Conventional Wear Test Research Articles

Nanoindentation study of mechanical and wear properties of spark plasma sintered Ti-6Ni-xTiCN composites

In this study, monolithic pure Ti and Ti-6Ni-xTiCN composites were fabricated by the spark plasma sintering method and the mechanical and anti-wear characteristics of the fabricated samples were investigated using the nanoindentation technique. Microstructural and phase analysis of the sintered samples showed the predominance of the α-Ti phase in the unreinforced pure Ti matrix. In addition to the α-Ti phase, in-situ TiN, Ti2Ni intermetallic, and undissolved TiCN phases were detected in the matrix of the composites. Nanoindentation results revealed that the hardness (H), elastic modulus (Er) and elastic recovery index (We/Wt) of the investigated samples increase with increasing reinforcement contents under varying loads of 50 mN, 100 mN and 150 mN. The nanomechanical and anti-wear properties of the analysed samples indicated dependency on the applied indentation load. The Ti-6Ni-xTiCN composites displayed higher H/Er,H3/Er2 and We/Wt ratios that signified better wear and impact resistance than the unreinforced pure Ti. Microstructural integrity, which ensures consistency between the anti-wear characteristics obtained through the nanoindentation technique and the conventional wear testing, was achieved in composites containing TiCN nanoceramic contents up to 10 wt%. Ti-6Ni-10TiCN composite displayed the optimum combination of the nanomechanical and anti-wear properties across the applied loads.

Wear of nanostructured composite tool coatings

The lifetime of forming tools can be increased by surface functionalization using novel, nanostructured coatings. A special centre of focus of this is the tribological requirements on the coating. Within the framework of the BMBF project, the friction and wear behaviours of 3 newly developed nanostructured composite tool coatings: VAIN, VAlN/VCAlN and VAlN/VCAlN with a carbon-enriched top layer, were examined and compared to each other. Because a conventional wear test would have required a large number of tests (⪢10,000) with a concomitantly high consumption of sheet metal, the examinations were run in a model trial at an increased surface pressure of 150MPa, to accelerate the wear of the tool. Wear analysis was carried out by considering the changes in topography and hardness of the tool surface.

Wear characterisation of small PM rotors and oil pump bearings

The mechanical, micro and physical properties exhibited by PM rotors and journal bearing employed in oil pumps of automobiles, decides life of the pump. In this work, the factors that markedly characterise wear are featured. Tip clearance between the driving and driven gears influences the volumetric efficiency of the pump. When the tip clearance exceeds 0.20 mm (0.007 in.), and the face clearance exceeds 0.1 mm (0.004 in.) the discharge drops below the desired volumetric efficiency of 70%. Relationships between microstructure, micro-hardness, surface roughness, tip clearance of fresh and worn out parts are investigated. PM bearing bushings are finding increasing use in automobiles and consumer durable products owing to favorable size to weight ratio and cost advantages. Superior life and torque characteristics of PM bearings are related to density, size and geometry. Bushings at 6.8 g/cc with a 0.8 μm bearing clearance were determined to give improved life. Apart from the conventional wear test practices in industries, the concept of accelerated wear test (AWT) is employed to simulate equivalent wear on rotors and bearings; the results obtained are compared with the actual field samples. An empirical data on wear behavior is arrived from experimental studies, which can be used for simulated endurance test of these parts. Possible remedies applicable to achieve optimum life are identified. By optimising the material properties, higher wear resistant PM rotors and bearings could be manufactured economically.

Friction and wear of rotating pivots in MEMS and other small scale devices

Micro-electromechanical systems (MEMS) is a rapidly growing interdisciplinary technology dealing with the design and manufacture of miniaturised machines or moving (or micro) mechanical assemblies (MMAs) with major dimensions at the scale of tens, to perhaps hundreds, of microns. Because they depend on the cube of a representative dimension, component masses and inertia rapidly become small as size decreases whereas surface or tribological effects, which scale with the square of dimension, become increasingly important. In this paper, the effects of design, material properties and applied operating conditions on the evolution of both friction forces and dimensional and volumetric wear rates are explored for normally loaded rotating pivots of various geometries. It is demonstrated that if such MEMS–MMAs are to have acceptable lifetimes then loaded contacting surfaces will need to be of inherently low wear material pairings. The difference in scale between these small devices and conventional wear testing rigs also creates problems in matching conditions between micro- and macro-situations and suggests that wear data might usefully be obtained from suitably designed MEMS devices acting as miniature wear test machines.

Nanomechanical properties of films derived from zinc dialkyldithiophosphate

We have applied scanning force microscopes to the problem of determining the nanomechanical properties and topography of films derived from the antioxidant/antiwear oil additive zincdialkyldithiophosphate (ZDDP). The enhanced capabilities of the interfacial force microscope (IFM) are exploited to obtain quantitative force-displacement data and pre- and post-indent images, and the atomic force microscope (AFM) enables us to survey topography up to much larger spatial dimensions. A film which has been generated by static immersion of a steel coupon in heated ZDDP/oil solution displays a nano indentation response similar to that of lightly loaded regions of a film which has been prepared by conventional wear testing using the same starting materials. More interestingly, highly loaded regions of the same wear specimen exhibit a much different nanomechanical response, which signals the presence of at least two different film materials. The film material in highly loaded regions displays an amazing capacity tode form in a predominantly elastic mode, which is in sharp contrast with the elastic-plastic properties of lightly loaded regions, and of the film generated by static immersion. Our results are notin consistent with the possibility of friction-induced glass as a proper description for highly loaded regions of the wear specimen.

Simulation of cutting tool wear by a modified pin-on-disc test

Metal cutting is characterized by extreme contact conditions at the tool-workpiece interface which cannot be simulated in a conventional wear test. Consequently, the performance of the tool material is normally evaluated by full-scale, comparative cutting tests. In this type of test, the observed tool lives are determined by both gradual wear and edge chipping. This creates a problem in the development of new tool materials and coatings since the tool material wear resistance cannot be determined separately. In order to overcome this experimental difficulty, a modified pin-on-disc test has been developed. In this test, the contact conditions in machining are reproduced by letting the pin slide against a newly formed, unoxidized countermaterial surface. In the present work, the performance of this new test has been evaluated for high speed steel tool wear with a quenched and tempered steel, AISI 4340, as countermaterial. The influence of normal force, sliding speed and sliding distance on wear and friction has been investigated. The observed wear rates and wear mechanisms are compared to results from conventional laboratory wear testing (using the same test set-up) and machining. The experimental results demonstrate that the new wear test produces wear characteristics that closely correspond to tool wear. Thus, the modified pin-on-disc test exhibits great potential as a first screening wear test of new tool materials and coatings.

Sliding wear of hard materials — the importance of a fresh countermaterial surface

The possibility of reproducing the contact conditions at a tool-workpiece interface in machining, using a laboratory wear test, has been investigated. For this purpose, a modified pin-on-ring test with continuous introduction of fresh countermaterial was designed. Using this equipment the wear characteristics of several hard materials (high speed steel, uncoated and coated cemented carbide), sliding against a quenched and tempered steel, were investigated. The results obtained in the modified test were compared with results from conventional pin-on-ring testing, and machining. Post-test metallographic examination demonstrated that it is possible to reproduce the contact conditions and wear processes in machining under controlled laboratory conditions using the modified pin-on-ring test. The dominant sliding wear mechanisms for hard materials against a fresh surface appear to be adhesive wear and solution wear. A conventional wear test cannot be used for wear testing of tool materials since transfer of pin material, depletion of alloying elements and changes in contact geometry produce a contact condition which differs significantly from the intended application.

Zirconium nitride films prepared by cathodic arc plasma deposition process

Zirconium nitride has been reactively deposited using the cathodic arc plasma deposition process. Deposited films have been analyzed for their surface morphology, crystal structure, microhardness and composition. Performance of the films was evaluated by conventional wear testing methods and the potential for decorative applications by reflectivity measurements. Wear test results indicated that ZrN is marginally superior to titanium nitride in conventional metal cutting applications, but outperforms TiN by a factor of two when cutting titanium alloys. Reflectance measurements indicate that ZrN-doped films are very similar to gold films.

Debris control in dry wear testing

In a conventional wear test, debris accumulated from the repeated sliding of the wear pin over the same track dominates the nature of the interaction between the pin and the countersurface. Brush materials to remove the wear debris have been investigated so that more basic interactions between the pin and the countersurface can take place. The most successful brush was made from layers of Kimwipe (Kimberly-Clark of Canada Ltd.) laboratory tissue formed into a disc 8 cm in diameter and 2 cm thick. The Kimwipe disc was rotated under a load of 15 N at a frequency of 1 Hz across the wear track on the countersurface. The appearances and wear rates of steel 1040 and Admiralty brass pins worn in the presence and absence of debris were very different. Pins worn in the absence of debris readily assumed the characteristics of the pins worn in the presence of debris when debris was allowed to accumulate on the wear track. The mode of wear in debris-free conditions is not known at present, but this mode is worthy of further consideration. Worn surfaces are relatively flat and can appear metallic or covered with a light coat of oxide. Wear rates of oxide-coated pins can be either faster or considerably slower than those of uncoated pins. However, under all conditions debris-free wear involves considerably less subsurface metal flow than that involved when debris is present.