Advanced Materials Research Vols. 105-106

Abstract: The wear resistance, corrosion resistance, high temperature resistance layers were prepared on the surface of ductile iron via laser alloying process, using the mixed ponder of sub-micron carbides power as starting materials. The microstructures of the different laser alloying layers were characterized by XRD, SEM, EDS, TEM. The microhardness and wear resisitance of the laser alloying layers were examined. The results reveal that the flat alloyed coating combines metallurgically with the substrate. the laser area was composed by alloyed zone ,heat-affected zone and matrix zone. The alloyed zone was composed mainly by ledeburite and carbide, while martensite and retained austenite were contained in the heat affected zone, there is no significant change in the Matrix zone. Under conditions that the laser power, spot diameter remain unchanged, with in 400 ~ 1000 mm/min scanning speed, the hardness of alloyed coating increases with increasing scanning speed. The weightlessness of the alloyed samples under the dry sliding friction is one-sixteenth of ductile iron. The wear resisitance of the alloyed coating has improved significantly.

Abstract: Porous TiC-Ni3Al performs were fabricated by using Ni, Al, Ti and graphite powder with self-propagating high-temperature combustion synthesis (SHS) method. Then, the porous perform were infiltrated with melt Ni3Al via the conventional pressureless infiltration process to prepare TiC/Ni3Al composites. Effects of the infiltration temperature and time on the microstructure, hardness and wear resistance of the composites were studied. XRD, SEM and EDS were used to analyze the phase identification and the solubility of Ni3Al and TiC in each other. The results show that pressureless melt infiltration is an effective method to fabricate dense TiC/Ni3Al composites. The infiltration time can greatly decrease when the infiltration temperature suitably increases. No obvious effect of the infiltration temperature and time on the hardness and the wear resistance of the composites were found. Ni3Al and TiC were well bonded, and they are the only two phases in the composites after infiltration. The wear resistance of TiC/Ni3Al composites including 70% and 80% TiC were promoted 3.25 and 4.33 times compared with pure Ni3Al, respectively.

Abstract: Nickel-based nano self-lubricating coatings were deposited on medium carbon steel by laser. The microstructure and tribological properties of the typical coating containing 10wt % nano-hBN powders were investigated using SEM incorporating EDS, and high temperature tribo-tester, respectively. It was found that the cladding layer and substrate was good metallurgical bonding. Dry sliding frictional tests suggested that the composite coating containing about 10wt % hBN powders has lower friction coefficient than that of pure Ni60 cladding at room temperature with a load of 40N and a speed of 2m/s, as well as 400°C with a load of 20N and a speed of 2m/s. The wear resistance of Ni60-hBN coating is about 10 times than that of Ni60 coating. The SEM analysis of the abrasion morphology found that wear mechanism of self-solid lubrication coating was adhesive wear, and wear mechanism of the cladding layer of non-lubricant was adhesive wear with abrasive wear.

Abstract: Alumina coatings were synthesized on Al–Cu–Mg alloy substrates through the Plasma enhance microarc oxidation (PMAO) route. Different oxidation times namely 1, 3, 5, 10, 20 and 30 minutes were employed and the coated samples were subjected to coating thickness and surface roughness measurements. Phase composition of the surface layers of the coatings was evaluated through X-ray diffraction. In addition, influence of the oxidation time on the kinetics of the coating formation, surface roughness and microhardness were investigated.

Abstract: A series of graded films of Cr/CrN/ CrNC/CrC/(Cr-DLC)/[(Cr-(Cr-DLC))×10] were deposited on Si(100) wafer and 4135 alloy structural steel using cathodic vacuum arc technique and direct current magnetron sputtering method combined with ion beam sputtering. The surface morphology, microstructure, nano-hardness, adhesion and wear properties of the films were investigated using 3-dimensional white-light interfering surface profiler, scanning electron microscopy, nanoindentation, scratch adhesion test, ball-on-disc test, etc. It was measured that the as-prepared Cr-doped DLC multilayered thin films have a strong adhesion to the substrates with a critical load exceeding 80 N, and the average friction coefficient during 30 min test in air was 0.23. This film will be promising in application against wear.

Abstract: High-temperature anti-oxidation coating was prepared by a milling process, which mainly composed of flake graphite and hexagonal BN (hBN). The coating was brushed on the sliding plate surface and dried in air for 24 h, The surface of the sliding plate painted was smooth and without peeling, suggesting a strong bonding strength. The samples were heated at 1200 °C for 20 min to evaluate the mass-loss rate. The mass-loss rate of the slide gate painted is 3.7%, less than the un-painted 5.1%. XRD and SEM techniques were used to characterize the as-heated samples. The results showed that the surface of the slide plate painted was skin rolling. And the graphite reacted with oxygen at an elevated temperature to reduce oxygen concentration. In addition, hBN also reacted with oxygen to form B2O3, which also has an oxygen-resistant role in the sliding plates. These coatings exhibited unique oxidation-resistant properties, and the service life of the coated sliding plates was obviously improved.

Abstract: The highly dense TiC/Fe ceramic coating was fabricated on Q235 steel surface by self- propagating high-temperature synthesis combined with pseudo hot iso-static pressing. The wear-resistant properties were examined by means of ball-on-disk contact wear test. The microstructure of TiC/Fe cermets coating was investigated. The results show that TiC/Fe cermets coating has an excellent wear-resistant property. There is little mass loss after 1200s under 30N loading under the condition of dry sliding wear testing. The major wear mechanisms are described by the following stages: sticking friction, grain abrasion and stripping of hard phase.

Abstract: A series of polyimide/ZnO films were successfully prepared via a solution process. The friction and wear behavior of the hybrid polyimide films in dry sliding against Si3N4 ball was examined on a DF-PM ball-on-block unidirectional friction and wear test rig. The worn surface morphologies of the films were observed with a scanning electron microscope. It was found that the introduction of zinc oxide led to improving the tribological characteristics and thermal stability of the polyimide films. The polyimide/zinc oxide hybrid films had much better friction-reducing ability and wear-resistance than the neat PI film.

Abstract: Ni-P-Al2O3 composite coatings with the uniform distribution of Al2O3 particles were prepared by adding Al2O3 particles into Ni-P plating solution and adopting optimum plating process. The morphology and microstructure of the coatings were investigated by using SEM, EDS and XRD. Being immersed in 10 vol.% H2SO4 solutions, the corrosion resistance of Ni-P-Al2O3 composite coatings was tested. The results show that when the solubility of Al2O3 particles in plating solution is 8 g/l, the corrosion resistance is best. Comparing with as-plated Ni-P-Al2O3 composite coatings, the corrosion resistance of heat-treated Ni-P-Al2O3 composite coatings decreases by raising the temperature to 300°C and then increases by raising the temperature to 450°C.

Abstract: In this work, we have investigated the influence of the pulsed substrate bias voltage on the evolution of the surface morphology and sp3 hybridization degree of Ag containing diamond-like carbon (Ag-DLC) films deposited by using a mid-frequency dual-magnetron sputtering system. The unipole substrate bias voltage at 0 V, -60 V, -100 V and -150 V, respectively, was employed on AISI 440 substrate with the duty ratio uniformly set at 70%. The surface morphology was observed by AFM and the hybridization degree of the DLC films was performed respectively using Raman Spectroscopy and Rockwell C indenter. In these samples, the surface morphology and sp3 hybridization degree of Ag-DLC films show a certain dependence on the pulsed substrate bias applied. The evolution tendency of the surface morphology is found different with that of the sp3 hybridization degree of the DLC films under action of the pulsed substrate bias. These phenomena imply that the energetic particles may induce a balance between recombination of the particles and change of the internal stress in the DLC films.