing.

Chemical vapor deposition (CVD) involves the formation of a coating by the reaction of the coating substance with the substrate. Serving as an introduction to CVD, the article provides information on metals, ceramics, and diamond films formed by the CVD process. It further discusses the characteristics of different pack cementation processes, including aluminizing, siliconizing, chromizing, boronizing, and multicomponent coating.

The presence of certain impurities in coal and oil is responsible for the majority of fireside corrosion experienced in utility boilers. In coal, the primary impurities are sulfur, alkali metals, and chlorine. The most detrimental impurities in fuel oil are vanadium, sodium, sulfur, and chlorine. This article describes the two categories of fireside corrosion based on location in the furnace: waterwall corrosion in the lower furnace and fuel ash corrosion of superheaters and reheaters in the upper furnace. It discusses prevention methods, including changes to operating parameters and application of protective cladding or coatings.

Surface treatments are used in a variety of ways to improve the material properties of a component. This article provides information on surface treatments that improve service performance so that the design engineer may consider surface-engineered components as an alternative to more costly materials. It describes solidification surface treatments such as hot dip coatings, weld overlays, and thermal spray coatings. The article discusses deposition surface treatments such as electrochemical plating, chemical vapor deposition, and physical vapor deposition processes. It explains surface hardening and diffusion coatings such as carburizing, nitriding, and carbonitriding. The article also tabulates typical characteristics of carburizing, nitriding, and carbonitriding diffusion treatments.

The thermoreactive deposition and diffusion process is a heat-treatment-based method to form coatings with compacted layers of carbides, nitrides, or carbonitrides, onto some carbon/nitrogen-containing materials, including steels. The amount of active carbide forming elements/nitride forming elements, coating temperatures and time, and thickness of substrates influence the growth rate of coatings. This article lists carbide and nitride coatings that are formed on carbon/nitrogen-containing metallic materials, and describes the coating process and mechanism of coating reagents. It details the growth process and nucleation process of carbide and nitride coatings formed on the metal surface. The article discusses the advantages, disadvantages, and characteristics of the various coating processes, including high-temperature salt bath carbide coating, high-temperature fluidized-bed carbide coating, and low-temperature salt bath nitride coating.

Surface hardening improves the wear resistance of steel parts. This article focuses exclusively on the methods that involve surface and subsurface modification without any intentional buildup or increase in part dimensions. These include diffusion methods, such as carburizing, nitriding, carbonitriding, and austenitic and ferritic nitrocarburizing, as well as selective-hardening methods, such as laser transformation hardening, electron beam hardening, ion implantation, selective carburizing, and surface hardening with arc lamps. The article also discusses the factors affecting the choice of these surface-hardening methods.

This article presents the principles of chemical vapor deposition (CVD) with illustrations. It discusses the types of CVD processes, namely, thermal CVD, plasma CVD, laser CVD, closed-reactor CVD, chemical vapor infiltration, and metal-organic CVD. The article reviews the CVD reactions of materials related to hard, tribological, and high-temperature coatings and to free-standing structures. It concludes by reviewing the advantages, disadvantages, and applications of CVD.

This article describes various quenchants, namely, water and inorganic salt solutions, polymers (polyvinyl alcohol, polyalkylene glycol, polyethyl oxazoline, polyvinyl pyrrolidone and sodium polyacrylates), quench oils, and molten salts, which are used for heat treatment of ferrous alloys. It also provides information on the steps for controlling quenching performance for polymer quenchants and oils with an emphasis on measuring quenchant performance, safety measures, and oxidation.

This article describes the specific features and mechanisms of oxidation in thermal spray coatings. It discusses the two forms of hot corrosion in sulfur-containing combustion, namely high-temperature hot corrosion and low-temperature hot corrosion. The article reviews the behavior of corrosion-resistant coatings in boilers. The effects of high-temperature corrosion in waste incinerators are detailed. The article also examines the effects of erosion-corrosion in fluidized bed combustion boilers.

This article discusses the methods of pulp production, pulp processing, pulp bleaching, and paper manufacturing. It describes various types of digesters, their construction materials, the corrosion problems encountered, and methods to protect these digesters from corrosion. The article examines the corrosion problems in high-yield mechanical pulping, sulfite process, neutral sulfite semichemical pulping, chemical recovery, tall oil plants, wastewater treatment, and recovery boilers. It explains the stages of chlorine-based and nonchlorine bleaching, process water reuse for elemental chlorine-free and nonchlorine bleaching stages, selection of material for bleaching equipment, developments in oxygen bleaching, and the use of highly corrosion-resistant materials for bleach plant equipment. The article reviews the materials used in the construction of paper machine components and specific corrosion problems that affect them. It discusses the composition and corrosive nature of white water. The article also addresses the corrosion and chemical recovery associated with kraft pulping liquors.

This article provides an overview of key thermal spray coatings used in compressors, combustors, and turbine sections of a power-generation gas turbine. It describes the critical components, including combustors, transition ducts, inlet nozzle guide vanes, and first-stage rotating airfoils. Design requirements are reviewed and compared between aerospace and power generation coatings. Application process improvement areas are also discussed as a method of reducing component cost.

When metal is exposed to an oxidizing gas at elevated temperature, corrosion can occur by direct reaction with the gas, without the need for the presence of a liquid electrolyte. This type of corrosion is referred to as high-temperature gaseous corrosion. This article describes the various forms of high-temperature gaseous corrosion, namely, high-temperature oxidation, sulfidation, carburization, corrosion by hydrogen, and hot corrosion.

This article discusses the metallography and microstructures of carburized, carbonitrided, and nitrided steels, with illustrations. It provides information on the widely used metallographic techniques including sectioning, mounting, grinding and polishing, and etching.

Boronizing is a case hardening process for metals to improve the wear life and galling resistance of metal surfaces. Boronizing can be carried out using several techniques. This article discusses the powder pack cementation process for carrying out boronizing. It describes the structures of boride layers in ferrous materials and boride-layer structures in nickel-base superalloys. The primary reason for boriding metals is to increase wear resistance against abrasion and erosion. The article reviews the wear resistance and coefficient of friction of boride layers, as well as galling resistance of borided surfaces. It concludes with a discussion on boronizing plus physical vapor deposition (PVD) overlay coating.