Structure property relationship of suspension thermally sprayed WC-Co nanocomposite coatings.

Tribomechanical properties of nanostructured coatings deposited by suspension high velocity oxy-fuel (S-HVOF) and conventional HVOF (Jet Kote) spraying were evaluated. Nanostructured S-HVOF coatings were obtained via ball milling of the agglomerated and sintered WC-12Co feedstock powder, which were deposited via an aqueous-based suspension using modified HVOF (TopGun) process. Microstructural evaluations of these hardmetal coatings included transmission electron microscopy, x-ray diffraction, and scanning electron microscopy equipped with energy dispersive x-ray spectroscopy. The nanohardness and modulus of the coated specimens were investigated using a diamond Berkovich nanoindenter. Sliding wear tests were conducted using a ball-on-flat test rig. Results indicated that low porosity coatings with nanostructured features were obtained. High carbon loss was observed, but coatings showed a high hardness up to 1000 HV2.9N. S-HVOF coatings also showed improved sliding wear and friction behavior, which were attributed to nanosized particles reducing ball wear in three-body abrasion and support of metal matrix due to uniform distribution of nanoparticles in the coating microstructure

Inventory of current EU paediatric vision and hearing screening programmes

Background: We examined the diversity in paediatric vision and hearing screening programmes in Europe. Methods: Themes relevant for comparison of screening programmes were derived from literature and used to compile three questionnaires on vision, hearing and public-health screening. Tests used, professions involved, age and frequency of testing seem to influence sensitivity, specificity and costs most. Questionnaires were sent to ophthalmologists, orthoptists, otolaryngologists and audiologists involved in paediatric screening in all EU fullmember, candidate and associate states. Answers were cross-checked. Results: Thirty-nine countries participated; 35 have a vision screening programme, 33 a nation-wide neonatal hearing screening programme. Visual acuity (VA) is measured in 35 countries, in 71% more than once. First measurement of VA varies from three to seven years of age, but is usually before the age of five. At age three and four picture charts, including Lea Hyvarinen are used most, in children over four Tumbling-E and Snellen. As first hearing screening test otoacoustic emission (OAE) is used most in healthy neonates, and auditory brainstem response (ABR) in premature newborns. The majority of hearing testing programmes are staged; children are referred after one to four abnormal tests. Vision screening is performed mostly by paediatricians, ophthalmologists or nurses. Funding is mostly by health insurance or state. Coverage was reported as >95% in half of countries, but reporting was often not first-hand. Conclusion: Largest differences were found in VA charts used (12), professions involved in vision screening (10), number of hearing screening tests before referral (1-4) and funding sources (8)

Some Recent Results on the 3C-SiC Structural Defects

This work presents some recent results on the 3C-SiC structural defects, studied by transmission electron microscopy. The samples were grown in several laboratories, using different methods. There has always been special attention to the region close to the interface between the seed and the overgrown material. This is due to the fact that this region is very important to the evolution of defects during growth. The main defects in SiC are micropipes, double position boundaries, stacking faults and dislocations. The defects that are most frequently observed in 3C-SiC and more difficult to eliminate are inclusions of other polytypes, twins and microtwins and mainly stacking faults

A DISLOCATION MECHANISM FOR THE GROWTH OF TWINS IN DEFORMED HCP METALS

Des macles mécaniques ont été examinées par MET dans les métaux hexagonaux comme Zn, Cd, Zr, Ti. En particulier, les joints contenant des dislocations intrinsèques ont été examinés. Les caractéristiques de ces dislocations ont été étudiées à partir de leur contraste et par diffraction électronique. Il est déduit que dans les cas du Zn et du Cd, les macles mécaniques croissent par le mouvement de dislocations dont les vecteurs de Burgers sont déduits des caractéristiques des macles mécaniques. Dans le Zr et le Ti des familles de dislocations intrinsèques parallèles à la direction de coincidence sont observées.Deformation twins in hexagonal metals are examined by TEM. The materials studied are Zn, Cd, Zr, Ti. The observations are focussed on the twin boundaries that contain intrinsic dislocation structures. The characteristics of these dislocations are analysed using contrast and electron diffraction techniques. It is deduced that in Zn and Cd deformation twinning proceeds by a dislocation mechanism in which the glide of the dislocation as well as its Burgers vector are connected with the crystallographic elements of the twinning mechanism. In Zr and Ti parallel arrays of intrinsic dislocations, with lines along coincident direction in both grains, are also observed

Effect of Inter-Well Coupling between 3C and 6H in-Grown Stacking Faults in 4H-SiC Epitaxial Layers Effect of inter-well coupling between 3C and 6H in-grown stacking faults in 4H-SiC epitaxial layers

Abstract. Both 3C and 6H stacking faults have been observed in a low doped 4H-SiC epitaxial layer grown in a hot-wall CVD reactor on a heavily doped (off-axis) 4H-SiC substrate. They appear differently on the different parts of sample, with energetic dispersion ranging from 3.01 eV to 2.52 eV. Since they behave as natural type-II quantum wells in the 4H-SiC matrix, the thickness dependence of the excitonic recombination is investigated using the standard effective mass approximation. The results are discussed in terms of built-in electric field and inter-wells coupling effects

A TEM study of in-grown stacking faults in 3C-SiC layers grown by CF-PVT on 4H-SiC substrates

International audienceA transmission electron microscopy (TEM) study on the generation of stacking faults (SFs) and stacking fault (SF) induced inclusion during 3C-SiC growth by Continuous Feed Physical Vapour Transport (CF-PVT) method on 4H-SiC substrates is presented. A transition region of about 100 nm between the 4H-SiC substrate and 3C-SiC layer, where cubic and 4H-SiC sequences follow after each other is observed. A tendency for formation of multiple stacking faults (SFs) as opposed to the more common for fcc materials intrinsic (single) or extrinsic (double) SFs was observed. They rarely originate directly at the interface, but they are found to start on twin boundaries in some cases. Later during the CF-PVT growth process the density of SFs in the (111) and ((1) over bar 11) gradually increases. The ((1) over bar 1 1) SF density is the higher which leads to the formation of large 6H-SiC inclusions, extending to large lengths. (C) 2009 Elsevier B.V. All rights reserved