Recent Progress in Precision Machining and Surface Finishing of Tungsten Carbide Hard Composite Coatings

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.

Tribocorrosive Aspects of Tungsten Carbide, Silicon Nitride, and Martensitic Steel under Fretting-like Conditions

“…Such composites are summarized under the term metal matrix composite (MMC). WC-MMC fracture toughness of 8-30 MPa m 1/2 [26] is superior to ceramic materials such as silicon carbide or alumina [27]. A recent review of the microstructures of cemented carbides including the discussion of structure-based functional gradients achieved by post-sintering thermal treatment has been written by García et al [26].…”

Experimental study for optimizing superfinishing process parameters of high-quality alloy bearing steel

“…Accordingly, advanced finishing techniques such as superfinishing process have been introduced to produce high surface quality and accurate geometry, as well as to avoid corrosion, wear, fatigue damaging of rolling mechanical parts, and improper marks from the workpiece surface [2,3]. Superfinishing also improves the tribological performance in terms of low surface roughness and waviness [4]. Superfinishing processes use combination of three movements: workpiece rotation, travel velocity, and oscillating motion with a small amplitude and high frequency of the head with a tool [5].…”

“…Also, use of a chemical additive could increase the material removal rate and improve the surface roughness when compared to a lubricant. Micallef et al [4] summarized that superfinishing process could be controlled by adjusting the contact pressure, oscillation speed, selected stone grit size, and finishing time.…”

Rapid surface finishing of chemical vapour deposited tungsten carbide hard coatings by electropolishing

“…Nonetheless, such complex features often obstruct mechanical machining process and thus satisfactory surface finish can be difficult to achieve. Electropolishing is an attractive surface finishing technique for this reason, as it allows processing of parts with complex geometries and is independent of the material's hardness [20].…”