Abstract
Owing to their high hardness, fracture toughness and oxidation resistance, tungsten carbide (WC) coatings are extensively deposited on parts that operate in demanding applications, necessitating wear, erosion, and corrosion resistance. The application of thick and hard WC coatings has an inevitable effect on the original dimensions of the parts, affecting the geometrical tolerances and surface roughness. The capability of achieving a sub-micron surface finish and adhere to tight geometrical tolerances accurately and repeatably is an important requirement, particularly with components that operate in high-precision sliding motion. Meeting such requirements through conventional surface finishing methods, however, can be challenging due to the superior mechanical and tribological properties of WC coatings. A brief review into the synthesis techniques of cemented and binderless WC coatings is presented together with a comprehensive review into the available techniques which are used to surface finish WC-based coatings with reference to their fundamental mechanisms and capabilities to process parts with intricate and internal features. The binderless WC/W coating considered in this work is deposited through chemical vapour deposition (CVD) and unlike traditional cemented carbide coatings, it has a homogenous coating structure. This distinctive characteristic has the potential of eliminating key issues commonly encountered with machining and finishing of WC-based coatings. Here, six contact and non-contact surface finishing techniques, include diamond turning, precision grinding, superfinishing, vibratory polishing, electrical discharge machining, and electropolishing are discussed along with their current use in industry and limitations. Key challenges in the field are highlighted and potential directions for future investigation, particularly on binderless WC coatings, are proposed herein.
Highlights
Hard coatings are synthetic tribological layers which provide protection against wear, abrasion and corrosion, in extreme mechanical loading and elevated thermophysical conditions
WC1950s, as a industrial surface coating improve the functional performance use of WC as a surface coating to improve the functional performance and service life of components
Similar to other hard coatings in a form of transition metal oxides, nitrides, borides and carbides, WC composites are typically deposited by means of electrodeposition, thermal spray techniques, and vacuum deposition techniques, such as chemical vapour deposition (CVD) or physical vapor deposition (PVD) [24]
Summary
Hard coatings are synthetic tribological layers which provide protection against wear, abrasion and corrosion, in extreme mechanical loading and elevated thermophysical conditions They are commonly deposited on cutting, forming, machining and moulding tools to improve their functional performance and extend their service life – permitting cost reductions [1]. Materials with excellent hot hardness and fracture toughness, along with superior chemical stability and oxidation resistance at high temperature, are the best candidates for hard coatings. They are typically made of ceramics in the form of transition metal oxides, carbides, nitrides and borides, along with carbon-based compositions. WCHardness against other ceramics is shown in the Ashbyother diagram (Figureis1).shown in the Ashby diagram (Figure 1)
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