查看更多>>摘要：Many engineering (biomedical, automotive, aerospace etc.) structures suffer from wear and corrosion damage under service conditions and this situation shortens their useful life. In common cases, these damage mechanisms do not act on materials separately. On the contrary, their combined effect called as tribocorrosion cause more decrease in their lifetime than the individual effects of wear and corrosion. Tribocorrosion damages are directly related to surface properties of materials. In order to improve tribocorrosion performance of materials, different surface modifications were applied to enhance their performance and one of them is shot peening. However, tribocorrosion behavior of shot peened materials have not been clarified so far. Therefore, in this study, the effect of shot peening on the tribocorrosion properties of AISI 4140 low-alloy steel was investigated in detail. AISI 4140 samples were shot peened under different Almen intensities and their tribocorrosion performance were examined. The results revealed that the increasing Almen intensity changed the surface characteristics from hydrophobic to hydrophilic. Also, it was determined that the tribocorrosion performance of the material improved with the increasing shot peening intensity in terms of increased surface hardness.
查看更多>>摘要：Ternary surface hardening layers were prepared on the Q235 low-carbon steel by plasma electrolytic borocarbonitriding(PEB/C/N) under constant voltage of 260-300 V for 30 min. The microstructure, phase components and hardness depth profiles of the B + C + N ternary hardening layers were examined. The ternary hardening layers were composed of a boride layer with single Fe2B phase and a transition layer. The thickness of modified boride layers on the PEB/C/N samples was about 10 um, 15 um and 22 um at 260 V, 280 V and 300 V, respectively. The maximum hardness of boride layer was 2400 HV for the 300 V PEB/C/N sample. The surface free energy of bare Q235 steel and PEB/C/N samples at 260, 280 and 300 V were 41.084, 32.039, 26.906 and 25.726 mJ/m(2), which were calculated on the basis of their contact angles for water and n-hexadecane. Furthermore, the hardening layers exhibited excellent corrosion behavior due to the improved hydrophobicity for the dense boride layer. The lowest wear rate of PEB/C/N sample at 300 V is about 2.0375 x 10(-6) mm(3)/N center dot m, which is only 1/15 of the bare Q235 steel, the ternary hardening treatment shows a better wear resistance than the bare Q235 steel.
查看更多>>摘要：P91 ferritic/martensitic and AISI 304L austenitic stainless steels were hot dip aluminized (HDA) in 99.9% pure aluminum in a pit type vertical furnace at three different temperatures i.e. 750, 800 and 850 degrees C for 1 to 10 min. Evolution of interface morphology, type and distribution of phases and growth kinetics of the reaction zones were studied using a variety of experimental techniques. Though similar intermetallic compounds formed in both steels, their distribution, morphology and growth kinetics were distinctly different. In P91 F/M steel, aluminized surface adjacent to the substrate had wide Fe2Al5 layer with serrated morphology containing high volume fraction of 2-3 mu m sized Cr rich intermetallic phases. Width of FeAl3 phase present adjacent to this layer did not show much variation with HDA conditions. Above FeAl3, on the surface, the pure Al top coat contained nonequilibrium phases. Compared to P91 steel, width of the aluminized layer in 304L SS was less (35 +/- 5 mu m vs 120 +/- 15 mu m at 800 degrees C-10 min) and the Fe2Al5 layer had a planar interface with the substrate. Optimum temperature-time combination to get thin, uniform, defect free surface aluminide layer in P91 F/M and 304L steels were found to be 750 degrees C-2 min and 800 degrees C-1 min respectively. Growth kinetics of surface aluminide layers in both steels were studied, kinetic parameters were determined and compared with information available in literature.
查看更多>>摘要：The tetrahedral amorphous carbon (ta-C) coating is one of the fascinating surface coating for superior mechanical properties. Although its outstanding mechanical strength, it is hard to achieve adhesion stability due to high interfacial and residual stresses. Here, we introduce a new concept of pretreatment called large pulsed electron beam (LPEB) treatment. To specify the adhesion of the ta-C coating following the LPEB treatment, various adhesion tests, including the scratch test and Rockwell indentation test, were conducted. Thus, the ta-C coating pretreated with LPEB was found to have excellent adhesion through qualitative and quantitative analyses. Furthermore, to elucidate the mechanism for improving adhesion, analyses were conducted from two aspects: 1) deformation of the substrate and 2) stress change at the interface between the coating and the substrate. As a result, ta-C pretreated with LPEB increased the hardness of the substrate and supported the coating well. In addition, the thermal contraction of the coating was decreased after deposition, reducing the stress between the coating and the interface, and the adhesion was considerably improved.
查看更多>>摘要：Understanding of laser shock peening (LSP)-generated microstructural characteristics at the interfaces between hexagonal close-packed (HCP) and body-centered cubic (BCC) crystals and dislocation patterns could provide useful insights into designing the interface between both phases of dual- or multi- phase metallic materials, which is a key information for higher properties. Herein, with a severe plastic deformation process of LSP, a systematic work of the mechanism behind misfit dislocations at different grain size has been carried out. It demonstrates that, as the grain gradually is refined, extrusion and torsion of the lattice are important contributions to the modified d-spacing and quantity of misfit dislocation. Hence, the growth orientation and the style of bicrystal interface between HCP and BCC crystals are affected. Furthermore, the size effect of the LSP-generated dislocation pattern has a significant attribution to the stress of misfit dislocation originating from neighboring interfaces.
NSTL
Elsevier