1. of CrN-PVD coated spur gears used in

 1.       (IGARTUA)  Firstly, Low temperature PVD process toachieve the coatings at limited temp. of 160 C has been described by applyingthe newly developed technique namely “Enhanced Sputter Ionic Plating” .Secondly, the characterization of coatings in lubricated conditions was done byanalysing the tribological test results.Titanium derivative coatings resulted an increase in hardness which in turnimproved tribological performance under high stress conditions.  CrNcoatings exhibited improvement under low load, high speed working conditions.2.       (NAVINSEK)The CrN and TiN hard coatings of thickness of 3µm at a temperature of 200°C were applied on steel, sapphire and alumina substrates by plasma beamsputtering process and the effect on various characteristics was studied.

Theiroxidation behaviour was studied at temperatures up to 600 °C for TiN and up to800 °C for CrN coatings and the results showed that a stoichiometric CrN coatingcan remarkably be applied as a hard and oxidation-resistantcoating in real industrial environment, even if the working temperatures arehigher than 750 °C.3.      {Beliardouh)Effect on tribological properties of low alloy steel, under low load and lowspeed, was studied by applying the duplex coating consisting of 500 ?m thick low pressure carburizing layer and 2 ?m thick layer of Cr–(WC–Co) coating deposited by dual RFmagnetron sputtering. Experimental results showed that sliding wear, of theinvestigated duplex treated low alloy steels, is strongly dependent on thecounterface materials. While the wear performance of a Cr–WC coating (Cr/W ratio of 1.12:1) deposited onto the surface ofa carburized low alloy steel (0.61wt.

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% C; HV=654±5) was recommended the best,the duplex-treated samples suffered severe, concentrated wear against alumina.This wear is characterized by a combination of delamination, mild abrasion andoxidative wear.  4.      Baragetti(2007) Investigated the effect on fatigueresistance of CrN-PVD coated spurgears used in gearboxes for automotive applications by employing the numerical simulation of crack propagation todetermine the number of cycles necessary to reach specified crack depths incoated and uncoated steel and titanium spur gears. Results showed theimprovement in the fatigue life of coated gears over the uncoated gears. 5.

      Komarovs et al. 2016 studied the  effect of pre-hardening of steel substrate onmechanical and tribological properties of TiN and TiAlN coating–steelsubstrate composites and found that prior nitrocarburization of the steelsubstrate increased the microhardness by 7 times, the wear resistance of theworking surface of the composite upto 2.3 times &  the resilience by 4.5 times. A method was suggested to determine wear resistance of thedeposited coatings  &  the influenceof the hardness gradient and contribution of all layers to overall durabilityof such layered systems.

  6.      Souza et al.2009 carried the plasmacarburizing of AISI 316L at 480 °Cand 400 °C, during 20 h, using CH4 as carbon carrier gas allowing  introduction of carbon at temperatures below500 °C without carbide precipitationcausing the lattice distortion. This lattice distortion resulting from theexpansion and the associated compressive residual stresses increased thesurface hardness to 1040 HV0.025.   7.

      Saini & Gupta2012 investigated the fatigue crackpropagation behaviour of some commonly used low alloy steels in case carburisedcondition through fractographic observations on the fractured surfaces ofstandard fatigue test specimens failed under four-point rotating bendingfatigue tests. Most of the fatigue cracks initiated at the surface even afterthe induction of residual compressive stresses during case carburisation andfurther the crack propagated in a trangranular mode in all steels. But thesubsequent crack propagation was dependent on the contents of alloying elementsin particular steel. Higher content of chromium exhibited more inclinationtowards intergranular decohesion cracking. 8.

      Feng et al. 1999 experimentally investigated the effect of surface coatings of TiN & TiCN on the high cycle fatiguelife of Austempered ductile iron (ADI) castings. The results concluded that theTiCN coating caused higher increase in fatigue life of ADI as compared with TiNcoating because of higher hardness of TiCN coatings. Also the increase infatigue life was higher for the small size castings as compared with the largesize castings because of higher nodule count in small size castings. 9.      Casadeiand and Tului2013 developed aninnovative surface treatment, consisting of two consecutive phases:  deposition by reactive plasma spraying (RPS)of a thick hundreds of micrometres) composite Ti/TiN coating on the titaniumbased substrate and deposition by PVD of a thin &hard TiN coating, on thealready deposited thick coating. While the Ti/TiN interlayer limited thedeformation of the composite system by minimising the effects due to themechanical response, the uppermost layer of low friction TiN not only increasedthe wear resistance but also reduced the probability of debonding caused byinterfacial shear stress.  10.

  Chen etal.  2015 experimental studied the improvementin fatigue wear resistance of grey cast iron through “laser carburizing”. Experimentalresults demonstrated that laser carburizing is a more effective means ofimproving fatigue wear resistance than laser remelting and that the improvementis significantlyaffected by increase in energy density during treatment. Also it was revealedthat the unit not only removes the source of crack initiation, but alsoeliminates the bridging of cracks throughout the material.  11.

  Asi et al2007 evaluated the fatigue performance of gas carburized SAE 8620 steelgrades of different case depths achieved at typical carburizing times of 45min, 3 and 5 h at the temperature of 940 °C.  Fractured specimens were examined for crackinitiation and growth characteristics of the materials in the core andcarburized case by SEM equipped with EDX. The decrease in bending fatiguestrength with the increasing case depths could be attributed to increase in internaloxidation and non-martensitic transformation present at the surface. 12.  Espitiaet al. 2016, carried nano indentation test in the composite of expandedmartensite and small quantities of hexagonal ?-Fe24N10 ironnitrides to estimate the mechanical properties and to obtain an energydissipation coefficientin accordance of ASTMC1624 standard. The scratch test results showed acorrelation between the friction coefficientand the energy dissipation coefficient.

As compared to the non-nitrided martensitic stainless steel, the expandedmartensite resulted a significant decrease in friction coefficient. The criticalload was 14N and tensile cracking was the mechanical failure mode of the nitridedcase. 13.  Sliwa et al.2015, found the possibilityof employing the FEM in the evaluation of stress distribution in multilayerTi/Ti(C,N)/CrN, Ti/Ti(C,N)/(Ti, Al)N, Ti/(Ti, Si)N/(Ti, Si)N, and Ti/DLC/DLCcoatings. The difference between the mechanical and thermal properties &the structural changes which occur during the fabrication process caused the differencein internal stresses in the zone between the coating and the substrate.

An FEMmodel in ANSYS was established to simulate the internal stresses in thecoatings and the correctness of this model was to be validated withexperimental results.  14.  Beake et al.2015, showed that toollife of the coated tools could be improved by around 100% by applying thebilayer of AlCrN–TiAlN coating as compared to monolayer ofAlTiN PVD coating.

SEM was used toevaluate the Failure mechanisms. The micro scratch testing revealed thesuperior coating integration in case of   bilayer AlCrN–TiAlNcoating resulting in a very higher critical load required for fatigue failureunder wet milling conditions. 15.

  Glodezet al. 2017,experimentally investigated the low cycle fatigue behaviour of duplex (plasmanitrided and hard PVD coating) coated Cr-Mo-V steel which is used for theforging die inserts in hot forging operations. The experimental results showeda positive effect of PVD coating in high cycle fatigue regime but the effectwas negligible in low cycle fatigue regime. The low cycle fatigue parameters wereexperimentally derived for uncoated and duplex coated surface of treatedCr-Mo-V steel for operating temperatures of 150 ‘C and 500 ‘C. 16.

  Baragettiet al. 2011, studied the effect of a PVD  WC/C coating on the fatigue behaviour of asproduced and foreign object damaged (FOD) solution heat treated and aged 7075 aluminiumalloy. Testing results showed that the WC/C coating improved the fatigue behaviourof both smooth and especially damaged 7075-T6 specimens but the damaged WC/Ccoated samples showed the worst fatigue behaviour, probably due to multiplesevere micro notches caused by the fractured coating. 17.

  Baragetti2011 studied the rolling contact fatigue (RCF) behaviour of case-hardenedtransmission gears for racing motorcycles by analysing the as-produced andPVD-WC/C coated specimens. The experimental tests highlighted that, underlubricated conditions, the RCF resistance of the WC/C-coated steel gears washigher than that of the case-hardened ones and, therefore, the PVD WC/C coatingcould be taken into account to improve the RCF behaviour of these components. 

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