Materials Science Forum Vols. 561-565

Abstract: Precipitation-strengthened Cu-based alloys have limited use as structural materials at high temperatures due to precipitate coarsening and strength loss. We have recently shown that Curefractory metal alloys produced by various physical vapor deposition methods have stable, nanocrystalline microstructures and maintain their strength properties even when annealed at temperatures as high as 900 C for up to 100 hours. This paper presents discussions of how these alloys are processed and the resulting microstructures. X-ray and electron microscopy results will be presented to document the phase transformations that occur in these alloys and result in such exceptionally stable microstructures.

Abstract: HCPEB treatment of 316L stainless steel (SS) was carried out and the microstructure change in the modified surface layer were characterized with optical microscopy and X-ray diffractometry techniques. The evolution regularity of surface craters and grain refinement effect, as well as the preferred orientation of (111) crystal plane occurring in the HCPEB treatment at different working parameters were discussed combining with their influence on corrosion resistance.

Abstract: Corrosion of ultra-fine grain (UFG) copper fabricated by equal-channel angular pressing (ECAP) has been investigated in comparison with that of recrystallized coarse grain (CG) copper. Corrosion current was estimated by a Tafel extrapolation method to examine the kinetics of corrosion in a modified Livingstone etchant, which attack dislocations and grain boundaries preferentially. UFG copper have exhibited a lower corrosion current in comparison with that in its recrystallized coarse grain (CG) counterpart despite the fact that the dislocation density and total fraction of grain boundaries are much greater in UFG copper than in CG copper. Corrosion damage on its surface is macroscopically rather uniform whereas obvious attack at grain boundaries and selective corrosion of some grain interiors were observed in CG copper.

Abstract: The objective of this research was to find the best combination of factor levels that minimized the surface roughness of prototyped samples from Fused Deposition Modeling (FDM). Two sets of experiments were conducted for that purpose; a two-level three-factor full factorial experiment and a three-level two-factor full factorial experiment. The parameters chosen for this research were model temperature, layer thickness and part fill style. The results obtained from both experiments were compared and analyzed in order to determine the best combination of factors that minimized the surface roughness of the specimens. The significant factors, their interactions and the optimum setting are presented in this paper

Abstract: Effect of Ni/Cu multilayer coating on fatigue durability was investigated. The Ni/Cu multilayered films were coated on cylindrical copper specimens by electroplating technique. Thickness of individual component layers was h=20nm and 100nm and the total thickness was 5μm. The specimens with a conventional nickel coating and uncoated specimens were also prepared. Push-pull fatigue tests were carried out in air at room temperature. It was found that the specimens with the Ni/Cu multilayered coatings exhibited the fatigue lives longer than those of the conventional nickel coating. In particular, the fatigue life with the h=100nm multilayer was at least ten times longer than that with the nickel coating at the stress amplitude of 90MPa. From the electron channelling contrast imaging (ECCI) observation of subsurface areas of the copper specimens, dislocation structures peculiar to fatigue deformation was suppressed by the surface coatings.

Abstract: Co/Cu and Ni/Cu multilayers fabricated by electroplating technique were annealed at various temperatures in order to investigate thermal stability of multilayered structures. Vickers hardness tests on the annealed Co/Cu and Ni/Cu multilayers were conducted at room temperature. It was recognized that after the annealing at 1023K the Co/Cu multilayer still maintained the hardness of as-deposited state. On the other hand, the hardness of Ni/Cu multilayer was almost identical to copper substrate after the annealing at 903K.

Abstract: At present, cobalt is the most commonly used binder material in tungsten carbide based hardmetals. Current research on sliding wear performance of these cemented carbides, however, reveals promising results for nickel binder as well. Test samples of WC-Co and WC-Ni hardmetals have been machined and surface finished by wire-EDM and grinding. From comparative dry sliding pin-on-plate experiments on wire-EDM’ed, ground and polished grades, correlations are derived between wear volume loss and friction on the one hand and contact pressure, sliding distance, binder phase and microstructure on the other hand. The lowest wear levels are encountered with polished cemented carbides. The EDM induced surface modification turns out to deteriorate wear resistance, especially during the running-in stage of sliding. These findings are in agreement with Xray diffraction measurements of the residual stress level in the WC phase.

Abstract: A sliding wear test was conducted in a copper single crystal having (001) surface. Microstructures induced by the sliding wear were investigated by means of the electron channelling contrast (ECC) imaging and electron backscattered diffraction (EBSD) analysis. The microstructures below the worn surface consisted of the stack of dislocation cell structure, layered structure and equiaxed fine-grained structure. At the dislocation cell structure, there was no significant change in crystallographic orientation. On the other hand, the crystal at the layered structure rotated continuously around the axis which was perpendicular to sliding wear direction. In the fine-grained structure, preferential orientations no longer existed. The authors attempted to explain grain boundary formation in terms of a rotation angle gradient which is proportional to density of geometrically-necessary dislocations.

Abstract: In this paper, the anticorrosive performances of fastener coatings containing PTFE and/or nano aluminum particles were investigated by using electrochemical impedance spectroscopy, scanning electron microscope. The impedance spectroscopy was interpreted by means of analysis equivalent electrical circuits. The coating capacitance of the films was monitored with the immersion time to establish the water and ions permeability of these paint films. By comparison with clear coating, PTFE and PTFE- nano aluminum pigmented coatings, the results indicated that PTFE lowers the protective properties of the waterborne epoxy film although it can provide lubricating effect. The nano aluminum powder presented the best beneficial effect and resulted in a significant increase in corrosion resistance of the PTFE- nano aluminum composite coatings. The corrosion-resistant mechanism of the effect of PTFE and nano aluminum particles in the coating is discussed.

Abstract: Sensitivity to corrosion fatigue (CF) crack initiation has been investigated in a series of pure copper bicrystals with a symmetrical <110>-tilt grain boundary. Tests were performed by axial tension-compression tests in 1M NaNO2 solutions. The small-angle tilt bicrystals fractured in both intergranular and transgranular manners accompanied by a large amount of plastic strain to fracture while the large-angle bicrystals fractured in almost intergranular manner with a smaller plastic strain. Susceptibility to CF cracks increases with increasing misorientation. It seems that effect of grain boundaries structures, i.e., Σ-values is small in this experiment. Stress concentration generated by the pile-up of trapped dislocations at the grain boundary could account for the high susceptibility of the intergranular cracks in large-angle grain boundaries