مقاومت به اکسیداسیون پوشش آلومینایی روی زیرلایه مس

High temperature oxidation resistance and

microstructure change of aluminized coating on copper substrate

مقاومت اکسیداسیون دما بالا و تغییر ریزساختار پوشش آلومینایی روی زیرلایه مس

ABSTRACT

The outermost coating with single phase Ni2Al3 was obtained on copper surface by electrodepositing nickel followed by slurry pack aluminizing at 800 °C for 12 h. The oxidation resistance and microstructure of the coating oxidized in ambient air at 1000 °C for 25–250 h were investigated using SEM, X-ray diffraction and optical microscope methods. The results show that the copper with single phase Ni2Al3 coating possesses the best high temperature oxidation resistance, and the mass gain of the coating is 1/15 that of pure copper and 1/2 that of nickel coating, respectively. The specimen surface after being oxidized for 25 h still comprises Ni2Al3 phase. However, when the time of oxidizing treatment increases to 50 h, the NiAl phase is formed. It is also found that the Ni2Al3 phase completely turns into NiAl phase after oxidizing treatment for 100 h and above. The NiAl coating shows excellent high temperature oxidation resistance when oxidation time is 250 h.

 

محلول جامد هگزابورید قلیایی خاکی و خواص ترموالکتریک دما بالای آن ها

ssureHigh-pre densified solid solutions of alkaline earth

hexaborides (Ca/Sr,Ca/Ba,Sr/Ba) 

and their high-temperature thermoelectric properties

محلول جامد هگزابورید قلیایی خاکی (Ca/Sr, Ca/Ba, Sr/Ba)

متراکم شده تحت فشار بالا و خواص ترموالکتریک دما بالای آن ها

ABSTRACT

Solid solutions of alkaline earth hexaborides were synthesized and densified by spark plasma sintering at 100 MPa. The high-temperature thermoelectric properties (Seebeck coefficients, electrical and thermal diffusivities, heat capacities) were measured between room temperature and 1073 K. CaB6, SrB6, BaB6 and the ternary hexaborides CaxSr1−xB6, CaxBa1−xB6, SrxBa1−xB6 (x = 0.25, 0.5, 0.75) are n-type conducting compounds over the whole compositional and thermal ranges. The values of the figure of merit ZT for CaB6 (ca. 0.3 at 1073 K) were found to be significantly increased compared to earlier investigations which is attributed to the densification process.

 

شوک حرارتی دیرگدازها Thermal shock of refractories

Thermal shock  of  refractories 

شوک حرارتی دیرگدازها 

ABSTRACT

Being brittle and having low thermal conductivity, refractories suffer damage and sometimes fail in service as a result of thermal shock. While the approach of those making fine-grained technical ceramics is to make their products sufficiently strong to withstand thermal stresses the refractory technologist is more cunning. He uses, often little known, devices to provide resistance to thermal shock that minimise but do not eliminate damage to the component. In this paper the basic equations of thermal conduction and elasticity are presented and followed by some immediate results that should guide the designer of components subject to severe thermal environments. The influence of size and shape of the refractory components is then discussed along with ways in which refractory producers can engineer the thermal and mechanical properties. In particular, the methods used to tailor fracture behavior to optimize the thermal shock resistance are treated in some detail.

 

آلیاژ پایه NiAl هیپویوتکتیک منجمد شده به صورت جهت دار که با Hf و Ho دوپ شده

Effect of withdrawal rate on microstructure and mechanical

properties of a directionally solidified NiAl-based hypoeutectic alloy doped with trace Hf and Ho

تأثیر سرعت بیرون کشی بر ریزساختار و خواص مکانیکی آلیاژ پایه NiAl هیپویوتکتیک

منجمد شده به صورت جهت دار و دوپ شده با مقادیر اندک Hf و Ho

ABSTRACT

The hypoeutectic alloy, with nominal composition NiAle31Cre2.9Moe0.1Hfe0.05Ho (at.%), was directionally solidified at three different withdrawal rates by liquid metal (Sn) cooling technique. Microstructural examination reveals that directional solidification gave rise to a shift in the coupled zone for the eutectic growth towards the Cr(Mo) phase. With the withdrawal rates increasing from 3 mm/min to 15 mm/min, the volume fraction of primary dendritic NiAl increases from 21.1% to 25.9%, while the size and the arm spacing of NiAl primary dendrite reduces simultaneously. The room temperature (RT) fracture toughness and the tensile strength at RT and elevated temperature (1373 K) present the valley value at intermediate rate (8 mm/min) among the withdrawal rate range which could be attributed to the decrease in volume fraction of eutectic NiAl/Cr(Mo) microstructure and the refinement of microstructure resulted from the increase of withdrawal rates. In terms of RT tensile elongation, the DS alloy grown at different withdrawal rates all break with no plastic flow.

 

جلوگیری از خوردگی فولاد کربنی در حین اسیدشویی

Corrosion inhibition of carbon steel during acid pickling

جلوگیری از خوردگی فولاد کربنی در حین اسیدشویی

ABSTRACT

A novel cationic surfactant, N-(2-(2-mercaptoacetoxy)ethyl)-N,N-dimethyl dodecan-1-aminium bromide), has been synthesized to study its corrosion inhibiting effect against carbon steel in 1.0 M HCl solution. The corrosion inhibition efficiency was measured by using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, and weight loss methods. The inhibition efficiencies obtained from these methods were in good agreement. The inhibition efficiency slightly decreased in the temperature range 30–60 °C. The synthesized inhibitor acted as a mixed inhibitor. Thermodynamic adsorption and activation parameters were discussed. Adsorption of the synthesized inhibitor was found to follow the Langmuir adsorption isotherm. A chemical adsorption mechanism is proposed.

 

جوشکاری اصطکاکی اغتشاشی صفحات AA 2219 نورد شده

Interface behaviours and mechanical properties of filling friction stir weld joining AA 2219 

رفتارهای فصل مشترک وخواص مکانیکی جوشکاری اصطکاکی اغتشاشی

پرکردن اتصال AA2219

ABSTRACT

Being brittle and having low thermal conductivity, refractories suffer damage and sometimes fail in service as a result of thermal shock. While the approach of those making fine-grained technical ceramics is to make their products sufficiently strong to withstand thermal stresses the refractory technologist is more cunning. He uses, often little known, devices to provide resistance to thermal shock that minimise but do not eliminate damage to the component. In this paper the basic equations of thermal conduction and elasticity are presented and followed by some immediate results that should guide the designer of components subject to severe thermal environments. The influence of size and shape of the refractory components is then discussed along with ways in which refractory producers can engineer the thermal and mechanical properties. In particular, the methods used to tailor fracture behavior to optimize the thermal shock resistance are treated in some detail.

 

رفتار اصطکاکی و سایشی کامپوزیت های سرامیک- آلیاژ آلومینیوم

Friction and Wear Behaviour of Brake Pads Dry Sliding Against

Semi-Interpenetrating Network Ceramics/Al-alloy Composites

رفتار اصطکاکی و سایشی ناشی از سایش خشک لنت های ترمز بر روی

شبکه نیمه نفوذی کامپوزیت های سرامیک/ آلیاژ آلومینیومی 

ABSTRACT

Semi-interpenetrating network composites containing 40 vol.% ceramics (5Al2O3·8SiO2) and 60 vol.% Al-alloy were fabricated in place of cast iron available for automotive brake rotors. The friction and wear performances of brake pads dry sliding against the composites were measured using a SRV testing machine. The test procedures include friction fade and recovery, load sensitivity at 100 and 250°C, and wear. The friction was found to increase first and then decrease with increasing temperature, followed by the inverse recovery upon cooling. Wear showed an incremental tendency over a wide temperature range. For loads from 40 to 160 N, the friction decreased at 100 and 250°C. At load below 128 N, the former friction was inferior to the latter while at load above 128 N the friction exhibited an inverse tendency. Wear mildly increased with load at 100 °C and decreased dramatically at 250 °C. SEM and EDS investigations revealed that the worn pad surfaces at 250 °C were covered by more tribofilms, including more coke and graphite with friction-reducing action as well as fewer compounds (corresponding to Si and Al) with friction-increasing action in comparison with those at 100 °C. The compression of the tribofilms contributed to a large decrease in the friction and wear with increasing load. However, at 100 °C E-glass fibers exposed at the worn surfaces inhibited the excessive wear of the pad despite lack of more tribofilms. Their glossy surfaces decreased the friction. The proposed friction models explain some friction and wear behaviour better.

 

اثر هیدروژن بر روی تافنس شکست فلز جوش در فولاد زنگ¬نزن دوفازی

Hydrogen influence on fracture toughness of the weld metal in

super duplex stainless steel (UNS S32750) welded with two different heat input

اثر هیدروژن بر روی تافنس شکست فلز جوش در فولاد زنگ نزن دوفازی

(UNS S32750) جوشکاری شده با دو حرارت ورودی مختلف

ABSTRACT

The super duplex stainless steels have a microstructure composed by two phases, ferrite (α) and austenite (γ). This dual microstructure improves simultaneously the mechanical and corrosion resistance properties. However, the welding of these steels is often a critical operation. The present work evaluated the fracture toughness through critical tip open displacement (CTOD) tests of welded joints, with two different heat input, 1.1 kJ mm−1 and 2.0 kJ mm−1. The steel used was a super duplex stainless steel (UNS S32750) in presence of hydrogen. The CTOD tests (according BS 7448-1 and BS 7448-2 standards) were performed in air and under different times of hydrogenation. The procedure of hydrogenation has been performed using cathodic potential of −1400 mVSCE by 96 and 360 h. The microstructural analysis allowed to determine relevant aspects (α/γ balance, inter austenitic spacing and γ morphology) and to compare with CTOD results. The results showed strong evidence that the reductions of CTOD values is related to differences in the γ2 morphologies. Another important result was the high statistic dispersion in the measures of austenitic spacing, according DNV RP F112-08, which implies in low reliability of using this standard in presence of high anisotropy. The paper also aims to discuss and evaluate which is the best approach to hydrogenated duplex stainless steels: linear elastic fracture mechanics or elasto plastic fracture mechanics.

 

رفتار خوردگی-خستگی آلیاژ آلومینیوم 7075-T651 تحت بارگذاری های متناوب

Corrosion-fatigue behaviour of 7075-T651 aluminum

alloy subjected to periodic overloads

رفتار خوردگی-خستگی آلیاژ آلومینیوم 7075-T651  تحت بارگذاری های متناوب

ABSTRACT

The corrosion-fatigue behaviour of 7075-T651 aluminum alloy subjected to periodic overloads was examined. This aluminum alloy is typically used in aerospace structural components such as the wing spars of aircraft. Axial fatigue specimens were subjected to a loading spectrum that consisted of a fully reversed periodic overload of near-yield magnitude followed by 200 smaller cycles at high Rratio. The specimens were fatigue tested while they were fully immersed in an aerated and recirculated 3.5 wt% NaCl simulated seawater solution.

 

مدل‎های چند مقیاسی از کامپوزیت‎های زمینه سرامیکی بافته شده

Multiscale model of woven ceramic matrix composites

considering manufacturing induced damage

مدل‎های چند مقیاسی از کامپوزیت‎های زمینه سرامیکی بافته شده

با توجه به آسیب‎های ایجاد شده‎ی تولید

ABSTRACT

Multiscale models play an important role in capturing the nonlinear response of woven carbon fiber reinforced ceramic matrix composites. In plain weave carbon fiber/silicon carbide (C/SiC) composites, for example, when microcracks form in the as-produced parts due to the mismatch in thermal properties between constituents, a multiscale thermoelastic framework can be used to capture the initial damage state of these composites. In this paper, a micromechanics-based multiscale model coupled with a thermoelastic progressive damage model is developed to simulate the elastic and damage behavior of a plain weave C/SiC composite system under thermal and mechanical loading conditions. The multiscale model is able to accurately predict composite behavior and serves as a valuable tool in investigating the physics of damage initiation and progression, in addition to the evolution of effective composite elastic moduli caused by temperature change and damage. The matrix damage initiation and progression is investigated at various length scales and the effects are demonstrated on the global composite behavior.