Proceedings of SerbiaTrib '13

(10, 50 and 100 N) against surface of the test sampleand moved with constant speed (4 mm/s), producingthe scratch of certain width and length (10 mm) onthe test sample. Indenter had Rockwell shape andthe cone was diamond with radius of 0.2 mm.Figure 2. Schematic diagram of scratch testingOn surface of each material under investigationat least three scratches are made with a gap betweenscratches of at least 1 mm. Before and after testing,both the indenter and the test samples are degreasedand cleaned with benzene. The wear scar widths onthe surface of the test samples are measured fromSEM images at the end of testing. The wear scarwidths and the known indenter geometry are usedto calculate the volume loss. After testing, themorphology of the test samples worn surfaces isexamined with SEM.3. RESULTS AND DISCUSSIONThe results of the wear tests are presented inFigures 3, 4 and 5. Taking into account significantdifferences in structure homogeneity of thehardfaced coatings (Fig. 1), the repeatability of theresults, in terms of standard deviations, issatisfactory (within 16 %). Wear rate of the testedmaterials (volume loss divided by scratch length)increases with normal loading, as expected. Thehighest wear exhibits coating 7888 T. Nevertheless,wear rates for all coatings are high, even forabrasive wear. The reason for this is primarily dueto the experimental conditions.The test conditions were specific, i.e. the speedswere very low (4 mm/s) and the contact stressesvery high. At the end of test, the normal stresseswere between 2 and 5 GPa, which depends on thematerial, i.e. scratch width and applied normal load.With these conditions, a high-stress or evengouging abrasion can be expected. With high-stressabrasion, the worn surface may exhibit varyingdegrees of scratching with plastic flow ofsufficiently ductile phases or fracture of brittlephases. In gouging abrasion, the stresses are higherthan those in high-stress abrasion, and they areaccompanied by large particles removal from thesurface, leaving deep groves and/or pits [8].The relation between the wear rate and thehardness of tested hardfaced coatings is shown inFigure 6. The first feature is that the abrasive wearrate decreases as the hardness increases, i.e. thehardest material (coating 5006) showed the highestabrasive wear resistance.Wear rate, mm 3 /mWear rate, mm 3 /mWear rate, mm 3 /m3.22.82.42.01.61.20.80.40.0Coating 4541(v = 4 mm/s)0.100.751.8810 50 100Normal load, NFigure 3. Wear rates of coating 4541 for differentnormal loads3.22.82.42.01.61.20.80.40.0Coating 5006(v = 4 mm/s)0.090.681.6710 50 100Normal load, NFigure 4. Wear rates of coating 5006 for differentnormal loads3.22.82.42.01.61.20.80.40.0Coating 7888 T(v = 4 mm/s)0.211.242.8810 50 100Normal load, NFigure 5. Wear rates of coating 7888 T for differentnormal loads13 th International Conference on Tribology – Serbiatrib’13 77