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through an arc cathodic equipment. The so producedspecimens were subjected to a program of cyclicimmersions in molten aluminium alloy bath. Theassessment of damages on the cycled specimens wasperformed through optical and SEM microscopy ofboth surfaces and transverse sections, so as toanalyse the presence, if any, of soldering pits.2 EXPERIMENTAL PART2.1 Specimens fabricationA parent block was cut from an annealed AISI H11hot rolled bar, produced through vacuum meltingand remelting processes. From this test coupon a setof cubic specimens were fabricated. Thesespecimens were then vacuum heat treated accordingto the following parameters: austenitizing at 1,000°C– quenching with 5 bar nitrogen flow - firsttempering at 550°C – second and third tempering at595°C to about 45.5 HRC, which is rather typical forhot work tool steels.Ceramic coatings were deposited through thePhysical Vapor Deposition (PVD) process providedby the PL-55 prototype unit installed at the CleanNT Lab. The unit is equipped with the innovativeLateral Arc Rotating Cathodes (LARC ® ) system.Two rotating cylindrical cathodes allow enlargedtarget surface and continuous surface refreshingduring evaporation of the metallic constituentscharacterizing the ceramic coating.The CrAlSiN coating systems were deposited on theall specimens steel base material AISI H11 withdifferent modulations of the chemical compositionwere developed so as to increase either thechromium or the aluminium-silicon content. Theobtained coatings were roughly 3 μm thick. Theywere characterized by a multilayered structurecovering about 50% of the entire coating depth,followed by a complementary massive monolayer ofdefined chemical composition. Six chemicalcomposition modulations of the external layer wereprepared according to the variations of the cathodearc current and of the nitrogen flow.The coating thickness was evaluated through the ballcrater technique. A Rockwell indenter was used tostudy the adhesion properties of the deposited filmsby the indentation method.Fracture cross-section of the coated AISI H11samples was prepared to the scanning electronmicroscope (SEM) morphology investigation. X-raydiffraction (XRD) analysis was performed using aSiemens D5000 X-ray diffractometer.Monochromatic Cu-Kα radiation, produced at anacceleration voltage of 40 keV and 40 mA current,was used an initial incidence angle of 10°.Table 1. Deposition parameters used for the fabrication of thesix different CrAlSiN coating systemsCathodic arc current AlSi/Cr [A]N 2 [sccm] 110 / 70 100 / 90 80 / 100 60 / 110120 A1 D1150 B2 C2190 A3 D3The coatings hardness was determined using aMitutoyo MVK-G1 microharness tester at 100, 50,25, 10 g loads. Later the hardness of the differentcoatings was extrapolated from the evaluation ofmicrohardness at increasing weights and applying amodified form of the work-of-indentation model.HHCf− H− HSS=1+1( β β ) X0Where H c is the composite hardness, that is thehardness due to the effects of the film and thesubstrate; Hs is the substrate hardness; H f is the filmhardness; β is the relative indentation depth (RID),defined as the ratio of the maximum indenterpenetration depth to the coating thickness; β 0 and Xare systems parameters.Tribological properties of the coatings deposited onAISI H11 substrates were evaluated by means oflow frequency (5 Hz) reciprocating sliding wear test(at 5 N normal load for 500 m sliding distance) witha 10 mm diameter SAE 52100 hardened steel ball, ata temperature 25 ± 2 °C and 50 ± 5 % relativehumidity and amplitude 10mm (according to theASTM G133 standard). The wear scar was observedthrough electronic microscopy (SEM) and EDS spotanalysis was used to confirm whether the coatinghad failed or if there was simply transfer ascounterface material from the steel ball.The specimens were then subjected to cyclicimmersions in a molten aluminium alloy so as tosimulate the environmental conditions that occur atthe surface of a high pressure die casting. The(1)
aluminium alloy was AlSi 8 Cu 3 Fe, commonly usedfor die casting. The cooling bath is constituted of adiluted solution (1:80) of a commercial die lubricant.The duration of a typical cycle is of 30s with anactual immersion time of 4s for both the aluminiumalloy and cooling baths. All the specimens testedwere periodically analyzed to detect the formation ofsurface defects by SEM inspection.3 RESULTS AND DISCUSSIONThe reflected light micrograph of the ball crater(figure 1) clearly shows the multilayer structure ofthe coatings and led to a thickness measurement of2.875±0.074 μm, and clearly shows the multilayeredstructure of the coatings.Fig. 2. Adhesion Test: appearance of Rockwell indentations onspecimen A3The coatings deposited tested in reciprocatingsliding in term of friction coefficient exhibited asimilar trend, where the friction coefficient increasedgradually from 0.55 to 0.65. SEM micrographs ofthe wear scars for coatings A1, A3, B2 and C2(figure 3) shows ploughings marks along thedirection of sliding, instead for coatings D1 and D3(figure 4) demonstrate ploughings marks along thedirection of sliding plus signs of delamination areas.Fig. 1. Reflected light micrograph of a ball crater on A1The appearance of Rockwell C indentation onrepresentative coated systems is reported in figure 2.The adhesion was evaluated on the base of anobservation of the aspects of the cracks and of thepresence of coating detachments around theindentation. The adhesion evaluated through this testcan be considered good since no detachments of thecoating along the edge of the indentation could berevealed.Fig. 3. SEM micrographic wear scars specimen A1The hardness evaluations for the different coatingsas a function of increasing applied weights and, as aconsequence, of increasing indentation depth. The Acoatings presented the highest film hardness (46GPa), the D coatings the lowest (38 GPa), whereasthe B and C coatings exhibited an intermediatehardness value (43 GPa).Fig. 4. SEM micrographic wear scars specimen D1
Page 1 and 2: Development of a friction modelling
Page 3: The evolution of heat flux transmit
Page 6 and 7: 2.2 Toolkit and specimen geometryFi
Page 8 and 9: In general, the friction coefficien
Page 10 and 11: determining a relative movement bet
Page 12 and 13: force needed to move the pin (frict
Page 14 and 15: and specimens are parts of actual i
Page 16 and 17: 4.3 Effect of lubricant particle si
Page 18 and 19: 2 EXPERIMENTAL2.1 PSCT set-up and p
Page 20 and 21: found here only in a low strain rat
Page 22 and 23: pieces are scaled by the same scali
Page 24 and 25: the experimental one shows nearly n
Page 26 and 27: 2 NUMERICAL TOOL2.1 General descrip
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Page 30 and 31: transfer across the roll-strip inte
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Page 40 and 41: other hand, it has not been observe
Page 42 and 43: corresponds to the minimum energy s
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Page 46 and 47: 2 EXPERIMENTAL PROCEDURETwo lubrica
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Page 52 and 53: To verify the absence of coating in
Page 54 and 55: angle, and m 0 the constant frictio
Page 56 and 57: 4 NUMERICAL MODELLING4.1 Upsetting
Page 58 and 59: indenter. T-shape compression, a ne
Page 60: Tangential force / Normal force0.35

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