A New Al2 O3 -Protected EB-PVD TBC with Superior CMAS Resistance.

Calcium-magnesium-aluminium-silicate (CMAS) attack is a longstanding challenge for yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs) particularly at higher engine operating temperature. Here, a novel microstructural design is reported for YSZ TBCs to mitigate CMAS attack. The design is based on a drip coating method that creates a thin layer of nanoporous Al2 O3 around YSZ columnar grains produced by electron beam physical vapor deposition (EB-PVD). The nanoporous Al2 O3 enables fast crystallization of CMAS melt close to the TBC surface, in the inter-columnar gaps, and on the column walls, thereby suppressing CMAS infiltration and preventing further degradation of the TBCs due to CMAS attack. Indentation and three-point beam bending tests indicate that the highly porous Al2 O3 only slightly stiffens the TBC but offers superior resistance against sintering in long-term thermal exposure by reducing the intercolumnar contact. This work offers a new pathway for designing novel TBC architecture with excellent CMAS resistance, strain tolerance, and sintering resistance, which also points out new insight for assembly nanoporous ceramic in traditional ceramic structure for integrated functions.

Effect of Scanning Strategy on the Microstructure and Triboperformance of FeNiCrMo Coating Manufactured by Plasma Transferred Arc.

To increase the coating thickness and service life of the FeNiCrMo coating, a plasma transferred arc (PTA) double-track alloying technique was employed to enhance the surface triboperformance of the ductile iron. Optical microscopy (OM), X-ray diffraction (XRD), electron probe X-ray microanalyzer (EPMA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Vickers hardness tester, and tribological tester were subsequently used to evaluate the effect of the double alloying treatment tracks on the microstructure and triboperformance of the coating. The results indicate that the content of the cementite in the sample with a double-track treatment increases 3.90 wt.% and the content of the martensite decreases 13.04 wt.% compared with the sample with a single-track treatment, which results in the maximum microhardness of the sample fabricated by double track increasing from 837 ± 10 HV0.2 for the sample fabricated by single track to 871 ± 7 HV0.2. Thus, the wear rate is lower than that of the sample with a single-track treatment. In addition, the distribution of alloying elements is more uniform and coating thickness is higher in the double track than those of the single-track-treated one. Therefore, the double-track PTA alloying treatment is favored for hardfacing ductile iron with a FeNiCrMo alloy coating due to its enhanced triboperformance and longer service life.

Status and Perspective of High-Energy Beam Surface Strengthening: High-Speed Steel.

High-speed steel (HSS) is primarily used to manufacture cutting tools and roll materials for various machine tools. Improving the hardness, wear resistance, and corrosion resistance of HSS is of great significance to the development of the manufacturing and tool industries. The high-energy beams, consisting of laser, plasma beam, and electron beam processing (e.g., surface remelting, cladding, and alloying), have the advantageous characteristics of high heat source energy and good surface processing effect. The research status and perspective of the above three processing techniques on the surface properties (in particular, hardness, wear resistance, and corrosion resistance) of HSS is reviewed, and the principles, advantages, and disadvantages of the three strengthening methods are discussed. High-energy beam surface alloying appears to be the most cost-effective of HSS surface strengthening methods and is promising to receive increasing research attentions in the future.

Temperature-Adaptive Ultralubricity of a WS2/a-C Nanocomposite Coating: Performance from Room Temperature up to 500 °C.

This study reports on the ultralubricity of a high-temperature resilient nanocomposite WS2/a-C tribocoating. The coefficient of friction of this coating remains at around 0.02 independently of a thermal treatment up to ∼500 °C, as confirmed by high-temperature tribotests. Moreover, the coating annealed at 450 °C keeps exhibiting a similar ultralubricity when cooled back down to room temperature and tested there, implying a tribological self-adaptation over a broad temperature range. High-resolution TEM observations of the tribofilms on the wear track unveil that WS2 nanoplatelets form dynamically via atomic rearrangement and extend via unfaulting geometrical defects (bound by partial climb dislocations). The (002) basal planes of the WS2 nanoplatelets, reoriented parallel to the tribo-sliding direction, contribute to a sustainable ultralubricity. The declining triboperformance beyond 500 °C is associated with sulfur loss rather than the transformation of WS2 into inferior WO3 via oxidation as suggested earlier. This self-adaptive WS2/a-C tribocoating holds promise for a constant ultralubrication with excellent thermal performance.

The Role of Distribution Forms of Fe-Cr-C Cladding Layer in the Impact Abrasive Wear Performance of Hadfield Steel.

To investigate the role of different distribution forms of Fe-Cr-C cladding layer in the impact abrasive wear performance of Hadfield steel, the over-lapped Fe-Cr-C cladding layer and dot-shaped Fe-Cr-C cladding layer were deposited, respectively, by plasma transferred arc (PTA) cladding on Hadfield steel. The microstructure, microhardness and impact abrasive wear performance of the two cladding layers under the impact of glass sand, granite and quartz sand were investigated. The results showed that both microstructures of the cladding layers were hypoeutectic Fe-Cr-C microstructures. The average microhardness of the over-lapped cladding layer and dot-shaped cladding layer was around 560 HV0.2 and 750 HV0.2, respectively. The over-lapped Fe-Cr-C cladding layer could only improve the impact abrasive wear resistance of the Hadfield steel under the wear condition of the glass sand. Meanwhile, the dot-shaped Fe-Cr-C cladding layer could improve the impact abrasive wear resistance of the Hadfield steel under all the three kinds of the abrasives because of the overall strengthening effect of its convex shape and the hypoeutectic FeCrC microstructure.

Pt/ZrO2 Prepared by Atomic Trapping: An Efficient Catalyst for the Conversion of Glycerol to Lactic Acid with Concomitant Transfer Hydrogenation of Cyclohexene.

A series of heterogeneous catalysts consisting of highly dispersed Pt nanoparticles supported on nanosized ZrO2 (20 to 60 nm) was synthesized and investigated for the one-pot transfer hydrogenation between glycerol and cyclohexene to produce lactic acid and cyclohexane, without any additional H2. Different preparation methods were screened, by varying the calcination and reduction procedures with the purpose of optimizing the dispersion of Pt species (i.e., as single-atom sites or extra-fine Pt nanoparticles) on the ZrO2 support. The Pt/ZrO2 catalysts were characterized by means of transmission electron microscopy techniques (HAADF-STEM, TEM), elemental analysis (ICP-OES, EDX mapping), N2-physisorption, H2 temperature-programmed-reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Based on this combination of techniques it was possible to correlate the temperature of the calcination and reduction treatments with the nature of the Pt species. The best catalyst consisted of subnanometer Pt clusters (<1 nm) and atomically dispersed Pt (as Pt2+ and Pt4+) on the ZrO2 support, which were converted into extra-fine Pt nanoparticles (average size = 1.4 nm) upon reduction. These nanoparticles acted as catalytic species for the transfer hydrogenation of glycerol with cyclohexene, which gave an unsurpassed 95% yield of lactic acid salt at 96% glycerol conversion (aqueous glycerol solution, NaOH as promoter, 160 °C, 4.5 h, at 20 bar N2). This is the highest yield and selectivity of lactic acid (salt) reported in the literature so far. Reusability experiments showed a partial and gradual loss of activity of the Pt/ZrO2 catalyst, which was attributed to the experimentally observed aggregation of Pt nanoparticles.

Copper-mediated homogeneous living radical polymerization of acrylamide with waxy potato starch-based macroinitiator.

Cu0-mediated living radical polymerization (Cu0-mediated LRP) was employed in this research for the synthesis of starch-g-polyacrylamide (St-g-PAM). The use of a controlled radical grafting technique is necessary, as compared to the traditional free-radical polymerization methods, in order to obtain a well-defined structure of the final product. This is in turn essential for studying the relationship between such structure and the end-properties. Waxy potato starch-based water-soluble macroinitiator was first synthesized by esterification with 2-bromopropionyl bromide in the mixture of dimethylacetamide and lithium chloride. With the obtained macroinitiator, St-g-PAM was homogeneously synthesized by aqueous Cu0-mediated LRP using CuBr/hexamethylated tris(2-aminoethyl)amine (Me6Tren) as catalyst. The successful synthesis of the macroinitiator and St-g-PAM was proved by NMR, FT-IR, SEM, XRD and TGA analysis. The molecular weight and polydispersity of PAM chains were analyzed by gel permeation chromatography (GPC) after hydrolyzing the starch backbone. Monomer conversion was monitored by gas chromatography (GC), on the basis of which the kinetics were determined. A preliminarily rheological study was performed on aqueous solutions of the prepared materials.