مقایسه جوشکاری EBW و اتصال خود فشاری حرارتی برای آلیاژ Ti6Al4V

A comparative study on electron beam welding and

rigid restraint thermal self-compressing bonding for Ti6Al4V alloy

بررسی مقایسه ای جوشکاری پرتوی الکترونی

و اتصال خود فشاری حرارتی سخت مقیدشده برای آلیاژ Ti6Al4V

ABSTRACT

This study focuses on the influence of joining method difference on the joint microstructure and properties. Unlike vacuum electron beam welding (EBW) utilizing electron beam as fusion heat source, rigid restraint thermal self-compressing bonding (TSCB), a new solid-state bonding method proposed by authors, employs vacuum electron beam as the non-melt heat source to bond materials in this work. Meanwhile, a comparative study on the microstructure and mechanical properties of EBWjoint and rigid restraint TSCB joint was conducted to investigate the effect of this difference on joint microstructure and properties. Results show that compared with EBW joints, the rigid restraint TSCB joints as solid-state joints are homogeneous in terms of microstructure and microhardness profile. Strength of both joints are comparable with that of base metal, but the elongation of the rigid restraint TSCB joint is more close to that of base metal. Rigid restraint TSCB joint has better combination of strength and ductility.

 

اثر اندازه نمونه بر ریزساختار فاز بین فلزی Al2Cu

Effect of sample size on intermetallic Al2Cu microstructure and

orientation evolution during directional solidification

اثر اندازه نمونه بر ریزساختار فاز بین فلزی Al2Cu

و روند جهت گیری آن در حین انجماد جهت دار

ABSTRACT

Al-40% Cu hypereutectic alloy samples were successfully directionally solidified at a growth rate of 10 μm/s in different sizes (4 mm, 1.8 mm, and 0.45 mm thickness in transverse section). Using the serial sectioning technique, the three-dimensional (3D) microstructures of the primary intermetallic Al2Cu phase of the alloy can be observed with various growth patterns, L-shape, E-shape, and regular rectangular shape with respect to growth orientations of the (110) and (310) plane. The L-shape and regular rectangular shape of Al2Cu phase are bounded by {110} facets. When the sample size was reduced from 4 mm to 0.45 mm, the solidified microstructures changed from multi-layer dendrites to single-layer dendrite along the growth direction, and then the orientation texture was at the plane (310). The growth mechanism for the regular faceted intermetallic Al2Cu at different sample sizes was interpreted by the oriented attachment mechanism (OA). The experimental results showed that the directionally solidified Al-40% Cu alloy sample in a much smaller size can achieve a well-aligned morphology with a specific growth texture.

 

بررسی مواد کامپوزیتی زمینه آلومینیم تقویت شده با نانولوله های کربنی

Investigation of carbon nanotube reinforced

aluminum matrix composite materials

بررسی مواد کامپوزیتی زمینه آلومینیم تقویت شده با نانولوله های کربنی

ABSTRACT

We have increased the tensile strength without compromising the elongation of aluminum (Al)–carbon nanotube (CNT) composite by a combination of spark plasma sintering followed by hot-extrusion processes. From the microstructural viewpoint, the average thickness of the boundary layer with relatively low CNT incorporation has been observed by optical, field-emission scanning electron, and high-resolution transmission electron microscopies. Significantly, the Al–CNT composite showed no decrease in elongation despite highly enhanced tensile strength compared to that of pure Al. We believe that the presence of CNTs in the boundary layer affects the mechanical properties, which leads to well-aligned CNTs in the extrusion direction as well as effective stress transfer between the Al matrix and the CNTs due to the generation of aluminum carbide.

 

انواع خوردگی Corrosion

Corrosion

خوردگی 

ABSTRACT

Corrosion is often associated with welded structures, since the microstructure, properties, and composition of the weld metal and HAZ may be quite different than those of the base metal. Corrosion takes a number of forms, as described in the  following section, and may result in general (uniform), localized, or microstructurespecific attack.

Often, the corrosion rate associated with welds is much higher than the base metal. The reason for this is usually a combination of the effect of microstructure and residual stress. Highly stressed regions surrounding welds may result in accelerated corrosion relative to the base metal. For example, the spot welds in automotive steels are normally the first place where corrosion attack takes place in car bodies.

 

پیشرفت‌ها در فناوری پالایش فولاد و چشم‌انداز آینده

Advances in Steel Refining Technology and Future Prospects

پیشرفت‌ها در فناوری پالایش فولاد و چشم‌انداز آینده

ABSTRACT

By the 1980s, Nippon Steel Corporation established a separated refining process based on hot-metal pretreatment,2) whereby the contents of silicon, sulfur, and phosphorus in hot metal were decreased before the decarburization in converters, using torpedo ladle cars, hot-metal ladles, or converters as the reaction vessels. Thereafter, technical developments such as the following were achieved:
separation of desulfurization from the other hot-metal pretreatment; separate processing of hot-metal dephosphorization from decarburization; development of hot-metal dephosphorization using converters as the reaction vessels and not requiring fluorine; improvement in reaction efficiency of these processes; recycled use of slag; adjustment of silicon content in hot metal in case of excessively high Si; and increase in converter capacity for hot-metal dephosphorization in converters.

 

چقرمگی شکست یک فولاد ضدزنگ سوپر داپلکس جوشکاری شده

Fracture toughness of a welded super duplex stainless steel

چقرمگی شکست یک فولاد ضدزنگ سوپر داپلکس جوشکاری شده

ABSTRACT

Fracture toughness testing was conducted on standard single-edge notched bend bar specimens of base and weld metal. The material was the SAF 2906 super duplex stainless steel. The aim was to evaluate the susceptibility for brittle failure at sub-zero temperatures for the base and weld metal. The base metal was tested between −103 and −60 °C and was evaluated according to the crack-tip opening displacement method. The fracture event at and below −80 °C can be described as ductile until critical cleavage initiation occurs, which caused unstable failure of the specimen. The welding method used was submerged arc welding with a 7 wt% nickel filler metal. The welded specimens were post-weld heat treated (PWHT) at 1100 °C for 20 min and then quenched. Energy-dispersive X-ray spectroscopy analysis showed that during PWHT substitutional element partitioning occurred which resulted in decreased nickel content in the ferrite. The PWHT weld metal specimens were tested at −72 °C. The fracture sequence was critical cleavage fracture initiation after minor crack-tip blunting and ductile fracture.

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مواد الکتروکرومیک

Electrochromic Materials

مواد الکتروکرومیک

ABSTRACT

 A set of materials exhibit electrochromic activity when constituted as a thin film structure whose coloration can be changed reversibly by electrical charging and discharging . there are two types of such electrochromic materials . The first type is uncolored when unpowered and changes to a colored state when a voltage is applied and returns to its uncolored state when the voltage is removed . In the second type an opposite voltage is required to be applied for bleaching ( or decoloration ) .The degree of coloration is a direct visual indication of the state of charing present in the material .

مواد ابر رسانا

Superconducting Materials

مواد ابر رسانا

ABSTRACT

The phenomenon of superconductivity came to be known in 1911 by observing that a capillary column of mercury immersed in a liquid helium bath woud show an abrupt reduction in resistance and at 4.2 K it became impossible to measure the low resistance exhibited by the column with the then available measurement techniques . It was concluded that below a critical temperature (T_c) the mercury had passed into a new state . Subsequent studies on superconduction were pursued with tin and lead as candidate materials and it was discovered that a critical current density (J_c) is carried by a superconduction sample before it returns to its normal ( metallic ) state .

مقدمه الزامات مهندسی برای مواد کامپوزیتی صنعت هوافضا

Introduction: engineering
requirements for aerospace
composite materials

مقدمه الزامات مهندسی برای مواد کامپوزیتی صنعت هوافضا 

ABSTRACT

Composite materials have gained popularity (despite their generally high cost) in high performance products that need to be lightweight, yet strong enough to take high loads such as aerospace structures (tails, wings and fuselages), boat construction, bicycle frames and racing car bodies. Other uses include storage tanks and fishing rods. Natural composites (wood and fabrics) have found applications in aircraft from the first flight of the Wright Brothers’ Flyer 1, in North Carolina on December 17, 1903, to the plethora of uses now enjoyed by man-made (engineered) composite materials on both military and civil aircraft, in addition to more exotic applications on unmanned aerial vehicles (UAVs), space launchers and satellites. Their adoption as a major contribution to aircraft structures followed on from the discovery of carbon fibre at the Royal Aircraft Establishment at Farnborough, UK, in 1964.

وضعیت صنعت در کنترل آخال ها در طی ریخته گری شمش فولادی

State of the Art in the Control of Inclusions during Steel
Ingot Casting

وضعیت صنعت در کنترل آخال ها در طی ریخته گری شمش فولادی

ABSTRACT

This article extensively reviews published research on inclusions in ingot steel and defects on ingot products, methods to measure and detect inclusions in steel, the causes of exogenous inclusions, and the transport and entrapment of inclusions during fluid flow, segregation, and solidification of steel cast in ingot molds. Exogenous inclusions in ingots originate mainly from reoxidation of the molten steel, slag entrapment, and lining erosion, which are detailed in this article. The measures to prevent the formation of exogenous inclusions and improve their removal are provided, which are very useful for the clean steel production of ingot industries.