new materials in automotive tribology

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NEW MATERIALS IN AUTOMOTIVE TRIBOLOGY Presented by, K.Arun (094ED101) ME-ED BIT-Sathy, Tamilnadu India

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Contents Trends of Automotive Tribology Materials for automotive tribo-components Cylinder, piston and piston ring Plane bearings Valve trains New material processing for tribo-components Conclusion

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Trends of Automotive Tribology The main demands for a passenger car are: Efficient use of resources (recyclability, substitute fuel and fuel economy) Environmental protection (fuel economy, reduction of emissions of exhaust and toxic or polluting substances) Customer satisfaction (reliability, fuel economy, safety, low maintenance, comfort and low cost)

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There are essentially three ways to approach an optimum tribological solution lubrication, design and materials(so called LUDEMA)

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Materials for automotive tribo-components Engine group The engine system is divided into three components: A piston component (a cylinder, a piston and a piton ring) A crank component (a crank shaft, bearings and a connecting rod A valve-train component (a cam, a shim, a valve, a valve sheet and a valve guide)

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Cylinder, piston and piston ring In order to improve fuel economy, reduction of the weight of any components and of the friction loss of tribo-components is important, they are closely related to the design of the engine system Engine cylinder block made of cast iron is the heaviest unit, and largest friction loss occurs in the engine An aluminum-alloy (Al–Si–Cu) engine block with an insert of cast iron cylinder liner Achieving a 30% weight reduction

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Wear-resistant overlays or surface modifications on the inner face of the aluminum alloy have also to be developed, where SiC dispersed Ni–P plating, plasma spray coating of hard ferrous or nonferrous alloys, etc Surface modifications and coatings are applied on the piston crown and piston ring groove made of aluminum alloy Thermal-resistant coating is required on the crown part of the piston Wear resistance is required for the piston ring groove, where typical surface treatments are anodic oxidizing and electroplating with Ni or Cr

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The friction coefficient of the newly developed coating on the engine skirt was 0.035 in an engine bench test, which was 20% smaller than that of conventional resin bonded coatings Recently, a Cr–N ion plated stainless steel ring, prepared by an arc-ion plating method, has been developed (thickness is 50 µm) Application of the Cr–N ion-plating resulted in a 90% reduction of the top ring wear and about 15% reduction of the cylinder bore wear compared to a conventional Cr plated ring

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Plane bearings Recent trends towards higher power efficiency of engines with multiple valves, turbo-charger systems, direct injection of fuel, etc.. Mean that bearings must have a higher load-carrying capacity and better anti-seizure performance In a conventional bearing, tribological problems occur in that frictional heat raises the temperature of the lubricating oil, reducing oil thickness As a result, the bearing surface sometimes melts

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The tribo-materials used for crankshaft bearings require high performance in terms of running-in, wear resistance and embeddability of foreign particles A conventional bearing is typically composed of a top layer of Pb–Sn–In or Pb–Sn–Cu plating of thickness 10–25 µm A second layer of Cu–Pb Kelmet alloy or Al–Sn alloy 200–300 µm thick and a cold-rolled steel sheet as the backing metal An Ni barrier plating of 1–3 µm thick is made between top plating layer and a second Kermet layer to prevent thermal diffusion of Pb from the second to top layer

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Electro-deposition method could be applied to the bearing overlay Crystallographically-oriented Pb alloy electro-deposit having the plane on the bearing exhibited good wettability for lubricating oil The anti-seizure parameter of PV value of the oriented deposit on the bearing was improved by as much as 30% compared with that of a conventional deposit A bearing having a micro-groove depth of 4–4.5 m and pitch of 0.2–0.25 mm at the surface has been developed and its running-in performance were improved

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Valve trains Valve-train friction accounts for approximately 30% of all engine friction Valve-train components are operated under cyclic loading and exposure to high temperature exhaust of about 900 C Heat-resistant materials are required for the valve-train components A conventional valve is made of heat-resistant steel on which Co or Ni based alloys are deposited on the valve face for wear resistance High wear resistance and low abrasion effect against the valve are required for the valve sheet material

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The exhaust valve is subjected to severe thermal effects, the valve sheet material should have a high thermal diffusivity An inserted ring, however, has a problem of lower thermal diffusivity To overcome this problem, laser-cladding of Cu–Ni–Si alloy directly fabricated on an aluminum alloy cylinder has been utilized in practice A ferrous alloy ring, electroplated with Cu, Zn or Sn of 2 µm thick, was bonded well on the aluminum alloy by means of an electric resistant-bonding method

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New material processing for tribo-components Various types of surface modifications and coatings have been utilized for a variety of tribo-components in automobiles to improve the friction and wear properties The hardness of modifications and coatings against process temperature Laser hardening and cladding have been utilized, because localized modifications can be made on a desired part of the component

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Further development of laser technologies is desired to create high performance tribo-materials A promising technique is a combination of laser with low-pressure plasma spraying (LPPS) Laser plasma hybrid spraying (LPHS) has the potential to create metallic alloy coatings having a fine-grained structure and also coatings having mixed-metal phases The LPHS coatings of Mo–Cu showed better tribological performance than the LPPS coating

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Physical vapor deposition (PVD) was successfully developed to form metallic compound films, such as TiN and CrN for practical tribo-applications Diamond and diamond-like films produced by PVD or chemical vapor deposition (CVD) may also be applied to sliding parts such as a valve-train components Because they show a lower friction coefficient of 0.05–0.1 without lubricants

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Mass-produced automobiles have to be optimized by considering the best balance between automotive technologies and the environments and resources Most of materials used can be recycled and working to replace the petroleum fuel engine with other types of engine based on new energy sources such as bio-mass based fuel, electric, hydrogen and others The respective technologies require new design of the system, in which tribo-components must operate well under more severe conditions Conclusion

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