Self‐Lubricating Physical Vapor Deposition Coatings for Dry Cold Massive Forming

Abstract

Cold massive forming, particularly forward extrusion of steel, is characterized by high material utilization, product quality, and resource efficiency. Currently, enormous quantities of mostly ecologically harmful lubricants are required, leading to the demand for lubricant-free cold forming. Furthermore, cost savings are achievable due to shorter lead times. However, the requirements for the tools cannot be met without the application of wear-resistant and friction-reducing hard coatings. The self-lubricating hard coatings (Cr,Al)N þ Mo:S and (Cr,Al) N þ W:S with attuned material design deposited by physical vapor deposition (PVD) offer high potential for the realization of dry cold forming of steel. The process chain for the comprehensive characterization of the developed coating systems comprises analyses of coating and compound properties as well as two different model tests to determine the tribological behavior. One of the used tribometers represents an open tribological system, which is particularly suitable for simulating the loads occurring during cold massive forming of steel. The analyses reveal that with Mo and S modified coatings exhibit higher potential for ecologically sustainable cold forming due to their better mechanical properties and compound properties between the coatings and the cold work steel substrate compared with W and S modified coatings.

Approaches for Preventing Tool Wear in Sheet Metal Forming Processes

“…PVD self-lubricating (Cr,Al)N+Mo:S and (Cr,Al)N+W:S hard coatings offer high potential for application on cold forming tools. Bobzin et al [169] characterised self-lubricating tool coatings based on (Cr,Al)N, which were modified with W and S, as well as Mo and S. Coatings introduced with Mo and S showed much better adhesion between the coating and the substrate compared to the systems modified with W and S. Showing excellent adhesion to the substrate, a significant reduction in COF and high wear resistance, the (Cr,Al)N+Mo:S coatings demonstrated the highest potential for use on deep drawing tools. The self-lubricating properties of PVD-deposited tool coatings are based on the formation under tribological loads of reactive layers consisting of friction-reducing transition metal dichalcogenides.…”

Self-Lubricating PVD Hard Coatings through Tribological Activation

“…In addition, their application is also restricted by its low loadbearing capacity, poor coating adhesion and low hardness [23]. A promising approach to overcome these restrictions, is to combine PVD hard coating with elements which are able to form selflubricating TMD structures under tribological loads [4].…”

“…This possibility is estimated by the current oil lubrication market at $ 18.7 bn for the USA alone [3]. Friction reducing PVD coatings can be used either as alternative for lubricants or as a further support for highly loaded tribological systems [2,4]. Overall, it is not only a challenge to develop hard coatings with a self-lubricating effect, but also to meet the thermal requirements that lead to their activation and maintenance [5].…”

“…Overall, it is not only a challenge to develop hard coatings with a self-lubricating effect, but also to meet the thermal requirements that lead to their activation and maintenance [5]. Examples for a successful change from liquid lubricants to hard coatings with an integrated self-lubricating effect can be found in cutting and forming applications as well as in components for automotive engineering [2,4]. The predominant ambient conditions and operating temperatures of these applications cover a wide range.…”

Effects of Al, Ti, and Cr content with different interlayer configurations on tribological behavior of AlCrN and AlTiN multilayer coatings

“…Additionally, nitride-based hard composite coatings produced by physical vapor deposition (PVD) deposition offer high hardness, wear, and corrosion resistance that increase tool life. [12][13][14][15] Kumar et al 16 reported that TiN coated AISI O1 cold work tool steel had 53.5% and 308% higher elastic modulus and hardness than simply heat-treated steel, respectively, and TiN coated steel had only about two times lower wear rate. According to Hsu et al, 17 a mixed-phase (Ti, Al) N coated AISI D2 cold work tool steel produced by concurrently using Ti and Ti-Al alloy targets in the cathodic arc process increased abrasion resistance by about 5 times.…”