CVD vs. Hard chrome: Choosing the best coating for durability and performance

The choice of surface coating for industrial components is pivotal to enhancing durability, optimising performance, and extending their lifespan in wear, corrosion and erosive operating environments. 

Chemical Vapour Deposition (CVD) coatings and Hard Chrome Plating (HCP) are two leading methods employed to achieve these ends. However, the former outperforms the latter when it comes to key resistances, sustainability and coating complex geometries. 

As technology and regulatory landscapes shift, understanding these distinctions is essential for making informed choices in coating selection.

A brief overview of CVD and hard chrome coatings

Chemical Vapour Deposition (CVD) is a process whereby a coating material, often a metal such as tungsten or tungsten carbide, is deposited as a thin, durable layer on a substrate. CVD coatings offer high hardness, toughness, and corrosion resistance, making them suitable for demanding applications across aerospace, energy and manufacturing sectors​​. The nanostructured, atom-by-atom application allows CVD coatings to be uniformly applied to both external and internal surfaces, including complex geometries​.

Hard Chrome Plating (HCP), in contrast, involves the electrolytic deposition of chromium from a toxic and carcinogenic hexavalent chromium salt solution. HCP forms a hard, wear-resistant layer but also presents environmental and health hazards. This has led to increasingly strict regulations under REACH and the TSCA which have made the coating less accessible. 

Performance and wear resistance - which comes out on top? 

Wear resistance

Hard chrome offers considerable wear resistance, but CVD coatings have higher hardness and demonstrated significantly higher performance in harsh environments. For instance, CVD tungsten carbide coatings have shown up to 24 times the wear resistance of hard chrome, offering superior protection against abrasive wear. This is especially valuable in applications where components are exposed to constant wear from sand, slurry, or other abrasive materials​.

Impact resistance and toughness

The nano-structured nature of CVD coatings provides enhanced toughness. Unlike hard chrome, which tends to form micro-cracks, CVD coatings resist cracking and chipping even under impact or shock loads. This feature extends the lifespan of components in high-stress environments, such as turbine blades or drilling tools​.

Corrosion resistance

Both CVD and hard chrome coatings offer corrosion protection, but CVD’s pore-free structure provides a more effective barrier. Unlike HCP, which usually has micro-cracks that allow corrosive agents to reach the substrate, CVD coatings are homogenous and contain no pores, reducing the risk of corrosion and maintaining the integrity of components in chemically aggressive environments​​.

How HCP falls short when it comes to environmental impact and sustainability

Hexavalent chromium used in hard chrome plating is carcinogenic and poses serious health risks to workers. The toxic process effluents are also very hazardous to the surrounding environment. Stringent regulations under REACH and OSHA have limited the use of hexavalent chromium, driving industries to seek safer alternatives. Since 2017, the REACH “sunset date” has required special authorisation to use hexavalent chromium in the EU, adding cost and complexity to HCP processes. Many companies are exploring CVD as an environmentally friendly alternative, particularly in sectors like aerospace, which demand REACH-compliant solutions​.

CVD coatings are typically applied REACH compliant methods that are controlled. This makes CVD a preferable choice for companies looking to minimise their environmental footprint and comply with global safety standards. The increased durability of CVD coatings also translates into longer intervals between component replacements, reducing resource consumption and waste​​. 

Why CVD is superior when it comes to complex geometries 

Coating complex geometries

CVD coatings provide a significant advantage over HCP in terms of application flexibility. The CVD process allows uniform coating on complex geometries, including internal and recessed surfaces, which are challenging or impossible to coat with HCP. This capability is essential for components with intricate designs, such as pump impellers, turbine blades or internal threads that require comprehensive protection across all surfaces​​.

Thickness and precision

Hard chrome can be deposited in thicker layers than traditional CVD, making it suitable for applications requiring high load-bearing capacity. However, the electrolytic process produces a thicker coating on the edges, resulting in a “dog bone” effect that requires grinding to achieve uniformity. Modern CVD coatings have reached comparable thicknesses of 50-100 microns while maintaining superior hardness, toughness and uniformity. The atom-by-atom deposition of CVD also allows for precise control of coating thickness, enhancing the accuracy of coated components​​.

Choosing the optimal coating for durability and compliance

Whilst hard chrome plating (HCP) has long been regarded as a reliable and well-established coating solution, its inherent toxicity and significant environmental impact have made it increasingly unusable in today’s regulatory and sustainability-driven landscape. As industries adapt to stricter standards and the need for greener alternatives, HCP is rapidly losing favour and is on a path towards obsolescence.

For engineers seeking a long-lasting, sustainable coating solution that meets stringent environmental standards, CVD coatings present a highly effective alternative. Hardide’s advanced CVD coatings, for example, have demonstrated exceptional durability and have been adopted by leading aerospace, energy, and manufacturing companies as a replacement for hard chrome. With the added benefits of compliance with REACH and other health and safety standards, CVD stands as the forward-looking choice for the industry’s most demanding applications.