افزودن کربن و سیلیسیم بر خواص خزشی آلیاژهای آهن-آلومینیوم

The effect of carbon and silicon additions on

the creep properties of Fe-40 at. % Al type alloys

at elevated temperatures

اثر افزودن کربن و سیلیسیم بر خواص خزشی آلیاژهای آهن

دارای 40 درصد اتمی آلومینیوم در دماهای بالا

ABSTRACT

The mechanical properties of Fe–Al alloys with 39–43 at.% Al, C contents up to 4.9 at.% and Si contents up to 1.2 at.% were studied using uniaxial compressive creep at temperatures from 600 to 800 °C. The stress and temperature dependence of the creep rate were determined by stepwise loading and evaluated in terms of the stress exponent n and the activation energy Q, respectively. These quantities can be interpreted by means of dislocation motion controlled by climb and by the presence of second-phase particles. The dislocation motion is obstructed by precipitates of carbide κ in alloys E and F and by particles of Al4C3 in the alloys with either higher content of C or of C and Si. Both carbon and silicon improved the creep resistance, but the effect of silicon was more significant.

 

سنتز هیدروکسی آپاتیت با استفاده از عملیات مکانوشیمیایی

Synthesis of hydroxyapatite via mechanochemical treatment

سنتز هیدروکسی آپاتیت با استفاده از عملیات مکانوشیمیایی

ABSTRACT

Hydroxyapatite powder was synthesized with calcium pyrophosphate (Ca2P2O7) and calcium carbonate (CaCO3) through solid-state reaction. The two powders were mixed in acetone and water, respectively, and the single phase of hydroxyapatite was observed to occur only in the powder milled in water, without the additional supply of water vapor during heat-treatment at 1100°C for 1 h. The results were explained in terms of the mechanochemical reaction that could supply enough amount of hydroxyl group to the starting powders to form a single phase of hydroxyapatite. Practical implication of the results is that the powder of high crystalline hydroxyapatite can be obtained by the simple milling in water and subsequent heat-treatment.

 

استحکام جوش و چقرمگی در جوشکاری اینکونل 625 و فولاد ضد زنگ سوپر دوپلکس

Characterization of weld strength and toughness in

 the multi-pass welding of Inconel 625 and

 Super-duplex stainless steel UNS S32750

مشخصه‌یابی استحکام جوش و چقرمگی در جوشکاری چند پاس

اینکونل 625 و فولاد ضد زنگ سوپر دوپلکس UNS S32750

ABSTRACT

The present study investigated the weldability of dissimilar metals involving Inconel 625 and Super-duplex stainless steel obtained from continuous current (CC) and pulsed current (PC) gas tungsten arc welding (GTAW) processes employing ER2553 and ERNiCrMo-4 fillers. A comparative analysis on these dissimilar weldments was carried out to establish the structure-property relationships. Microstructure examination was carried out using optical microscopy (OM) and scanning electron microscopy (SEM) techniques. Grain coarsening was observed at the HAZ of UNS S32750 for all the cases. Mechanical tests ascertained that the PCGTA weldments employing ERNiCrMo-4 offered better weld strength and impact toughness. Elaborative studies on the structure – property relationships of these dissimilar weldments were discussed.

 

شرایط جفت شدگی ضعیف جوشکاری مقاومتی نقطه ای

Poor fit-up condition in resistance spot welding

شرایط جفت شدگی ضعیف جوشکاری مقاومتی نقطه ای

ABSTRACT

An experimental setup for poor fit-up condition research, which makes it possible to analyze poor fit-up conditions of different intensities and also quantify them is presented. The intensity of poor fit-up condition can be estimated by measuring the welding force during the initial contact between the electrode tips and the weldpieces. In order to reduce the negative influence of the poor fit-up condition on weld strength an addition of preheating phase was studied. Although it helps to increase the weld strength, a significant gap remains between the weld strength of non-deformed welds and poor fit-up welds even at large preheating currents.

 

نیتروژن دهی پلاسمایی فولاد ضدزنگ سوپرمارتنزیت

Plasma nitriding of HP13Cr supermartensitic stainless steel

نیتروژن دهی پلاسمایی فولاد ضدزنگ سوپرمارتنزیت HP13Cr

ABSTRACT

Supermartensitic stainless steels (SMSS) are commonly employed in the oil exploitation industry and present a good balance between the necessary physical and chemical properties and financial costs. Certain applications, such as in extreme corrosive and abrasive environments, demand improvements in the surface properties of these steels. In the present work, HP13Cr SMSS with a fully martensitic microstructure were plasma nitrided in the 350–450 °C range. The high diffusivity and low solubility of nitrogen in the martensitic structure allowed the production of thick layers (16–61 μm) containing ɛ-Fe2–3N, γ′-Fe4N and expanded phase (αN) in all the temperatures. In addition, anisotropic sputtering rate and N-diffusion were observed for different grain orientations. Mechanical properties were measured by instrumented indentation, appropriately corrected from roughness effects on the results. Hardness profiles increased from 3.8 GPa (bulk) to ∼14 GPa (near surface region) in all the working temperatures, whereas the elastic modulus was 230 GPa, presenting no statistically significant differences with respect to the bulk value. Nanoscratch tests revealed a hardened-ductile like behavior of these nitride layers. The surface tribo-mechanical behavior was correlated with elastic–plastic responses of the precipitate-containing texturized layers. Results are interpreted in light of the effectiveness of plasma nitriding to modify the surface properties of SMSS.

 

خواص سطحی فولاد کم آلیاژ نیتروکربوریزه شده Surface properties of low alloy steel

Surface properties of low alloy steel treated by

plasma nitrocarburizing prior to laser quenching process

خواص سطحی فولاد کم آلیاژ عملیات شده توسط نیتروکربوریزه کردن

پس از روش کوئینچ کردن با لیزر

ABSTRACT

Laser quenching (LQ) technique is used as a part of duplex treatments to improve the thickness and hardness of the surface layers of steels. The present study is to investigate the surface properties of low alloy steel treated by plasma nitrocarburizing (PNC) prior to a laser quenching process (PNC+LQ). The microstructure and properties of PNC+LQ layer determined are compared with those obtained by PNC and LQ processes. OM, XRD, SEM and EDS analyses are utilized for microstructure observation, phases identification, morphology observation and chemical composition detection, respectively. Microhardness tester and pin-on-disc tribometer are used to investigate the mechanical properties of the modified layers. Laser quenching of plasma nitrocarburized (PNC+LQ) steel results in much improved thickness and hardness of the modified layer in comparison with the PNC or LQ treated specimens. The mechanism is that the introduction of trace of nitrogen decreases the eutectoid point, that is, the transformation hardened region is enlarged under the same temperature distribution. Moreover, the layer treated by PNC+LQ process exhibits enhanced wear resistance, due to the lubrication effect and optimized impact toughness, which is contributed to the formation of oxide film consisting of low nitrogen compound (FeN0.076) and iron oxidation (mainly of Fe3O4).

 

خواص مواد نانوساختار مس- WC

Characterisation of nanostructured copper - WC materials

خواص مواد نانوساختار مس- WC

ABSTRACT

Purpose: The aim of this work was to determine the microstructure and properties stability of nanocrystalline copper dispersion hardened with nanoparticles of tungsten carbides.

Design/methodology/approach: Tests were made with Cu and Cu – WC micro – composites containing up to 3% of a hardening phase. The materials were fabricated by powder metallurgy techniques, including milling of powders, followed by their compacting and sintering. The main mechanical properties of the materials were determined from the compression test, and, moreover, measurements of the HV hardness and electrical conductivity have been made. Analysis of the initial nanocrystalline structure of these materials was made and its evolution during sintering was investigated.

 

حرکت دانه های هم محور در حین انجماد جهت دار تحت میدان مغناطیسی استاتیک

Motion of equiaxed grains during directional solidification

under static magnetic field

حرکت دانه های هم محور در حین انجماد جهت دار تحت میدان مغناطیسی استاتیک

ABSTRACT

The in situ and real time observations of the equiaxed grain motion during directional solidification of Al–10 wt% Cu under static magnetic field has been carried out by means of synchrotron X-ray radiography. It was observed that equiaxed grains moved approximately along the direction perpendicular to both the imposed magnetic field and the temperature gradient. Based on the radiographs, the motion of the solid grains was analyzed for various temperature gradients, and it was shown that the trajectories were imposed by the combination of the Thermo-Electric Magnetic forces, induced by the coupling of thermo-electric currents with the permanent magnetic field and the gravity force. The variations of the velocities and sizes of grains during the equiaxed growth under static magnetic field were measured and compared to a simple analytical model for the Thermo-Electric Magnetic forces and the Stokes law. A good agreement was achieved for the deviation angle as a function of the grain diameter, while a large discrepancy was observed for the velocity intensity when the dimensions of the equiaxed grains increased. In the latter case, it was shown that the corrections for both sample confinement and grain morphology were mandatory to explain the very low values of grain velocities.

 

متالورژی پودر بیوکامپوزیت Ti35Nb2.5Sn و زینترسازی

Effect of milling time on microstructure of Ti35Nb2.5Sn/10HA

biocomposite fabricated by powder metallurgy and sintering

تاثیر زمان آسیاب کردن بر ریزساختار بیوکامپوزیت Ti35Nb2.5Sn/10HA

تولید‌شده با متالورژی پودر و زینتر‌سازی

ABSTRACT

A new β-Ti based Ti35Nb2.5Sn/10 hydroxyapitite (HA) biocompatible composite was fabricated by mechanical milling and pulsed current activated sintering(PCAS). The microstructures of Ti35Nb2.5Sn/10HA powder particles and composites sintered from the milled powders were studied. Results indicated that α-Ti phase began to transform into β-Ti phase after the powders were mechanically milled for 8 h. After mechanical milling for 12 h, α-Ti completely transformed into β-Ti phase, and the ultra fine Ti35Nb2.5Sn/10HA composite powders were obtained. And ultra fine grain sized Ti35Nb2.5Sn/10HA sintered composites were obtained by PCAS. The hardness and relative density of the sintered composites both increased with increasing the ball milling time.

 

فرآیند نیتروژن دهی پلاسمایی در فولاد قالب تزریق پلاستیک

A Study on Formation and Growth Mechanism of

Nitride Layers During Plasma Nitriding Process of

Plastic Injection Mold Steel

تحقیق روی مکانیزم رشد و تشکیل لایه های نیتریدی

حین فرآیند نیتروژن دهی پلاسمایی در فولاد قالب تزریق پلاستیک

ABSTRACT

Ion nitriding modifies composition of surface layer in steel used in plastic mold application and this consequently improves their lifecycle. In this study, pulsed plasma nitriding technique was used to produce a protecting hard layer on AISI P20 steel at three process temperatures of 450°C, 500°C, and 550°C for durations of 2.5, 5, 7.5, and 10 h at a constant gas mixture of 75% N2–25% H2. Surface morphology was studied by optical and scanning electron microscope and the phases formed on the surface layer were determined by X-ray diffraction (XRD). Elemental depth profile was measured by techniques including energy dispersive spectroscopy, wavelength dispersive spectrometer, and glow discharge spectroscopy and for identifying hardness profile, microhardness variations from surface to core of samples were recorded. Results showed that, thickness of compound layer of plastic mold steel AISI P20 was negligible. Moreover in ion nitriding of AISI P20, nitride were formed and grown in some preferred directions and upward diffusion of carbon and downward diffusion of nitrogen occurred during ion nitriding of AISI P20. XRD results showed that, ϵ-nitride is the dominant phase after plasma nitriding in all strategies. Furthermore, ion nitriding improved hardness of AISI P20 up to three times and as time and temperature increased, hardness and hardness depth of diffusion zone increased considerably.