**1. Introduction**

Optical glass lenses have a broad range of applications (e.g., telescopes, cameras, medical equipment, and high-power lasers) because of their good refractive index, excellent chemical stability, light permeability, and high image quality [1–3]. Conventional manufacturing technologies include several techniques (e.g., precision grinding, and ultra-precision lapping and polishing), but these methods are time-consuming and difficult to use for the fabrication of complex shapes [4]. Precision molding, however, has low cost, high efficiency, can be applied to net forming, and is environmentally friendly. These characteristics have attracted great interest from optical manufacturers [5–7]. Unfortunately, the adhesive wear of glass blanks greatly degrades the molding life of the forming die and eventually decreases the quality of the optical glass component surface [8,9].

It has been reported that protective coatings can effectively improve the anti-sticking and anti-wear performance of forming dies [10–18]. Precious metal coatings are widely used in molding manufacturing due to their excellent anti-sticking and anti-oxidation properties [10–12], but they are also expensive for their wide industrial applications. Diamond-like carbon (DLC) films exhibit good self-lubrication and anti-wear performance, however, their poor thermal stability greatly limits any molding application [13,14]. Recently, the application of transition metal nitride coatings to glass molding has received great interest due to the favorable chemical inertness and anti-wear properties of these materials [15–18]. Most current studies focus on the anti-sticking and anti-oxidation properties of transition metal nitride coatings. WCrN coatings have been reported to have good anti-sticking properties at 400 ◦C, but also exhibited poor anti-sticking performances at 500 ◦C due to the formation of oxides [19]. CrWN coatings have been reported to experience severe mechanical degradation and coarsening in high temperature nitrogen atmosphere due to the formation of WO3 phases [20].

The life of glass molding coatings is determined mainly by their anti-sticking and anti-oxidation properties, as well as by their thermal stability. However, relatively little work has been published on the thermal stability of this type of coatings. In this study, CrWN coatings with different W contents are synthesized using PEMS. Detailed characterizations of these coatings were performed to study the evolution of their microstructures, as well as the mechanical properties of the as-deposited coatings after vacuum annealing. The potential effect of the W content on the thermal stability of the annealed coatings will be discussed systematically in the following sections.
