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Ward L.P.,RMIT University | Pilkington A.,RMIT University | Pilkington A.,Defence Materials Technology Center, Australia | Dowey S.J.,Sutton Tools Pty. Ltd. | Dowey S.J.,Defence Materials Technology Center, Australia
Australasian Corrosion Association Annual Conference: Corrosion and Prevention 2015, ACA 2015

One of the major limitations associated with physical vapour deposited (PVD) metal nitride coatings, particularly TiN, acting as barriers to corrosion is increased porosity due to the presence of coating defects such as macro-particles, voids and pin-holes. This can result in direct attack of the underlying substrate through the pore channels, thus reducing their resistance to corrosion. It is envisaged that post deposition treatments, commonly used for cleaning, polishing and de-burring may improve the surface texture but could also affect the corrosion properties of the coating. Few research studies have been conducted on the effects of mechanical surface treatments which modify the PVD coating surface. Hence the influence on "through" porosity is not known. In the current study, four post deposition treatments, namely wet blasting (WB), dry blasting (DB), nylon abrasive filament (NAF) brushing and drag polishing (DP) were employed on TiN coatings deposited on 1020 carbon steel substrates using a low voltage electron beam PVD process (Balzers 830 MR system). Electrochemical corrosion studies were conducted using potentiodynamic scanning in 0.5 M H2SO4 and 3.5% NaCl solutions. Infinite focus microscopy (IFM) was used to determine surface coating texture. Structural characterization of the coating surface prior to and after corrosion was conducted using optical and SEM imaging. The results of the study revealed that overall, no significant improvements were observed in the corrosion behaviour after the various treatments were conducted. Dry blasted and drag polished surfaces exhibited corrosion rates similar to the non-treated TiN coating in saline solutions. In acidic media, lowest corrosion rates were observed from wet blasted surfaces, which were similar to the non-treated TiN coating, however a marked reduction in the corrosion resistance was observed for the dry blasted surface finish. Source

Rousseau A.F.,RMIT University | Rousseau A.F.,Sutton Tools Pty. Ltd. | Partridge J.G.,RMIT University | Gozukara Y.M.,CSIRO | And 2 more authors.

We report on the hardness response of vacuum heat treated (VHT) M35 HSS as a function of the thickness of oxide present during VHT. An almost linear relationship existed between the hardening response post-VHT and the oxide thickness pre-VHT. A similar relationship existed between the thickness of oxide pre-VHT and the carbon content post-VHT. CO evolution during VHT was observed from ∼800°C. In combination, these measurements show that CO evolution and carbon loss are increased in M35 HSS covered with surface oxide whilst hardening response is reduced. A full hardening response and unchanged carbon content were measured in M35 HSS VHT with surface oxide removed. © 2015 Elsevier Ltd. Source

Rousseau A.F.,RMIT University | Rousseau A.F.,Defence Materials Technology Center, Australia | Rousseau A.F.,Sutton Tools Pty. Ltd. | Partridge J.G.,RMIT University | And 8 more authors.
Surface and Coatings Technology

We describe a duplex nitriding and TiAlN coating process performed with no break in vacuum in an industrial scale deposition chamber. Plasma nitriding at 480. °C resulted in a fracture tough diffusion zone with no evidence of either a compound layer or grain boundary precipitation. Untreated, plasma-nitrided, coating-only and duplex-coated High Speed Steel (HSS) M2 coupons were microstructurally and mechanically characterised whilst similarly treated M2 1/4-inch jobber drills were subjected to accelerated drill testing (using D2 tool steel). In these tests, the duplex treated drills exhibited significantly improved wear performance and tool lives when compared with the other drills. After sectioning and electron microscopy, this extended tool life was attributed to increased toughness of the nitrided cutting edges coupled with improved adhesion at the substrate-TiAlN interface. © 2015 Elsevier B.V. Source

Pilkington A.,RMIT University | Pilkington A.,Defence Materials Technology Center, Australia | Dowey S.J.,RMIT University | Dowey S.J.,Defence Materials Technology Center, Australia | And 5 more authors.
Tribology International

AlCrOxN1-x coatings were arc deposited onto HSS drills and WC-Co end mills at N2/O2 ratios of 0.9-0.75 using DC or 10 kHz pulse bias. Lower O2 content coatings had a hardness of 32.5 GPa. whereas 0.25 O2 ratio coatings were 24-25 GPa. AlCrOxN1-x coated 6.35 mm Dia. HSS jobber drills were tested by drilling 2.5D holes in AISI D2. 10 kHz 0.9 N2 0.1 O 2 coatings drilled a mean of 17.6 holes/mm, similar to commercial AlCrN coated drills at 17.8 holes/μm, whereas DC 0.75 N2 0.25 O2 coatings drilled 9 holes/mm. AlCrOxN1-x coatedWC-Co end mills had low steady state wear in milling AISI 316L (70 m/min, MQL) and cut > 24 m whereas uncoated tools cut 6 m. In contrast to drilling DC 0.75 N2 0.25 O2 tools had the least corner wear and low adhesion on the rake face. © 2013 Elsevier Ltd. All rights reserved. Source

Ward L.P.,RMIT University | Pilkington A.,RMIT University | Pilkington A.,Defence Materials Technology Center, Australia | Dowey S.J.,RMIT University | And 7 more authors.
Annual Conference of the Australasian Corrosion Association 2013: Corrosion and Prevention 2013

Metal nitride coatings, such as physical vapour deposited (PVD) CrN TiN and TiAlN, are well established in areas requiring improved tribological properties. In particular, alternative nitride coatings such as AlCrN are of interest, as a result of improved abrasion and oxidation resistance at high temperatures ~700-900 °C. However, less information is available on the corrosion resistance of this category of coatings in a range of aqueous environments, particularly the oxy - nitride multi-component coatings, where additions of oxygen to AlCrN coatings may assist in the formation of protective passive oxide layers. The focus of this paper is on the aqueous corrosion behaviour of AlCrON coatings deposited by the cathodic arc PVD technique onto AISI CS1020 (mild steel) substrates in the thickness range of 4-5.5 microns. The reactive gas composition was varied during deposition so that the AlCrON coatings contained up to 30 At. % O2. Corrosion studies were carried out using potentiodynamic scanning in 3.5% NaCl solution and compared with uncoated and AlCrN coated mild steel. Coating morphology and chemical composition were characterised using SEM and EDX (Energy Dispersive Analysis of x-rays) analysis, prior to and after testing. The PVD coatings increased the Ecorr values from the -700mV of the substrate to -660 to -200 mV. The best corrosion performance was AlCrON made with 75:25 N2:O2 ratio and the 5 μm AlCrN coating had lower icorr and was affected less by pitting than a 2 μm AlCrN coating. The results highlight the effect of (i) coating thickness, (ii) additions of O2 and (iii) O2/N2 ratio on the corrosion performance of the coatings and interpretation of the results in terms of morphological, topographical and structural features. Copyright © 2013 by the Australasian Corrosion Association. Source

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