تحقیق روی رفتار خوردگی اتصالات لحیم کاری مس

Investigation on Corrosion Behaviour of Copper Brazed Joints 

تحقیق روی رفتار خوردگی اتصالات لحیم کاری مس

ABSTRACT

DHP (Deoxidized High Phosphorus(copper is widely used in various heat transfer units such as, air conditioners, refrigerators, evaporators and condensers. Copper sheets and tubes (ISODHP) were brazed with two different brazing alloys. Corrosion resistances of the joints were examined by polarization test. The selected fillers consisted of a silver-based brazing alloys (hard solder); AWS-BCu5, and a copper-based filler AWS BCuP2. All the joints were brazed utilizing two different brazing processes including furnace brazing under argon and air atmosphere. All of the fillers were used with and without flux. The microstructure of the brazed sheets was examined using both optical and scanning electron microscope (SEM). Hardness and leak tests were carried out on all the brazed tubes. In all brazing alloys selective and galvanic corrosion were observed in filler metals, but in copper phosphor alloys the copper adjacent to the joints were noticeably corroded by pitting method. It was found that the samples brazed with BAg5 filler metal using argon furnace show a higher resistance to corrosion. They also have a good ductility in the brazed zone.

 

اتصال سرامیک Si3N4 با استفاده از آلیاژ پرکننده لحیم

Joining of Si3N4 Ceramic Using PdCo(NiSiB)-V System

Brazing Filler Alloy and Interfacial Reactions

اتصال سرامیک Si3N4 با استفاده از آلیاژ پرکننده لحیم

در سیستم PdCo(NiSiB)-V و واکنش های مرزی

ABSTRACT

The wettability of V-active PdCo-based alloys on Si3N4 ceramic was studied with the sessile drop method. And the alloy of Pd50.0–Co33.7–Ni4.0–Si2.0–B0.7–V9.6 (wt%), was developed for Si3N4 ceramic joining in the present investigation. The rapidly-solidified brazing foils were fabricated by the alloy Pd50.0–Co33.7–Ni4.0–Si2.0–B0.7–V9.6. The average room-temperature three-point bend strength of the Si3N4/Si3N4 joints brazed at 1453 K for 10 min was 205.6 MPa, and the newly developed braze gives joint strengths of 210.9 MPa, 206.6 MPa and 80.2 MPa at high temperatures of 973 K, 1073 K and 1173 K respectively. The interfacial reaction products in the Si3N4/Si3N4 joint brazed at 1453 K for 10 min were identified to be VN and Pd2Si by XRD analysis. Based on the XEDS analysis result, the residual brazing alloy existing at the central part of the joint was verified as Co-rich phases, in which the concentration of element Pd was high up to 18.0–19.1 at%. The mechanism of the interfacial reactions was discussed. Pd should be a good choice as useful alloying element in newer high-temperature braze candidates for the joining of Si-based ceramics.

 

مارتنزیت پرآلیاژ در لایه سطحی غلتک های نورد

High-alloy martensite in the surfacing layer of

hot-rolling supporting rollers during the tempering process

مارتنزیت پرآلیاژ در لایه سطحی غلتک های پشتیبان نورد داغ در حین فرایند بازپخت

ABSTRACT

Flux-cored wire for surfacing hot-rolling supporting roller was developed and the specimens of surfacing layers were tempered at different temperatures. In order to characterize the high-alloy martensite in the surfacing layer during the tempering process, the microstructure and phase structure of the surfacing layer were analyzed, respectively. The nanoindentation hardness and phase transformation temperature of the high-alloy martensite were measured. The crystal structure of each phase was analyzed. The results show that the microstructure of the as-welded surfacing layer consists of martensite and retained austenite. Meanwhile, the high-alloy martensite with white reticular morphology is distributed on the crystal boundary. With increase of the tempering temperature, the high-alloy martensite disappears gradually, and the black reticular microstructure finally appears when the tempering temperature is 650 °C. The high-alloy martensite, whose average nanoindentation is 14.33 GPa, shows bulk morphology in field emission scanning electron microscope and starts to dissolve in the matrix at 420 °C. The contents of the alloy elements in the high-alloy martensite are higher than those in the normal one. However, the former decrease rapidly after tempering at 650 °C. The high-alloy martensite shows the body-centered tetragonal crystal structure, and the c-axis of the high-alloy martensite is longer than that of the normal one.

 

جوشکاری اصطکاکی-تلاطمی آلیاژ آلومینیوم به فولاد زنگ‌نزن

Friction stir welding of dissimilar Al 6013-T4 To

X5CrNi18-10 stainless steel

جوشکاری اصطکاکی-تلاطمی غیرهمجنس Al 6013-T4 به فولاد زنگ‌نزن X5CrNi  

ABSTRACT

The joining of dissimilar Al 6013-T4 alloy and X5CrNi18-10 stainless steel was carried out using friction stir welding (FSR) technique. The microstructure, hardness and fatigue properties of fiction stir welded 6013 aluminium alloy to stainless steel have been investigated. Optical microscopy was used to characterise the microstructures of the weld nugget, the heat affected zone (HAZ), thermo-mechanical affected zone (TMAZ) and the base materials. The results show that FSR can be used the joining of dissimilar Al 6013 alloy and X5CrNi18-10 stainless steel. Seven different zones of the microstructure in the welding are reported as follows: (1) parent stainless steel, (2) HAZ in the stainless steel at advancing side of weld, (3) TMAZ in the stainless steel at advancing side of weld, (4) weld nugget, (5) TMAZ in the Al alloy at retreating side of weld, (6) HAZ in the Al alloy at retreating side of weld and (7) parent Al alloy. A good correlation between the hardness distribution and the welding zones are observed. Fatigue properties of Al 6013-T4/X5CrNi18-10 stainless steel joints were found to be approximately 30% lower than that of the Al 6013-T6 alloy base metal.

 

فرآیند شکل دهی ادغام شده با لحیم کاری القایی Induction Brazing

Forming Process Integrated Induction Brazing 

فرآیند شکل دهی ادغام شده با لحیم کاری القایی

ABSTRACT

Processing steps additional to forming operations, such as joining, usually require a vast effort for transport and storage. Due to integration of currently external production steps, processes could be synchronized. Brazing represents an additional operation, which is likely to gain of importance in the light of an increasing relevance of light weight construction. Servo presses enable an adjustment of the ram motion to process requirements. Hence, the ram motion can be adjusted to create a time slot for the execution of additional processes inside the press. In this paper, the possibility to integrate brazing into forming process chains is investigated.  For a demonstration part, a tool that allows brazing inside a servo press is developed. Achievable part qualities and cycle times are  evaluated. 

 

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.

 

رفتار خزشی آلیاژ آلومینیوم - تیتانیوم

Creep behavior of Ti-6Al-4V from 450°C to 600°C

رفتار خزشی Ti-6Al-4V از 450  تا 600 درجه سانتیگراد

ABSTRACT

We present in this paper the creep behavior of Ti-6Al-4V from 450°C to 600°C under applied stress from 100 MPa to 500 MPa. Creep behavior is studied analyzing creep damage after tests and calculating stress exponent (n) and activation energy (Q). Operating creep deformation mechanisms characterization is possible by analyzing crept microstructure by TEM. A comparison of n and Q values with values from literature and a correlation with TEM micrographs will lead us to a discussion about operating creep deformation mechanisms.

 

رفتار خستگی خوردگی آلیاژ آلومینیوم جوشکاری شده

Corrosion fatigue behaviour of aluminium alloy 6061-T651 welded

using fully automatic GMAW and ER5183 filler alloy

رفتار خستگی خوردگی آلیاژ آلومینیوم 6061-T651 جوش داده شده با (GMAW)

با آلیاژ ER5183 به عنوان فیلر

ABSTRACT

The fatigue life of aluminium 6061-T651 at various applied stress amplitudes in the unwelded and welded condition was found to be significantly reduced on immersion in a 3.5% NaCl simulated sea water solution, compared to that measured in ambient air. The ratio of fatigue life in NaCl test solution to that in air increased as the stress amplitude decreased. The observed reduction in the fatigue life in the NaCl test solution was most likely due to the presence of pits which nucleated on second phase particles or precipitates. Welded joints performed using pulsed gas metal arc welding and ER5183 filler wire failed at the interface between the weld metal and the heat-affected zone as a result of a high pitting rate in this region.

 

میکروساختار و خواص سایشی فولاد ابزار

Microstructure and wear properties of AISI M2 tool steel

on RF plasma nitriding at different N2–H2 gas compositions

میکروساختار و خواص سایشی فولاد ابزار AISI M2

نیتروژن دهی پلاسمایی RF شده در ترکیب های مختلف از گازهای N2–H2

ABSTRACT

Wear behavior of quenched-tempered AISI M2 tool steel samples has been studied after plasma nitriding at different N2–H2 plasma gas flows containing 25, 50 and 75 sccm N2. Plasma nitriding was performed at 450 °C for 8 h under floating potential using a plasma reactor equipped with a radio frequency power generator. Microstructure, phase composition, nitrided layer thickness, hardness and surface roughness of the samples were studied using optical microscopy, X-ray diffraction, microhardness and surface profilometry measurements. Dry sliding wear resistance of samples was determined by performing ball-on-disc wear testes. The results revealed formation of mainly a diffusion zone at the 25 sccm N2–75 sccm H2 gas flow and mono-phase ε-Fe2–3N compound layer at higher N2 concentrations. Plasma nitriding increases near surface hardness up to 50% (about 1600HV0.025) irrespective of the N2:H2 ratio, where nitrided layer depth and surface roughness increase with increasing the N2 flow rate in the plasma gas. Depending on the nitrogen content, sliding wear resistance may be improved between 20 and 90% with respect to the un-nitrided substrate. Among the nitrided samples the maximum and minimum wear resistance was obtained at plasma gases containing higher and lower H2 fractions, respectively. Decreasing wear resistance with increasing N2 flow rate in the plasma gas attributed to formation of the hard and brittle compound (white) layer on the sample surface and development of residual stress profiles.

 

خوردگی ترک تنشی بر روی خطوط انتقال گاز

Stress-Corrosion Cracking On Gas-Transmission Pipelines

history, causes, and mitigation

خوردگی ترک تنشی بر روی خطوط انتقال گاز :

تاریخچه، علل ایجاد و راه های کاهش خطرات

ABSTRACT

This paper reviews the historical data concerning external stress-corrosion  cracking (SCC) of gas transmission pipelines as it has evolved since 1965 and the factors controlling such SCC (eg, pipe environment, steel, and operation). Discussion of these Factors leads to identification of ways in which this cracking can be controlled / mitigated – in the practical setting of an operating pipeline that is expected to provide a reasonable return on equity.