ICMCTF2003 Session E1-2: Friction and Wear of Coatings
Thursday, May 1, 2003 1:30 PM in Room California
Time Period ThA Sessions | Abstract Timeline | Topic E Sessions | Time Periods | Topics | ICMCTF2003 Schedule
E1-2-1 Mapping Erosion and Wear of Surface Coatings in Corrosive Environments: Some New Perspectives
M.M. Stack (University of Strathclyde, United Kingdom)
Erosion and wear of materials in corrosive environments occur in many diverse industries, ranging from power generation to offshore environments. The extent of wastage is dependent on the materials involved in the tribo-contact and any corrosion product arising from the tribological action and the environment. In such cases, there is said to be either a "synergy" or "antagonism" between the processes, where the corrosion product can either enhance, or inhibit, the overall wastage rate.
A significant advance in recent years has been the construction of engineering maps to characterise tribo-corrosion processes. Such maps may identify the mechanism of damage and the extent of wastage. More recently, the extent of "synergism" and "antagonism" between the processes has been delineated on such maps, thus providing a powerful tool of highlighting regions where corrosion may have a significant effect on the overall wastage rate.
This paper describes recent mapping research for particulate erosion-corrosion of a range of PVD coated steels. The rationale for identification of wastage mechanisms and the extent of "synergy"/"antagonism" is described, and the application of such mapping approaches to other tribo-corrosion processes (such as sliding wear-corrosion and abrasion-corrosion) is also addressed. Future work on the development of theoretical mapping approaches for coated systems in tribo-corrosion processes is discussed, in terms of the range of possible variables involved, and the complexities of the individual tribo-chemical interactions.
E1-2-3 Micro-abrasion Mapping of WC/Co Based Coatings
M. Mathew, M.M. Stack (University of Strathclyde, United Kingdom)
Significant progress has been made in recent years on the study of micro-abrasion mechanisms of materials. Regimes of micro-abrasion have been proposed which identify whether the wear occurs either by a two body, or three body mechanisn. Micro-abrasion maps have been constructed showing the variation in wear regime, as a function of applied load and velocity.
There has, however, been little work carried out to date on the micro-abrasion of composite coatings in such conditions. Here, because the size of the contact zone of the abrasion event may approach that of the abradent and the reinforcement (both typically less than 10 µm), the wear mechanism is complex. In such cases, the properties of the reinforcement and the matrix material of the coatings may have a significant effect on the overall wastage rate.
In this study, the micro-abrasion resistance of a range of WC/Co based coatings was studied in aqueous media. Micro-abrasion mechanism maps were constructed indicating the wear regimes in such conditions. Possible reasons for the variation of the boundaries of the maps for the different WC/Co based coatings are outlined, with reference to the mechanical and chemical properties of the individual coatings exposed the abrasive environment.
E1-2-5 Wear Mapping of Materials and Coatings
S. Hsu (NIST)
Wear maps have been used successfully to show the complexity of wear and the effect of speed and load on wear mechanisms. Wear mechanism maps allow various wear equations to be developed to describe wear in that particular regime. The effect of lubricants, wear transitions can be shown clearly for a system. Various wear mapping techniques will be discussed and compared on different materials.
Wear mapping on coatings and thin films have additional complications in residual stress, coating thickness, and delamination at the coating-substrate interface. How these parameters can be handled in wear maps require additional treatment. This paper will show the current state of the art in wear mapping, the techniques used to construct wear maps, and special accommodations to coatings and thin films.
E1-2-8 Improved Tribological Coating Performance Through Optimised Selection of Substrate Material and Surface Preparation
S. Hogmark, S. Jacobson, U. Wiklund, M. Larsson (Uppsala University, Sweden)
This paper treats the importance and benefits of making an optimised selection of substrate and surface preparation when applying thin (1 - 10 µm) coatings on tools and mechanical components. Different aspects of the selection are discussed, examples of good and bad choices are given and some general recommendations are presented.
The selection of substrate material will be discussed in terms of chemical composition, hardness, size and distribution of second phases, in relation to the properties of the counter material. Generally, metal cutting and hot-forming applications demand higher hardness and better thermal resistance of the substrate, but are less demanding with respect to contact fatigue than are lubricated machine components such as gears, bearings, seals, etc.
The selection of surface preparation is discussed in terms of topography achieved and possible impairment of the substrate structure and hardness. Normally the substrate surface of both tools and mechanical components should be made as smooth as possible, while avoiding high temperatures in the preparation process which could result in annealing and loss of hardness. It will be demonstrated that the critical load for coating failure in scratch testing and in sliding contacts increases with reduced roughness down to an Ra value of about 0.1 µm. The benefits of simple post polishing of the coating surface will be demonstrated for different application types. The mechanisms of material pick-up and increased friction due to protruding asperities on tool and component surfaces will be demonstrated and discussed.
E1-2-10 Influence of a Tough Alloy Addition in the Abrasive Wear Resistance of Thermally Sprayed WC-Co Coatings
C. Godoy, M.M. Lima (Universidade Federal de Minas Gerais, Brazil); J.C. Avelar Batista (University of Hull, United Kingdom)
The models for abrasive wear by plastic deformation predict that the volume of material removed by abrasion should vary inversely with the hardness of the material, H. Otherwise the models for wear by brittle fracture predict an inverse correlation between wear rate and some power of the material's fracture toughness. In this work, the significance of the H/E ratio was also discussed for WCCo thermal sprayed coatings. Four conjugates was constructed having an AISI 1020 steel as a substrate and the following coatings: WC12Co; 50%(WC12Co) 50%(NiCr) "as sprayed" and "as post-melted"; and a duplex conjugated with a WC12Co top layer and a NiCrAl intermediate layer. It was produced two wear modes: soft abrasion and severe abrasion. In the soft abrasion mode, a correlation was found between wear resistance and the H/E ratio. The high hardness and low elastic modulus (measured by Knoop indentation method), presented by the WCCo coating, assured a higher H/E ratio and a lower wear rate than the 50%(WC12Co) 50%(NiCr) coatings. In the severe abrasion mode, the 50%(WC12Co) 50%(NiCr) coating, "as post-melted", presented the lowest wear rate. The addition of the NiCr alloy in the WC-12Co reduced the hardness and increased the elastic modulus. But its fracture toughness, measured by Vickers indentation, was higher than the conjugated "as sprayed" and the WCCo conjugate, assessing a high wear resistance. The best wear resistance presented by the duplex conjugate relative to the WC-12Co conjugate, in both wear modes, was attributed to the addition NiCrAl layer intermediate. A reduce of elastic modulus and an increase of toughness of the conjugate as a system, guaranteed its good performance.
E1-2-12 Microstructure, Mechanical Properties and Cutting Performance of Superhard (Ti,Si,Al)N Nanocomposite Films Grown by d.c. Reactive Magnetron Sputtering
S. Carvalho, E. Ribeiro, L. Rebouta, J.P. Mendonca (Universidade do Minho, Portugal); N.J.M. Carvalho (University of Groningen, The Netherlands); E. Alves (ITN, Portugal); Th.M. De Hosson (University of Groningen, The Netherlands); A. Caetano Monteiro (Universidade do Minho, Portugal)
This paper reports the optimization of coating properties for improving the performance of tools in dry cutting applications. The performance and the wear mechanisms of tungsten carbide tools coated with (Ti,Si,Al)N have been investigated. A d. c. reactive magnetron sputtering technique was used to deposit the (Ti,Si,Al)N coatings. In order to quantify changes in the microstructure and hardness before and after cutting, RBS, XRD and nanoindentation experiments were performed on the coated tools. Before the cutting experiments, the XRD results revealed a structure indexed to fcc TiN. Tool life and tool failure modes were examined for various cutting conditions. The tools were thoroughly examined under SEM and EDX spectroscopy, showing the results that after 15 min. at low cutting speed (100 m/min) the cutting edge of all coatings still remained in a good condition. At a higher cutting speed (200 m/min) the commercial TiN coating which was used as a reference - presented a longer tool life than the (Ti,Si,Al)N tool. However, regarding the final surface finish of the steel workpiece, one (Ti,Si,Al)N tool outperformed the TiN tool, since the roughness of the workpiece in the former case is smaller (4 microm) than the corresponding to the latter (12 microm).