Zirconium nitride multilayer coating

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Zirconium nitride multilayer coating (MLB) Zr-CrC-CrCN-Cr is a multi-layer coating that is used to improve wear properties and corrosion resistance. The MLB is a metallic hard material with a gold-colored surface. The ceramic material is characterized by very high hardness, biocompatibility and corrosion resistance, which results in a number of medical technology applications.

Properties ZrN multilayer coating

The top layer made of zirconium nitride is a ceramic material with great hardness and corrosion resistance .

The hardness is 2600 HV. In applications with high levels of wear, a ZrN coating can significantly reduce this.

ZrN coatings are mainly used in medical technology for coating artificial endoprostheses . This means that the implants are less subject to wear. Compared to the CoCrMo base material normally used for the metallic components of a knee prosthesis, wear is reduced by 60% with a ZrN coating.

The ceramic material is also very biocompatible and is therefore used in patients with metal allergies.

The five graded CrN-CrCN layers bridge the hardness and residual stress gradient between the softer base material CoCrMo (300 HV) and the very hard ZrN top layer (2600 HV) and thus guarantee the mechanical integrity of the system. The interfaces between the layers represent an additional diffusion barrier for ions from the base material. A Cr adhesive layer ensures good adhesion of the layers to the base material CoCrMo.

The coating, which consists of a total of 7 layers, has a layer thickness of approx. 3.5-5 µm.

Manufacturing PVD

In the PVD (Physical Vapor Deposition) process, an ionized metal vapor is generated that reacts with various gases in the plasma and deposits a thin layer on the workpiece surface. The most widely used PVD methods today are arc deposition and sputtering . Both methods are carried out under high vacuum conditions in a coating chamber.

Process temperature

The normal process temperature for PVD coatings is between 250 ° C and 450 ° C. In some cases, however, PVD coatings can be applied at temperatures below 70 ° C or up to 600 ° C, depending on the application or coating.

Coated workpieces

The PVD process can be used to apply coatings to a wide variety of substrates . Applications include cutting and forming tools, consumables, medical equipment, and decorative products. The palette of possible substrate materials ranges from steels and hard metals to pre-coated plastics.

Typical coatings

As a rule, TiN, AlTiN, TiAlN, CrN, CrCN, TiCN and ZrN are used as coatings. More complex coatings can consist of TiAlCrYN or a WC: H / DLC combination. The coatings can be applied in one layer, multiple layers or in graded layers. The coating structures can be modified in terms of crystallographic alignment and nano-composite structure so that the desired properties for hardness, elasticity, adhesion, etc. are obtained. The thickness of the coating ranges from 1 to 5 microns , but in some cases 0.5 microns or 15 microns and more are possible. The cycle time depends on the loading density and the type and thickness of the coating.

application

  • Multilayer coating for a knee prosthesis

The ZrN multilayer surface coating is mainly used in medical technology . Up to 13% of the population suffers from so-called contact allergies to metals such as nickel, cobalt or chromium. If these patients receive an endoprosthesis, which consists primarily of metal alloys, the risk of an allergic reaction to the implant increases. The ZrN multilayer coating reduces the release of metal ions below the medical threshold so that these patients no longer have to reckon with an allergic reaction.

Individual evidence

  • www.ionbond.com, data sheet coating portfolio May 6, 2011.

literature

  • J. Reich, L. Hovy, HL Lindenmaier, R. Zeller, J. Schwiesau, P. Thomas, TM Grupp: Preclinical results of coated knee implants for allergy sufferers. In: Orthopedist. 39 (5), 2010 May, pp. 495-502.
  • T. Schäfer, E. Böhler, S. Ruhdorfer et al: Epidemiology of contact allergy in adults. In: Allergy. 56, 2001, pp. 1192-1196.
  • P. Thomas: Allergies from implant materials. In: Orthopedist. 32 (1), 2003 Jan, pp. 60-64.
  • N. Hallab, K. Merritt, JJ Jacobs: Metal sensitivity in patients with orthopedic implants. In: J Bone Joint Surg Am . 83-A (3), Mar 2001, pp. 428-436.
  • R. Eben, R. Walk, B. Summer, S. Maier, M. Thomsen, P. Thomas: Implant allergy register - a first experience report. In: Orthopedist. 38 (6), 2009 Jun, pp. 557-562.
  • M. Thomsen, M. Rozak, P. Thomas: Pain in a chromium-allergic patient with total knee arthoplasty: disappearance of symptoms after revision with a special surface-coated TKA - a case report. In: Acta Orthop. 2011 Apr 20. [Epub ahead of print]