لحیم کاری قطره ای لیزری برای اتصال الکتریکی مواد کامپوزیتی

Laser droplet brazing for electrical contacting of composite

materials with integrated active elements

لحیم کاری قطره ای لیزری برای اتصال الکتریکی مواد کامپوزیتی ادغام شده با عناصر فعال

ABSTRACT

To be used as actuators or sensors, piezoceramic components have to be electronically contacted. A temperature stable connection can be achieved with brazing techniques. Since piezoceramics are susceptible to damage by high temperatures and temperature gradients, it is important to control the energy input in the brazing process. Therefore, we use a laser  droplet brazing method which allows for precise contacting of piezoceramics and avoids thermal damage. The influence  of the laser parameters on the brazing process and the contacting accuracy is presented in this paper.

 

ساختار و استحکام کامپوزیت کربن- تقویت شده با کربن

Strength and structure of carbon–carbon reinforced composite

ساختار و استحکام کامپوزیت کربن- تقویت شده با کربن

ABSTRACT

The atomistic simulations of carbon nanotube (CNT) – carbon reinforced composite material are reported. The studied composite samples are obtained by impregnating certain amounts of CNTs (3,3) and (6,6) into a pristine graphite matrix. The addition of CNTs is found to be of significant usefulness for the CNT–reinforced composites, since it allows to achieve extreme lightness and strength. Being impregnated into graphite matrix, CNTs are able to increase the critical component of its initially highly anisotropic Young modulus by 2–8 times. The linear thermal expansion coefficients do not exceed 10−6 to 10−5 K−1, making this material applicable for novel aviation and space vehicles. The degree of dispersion of CNTs within graphite matrix is found to drastically influence composite properties.

 

مقاومت به فرسایش و اکسیداسیون پوشش SiC برای کامپوزیت های کربن- کربن

Oxidation and ablation resistance of ZrB2–SiC–Si/B-modified

SiC coating for carbon/carbon composites

مقاومت به فرسایش و اکسیداسیون پوشش SiC اصلاح شده با ZrB2-SiC-Si/B

برای کامپوزیت های کربن/ کربن

ABSTRACT

ZrB2–SiC–Si/B-modified SiC coating was prepared on the surface of carbon/carbon (C/C) composites by two-step pack cementation. The coating could efficiently provide protection for C/C composites from oxidation and ablation. The improvement of oxidation resistance was attributed to the self-sealing property of the multilayer coating. A dense glassy oxide layer could afford the high temperature up to 2573 K and efficiently protect C/C composites from ablation.

اثر فشار اکسیژن بر خواص فیلم های ZnO دوپ شده با Nb

Influence of oxygen pressure on the structural, electrical and optical

properties of Nb-doped ZnO thin films prepared

by pulsed laser deposition

اثر فشار اکسیژن بر خواص ساختاری، الکتریکی و نوری فیلم های ZnO

دوپ شده با Nb آماده شده توسط لایه نشانی لیزری پالسی

ABSTRACT

Nb-doped zinc oxide (NZO) transparent conductive thin films with highly (0 0 2)-preferred orientation were deposited on glass substrates by pulsed laser deposition method in oxygen ambience under different oxygen pressures. The as-deposited films were characterized by X-ray diffraction (XRD), Field emission-scanning electron microscopy (FE-SEM), electrical and optical characterization techniques. It was found that a desirable amount of oxygen can reduce the related defect scattering and enhance the carrier mobility. The resistivity and average optical transmittance of the NZO thin films are of 10−4 Ω cm and over 88%, respectively. The lowest electrical resistivity of the film is found to be about 4.37 × 10−4 Ω cm. In addition, the influence of oxygen pressure on optical properties in NZO thin films was systematically studied as well.

 

بررسی مواد کامپوزیتی زمینه آلومینیم تقویت شده با نانولوله های کربنی

Investigation of carbon nanotube reinforced

aluminum matrix composite materials

بررسی مواد کامپوزیتی زمینه آلومینیم تقویت شده با نانولوله های کربنی

ABSTRACT

We have increased the tensile strength without compromising the elongation of aluminum (Al)–carbon nanotube (CNT) composite by a combination of spark plasma sintering followed by hot-extrusion processes. From the microstructural viewpoint, the average thickness of the boundary layer with relatively low CNT incorporation has been observed by optical, field-emission scanning electron, and high-resolution transmission electron microscopies. Significantly, the Al–CNT composite showed no decrease in elongation despite highly enhanced tensile strength compared to that of pure Al. We believe that the presence of CNTs in the boundary layer affects the mechanical properties, which leads to well-aligned CNTs in the extrusion direction as well as effective stress transfer between the Al matrix and the CNTs due to the generation of aluminum carbide.

 

مواد کامپوزیت دی الکتریک

Composite Dielectric Materials

مواد کامپوزیت دی الکتریک

ABSTRACT

Composite dielectrics represent, in general, a heterogeneous system of multiconstituent materials. Typically, a two-phase composite dielectric is constituted by a host material with an inclusion of another material. This host-inclusion system could be formed by a combination (or a mixture) of dielectric-dielectric, dielectric-conductor, and/or dielectric-semiconductor phases. The constituent phases may form structurally an embedment system consisting of multi-layer "layups" or random dispersion of the inclusions across the host medium; or there could be a structured matrix of specific type to yield certain desirable dielectric properties. Generically, a composite dielectric can be treated as as a mixture-medium, largely heterogeneous and could be anisotropic and nonlinear, as well.