Nikasil

from Wikipedia, the free encyclopedia

Nikasil is a brand of the automotive supplier Mahle from Stuttgart for a cylinder surface coating made of nickel and silicon carbide (SiC) for aluminum engine blocks of piston engines .

The coating is an alternative to cylinder liners .

The acronym Nikasil is made up of the first letters of nickel , carbide and silicon . Other brand names for nickel dispersion coatings include: a. GALNICAL ( Kolbenschmidt AG / KS Aluminum-Technologie AG ), GILNISIL (Gilardoni Vittorio SrL, Italy) and NICOM (US Chrome Corporation).

The nickel dispersion layer is applied to the cylinder liner in an electrochemical (usually galvanic ) process. The resulting layer consists of a nickel matrix in which silicon carbide particles are evenly distributed. As a result, cylinder liners coated in this way have very good running properties, show little wear, and the known piston and piston ring materials or piston coatings can be used. Due to the hardness of the SiC, the machining is carried out with diamond-tipped tools. The good sliding properties of the coating make it possible for light metal pistons to run directly in the bores of an engine block made of aluminum alloys without having to pull in separate liners - for example made of gray cast iron . The Nikasilb coating was developed in 1967 for the housing running surfaces of rotary engines .

Nickel dispersion coatings are often used on single cylinders of motorcycle engines. The coating is also used for cylinder repairs.

durability

In principle, the Nikasil coating is durable and was used by various motor vehicle manufacturers for the cylinder coating of aluminum engine blocks, e.g. B. at BMW ( BMW M52 , BMW M60 , BMW M62 ), Jaguar AJ-V8 (1997-2000, XK-series, FGN 001036-042775 and XJ-V8-series, FGN 812256-878717), Maserati ( Biturbo II ) , NSU (Wankel engines) and Corvette C4 ZR1 . Nonetheless, engine damage occasionally occurred in nikasil-coated engines, which can be attributed to a failure of the Nikasil coating. The excessive wear of the coating found in the process could be linked to the use of insufficiently desulfurized fuel .

In a company publication, the problem with nickel-plated cylinder sliding surfaces is explained as follows:

“There were problems in production with cast porosities on the cylinder surface, which resulted in delamination. In the past, problems arose even with frequent short journeys in connection with fuel containing sulfur. In engines that rarely or never reached their operating temperature, short-haul operation led to the formation of condensate, which, together with the sulfur content, produced sulphurous acid from the combustion . These acidic combustion products led to corrosion, to the aforementioned delamination and ultimately to a move away from nickel-coated cylinder sliding surfaces in the production of passenger cars. "

This explanation is not very convincing, however, since nickel is resistant to non-oxidizing and not too strong acids. Nickel is resistant up to concentrations of 60% in cold, diluted hydrofluoric acid and up to concentrations of 70% in sulfuric acid.

A characteristic of the Nikasil coating is the carrier material made of a special nickel alloy in which the silicon carbide particles are embedded. The good tribological properties of silicon carbide ensure that the coating is wear-resistant.

The disadvantage, however, is the great sensitivity of nickel (and its alloys) to sulphurous gases, which favor nickel sulphide formation at the grain boundaries and thus lead to cold and red brittleness of the nickel. Nickel has a high affinity for sulfur , which is soluble in nickel up to about 0.005% and is also deposited in the grain boundaries as a nickel sulfide film. In addition, the melting point of nickel is extremely lowered by sulfur (from 1452 ° C to 645 ° C with eutectic composition, i.e. a eutectic forms between nickel and the nickel sulfide Ni 3 S 2 at 645 ° C and 21.5% by weight sulfur ). Even 100 K below this melting point, annealing in sulphurous gases leads to the penetration of the sulfur into the interior of the nickel, especially along the grain boundaries, which leads to the material becoming brittle. Sulfur can therefore have a particularly damaging influence on materials with a high nickel content. For the operation of nicasil-coated engines, the use of sulfur-free fuel and low-sulfur engine oil (which is common nowadays in Europe due to desulfurization ) is therefore recommended.

Individual evidence

  1. ↑ Information on the Nikasil brand  in the register of the German Patent and Trademark Office (DPMA)
  2. ↑ Information on the Galnical brand  in the register of the German Patent and Trademark Office (DPMA)
  3. ↑ Information on the GALNICAL brand  in the register of the German Patent and Trademark Office (DPMA)
  4. ↑ a b engine components . In: Richard van Basshuysen , Fred Schäfer (Hrsg.): Handbook Internal Combustion Engine: Fundamentals, Components, Systems, Perspectives . 5th edition. Vieweg + Teubner, Wiesbaden 2010, ISBN 978-3-8348-0699-4 , Chapter 7.5: Cylinder, p.  127 .
  5. ^ Slide Show repair techniques. (No longer available online.) Langcourt.com, archived from the original on September 16, 2016 ; accessed on September 15, 2016 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot / www.langcourt.com
  6. ↑ NiCom (Nikasil) Plating and Honing for the Porsche 928, Cayenne, 944, & 951.928motorsports.com, accessed on September 15, 2016 (English).
  7. ↑ Engines built with 'Nikasil' liners. go-lpg.co.uk, accessed on September 15, 2016 (English).
  8. ↑ R&T staff: Drive Flashback: 1990 Chevrolet Corvette ZR-1. Retrieved May 6, 2015, April 6, 2020 (American English).
  9. ↑ Overhaul of aluminum engine blocks. (PDF; 2.8 MB) 2.4.5 Nickel-plated cylinder sliding surfaces. MSI Motor Service International GmbH, 2006, accessed on September 15, 2016 .
  10. ↑ a b Nickel and nickel alloys . In: Werner Schatt , Elke Simmchen, Gustav Zouhar (Hrsg.): Construction materials of machine and plant construction . 5th edition. Wiley-VCH, Weinheim 1998, ISBN 3-527-30955-1 , Chapter 7: Materials for corrosive stress, p.  304 .
  11. ↑ Richard Ergang: Behavior in gases . In: Karl Erich Volk (Hrsg.): Nickel and nickel alloys - properties and behavior . Springer-Verlag, Berlin / Heidelberg 1970, Chapter G 3.3: Behavior in gases containing sulfur, p. 345 .