Formation Mechanisms,Structure, and Properties of HVOF-Sprayed WC-CoCr Coatings: An Approach Toward Process Maps

Our study focuses on understanding the damage tolerance and performance reliability of WC-CoCr coatings. In this paper, the formation of HVOF-sprayed tungsten carbide-based cermet coatings is studied through an integrated strategy: First-order process maps are created by using online-diagnostics to assess particle states in relation to process conditions. Coating properties such as hardness, wear resistance, elastic modulus, residual stress, and fracture toughness are discussed with a goal to establish a linkage between properties and particle characteristics via second-order process maps. A strong influence of particle state on the mechanical properties, wear resistance, and residual stress stage of the coating was observed. Within the used processing window (particle temperature ranged from 1687 to 1831 °C and particle velocity from 577 to 621 m/s), the coating hardness varied from 1021 to 1507 HV and modulus from 257 to 322 GPa. The variation in coating mechanical state is suggested to relate to the microstructural changes arising from carbide dissolution, which affects the properties of the matrix and, on the other hand, cohesive properties of the lamella. The complete tracking of the coating particle state and its linking to mechanical properties and residual stresses enables coating design with desired properties.     

Novel iron oxide–silica coreshell powders compacted by using pulsed electric current sintering: Optical and magnetic properties

The properties of the bulk materials consolidated of silica coreshell powders with iron oxide core have been studied. Iron oxide nanoparticles smaller than 20 nm in size were synthesized by a reverse co-precipitation process in ambient atmosphere. Coreshell structures with various amounts of iron oxide were prepared via a modified Stöber method. The powders were compacted by using pulsed electric current sintering (PECS) at 1373 K. The morphologies, microstructures, phases, optical, and magnetic properties of the samples were studied by using transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffraction (XRD), UV–visible spectroscopy (UV–Vis), and vibrating sample magnetometer (VSM). Transmittance values in the 250–800 nm range varied with the amount of iron oxide. Sample with the lower content was transparent while the sample with the highest content was opaque with microporosity. The compact with the highest iron oxide content showed the ferromagnetic behaviour at 300 K. The phase transformations in the coreshell powders during the sintering process are discussed.     

Strain aging and load relaxation behavior of type 316 stainless steel at room temperature

The strain aging and load relaxation behavior of type 316 stainless steel (SS) at room temperature were studied. It is shown that rapid aging occurs in 316 SS at room temperature to an extent that affects the load relaxation behavior of the material. Qualitatively, the aging behavior was found to agree with those reported earlier for Fe-Ni-C-alloys, and the observed aging characteristics could be explained by using an earlier proposed vacancy-interstitial mechanism. The load relaxation behavior is analyzed in terms of Hart’s state variable model. Effects of strain aging and strain hardening on the load relaxation behavior and the scaling of the relaxation curves are determined. It is shown that aging can be accounted for by a time-dependent change in a model parameter, which is dependent on the mobile dislocation density and the dislocation mobility. In addition, a dependency on plastic state of the same parameter previously held constant was found. It is concluded that this phenomenon, which in 316 SS could be rationalized in terms of increasing forest dislocation density, is likely to be more general, and a provision for it should be made in the state variable theory. S. P. Hannula formerly Research Associate in the Department of Materials Science and Engineering, Cornell University, Ithaca, NY M. A. Korhonen, formerly Visiting Assistant Professor in the Department of Materials Science and Engineering, Cornell University, Ithaca, NY     

The influence of CSF on EEG sensitivity distributions of multilayered head models

We examined how the cerebrospinal fluid (CSF) affects the distribution of electroencephalogram (EEG) measurement sensitivity. We used concentric spheres and realistic head models to investigate the difference between computed-tomography (CT) and magnetic resonance image (MRI) models that exclude the CSF layer. The cortical EEG sensitivity distributions support these phenomena and show that the CSF layer significantly influences them, thus identifying the importance of including the CSF layer inside the head volume conductor models. The results show that the highly conductive CSF channels the current, thus decreasing the maximum cortical current density relative to models that do not include the CSF. We found that the MRI and CT models yielded HSV results 20% and 45%, respectively, too small when compared with CSF-inclusive models.     

Phenotypic and genotypic characterization of oral yeasts from Finland and the United States

A total of 4-22 isolates of oral yeasts per subjects from 48 yeast-positive Finnish and American subjects (25 females and 23 males) were phenotyped and genotyped to determine the frequency of simultaneous oral carriage of multiple yeast taxa. An oral sample from either periodontal pockets, oral mucosa or saliva was obtained. All subjects yielded Candida albicans and 3 subjects an additional yeast species (Candida krusei, Candida glabrata or Saccharomyces cerevisiae). The API 20C Aux kit distinguished 9 different carbohydrate assimilation profiles among the C. albicans isolates. Thirty-eight of 46 C. albicans biotype I isolates were categorized in a single numerical profile. PCR analysis, using a random primer OPA-03 and a repetitive primer (GACA)4, detected 2 major genotypic groups among the C. albicans isolates; 44 subjects showing isolates with a "typical" PCR-profile and 4 subjects isolates with an "atypical" PCR-profile. The "atypical" PCR-profile was similar to that of Candida dubliniensis. All C. albicans isolates assimilated xylose, except 5, including the 4 with an "atypical" PCR-profile. No difference was found in distribution of oral yeast species, and of C. albicans phenotypes and genotypes between Finnish and American subjects. The present PCR method may offer a rapid and easy means of distinguishing oral Candida species.     

The development of situational interest during a digital mathematics game

The present study focused on 212 fifth graders' situational interest trajectories during an intervention with a digital mathematics game called Number Navigation. Our aims were to explore the development of situational interest whilst playing the game and to investigate the relationship between situational interest and individual math interest. Growth mixture model analyses showed that in the whole sample situational interest was stable within sessions but decreased across sessions. Three different situational interest trajectories were found. Situational interest trajectories were predicted by pre‐test individual interest. In turn, situational interest had an effect on post‐test individual interest. Students whose situational interest trajectories were stable (either high or low) presented no changes in individual interest, yet the individual interest of students whose situational interest was triggered but not maintained markedly decreased from pre‐test to post‐test. Results suggest that it is important to use game‐based learning not because games are believed to be “motivating”; rather, games with proven learning outcomes should be carefully selected.     

超音速火焰喷涂碳化物粒径不同的WC-10Co4Cr涂层在粗细磨粒下的磨损性能

改进的ASTM G65橡胶轮测试方法可采用220nm二氧化钛颗粒和368μm的砂粒分别在潮湿和干燥条件下使用。在由碳化物粒径不同(传统和亚微米)的两种粉末所制备的WC-CoCr涂层上开展试验,研究碳化物大小和磨损介质特性对涂层磨损性能的影响。采用扫描电镜对同一位置磨损前后的低倍和高倍形貌进行观察,并分析了涂层的磨损机理。结果表明:磨损机理取决于碳化物和磨粒的相对大小。在样品上进行磨损定量分析,通过调整碳化物尺寸可改善磨损性能,测试涂层的一些力学性能用于对比。     

The effect of cooling rate on beef tenderness: The significance of pH at 7 °C

To study the effects of cooling regime on beef tenderness, seven commercial beef slaughterhouses with different cooling regimes were selected to obtain different carcass cooling rates. The pH values and temperatures of 8 M. longissimus dorsi (LD) and M. semimembranosus (SM) muscles from each slaughterhouse were monitored for 30 h. The muscles of the monitored carcasses were excised and vacuum packed for Allo-Kramer shear force (SF) determinations. Samples were kept at 3-4 °C for 5 or 21 d. The slaughterhouses were grouped by their average pH values of the muscles, prevailing at the moment when the temperature of the muscles reached 7 °C. The pH groups for LD were (i) low (5.52-5.63), (ii) medium (5.84-5.97) and (iii) high (6.16-6.17). The highest shear forces were in group (iii), being the toughest: 155-152 N/g, and the lowest in group (i) (the most tender): 108-116 N/g, respectively. The regression equation or the shear force was SF=-295.4+73.0?(pH at 7 °C); (R(2)=87%). There was no significant correlation between the cooling rate and tenderness in SM, indicating that it is difficult to control the tenderness of all muscles using the same cooling regime. The ageing effect was more marked and the variation in the shear forces smaller in the slaughterhouses generating carcasses with low pH values at 7 °C than in those generating high ones. It was concluded that a low cooling rate, or more specifically, the temperature/pH at the onset of rigor mortis, is important for beef tenderness. The pH of LD must fall to values below 5.7 before/when the temperature reaches 7 °C.     

Investigation of some microstructural features related to corrosion initiation in titanium-aluminium nitride coated steel

In this work the microstructural features and defects identified previously in corrosion and porosity tests of the coatings were studied. The influence of surface roughness was evaluated with (Ti, Al)N coatings on two different types of substrates. Coatings deposited on the roughest surfaces on either a high speed steel or a stainless steel had the highest porosity. However, the dependence of the porosity on the surface roughness was not straightforward. Interrupted coating runs were carried out to obtain more information on the initiation of defects in the substrate-coating interface. Samples produced in the interrupted runs were analysed using metallographic methods, scanning electron microscopy with X-ray analysis, Rutherford backscattering spectrometry and secondary ion mass spectroscopy. Sputtering was found to be effective in removing the impurities from the interface and none of the non-metallic elements (carbon, oxygen, sulphur) studied exhibited any enrichment on the interface. The use of a tungsten filament for enhancement of the plasma was found to result in a tungsten-enriched layer at the substrate-coating interface, which may have an effect on adhesion and corrosion properties of the coating. However, no droplet types of formations were detected after sputter cleaning or when either titanium or aluminium evaporation was started, suggesting that tungsten was evenly distributed in the coating.