High temperature tribological performance of CrAlYN/CrN nanoscale multilayer coatings deposited on γ-TiAl

Abstract

Nanoscale multilayer nitride coatings deposited by advanced PVD techniques have shown particular promise in improving the tribological properties of a number of modal alloy steels [1]. In this study, we report the effect of temperature on the friction and wear behaviour of a CrAlYN/CrN multilayer coating with a CrAlYON/CrON topcoat deposited on γ-TiAl. Deposition was performed by unbalanced magnetron sputtering following a high power impulse magnetron sputtering (HIPIMS) pre-treatment of the polished substrate. A series of pin-on-disc type experiments, sliding against a polycrystalline alumina counterpart, were carried out at four temperatures: 20ºC, 120ºC, 300ºC and 650ºC. An increase in the average steady-state dynamic friction coefficient was observed between the material couple, from 0.56 at room temperature to 0.65 at 120ºC. However at higher test temperatures of 300ºC and 650ºC a decrease in these values was observed to 0.59 and 0.40, respectively. Scanning electron microscopy and energy dispersive X-ray analysis showed evidence of oxidation at the worn surface of all test temperatures investigated, whilst laser confocal microscopy indicated the formation of an interactive tribo-layer above the plane of the original test surface. Focused ion beam sectioning has been used to prepare site specific samples of the tribo-layers for transmission electron microscopy. The evolution of the wear scar composition and structure and its influence on the reduction in dynamic friction coefficient at elevated temperatures is discussed.

Temperature dependent friction and wear of magnetron sputtered coating TiAlN/VN

“…In case of the current study, the  max values for a fixed applied load of 5N were estimated to be 630 and 900 MPa respectively for the friction coefficients of 0.6 and 0.9, denoting approximately 43% increase of the  max at the elevated temperatures between 200 and 400 0 C. The increased tensile stress would accelerate the generation of tensile cracks. Similar cracking behaviour was recently report in the high temperature sliding wear of another transition metal nitride coating CrAlYN/CrN [16]. Then concerning the increase tangential loading on the sliding surface, the enhanced worn surface deformation has been indicated by the increased Knoop hardness in the top layer as shown in Figure 8.…”

“…Nevertheless, an adhesive film of wear debris agglomerates was formed on the worn surface, leading to conformal sliding contact in the steady state sliding. such as TiN [17], VN [19,33], CrN [12], VTiN [15], and CrAlN/CrN [16].…”

“…Instead, they are response of sliding surfaces under the applied test conditions. According to published experimental studies [12][13][14][15][16][17][18][19][20][21], environment temperature has significant influence on the sliding friction and wear behaviour of transition metal nitrides. For example, a Cl-containing TiN coating grown by chemical vapour deposition showed extraordinarily low friction of µ < 0.2 and high friction of µ = 0.6 -0.8 at 100 -300 0 C [17].…”

Fe nano-particle coatings for high temperature wear resistance

“…This can be explained by two factors: when metallic debris undergoes oxidation there is an associated volume expansion due to the lower density of iron oxide species compared to iron, but also because, as shown in this and other works [30][31][32], the surface oxide film generated as a result of tribooxidation is a somewhat porous structure. The material in the tribo-contact was not all metallic debris of the same density as the substrate but tribo-oxidation products, as proved by the contact potential and SIMS data.…”

“…The formation of a compact oxide tribo-layer on top of a more porous debris structure demonstrates classic 'glaze' layer formation, although the term may not be universally applied to the present work as such layers are often associated with a significant reduction in friction [30][31][32][33]. An increased depth of deformation of the substrate was also noted, with the absence of large pearlite and ferrite grains observed at 300°C, rather a surface deformed layer aligned towards the individual asperity sliding direction, again as a result of tempering due to the elevated temperature.…”