In the present work, the dissimilar joints between C45 carbon steel and nickel-chromium 16NiCr6 steel rods were produced using rotary friction welding process. Statistical analysis based on response ...surface methodology (RSM), microstructural examination using scanning electron microscopy with backscattered electron diffraction (EBSD) and mechanical tests were performed to investigate the friction weld joints. The results showed that friction time and rotation speed were the most effective parameters on the weld joint quality with the highest t-ration of − 4.27, where the maximum bending strength of 1406.9 MPa was obtained at 2000 rpm for 13 s friction time. Increasing friction time to 13 s resulted in remarkable decrease in grain size (about 35%) at the weld interface, which increased the hardness (350HV0.1) and elastic modulus (260 GPa).
Graphical abstract
Mechanical and tribological properties of nanocomposites with silicon nitride matrix with addition of 1 and 3wt% of various types of graphene platelets were studied. The wear behavior was observed by ...means of the ball-on-disk technique with a silicon nitride ball used as the tribological counterpart at room temperature in dry sliding. Coefficient of friction and specific wear rates were calculated and related to the damage mechanisms observed in the wear tracks. The measured properties were then assessed with respect to the type and volume fraction of the graphene additives. It is shown that addition of such amounts of carbon phases does not lower the coefficient of friction. Graphene platelets seem to be integrated into the matrix very strongly and they do not participate in lubricating processes. The best performance offers materials with 3wt% of larger sized graphene, which have the highest wear resistance.
Silicon nitride materials containing 1–5wt% of hexagonal boron nitride (micro-sized or nano-sized) were prepared by hot-isostatic pressing at 1700°C for 3h. Effect of hBN content on microstructure, ...mechanical and tribological properties has been investigated. As expected, the increase of hBN content resulted in a sharp decrease of hardness, elastic modulus and bending strength of Si3N4/BN composites. In addition, the fracture toughness of Si3N4/micro BN composites was enhanced comparing to monolithic Si3N4 because of toughening mechanisms in the form of crack deflection, crack branching and pullout of large BN platelets. The friction coefficient was not influenced by BN addition to Si3N4/BN ceramics. An improvement of wear resistance (one order of magnitude) was observed when the micro hBN powder was added to Si3N4 matrix. Mechanical wear (micro-failure) and humidity-driven tribochemical reaction were found as main wear mechanisms in all studied materials.
The orientation dependence of hardness and nanoindentation-induced deformation mechanisms of differently orientated tungsten carbide (WC) grains in WC–Co hardmetal were studied. Electron backscatter ...diffraction, atomic force microscopy and scanning electron microscopy investigations were performed to determine the grain orientation, and to study the surface morphology and the resulting deformation fields around the indents. The hardness of the differently orientated WC grains showed significant angle dependence from the basal towards the prismatic directions, but there was only a slight change in hardness between the two types of prismatic orientations ((101¯0) and (21¯1¯0)). Sink-in and pile-up effects, together with highly deformed regions and dislocation steps, were revealed around the imprints in the case of basal and prismatic orientations, respectively. A theoretical model is proposed in which the critical force for slip activation is determined as a function of orientation, based on the possible slip systems of WC. The predictions of the present model concerning the measured hardness values and the deformation field around the indents together with the sink-in effect are in good agreement with the experimental results.
In this work, dissimilar rapid Rotary Friction Welding of WC-Co cermet to AISI 304 L austenitic stainless steel has been conducted using different friction times. The microstructural examination ...showed that the increase in friction time from 4s to 12s increases the grain size in both the heat affected zone and the thermo-mechanically affected zone and enlarges the extent of the fully dynamically recrystallized zone. EDS analysis revealed the existence of a FeCrW rich band along the WC-Co/AISI 304 L interface in the central region of the weld joint and its absence from the peripheral region. The formation of this band suggests the occurrence of a mutual inter-diffusion between the cermet and the steel which enhanced the metallurgical bonding of the interface. The mechanical behavior investigated by nano-indentation measurements and nano-scratch tests revealed that, regardless the friction time effect and considering the 304 L ASS side, the highest hardness (HIT) and the lowest Young's modulus (EIT) values were recorded in the fully dynamically recrystallized zone. Besides, the increase of friction time resulted in an increase of hardness and Young's modulus of each zone in the AISI 304 L steel side.
Silicon nitride+1wt.% graphene platelet composites were prepared using various graphene platelets with the aim to improve the fracture toughness of Si3N4. The fracture toughness was significantly ...higher for all composites in comparison to the monolithic Si3N4, with the highest value of 9.92MPam0.5. The main toughening mechanisms originated from the presence of graphene platelets, and the increase in the fracture toughness values was attributable to crack deflection, crack branching and crack bridging.
Silver and graphene nanoplatelets (Ag-GNPs) have been employed as reinforcements to prepare the self-lubricating silicon nitride matrix composites via 3D ball milling (Turbula) and spark plasma ...sintering. The prepared composites were characterized by scanning electron microscope with energy dispersive spectroscopy, Vickers hardness tester and reciprocating ball tribometer. Fracture surface morphology of the sintered composites indicated the potential reinforcement by the ductile silver phase. The mechanical property testing revealed that Si3N4 composites with Ag and GNPs incorporation exhibited lower hardness and slightly lower toughness compared with Si3N4 monolithic material. However, the coefficient of friction and wear in composites exhibited the lower values in 1 N friction force testing range.
The recovery of worn and damaged drilling tools in oil and petroleum industries, which no longer meet reliable technological use, could significantly reduce the drilling cost and, therefore, the ...emission of toxic materials. The present study demonstrates first time an innovative solution for this problem using a WC-Ni/Cr Tungsten Inert Gas (TIG) hardfacing technology by which a damaged WC-based metal matrix composite was coated. The microstructure analysis of the recovered sample revealed remarkable diffusion activity of Cr and Cu elements across composite/hardfacing interface. This inter-diffusion depleted WC particles on both sides which enhanced the metallic bonding of the interface, creating a durable and strong adhesion. A significant amount of WC particles was fragmented and dissolved into the NiCr metallic matrix, which resulted in the formation of Cr23C6, W2C carbides and Ni2W4C secondary carbide. There was found a more than 100 % increase in micro-hardness of the metallic matrix of the recovered sample compared to the as-infiltrated sample. The tribological tests of the as-infiltrated and the TIG hard-faced specimens conducted in dry, water and fuel oil environments revealed that the highest coefficient of friction (0.75) was recorded for the as-infiltrated sample under dry conditions with the highest wear loss (0.8 mg) while the TIG hard-faced coated one exhibited improved wear properties (0.09 and 0.15 mg, respectively). This was attributed to the change of wear mechanism from WC particle pullout to abrasive and oxidative wear through the formation of SiO2 and WO3 oxides films. Thus, the TIG hardfacing process shows new and promising technology to recover WC-based metal matrix composites, improving their lifetime, and at the same time, both their mechanical and tribological properties.
•Hardfacing of WC-based composite drilling tool was successfully performed using a Tungsten Inert Gas process.•High diffusion activity of Cr and Cu across composite/hardfacing interface enhanced the metallurgical bonding of the TIG coating.•Fragmentation, dissolution and decarburization of WC particles into the metallic matrix resulted in formation of Cr23C6 and W2C, which increased the composite hardness.•The TIG hard-faced coating had a comparable tribological performance under different wear conditions as the as-infiltrated specimen.
Tribological characteristics of fine-grained dual-phase high-entropy carbide/boride ceramics were investigated using the ball-on-flat dry sliding method in air, applying linear reciprocation motion ...with SiC counterpart. Detailed fractographical analyses were used for the characterization of the deformation and damage mechanisms. The investigated system with composition (Ti0.14Zr0.2Nb0.2Hf0.2Ta0.26)C + (Ti0.38Zr0.18Nb0.22Hf0.115Ta0.105)B2 showed density with value 8.72 g/cm3 and very high hardness of HV1 29.4 ± 2.0 GPa. The friction coefficient at the test with 5 N was 0.56 and during the test with 10 N and 25 N loads were 0.48 and 0.5, respectively. The effective wear rates at the loads of 5 N and 25 N were very similar with values of 7.93 × 10−7 mm3/Nm and 6.63 × 10−7 mm3/Nm. At load 50 N the effective wear rate is significantly higher with a value of 9.11 × 10−6 mm3/Nm. Detailed fractography revealed that the dominant wear mechanisms at loads of 5 N and 25 N were an oxidation-driven tribochemical reaction and tribo-layer formation in boride grains and mechanical wear in carbide grains and at the load of 50 N fracture of boride and carbide grains and formation of chemically complex tribolayers.
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