نانوسرامیک های هیدروکسی آپاتیت

Hydroxyapatite nanoceramics: Basic physical

properties and biointerface modification

نانوسرامیک های هیدروکسی آپاتیت : خواص فیزکی اصلی و  اصلاحbiointerface 

ABSTRACT

A new method of surface energy modification and engineering of the hydroxyapatite (HAp) nanoceramics coatings is presented. It is performed by electron-induced surface energy modification resulting in deep and tunable variation of its wettability state. It is found from electronic traps state spectroscopy studies of the HAp ceramics implemented by various methods such as photoluminescence and surface photovoltage spectroscopy, that the HAp nanoceramics is a wide band gap p-type semiconductor with complex structure of electron/hole bulk and surface localized states. It is shown that a low-energy electron irradiation leads to surface potential modulation and provides tailoring any wettability state in a wide range of contact angles by variation of injected and trapped electron charge. The diverse wettability states engineered on the HAp surface enable selective adhesion of basic biological cells such as proteins, DNA and various bacteria.

 

نانوپودرهای هیدروکسی آپاتیت: سنتز، چگال سازی و برهم کنش سلول- مواد

Hydroxyapatite nanopowders: Synthesis, densification

and cell–materials interaction

نانوپودرهای هیدروکسی آپاتیت: سنتز، چگال سازی و برهم کنش سلول- مواد

ABSTRACT

Hydroxyapatite (HA) nanopowders with different aspect ratios were synthesized using reverse micelle template system. Nanopowders were characterized using X-ray diffraction (XRD), BET specific average surface area analysis and transmission electron microscopy (TEM). It was observed that increase in aqueous to organic ratio (A/O) and pH decreased the aspect ratio of the nanopowders. HA nanopowders with the highest aspect ratio (rod-shaped) of 7.2 ± 3.2 and the lowest aspect ratio (spherical) of 1.3 ± 0.3 were synthesized for processing dense compacts. Effect of powder morphology on densification at 1250 °C was studied with different amount of rod-shaped and spherical nanopowders. It was observed that an increase in high aspect ratio powder content in the compacts decreased sintered density under pressureless sintering condition. Also, due to excessive grain growth, no nanoscale morphology could be retained in the sintered microstructure. Mineralization study in simulated body fluid (SBF) showed formation of apatite layer on the entire surface of both compacts made with spherical and rod-shaped particles. Cytotoxicity result with OPC1 human osteoblast cells showed excellent cell attachment and cell spreading on samples after 5 days in culture.

 

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.

 

ورق های تیتانیوم EBW به عنوان ماده ای برای قطعات کشیده شده

EBW  titanium  sheets  as  material  for  drawn  parts

ورق های تیتانیوم EBW به عنوان ماده ای برای قطعات کشیده شده

ABSTRACT

The growing demand for high strength, lightweight and corrosion-resistant drawn parts has created increasing interest in the use of titanium and its alloys. Additional benefits may result from the use of tailor-welded blanks, allowing for significant savings in material, and the possibility of applying higher strength sheets exactly where needed. When forming welded blanks, it is necessary to overcome many technological barriers which are not reflected in technical literature. Therefore, some prior experience in numerical simulations is needed before embarking on further studies of welded blanks formability. For this purpose, it is necessary to determine the mechanical parameters of the base materials, as well as the fusion and heat-affected zones.

 

اتصال Inconel 625 به UNS 32205 به روش جوشکاری پرتو الکترونی

Investigations on the structure – Property relationships of

electron beam welded Inconel 625 and UNS 32205

بررسی روابط خواص-ساختار اتصال Inconel 625 به UNS 32205

به روش جوشکاری پرتو الکترونی

ABSTRACT

The metallurgical and mechanical properties of electron beam welded Ni based superalloy Inconel 625 and UNS S32205 duplex stainless steel plates have been investigated in the present study. Interface microstructure studies divulged the absence of any grain coarsening effects or the formation of any secondary phases at the heat affected zone (HAZ) of the electron beam (EB) weldments. Tensile studies showed that the fracture occurred at the weld zone in all the trials and the average weld strength was reported to be 850 MPa. Segregation of Mo rich phases was witnessed at the inter-dendritic arms of the fusion zone. The study recommended the use of EB welding for joining these dissimilar metals by providing detailed structure – property relationships.

 

جوشکاری اینکونل 625 و فولاد زنگ‎نزن L 304 با پرتوی الکترونی

Microstructure and hardness studies of electron beam

welded Inconel 625 and stainless steel 304L

مطالعه ریزساختار و سختی اینکونل 625 و فولاد زنگ‎نزن L 304

جوشکاری شده با پرتوی الکترون

ABSTRACT

In this study, electron beam welding of dissimilar Inconel 625 and SS 304L alloys was successfully performed by employing optimized electron beam welding parameters. The welded joint was characterized using SEM/EDS, XRD and micro-hardness tester. The welded joint was found homogeneous, well bonded and defect free. Two types of microstructure i.e. columnar dendritic and cellular dendritic were observed in the fusion zone. The development of different microstructures in the fusion zone was attributed to the localized cooling effects during solidification. Few micro-cracks along with dendrites splitting were observed in the vicinity of end crater that was mainly due to the segregation of S element. A significant variation of Ni and Fe was observed across Inconel/FZ and FZ/SS interfaces due to their fast diffusion in the melt pool. Micro-hardness measurements across Inconel/FZ and FZ/SS interfaces showed an increasing trend in the FZ from SS 304L towards Inconel base alloy.

 

اثر ریزساختار بر رفتار سایشی گلوله‌های آسیاب از جنس چدن پرکروم

Effect of microstructure on wear behavior of

high Chromium cast iron milling balls

اثر ریزساختار بر رفتار سایشی گلوله‌های آسیاب از جنس چدن پرکروم

ABSTRACT

In milling and grinding of minerals, balls which can be made of high chromium white cast iron are loaded into the milling container. Under the operating conditions of milling, the balls are subjected to impact, rolling, fatigue and corrosion wears which cause fracture and deforming the balls [1,2]. Since the wear conditions are unchangeable and inevitable, control of the ball dimensions, ball material, alloying and heat treatment must meet the required conditions to provide good wear and erosion resistance [3,4]. Generally, the balls are chosen from high chromium cast iron to provide hard carbide within the martensitic matrix with a little retained austenite to result in the best wear resistance for the operating conditions of the balls [5].

 

کامپوزیت SiC-SiC در آزمون خزش و خستگی

Stress, strain and elastic modulus behaviour of

SiC/SiC composites during creep and cyclic fatigue

رفتار تنش، کرنش و مدول کشسانی کامپوزیت SiC/رشته ی SiC

در آزمون خرش و خستگی چرخه ای

ABSTRACT

Creep and fatigue tests of Hi-NicalonTM/SiC (SiC matrix contains glass-forming, boron-based particulates), Standard SiC/SiC (SiC matrix is pure SiC) and Enhanced SiC/SiC (SiC matrix contains glass-forming, boron-based particulates) were carried out in air at 1300°C. The stress–strain hysteresis loops during fatigue and creep were studied. The change of Young’s modulus during creep and fatigue was analysed and compared among the three kinds of materials. Creep strain rates of Hi-NicalonTM/SiC in air were similar to those of Enhanced SiC/SiC, but much lower than those of Standard SiC/SiC. Consequently, the time to rupture at a given stress in Hi-NicalonTM/SiC was similar to that in Enhanced SiC/SiC, but much longer than in Standard SiC/SiC. Fatigue resistance of Hi-NicalonTM/SiC was similar to that of Enhanced SiC/SiC, but much better than Standard SiC/SiC.

 

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.