查看更多>>摘要：Hard-coated high speed steels are commonly used as tool materials for metal cutting applications, where they are exposed to a complex load spectrum consisting of shear and compressive stresses near the interface to the hard coating. These steels consist of different microstructural components, which on the one hand increase the stiffness of the material and on the other hand can withstand damage such as wear and cyclic plastic deformation. Although MC carbides are essential for the wear resistance and in particular can significantly increase the strength of the interface to the hard coating, knowledge about the influence of the steel microstructure on the cyclic damage behaviour caused by application-oriented load spectra is incomplete for these systems. Hence, this study focuses on the influence of coarse carbides and the martensitic matrix on the cyclic damage behaviour of TiN-coated high speed steels. Using an inclined impact test, a combined shear-/compressive load is applied to the steel/TiN interface of two different specimens with systematically varied high speed steel microstructures. Scanning electron microscopy on cross sections placed in the remaining imprints prepared by means of focused ion beam milling reveal a strong cyclic plastic deformation of the substrate that occurred after surpassing a critical applied force. Scanning electron microscopy and nanoindentation measurements in the high-speed steel matrix suggest cyclic softening and cyclic plastification, which is assumed to induce cracking at the interface between MC carbides and TiN coating.
查看更多>>摘要：The influence of Ag content on the morphology, structure, hardness (H) and reduced Young's modulus (E), thermal stability, and oxidation resistance of TiAlSiN(Ag) coatings is investigated. The coatings were produced by DC reactive magnetron sputtering, with increasing Ag contents from 0 up to 15.9 at.%. All coatings exhibit a fcc type structure. The coating with 1.5 at.% Ag content displays the highest H and E values as a result of the coating densification and the grain refinement caused by the co-deposition of immiscible phases. Further Ag concentration degrades the H and E values of the coatings due to the incorporation of a softer Ag phase in the structure. Annealing at 800 C in protective atmosphere for 2 h enhances the coatings crystallinity, with small increments in the H and E values. The dynamic thermal gravimetric oxidation curves reveal that Ag additions do not affect the starting point of oxidation of the coatings (~990 C). However, it enhances their oxidation resistance. The improved oxidation resistance of the coatings with Ag incorporation is caused by the diffusion of Ag through the oxide scale to the surface, which modifies the composition of the Ti-Al-O layer, producing a more protective Al rich layer.
查看更多>>摘要：MoSi2 usually suffers pesting failure at 400- 700 degrees C due to severe oxidation of Mo, which has been a great hindrance for industrial applications. To address this issue, this work grew MoSi2(Si) thin films via magnetron cosputtering of a Si single element target and a MoSi2 compound target on Si wafer substrates at room temperature, followed by annealing at 950 degrees C in an argon atmosphere. The as-annealed thin films were heated in a muffle furnace at 700 degrees C in air to experience different duration of oxidation. After that, the oxidation resistance was evaluated by examining the thickness, morphology, structure and composition of the as-heated thin films using field emission scanning electron microscopy and X-ray diffraction, respectively. In comparison with the MoSi2 without doping of Si, the MoSi2(Si) film is denser and exhibits a C11b crystalline structure with a smaller crystal size of 30 nm. The oxidation of Mo is effectively inhibited. There is no big bulge on the film surface after 1 h oxidation. But the oxidation of Si is severe, resulting in the continuous growth of grey SiO2 layer which help preventing the further oxidation of Mo. SiO2 islands are observed after oxidation for 9 h. The early pesting sites gradually become healed by the grown SiO2 layer during oxidation for 60 h. The mechanism for suppressing the pesting failure of MoSi2 by Si doping is discussed in details. A model is developed to explain the process.
查看更多>>摘要：The limit of applicability of the correlation between the ratio of hardness to elastic modulus (H/E) of coating systems and their wear resistance has been explored. Experimental approaches to determine accurate H/E values by nanoindentation are discussed and best practice recommendations summarised. Small-scale tribo-testing has been used to simplify complex wear conditions, and the role of contact severity and damage tolerance studied to determine why and when coating optimisation strategies are effective. Case studies show the importance of relatively low coating elastic modulus in reducing tensile stresses in sliding/abrasive contact. This may be a key factor in why coating design for optimised H/E and resistance to plastic deformation, H-3/E-2, can be more effective than aiming for extremely high coating hardness since that is typically accompanied by high coating stiffness. The influence of substrate ductility and load support on the damage tolerance of the coating system in impact tests has been investigated by testing at different contact size. Results show that mechanical and microstructural factors should not be considered in isolation. The role of coating microstructural design and temperature on optimising coating performance in high speed machining is investigated.
查看更多>>摘要：In this article, a CrCoNbB thin film metallic glass (TFMG) is fabricated by DC power magnetron sputtering. Its microstructure, surface properties, mechanical properties and thermal stability are characterized. Results are compared with sputter-deposited chromium (Cr) coating which is an industrial popular choice of hard coating by physical vapor deposition (PVD). We obtained a fully amorphous Cr48Co31Nb7B14 TFMG with glass transition (Tg) and crystallization (Tx) temperatures at 530 ? and 615 ?, respectively. Nanoindentation revealed that Cr(48)Co(31)Nb(7)B(14)TFMG has significantly lower surface roughness and higher hardness than Cr. Also, in nano scratch test with normal load applied between 0.5 mN ~ 9 mN, Cr48Co31Nb7B14 TFMG has a lower coefficient of friction (CoF) than Cr. Annealing the TFMG above Tg at 550 C for 60 min showed no sign of crystallization, implying excellent thermal stability. Contact angle analysis also revealed that the TFMG has very low surface free energy (SFE), specifically a low polar component. We also discovered that spreading of molten low-density polyethylene (LDPE) on Cr48Co31Nb7B14 TFMG is weaker than on Cr film as a consequence of its low SFE. In summary, Cr48Co31Nb7B14 TFMG has advantages such as high hardness and thermal stability, low roughness, friction and surface energy compared to PVD Cr coating. Low adhesion to molten LDPE also suggests its potential in applications such as injection mold coating where lower friction and higher wear resistance is preferred.
查看更多>>摘要：Direct-current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS) were used to deposit understoichiometric Ti(1-x)Al(x)B(2-y )diboride coatings by sputtering from a segmented TiB2-AlB2 target using Ar and Kr as sputtering gas. For films with a fixed Al/(Ti + Al) ratio of x = 0.1 (Ti0.9Al0.1B2-y), the B content was varied with y & ISIN; (0.1, 0.6 and 0.7). For films with a fixed y = 0.7 (Ti1-xAlxB1.3), the Al content was varied with x & ISIN; (0.1, 0.4 and 0.7). Evaluation of the mechanical properties of the Ti1-xAlxB1.3 samples showed a reduction in both hardness and elastic modulus with increasing Al concentration, while the Ti0.9Al0.1B2-y samples showed a hardness increase with decreasing B content. Thus, Ti0.9Al0.1B1.3 films exhibited a superior hardness of 46.2 +/- 1.1 GPa and an elastic modulus of 523 & PLUSMN; 7 GPa, compared to the values for Ti0.9Al0.1B1.4 and Ti0.9Al0.1B1.9, showing a hardness of 44 +/- 1 GPa and 36 +/- 1 GPa, and an elastic modulus of 569 +/- 7 GPa and 493 +/- 6 GPa, respectively. The oxidation behavior of the mechanically most promising Ti0.9Al0.1B2-y sample series was investigated through air-annealing at 600 C for durations from 1 h to 10 h. All films formed a mixed non-conformal Al2O3-TiO2 oxide scale which acts as an inward and outward diffusion barrier, significantly reducing the oxidation rate compared to TiBz films, which form an oxide scale consisting of porous TiO2. The thinnest oxide scale after 10 h was found in the B-deficient samples, Ti0.9Al0.1B1.3 and Ti0.9Al0.1B1.4, at ~200 nm, which is significantly below that for Ti0.9Al0.1B1.9 at 320 nm. The enhanced oxidation resistance of highly understoichiometric films is due to the elimination of the B-rich tissue phase that is present at the grain boundaries for higher B content, where the latter has been shown to enhance the rate of oxidation in borides.
查看更多>>摘要：The assessment of adhesion property of thin films by scratch test method is still a big challenge, relying on understanding accurately the material response and failure modes during scratch. In this study, a model TiN film on stainless steel substrate was studied by carrying out scratch tests. The entire scratch tracks were observed cross-sectionally and by superficial analysis to characterize its adhesion properties, scratch failures, and material response. Other than cracks and ploughing wear, a series of microscopic deformations and fracture mechanisms were observed and formed the overall material response of the model TiN/substrate system. These responses included substrate plastic deformation, synergistic bulge deformation at the scratch track edge, pile-up in front of the stylus, and fragmentation of TiN film. The spallation failure at the edge of track, where the first spallation was generally assigned as critical load (Lc) Lc2 and features an adhesive failure, was found to be cohesive failure. Furthermore, the Lc3 site corresponded to cohesive failure in the substrate rather than the adhesive failure of the film peeling off completely. Therefore, the results of this study indicate more care should be paid in terms of using Lc to interpret the adhesion properties of other film/substrate systems. The adhesion of film should be evaluated by considering the whole film/substrate system, not solely superficial analysis of the film surface.
查看更多>>摘要：Biopolymer and carbon-based materials have found widespread applications, spanning across different industries, including the medical, energy storage, wind energy, and aerospace sectors. The increasing popularity of both types of materials in industry has created a driving force for the enhancement of their properties to meet the current and future requirements. Active-screen plasma (ASP) has attracted much attention as a versatile and powerful surface engineering solution to meet these growing demands, owing to its treatment uniformity, remote plasma nature, capability for treating both electrically conductive and insulating materials, ability to functionalise surfaces, and the unique combined function of surface activation and deposition (CFAD). Through the introduction of moieties, modification of chemical bonding, change of morphology, and improvement in wettability on the treated surfaces, recent studies have demonstrated the ability for ASP treatments to enhance the biocompatibility of biopolymers. Moreover, ASP has also been tested (and 'bespoke' ASP techniques developed) for advanced carbon-based materials for tailored applications with promising property/performance enhancements, including a) enhanced wettability and interfacial shear strength for carbon fibres in polymer matrix composites, b) improved catalyst layer growth on carbon paper, c) improved electrical conductivity and capacitive performance for carbon nanofibers, and d) enhanced electric and electrochemical properties for graphene oxide.This review evaluates the recent achievements and findings of ASP treatments performed on biopolymers and carbon-based materials from the Surface Engineering group in the University of Birmingham. The current status of ASP surface multi-functionalisation is communicated, along with the future research focus for materials with poor electrical conductivity and/or vulnerability to degradation.
Uglov, V. V.Abadias, G.Zlotski, S. V.Saladukhin, I. A....
8页
查看更多>>摘要：The work is dedicated to the study of the phase stability and surface erosion of a novel Zr-based multilayer system consisting of a combination of ceramic (ZrN) and metallic glass (Zr-Cu) nanoscale layers after He irradiation (40 keV and doses up to 1.1 x 1018 cm(-2)). Periodic ZrN/Zr(1-x)Cux multilayers with elementary layer thicknesses of 5 nm/5 nm and 5 nm/10 nm and Cu content x = 0.45, 0.53, 0.61 and 0.74 were grown by magnetron sputter-deposition from Zr and Cu targets at the substrate temperature of 300 C. X-ray diffraction and X-ray reflectivity analysis reveal that multilayered films consist of alternating nanocrystalline (nc) ZrN and amorphous (a) ZrCu layers with relatively sharp interfaces. The stability of the phase composition of nc-ZrN/a-Zr1-xCux multilayer films to irradiation with helium ions up to fluence of 1.1 x 1018 cm- 2 has been established. For x = 0.74, crystallization of the metallic glass layer was observed. The surface integrity of the multilayer films remained unaltered up to an ion fluence of 5 x 1017 cm(-2). At higher ion fluence, surface erosion of the nc-ZrN/a-Zr(1-x)Cu(x )films occurs by the flacking mechanism. In this case, an increase in the thickness of the amorphous Zr(1-x)Cux layer and in Cu content leads to improved radiation resistance as the critical fluence for delamination increases from 5 x 1017 cm(-2) upto 8 x 1017 cm(-2).
查看更多>>摘要：In this study, we investigated the microstructural evolution, surface hardening and general corrosion properties of a precipitation-strengthened Inconel 718 Ni-superalloy after triode-plasma nitriding (TPN) at low treatment temperatures of 400-450 degrees C (i.e. thermodynamic paraequilibrium conditions) and a high treatment temperature of 700 degrees C. At low treatment temperatures, apart from the formation of nitrogen-expanded austenite (gamma N) from the high-Cr gamma matrix, the pre-existing gamma' and gamma '' intermetallic nano-precipitates appear to exhibit different nitriding responses. The spheroidal N-modified gamma' (or gamma'(N)) precipitates were 'slightly-expanded', leading to slightly shifted XRD peaks, i.e. 2-theta angles of similar to 0.2 degrees from gamma(substrate)(111) and similar to 0.5 from gamma(substrate)(200). In contrast, N-modified gamma '' (or gamma ''(N)) could experience substantial lattice expansion close to that of the gamma(N) matrix. With increasing treatment temperature, nitride formation started as additional nano-sized precipitates (e.g.-3-6 nm diameter as observed at 450 degrees C) and grew into laths (e.g.-5-10 nm thick and-15-30 nm wide as observed at 700 degrees C). Without changing core microstructure/properties, surface nitrogen modification and hardening were obtained on alloy 718 after TPN (e.g. from-486 HV0.025 to-1212 HV0.025 after TPN at 400 degrees C). No degradation of corrosion performance was observed for the nitrogen-supersaturated surface after TPN at 400 degrees C. However, the 450 degrees C TPN-treated surface showed a slightly increased current density in the anodic region, which can be associated with early-stage nitride formation. The significantly deteriorated corrosion performance after TPN treatment at 700 degrees C is due to pronounced nitride formation and segregation of substitutional alloying elements.
NSTL
Elsevier