Combined Use of Surface Texturing, Plasma Nitriding and DLC Coating on Tool Steel

Elisangela Aparecida Dos Santos De Almeida,César Edil Da Costa,Cristiano Binder,José Daniel Biasoli De Mello,Julio Cesar Giubilei Milan,Henara Lillian Costa

doi:10.3390/coatings11020201

Abstract

In cold rolling, a textured roll can be used to imprint a desired surface topography onto the sheet during rolling. This work proposes the use of diamond-like carbon (DLC) coatings to protect the surface topography of the rolls in replacement of the carcinogenic hard chrome. For that, hydrogenated amorphous carbon (a-C:H) was deposited on plasma nitrided tool steel, both for ground and textured specimens. Changes in surface topography due to DLC coating were assessed using a confocal microscope. Coating adhesion was evaluated using the method VDI 3198. The specimens were characterized using X-ray diffraction (XRD), microhardness test and scanning electron microscopy (SEM). The coating was characterized using Raman spectroscopy (RS) and X-ray photoelectron spectroscopy (XPS). The results showed a soft multilayer coating consisting of a plasma nitrided layer for load support, a Si-rich interlayer to improve adhesion and an a-C:H top layer. DLC deposition reduced the roughness of the textured specimens. The coating resulted in relatively stable friction and good durability, with small damage and negligible wear even under dry sliding.

Highlights

Metalforming applications involve very high contact pressures, posing tribological challenges to the quality of the final product and the tool life
The morphology of the specimen textured by electric discharge texturing (EDT) (Figure 2c) shows recessed throughs corresponding to the ablated regions during EDT, as well as protruding features, corresponding to recast material, which is the typical morphology for surfaces textured by EDT [5,13]
Since the roughness of the tool should be transferred to the rolled sheet during the final step of cold rolling, it is very important that the original topography after surface texturing is preserved when diamond-like carbon (DLC) is deposited

Summary

Introduction

Metalforming applications involve very high contact pressures, posing tribological challenges to the quality of the final product and the tool life. Advanced approaches for surface engineering can greatly improve tribological properties during metalforming. Surface textures [1,2,3,4,5], plasma nitriding [6,7,8] and coatings [5,8,9,10,11] are promising avenues being explored to improve friction and wear of metalforming tools. Surface texturing of the roll is a current practice. Texturing of the roll can improve tribological performance during rolling, either by removing wear debris from the contact [2], by acting as lubricant reservoirs [4] or by generating plastohydrostatic and plastohydrodynamic lubrication mechanisms [14]. Surface textures in cold rolling are commonly random, produced by sandblasting or electric discharge texturing (EDT) [13]

Methods

Results

Discussion

Conclusion