تولید کامپوزیت‌های B4C-TiB2 با پرس گرم

Microstructure and mechanical properties of B4C–TiB2

composites prepared by reaction hot pressing using Ti3SiC2

ریزساختار و خواص مکانیکی کامپوزیت‌های B4C-TiB2 تولیدشده توسط پرس گرم

با استفاده از Ti3SiC2 به عنوان افزودنی

ABSTRACT

B4C–TiB2 composites were fabricated via reaction hot pressing at 2100 °C under a pressure of 25 MPa, using B4C and Ti3SiC2 powders as raw materials. The phase transformations, microstructure and mechanical properties were investigated by XRD, TG–DTA, SEM, TEM and EDS. It is found that the SiC and TiB2 particles are homogenously dispersed in the B4C–TiB2 composites, where nano-sized TiB2 particles are mainly located within the B4C matrix grains, while the large-sized TiB2 particles at the matrix grains boundaries. Due to the pinning effect of SiC and TiB2 particles on B4C grain growth, the grain size of the composite is significantly reduced, leading to a great improvement of the mechanical properties. B4C–TiB2 composite prepared from B4C-10 wt% Ti3SiC2 starting powder shows high flexural strength, fracture toughness and micro-hardness of 592 MPa, 7.01 MPa m1/2 and 3163 kg/mm2, respectively. Crack deflection and crack bridging are most likely the potential toughening mechanisms in the composites. Furthermore, according to the XRD and TG–DTA analysis, the possible reaction mechanisms leading to the in-situ formation of TiB2 were proposed.

جوشکاری لیزر CP Ti به فولاد زنگ‌نزن با شکل‌های ضربان زمانی مختلف

Laser welding of CP Ti to stainless steel with

different temporal pulse shapes

جوشکاری لیزر CP Ti به فولاد زنگ‌نزن با شکل‌های ضربان زمانی مختلف

ABSTRACT

CP Ti and stainless steel sheets were laser welded by using a pulsed wave Nd:YAG laser welding system. The effect of pulse profiles used in laser welding was studied by investigating weld appearance, weld geometry, microstructure, hardness variation, joint strength and failure mode of welds. Weld quality was strongly affected by the temporal pulse profile adopted in laser welding. In comparison with the use of a normal rectangular pulse profile, stronger welds with a better homogeneity and a complex fracture mode were achieved by using a ramp-down pulse profile. This quality enhancement was contributed from the less degree of intermixing between two welding materials in melting pools.

 

راهنمای عملیات حرارتی آلیاژهای غیرآهنی- آلومینیوم و آلیاژهای آن Heat Treaters Guide

Heat Treater's Guide Nonferrous Alloys Wrought Aluminum and Aluminum Alloys

راهنمای عملیات حرارتی آلیاژهای غیرآهنی- آلومینیوم و آلیاژهای آن

ABSTRACT

3003 Aluminum: Microstructures. (a) 3003-0 sheet, annealed. Longitudinal section shows recrystallized grains. Grain elongation indicates rolling direction, but not the crystallographic orientation within each grain. Polarized light. Barker's reagent. 100x. (b) 3003-0 sheet, annealed. Same as adjoining microstructure, but shown at a higher magnification. Dispersion of insoluble particles of (Fe,Mn)Als (large) and aluminum-manganese-silicon (both large and small) was not changed by annealing.

 

تنش پسماند حرارتی در فرآیند جوشکاری لیزری هیبریدی-GMA welding process

Numerical and experimental study of thermally induced residual stress in the hybrid laser–GMA welding process

مطالعه عددی و تجربی تنش پسماند حرارتی در فرآیند جوشکاری لیزری هیبریدی-GMA

ABSTRACT

A model based on a double-ellipsoidal volume heat source to simulate the gas metal arc welding (GMAW) heat input and a cylindrical volume heat source to simulate the laser beam heat input was developed to predict the temperature field and thermally induced residual stress in the hybrid laser–gas metal arc (GMA) welding process. Numerical simulation shows that higher residual stress is distributed in the weld bead and surrounding heat-affected zone (HAZ). Effects of the welding speed on the isotherms and residual stress of the welded joint are also studied. It is found that an increase in welding speed can reduce the residual stress concentration in the as-weld specimen. A series of experiments has been performed to verify the developed thermo-mechanical finite element model (FEM), and a qualitative agreement of residual stress distribution and weld geometrical size is shown to exist.

 

خزش در فلزات آمورف (شیشه فلزات) Creep in amorphous metals

Creep in amorphous metals

خزش در فلزات آمورف (شیشه فلزات)

ABSTRACT

This paper reviews the work on creep behavior of amorphous metals. There have been, overthe past several years, a few reviews of the mechanical behavior of amorphous metals. Ofthese, the review of the creep properties of amorphous metals by Schuh et al. though oldestof the three, is particularly noteworthy and the reader is referred to this article publishedin 2007. The current review of creep of amorphous metals particularly focuses on thoseworks since that review and places the work prior to 2007 in a different context where newdevelopments warrant.

 

مشخصه‎های ضخامت پوسته در ورق تولید شده به روش ریخته‎گری مداوم

Characteristics of shell thickness in a slab continuous casting mold

مشخصه‎های ضخامت پوسته در ورق تولید شده به روش ریخته‎گری مداوم 

ABSTRACT

It is of great importance to form a thick and sufficiently uniform solidifying shell in the mold to prevent breakout in the continuous casting process. Breakout starts to take place at the thinnest point commonly, and therefore, it is significant to investigate the slab thickness distribution in longitudinal and transverse directions to determine this point. Experimental and numerical simulations are the two ways for  measurement of shell thickness in the mold. The former such as adding sulfur into the mold [1], disturbs the normal production and obtains some useful data, which cannot characterize the shell thickness profiles thoroughly. On the other hand, several scholars have researched the flow, heat transfer, and solidification in the mold by numerical simulation . However, some profound researches on the characteristics of the shell thickness have been done.

  

فرایند انجماد و ساختار ریختگی در ریخته گری شمش

Solidification and Processes and Cast Structures

فرایند انجماد و ساختار ریختگی

ABSTRACT

This swction deals with three tranitional solidificationprocesses: ingot casting, continous casting, and welding. however, the last to processe hold a key importance in todays technology. almost entire molten metal is cast into solid state by either the traditional ingot casting or reatively modern continuous casting. the development of the ingot and continuously cast structure as well as fusion welding structure and weld cracking are briefly described.

 جهت دانلود رایگان نسخه لاتین این مقاله اینجا کلیک کنید .

 

رفتار زینترینگ و مقاومت هیدروژنی دولومیت واکنشی

Sintering, consolidation, reaction and crystal growth by

the spark plasma system (SPS)

رفتار زینترینگ و مقاومت هیدروژنی دولومیت واکنشی

ABSTRACT

Sintering of raw dolomite and hydroxides derived from dolomite was carried out in the temperature range 1350–1650 °C. The hydroxide derived from dolomite was developed through pre-calcination of dolomite followed by its hydration. For hydroxide development, after precalcination one sample was air-quenched and the other powder was furnace cooled before hydration. The air quenched samples showed better densification than that of the furnace cooling process at the same temperature. Fe2O3 addition enhances sintering by liquid formation at higher temperature. The grain size of doloma with Fe2O3 addition is bigger than that without additive. Hydration resistance was related to densification and grain size of sintered dolomite.

 جهت دانلود رایگان نسخه لاتین این مقاله اینجا کلیک کنید .