Assessment of creep rupture properties for dissimilar steels welded joints between T92 and HR3C

Dissimilar steels welded joints, between ferritic steel and austenitic stainless steel, are always encountered in high‐temperature components in power plants. As two new grade ferritic steel and austenitic stainless steel, T92 (9Cr0.5Mo2WVNb) and HR3C (TP310HCbN), exhibit superior heat strength at elevated temperatures and are increasingly applied in ultra‐supercritical (USC) plants around the world, a complete assessment of the properties for T92/HR3C dissimilar steels welded joints is urgently required. In this paper, metallographic microstructures across the joint were inspected by optical microscope. Particularly, the creep rupture test was conducted on joints under different load stresses at 625 °C to analyse creep strength and predict their service lives, while their fractograph were observed under scanning electron microscope. Additionally, finite element method was employed to investigate residual stress distribution of joints. Results showed that the joints were qualified under USC conditions, and T92 base material was commonly the weakest part of them.     

Diffusion bonding of investment cast γ-TiAl

Intensive alloy development studies on intermetallic gamma () based alloys in recent years has led to the development of several aerospace engine components using advanced -TiAl based alloys by ingot and powder metallurgical routes. These materials are of great interest to the aerospace industry owing to their very low density and good high temperature properties. Further application of this material will require the development of successful joining and cost effective fabrication methods. Joining of this intermetallic alloy by fusion joining processes, however, requires very careful process controlling, i.e. low cooling rates and very high preheat temperatures. On the other hand, solid state joining processes, particularly diffusion bonding, brazing, and friction welding, can readily be used to join this material. In the present work, successful application of solid state diffusion bonding to weld investment cast -TiAl alloys has been demonstrated. A series of diffusion bonds were produced without using an interlayer at temperatures ranging from 950 to 1100°C with different pressure levels and holding times. Bonds have been characterized using optical and scanning electron microscopy. Defect-free bonds were achieved for all the conditions studied. The bond qualities were assessed by shear testing at room temperature. Reasonable shear strength levels were obtained by bonding at 1000 and 1100°C for 3 h at pressures of 20 and 40 MPa, respectively. The bonds were also post bond heat treated at 1430°C for 30 min, which improved the bond quality in all cases.     

Microstructure and mechanical properties of diffusion bonded SiC/steel joint using W/Ni interlayer

This paper describes the design and examination of W/Ni double interlayer to produce a joint between SiC and ferritic stainless steel. Diffusion bonding was performed by a two steps solid state diffusion bonding process. Microstructural examination and mechanical properties evaluation of the joints show that bonding of SiC to steel was successful. EDS and XRD analysis revealed that W₅Si₃ and WC were formed at SiC/W interface. The diffusion products at W/Ni interface, Ni-rich solid solution Ni(W) or intermetallic compound Ni₄W, was found to be dependent on the second step joining temperature. Neither intermediate phases nor reaction products was observed at Ni/steel interface for the joints bonded at the temperature studied. The average tensile strength of 55 MPa which is insensitive to the second step process was measured for as-bonded SiC/steel joint and the failure occurred at SiC/W interface. The hardness near the various bonded interfaces was also evaluated.     

采用聚硅氧烷SR355与纳米Ni粉混合物连接无压烧结SiC陶瓷

无压烧结SiC陶瓷(SSiC)是重要的高温结构材料,连接技术是扩大其应用范围的关键技术之一。将活性填料纳米Ni粉添加到聚硅氧烷SR355中制成连接材料,通过反应成形连接工艺连接SSiC。研究了纳米Ni粉对SR355的裂解过程和陶瓷产率的影响,同时也研究了填料含量和连接温度对连接件强度的影响。结果表明, 纳米Ni粉的加入促进了SR355的裂解并提高了其陶瓷产率。当纳米Ni粉含量为1％（质量分数）、连接温度为1050℃时,连接件经3次浸渍增强处理后的连接强度达到最大值。微观结构研究表明,连接层均匀致密,且与母材间界面结合良好,界面处发生了元素的扩散,纳米Ni粉在连接过程中参与了化学反应并促进了界面结合。      

Challenges of Diffusion Bonding of Different Classes of Stainless Steels

Solid state diffusion bonding is used to produce monolithic parts exhibiting mechanical properties comparable to those of the bulk material. This requires diffusion of atoms across mating surfaces at high temperatures, accompanied by grain growth. In case of steel, polymorphy helps to limit the grain size, since the microstructure is transformed twice. The diffusion coefficient differs extremely for ferritic and austenitic phases. Alloying elements may shift or suppress phase transformation until the melting range. In this paper, diffusion bonding experiments are reported for austenitic, ferritic, and martensitic stainless steels possessing varying alloying elements and contents. Passivation layers of different compositions are formed, thus affecting the local diffusion coefficient and impeding diffusion across faying surfaces. As a consequence, different bonding temperatures are needed to obtain good bonding results, making it difficult to control the deformation of parts, since strong nonlinearities exist between temperature, bonding time, and bearing pressure. For martensitic stainless steel, it is shown that it is very easy to obtain good bonding results at low deformation, whereas ferritic and austenitic stainless steels require much more extreme bonding parameters.

     

Transient liquid-phase bonding of ferritic oxide dispersion strengthened superalloy MA957 using a conventional nickel braze and a novel iron-base foil

It has been shown that an iron foil based on the Fe-B-Si system is a suitable material for use as a high-temperature interlayer for transient liquid-phase (TLP) bonding of ferritic oxide dispersion strengthened alloys. TLP bonding produced ferritic joints, free from intermetallic precipitates and identical in composition to that of the parent metal. In contrast, however, TLP bonding using the nickel-base foil, Bni1a, resulted in an austenitic bond region stabilized by the high nickel concentration. Furthermore, the retention of the melting point depressants, particularly silicon, at the centre of the joints resulted in the bond solidifying with the formation of silicide-boride precipitates both at the bond centre and at the braze/parent metal interface. High-temperature heat treatments failed to remove the -Fe phase and the precipitates, and their presence detrimentally affected the mechanical properties of the joint. The formation of intermetallic precipitates at the braze centre has been attributed to the initial high concentration of chromium present in the Bni1a brazing foil. Preliminary mechanical tests showed that bond strengths of joints made using the iron-base foil were superior to those obtained using the commercial nickel braze. When the iron-base foil was used, bond strengths both at room temperature and at the service temperature (700 °C) were near parent metal strengths. However, at room temperature, failure was observed to occur away from the bond interface, whilst at elevated temperatures, joints failed along the bond interface; this was attributed to the effects of melt-back phenomenon characteristic in TLP bonding.     

Microstructure and Strength of the TiB2 Cermet/TiAl Joint Diffusion Bonded with Ni Interlayer

Vacuum diffusion bonding of TiB2 cermet to TiAl -based alloys using Ni interlayer has been carried out at 1123～1323 K for0.6～3.6 ks under 80 MPa. The effects of joining parameters on the microstructure of the joints and mechanical propertieswas investig     

碳纤维增强树脂基复合材料与铝/镁合金连接研究进展EI北大核心CSCD

运载工具的轻量化是解决当前能源危机和环境问题的重要手段之一,得到国内外学者的高度重视。碳纤维增强树脂基(carbon fiber-reinforced polymer,CFRP)复合材料和以铝镁为代表的轻合金具有一系列优异的力学性能与加工特性,是极具应用前景的轻量化材料,实现这两种材料之间的有效连接,成为当下研究的热点。然而由于异种材料之间理化性能差异较大,在生产过程中混合应用多种轻量化材料仍面临巨大挑战。本文通过对胶接、机械紧固、搅拌摩擦及其变种工艺连接技术的研究进展、优缺点、发展趋势进行汇总分析,考察不同连接方式下获得接头的微观形貌,总结了CFRP与铝镁轻合金搅拌摩擦连接的三种机理包括宏观锚定、微观机械嵌合与化学键连接。最后,基于以上三种连接机理,指出进一步提升混合接头性能的关键在于增大金属母材表面粗糙度,增加熔融高分子面积和采用混合连接工艺。     

Advances in fusion bonding techniques for joining thermoplastic matrix composites: a review

Joining composite materials is an issue because traditional joining technologies are not directly transferable to composite structures. Fusion bonding and the use of thermoplastic films as hot melt adhesives offer an alternative to mechanical fastening and thermosetting adhesive bonding. Fusion bonding technology which originated from the thermoplastic polymer industry has gain a new interest with the introduction of thermoplastic matrix composites (TPC) which are currently regarded as candidates for primary structures. The improvement of thermoplastic polymer matrices, with the introduction of recent chemistries such as PEEK, PEI and PEKEKK. exhibiting increased mechanical performance, service temperature and solvent resistance (for the semi-crystalline systems) also supported the growth of interest for fusion bonding. This review looks at the state of the art of fusion bonding technology and focuses particularly on the three most promising fusion bonding techniques: ultrasonic welding, induction welding and resistance welding. Physical mechanisms involved in the fusion bonding process for modelling purposes are discussed including heat transfer, consolidation and crystallinity aspects. Finally, the application of fusion bonding to joining dissimilar materials, namely thermosetting composites (TSC)/TPC and metal/TPC joints, is reviewed.     

Joining Technology in Metal-Ceramic Systems

Metallic alloys and ceramic materials are employed in aggressive and hostile environments, ranging from aerospace to energy production, from offshore to biological applications. Today, production requires materials able to survive for a long time at high temperatures, in highly aggressive atmospheres, both from the chemical and the mechanical points of view. No single material can offer these characteristics, so that “composite” structures (composites, multilayer materials, metal-ceramic joints) are designed and tested under extreme conditions.

In this paper are presented the basic principles underlying joining technologies, a short discussion of the thermodynamic background of wetting processes, recent developments related to non-reactive and reactive wetting, the influence of trace chemical elements (in the solid, liquid and gaseous phases), and some specific aspects of diffusion bonding, brazing and transient liquid phase joining processes.     

钛铝金属间化合物合金的扩散连接

钛铝金属间化合物合金具有比重轻、比强度高以厦良好的高温力学性能和抗氧化性，被认为是航空航天和军工领域最具有应用前景的高温结构材料。钛铝金属间化合物合金的工程实用化需要先进的连接技术，保证连接件既能够保留母材的性能而且接头具有高的变形和断裂抗力。固态扩散连接不存在熔化缺陷、焊接热裂倾向和组织热影响区等缺点。被认为是连接钛铝金属间化舍物合全有效的方法之一。本文简要地介绍近十多年来国内外对钛铝金属间化合物合金扩散连接研究的状况与进展。     

Investigation into the microstructure and mechanical properties of diffusion bonded TiAl alloys

TiAl alloys are potential candidates for replacing conventional Ti-alloys in gas turbine applications in the relatively lower temperature sections, owing to their low density and excellent high temperature properties. However, their intolerable ambient temperature brittleness hinders their use in such applications. Recently, TiAl alloys with some room temperature ductility were developed through alloy development programmes using special production routes such as powder metallurgy. However, the room temperature brittleness of these alloys could not be overcome. Sound joining of these alloys is a fundamental prerequisite for their successful integration into high temperature aerospace applications. It has been well demonstrated that diffusion bonding, a commonly used joining technology in conventional Ti-alloys, can successfully be used in joining of TiAl alloys both in as-cast or special-rolled conditions. In this study, diffusion bondability of a recently developed C containing TiAl alloy with a duplex microstructure using bonding parameters in the range of commercially available equipments was studied. Microstructural investigations in the joint area of the bonds were conducted to observe the presence of any weld defect. Additionally, the mechanical behaviour of the bonds was determined by shear testing to find out the optimum bonding parameters. Furthermore, the effect of post-bond heat treatment on the mechanical properties was investigated.     

Mechanical Properties of Friction Stir Welded Mg/Mg‐ and Mg/Al‐Joints

In a mobile world weight reduction is a predominant target of innovative products. In this context appropriate joining techniques are necessary for the integration of lightweight metals in complex mechanical components. Friction stir welding (FSW) is a newly established well suited process to realize high‐quality lightweight metal joints in solid state. In a research project of WKK the friction stir weldability of similar joints using die casted AZ91‐Mg‐alloy and MRI‐Mg‐alloys was investigated. Additionally the joining of hybrid joints between AZ91 and AA5454 aluminum alloy was performed. To describe and optimize the FSW‐process the welding temperatures and welding forces were recorded online during the process. The investigations of the monotonic properties of AZ91/AZ91‐joints and MRI/MRI‐joints yielded in tensile strength values at the level of the parent materials. For dissimilar joints an extreme increase of the nugget hardness was measured. By SEM investigations and EDX element mappings it could be proved that this is caused by intermetallic phases positioned as thin interlayers in the contact area between the Mg‐ and the Al‐alloy. As a consequence, in hybrid joints failures occur predominantly along these interlayers. Finally, for similar and dissimilar welds corrosion experiments in 5 mass% NaCl solution were carried out. The investigations showed that the nugget area was more susceptible to corrosion then the base material. To understand the corrosion behavior the affected areas were analyzed using SEM and EDX.     

Der Einfluß der Kohlenstoff-Diffusion auf die mechanisch-technologischen Eigenschaften von ferritisch-austenitischen Schweißverbindungen im Chemie-Betrieb

The effect of carbon diffusion on the mechanical properties of ferritic-austenitic weldments . Weldments between ferritic and austenitic steels indicate a diffusion of carbon from ferritic to austenitic partner as an influence of temperature stresses and due higher solubility of carbon in γ-iron in comparison to α-iron. Investigations on two characteristic weldments (German standard H II/1.4571 and H II/Ni) have been conducted in different annealed conditions to study the effect of carbon diffusion on the various mechanical properties. There is an observable impairement of the mechanical properties of the weldments. Increased hardness in the carburised zone causes cracking and tensile strength as well as notch toughness decrease in the decarburised area.     

Tensile and Impact Properties of Shielded Metal Arc Welded AISI 409M Ferritic Stainless Steel Joints

The present study is concerned with the effect of filler metals such as austenitic stainless steel, ferritic stainless steel and duplex stainless steel on tensile and impact properties of the ferritic stainless steel conforming to AISI 409M grade. Rolled plates of 4 mm thickness were used as the base material for preparing single pass butt welded joints. Tensile and impact properties, microhardness, microstructure and fracture surface morphology of the joints fabricated by austenitic stainless steel, ferritic stainless steel and duplex stainless steel filler metals were evaluated and the results were reported. From this investigation, it is found that the joints fabricated by duplex stainless steel filler metal showed higher tensile strength and hardness compared to the joints fabricated by austenitic and ferritic stainless steel filler metals. Joints fabricated by austenitic stainless steel filler metal exhibited higher ductility and impact toughness compared with the joints fabricated by ferritic stainless steel and duplex stainless steel filler metals.     

扩散连接技术在核聚变反应堆包层模块制造中的应用

国际受控热核聚变实验堆计划是全球规模最大、影响最深远的国际科研合作项目之一,有望彻底解决能源危机。核聚变反应堆关键部件——包层模块的结构复杂、体积庞大,且服役环境恶劣,焊接接头成为影响反应堆安全运行的薄弱环节。以扩散连接为代表的固相焊接技术对接头性能及组织影响较小,已逐渐取代熔化焊应用于包层模块复杂构件制造。在简要介绍扩散连接及其原理的基础上,对包层模块构件扩散连接的研究进展进行了阐述,包括低活化铁素体/马氏体钢及氧化物弥散强化钢构件的扩散连接,Be,W,Si C等其他先进高温材料的扩散连接等。     

Mechanical and Structural Properties of Similar and Dissimilar Steel Joints

The mechanical properties of specimens from similar and dissimilar weld joints were examined. A ferritic steel (St37-2) and an austenitic stainless steel (AISI 304) were joined by the gas tungsten arc weld (GTAW) process using an austenitic filler metal. Mechanical and metallographic properties of the specimens were obtained by means of microhardness testing, tensile testing, bending fatigue testing, and light optical and scanning electron microscopy. The highest microhardness values were recorded on the ferritic–austenitic dissimilar weld joint, whereas the highest tensile strength and bending fatigue life were obtained with the austenitic–austenitic joints. Ferritic and pearlitic structures were observed in the microstructure of the ferritic–ferritic joint. The microstructures of austenitic–austenitic and austenitic–ferritic joints showed small recrystallization grains in addition to the typical austenitic and ferritic structures. Scanning electron microscopy was used to observe the fracture surfaces of the specimens and the origins of the fatigue cracks.     

Effect of bonding variables on TLP bonding of oxide dispersion strengthened superalloy

Transient liquid phase (TLP) bonding has evolved as a successful alternative joining technique for high service temperature components (e.g., vanes and blades for aircraft gas turbine engines) made from superalloys when neither fusion welding nor solid-state bonding techniques are successful. However, study shows that the optimization of bonding variables is critical to achieve a metallurgically sound joint free from deleterious intermetallic constituents in the joint region. In this study, the influence of bonding pressure and interlayer thickness on microstructural developments at the joint region of TLP bonded oxide dispersion strengthened (ODS) superalloy MA758 was examined. A commercial interlayer based on the Ni–Cr–B (MBF-80) system was used and results showed that bonding pressure and interlayer thickness affected the final width of the joints. A theoretical study revealed that the TLP bonding time can also be reduced when there is an increase in bonding pressure.     

Reactive Diffusion Bonding of SiCp/Al Composites by Insert Powder Layers with Eutectic Composition

1.IntroductionSiCp reinforced aluminium metal matrix composites(SiCp/Al MMCs)have a unique combination of mechani-cal and physical properties,such as high specific strengthand specific modulus of elasticity,low thermal expansioncoefficient and high wearing resistance,and are expectedto be widely used in aerospace engineering,automotiveindustry,electronic packaging,medical appliances,etc.It is well known that joining is the indispensable pro-cessing for industrial applications of any material…     

Reactive brazing of ceria to an ODS ferritic stainless steel

This research study shows that a ceria ceramic can be bonded to an ODS ferritic stainless steel (MA956) by reactive brazing using a Ag₆₈-Cu_27.5-Ti_4.5 interlayer. The ability to join these materials provides an alternative to the current ceramic interconnects used in the development of solid oxide fuel cells. Initial results show that the ceramic-metal bonds survived the bonding process irrespective of the degree of porosity within the ceria ceramic. Metallographic analyses indicate that a reaction zone formed along the ceria/braze interface, which was not only titanium rich, but also consisted of a mixture of copper oxides. When the ceramic-metal bonds were exposed to high bonding temperatures or when subjected to thermal cycling at 700°C, this reaction layer increased in thickness and had a detrimental affect on the mechanical strength of the final joints.