Creep-Fatigue Cracking Near the Welded Interface in Friction Welding Dissimilar Superalloys INCONEL 718 and MAR-M247

A forged INCONEL 718 and a cast MAR-M247 alloy were joined by a friction welding process. The creep-fatigue strength of this joint was investigated. The life of the joint was significantly shorter than that of the base alloys. The joint failed near the interface of the INCONEL 718 side, although the life of INCONEL 718 was longer than that of MAR-M247. To understand this behavior, the stress field in the welding was numerically analyzed using a visco-elastic model. The results suggested that triaxiality in the stress state could be promoted near the welded interface and lead to an acceleration of creep-fatigue crack nucleation.     

Finite Element Modeling of the Inertia Friction Welding of Dissimilar High-Strength Steels

Finite element (FE) process modeling of inertia friction welding between dissimilar high-strength steels, AerMet^® 100 and SCMV, has been carried out using the DEFORM?-2D (v10.0) software. This model was validated against experimental data collected for a test weld performed between the materials; this included process data such as upset and rotational velocities as well as thermal data collected during the process using embedded thermocouples. The as-welded hoop residual stress from the FE model was also compared with experimental measurements taken on the welded component using synchrotron X-ray and neutron diffraction techniques. The modeling work considered the solid-state phase transformations which occur in the steels, and the trends in the residual stress data were well replicated by the model.     

Thermal Relaxation of Residual Stresses in Nickel-Based Superalloy Inertia Friction Welds

This article describes an experimental study aimed at characterizing the extent of residual stress relaxation during thermal treatment of inertia friction-welded alloy 720Li nickel-based superalloy welded tubular rings. In the as-welded condition, yield level tensile hoop stresses were found by neutron diffraction in the weld region along with axial bending stresses (tensile toward the inner diameter (ID)/compressive toward the outer). The evolution of these residual stress levels during postweld heat treatment (PWHT) was mapped experimentally over the weld cross section. After 8 hours of PWHT, the axial stresses relaxed by 70 pct, whereas the hoop stresses reduced by only 50 pct. Some scatter of residual stress evolution was found between samples, particularly for the axial stress direction. This was attributed to substandard tooling to grip the rings. The results on subscale samples were transferred to a full-scale aeroengine (650-mm diameter) compressor drum assembly that was postweld heat treated for 8 hours. It was found that the residual stresses, particularly in the axial direction, were noticeably lower in this full-scale weld component compared to the subscale weld heat treated for the same time. The differences seem to be best rationalized by the different standards of jigging used during joining these two types of welds.     

Friction Buttering: A New Technique for Dissimilar Welding

This work offers a fresh perspective on buttering, a technique often considered for fusion welding of dissimilar metals. For the first time, buttering was attempted in solid state using friction deposition. Using this new “friction buttering” technique, fusion welding of two different dissimilar metal pairs (austenitic stainless steel/borated stainless steel and Al-Cu-Mg/Al-Zn-Mg-Cu) was successfully demonstrated. The results show that friction buttering can simplify a tough dissimilar welding problem into a routine fusion welding task.     

Linear Friction Welding of Dissimilar Materials 316L Stainless Steel to Zircaloy-4

Metallurgical and Materials Transactions A - In the nuclear industry, there are a number of applications where the transition of stainless steel to Zircaloy is of technological importance. However,...     

On the Occurrence of Liquation During Linear Friction Welding of Ni-Based Superalloys

A combination of experimental and analytical methods was used to study the possible occurrence of liquation during LFW of the newly developed AD730^TM Ni-based superalloy. LFWed joints were produced using a semi-industrial size facility and the interfaces of the joints as well as the ejected flash were examined using optical and Field Emission Gun Scanning Electron Microscopy (FEG-SEM). Physical simulation of the LFW thermal cycle, using thermomechanical simulator Gleeble™ 3800, showed that incipient melting started from 1473 K (1200 °C). The analytical model, calibrated by experiments, predicted that the highest temperature of the interface was about 1523 K (1250 °C). The constitutive equations based on lattice and pipe diffusion models were developed to quantify the self-diffusivity of the elements and control the extent of liquation by considering the effect of LFW process parameters. Analytical results show that the application of compressive stresses during LFW results in 25 times increase in the diffusion of Ni atoms at the weld interface. Therefore, no presence of re-solidified phases, i.e., occurrence of liquation, was observed in the microstructure of the weld zone or the flash in the present study. Based on the obtained results, a methodology was developed for designing the optimum pressure above which no liquation, and hence cracking, will be observable.

     

Microstructure-Based Strength Distribution Across the Welds of Nickel-Based Superalloy Inconel 751 and Austenite Steel 21-4N Joined by Inertia Friction Welding

Welding dissimilar metals is always a challenge for their different physical property and microstructures. In this study, the two dissimilar metals 21-4N and Inconel 751 are welded together by inertia friction welding. Microstructure observation shows that the weld can be divided into three regions in 21-4N: the chemical composition mixture zone, shear zone, and base metal. The width of the chemical composition mixture zone (CMZ) is about 80 μm, with relatively larger grains and lower dislocation density distributed in this zone. Shear banding occurs in the shear zone, and carbides are found to have precipitated strongly along these shear bands noncontinuously. The base metal contains an austenite microstructure with carbides distributed in the matrix. In Inconel 751, only two typical zones can be observed: the CMZ and the base metal. The heat-affected zone is too small to be observed in the whole weld. Finally, a strength model based on microstructural evolution is proposed. The strength distribution along the axial direction of the welds is calculated. The results are in good agreement with the measurements.     

镁合金搅拌摩擦焊接技术

对5mm厚镁合金AZ31B板材的摩擦焊接技术进行了试验研究，结果表明：适合其板材的搅拌摩擦焊接的搅拌头，材料为W6MoSCr4V2高速钢，结构为凹面圆台形，根部直径5．5mm，端部直径为2．5mm，轴肩尺寸为12mm，长度为4．7mm。镁合金搅拌摩擦焊接头的抗拉强度可达母材的90％，延伸率可达母材的50％。搅拌摩擦焊接头焊合区为动态再结晶组织，在接头前进边焊合区与母材有明显的分界线，返回边过渡区有金属微熔的迹象。     

GH720Li合金的铸态组织和均匀化工艺

对GH720Li合金的铸态组织及均匀化工艺进行了研究,采用物理化学相分析的方法确定了该合金析出相的类型、数量和γ′相的粒径分布。结果表明：该合金在铸造状态下的析出相是γ′、Ti(C,N)、TiC和M2B2(痕),其中γ′相的质量分数高达34．187％。均匀化的结果表明：GH720Li合金适宜的均匀化温度为1190℃。     

钻杆惯性摩擦焊接角偏差控制

钻杆角偏差是在焊接过程中产生的,其影响钻杆直度并严重影响钻杆使用寿命。通过宝钢生产实践发现,惯性摩擦焊接角偏差控制较连续摩擦焊接困难。在分析惯性摩擦焊接与连续摩擦焊接工艺差别的基础上,研究了钻杆角偏差的产生机理。研究表明,惯性摩擦焊接初始转速快、焊接压力高,造成焊接初始阶段的扭矩峰值偏高;高扭矩容易造成焊接工件出现径向位移,由此导致角偏差增大。提出了改善钻杆惯性摩擦焊接角偏差的新方法：采用平面—锥面焊接结构,削减初始扭矩峰值;采用全浮动夹具并增大定心夹具刚性以及时纠正工件径向位移。     

镁-铝异种合金搅拌摩擦焊的研究现状及展望

镁合金具有高的比强度和比刚度,被广泛应用于各种工程领域。然而镁合金存在易腐蚀和成形性能差等缺点,极大地制约了镁合金的广泛应用。铝合金密度低,强度高,接近或超过优质钢,塑性好,可加工成各种型材,具有优良的导电性、导热性和抗蚀性,在工业上得到了广泛使用,使用量仅次于钢。在航空航天、轨道交通及汽车等精密工业中,异种合金间的焊接被认为是最复杂的工程之一。通过镁-铝异种合金的焊接,有效结合两种合金的优点,从而满足一些特殊工作环境对零件的使用要求。与此同时,镁-铝异种合金的焊接可显著节省材料从而降低成本,极大拓展了镁合金和铝合金的应用。搅拌摩擦焊可以显著改善传统熔焊工艺中存在的许多冶金问题,从而获得高质量的焊接接头。因此,不同牌号的镁-铝搅拌摩擦焊既有重大的科学研究价值又有巨大的工业应用价值。本文总结了镁-铝合金搅拌摩擦焊的研究进展,特别关注了搅拌摩擦焊工艺参数对微观组织演变、力学性能及相关缺陷的影响,并对后续的研究热点进行了展望。     

Laser Keyhole Welding of Dissimilar Ti-6Al-4V Titanium Alloy to AZ31B Magnesium Alloy

Laser keyhole welding of Ti-6Al-4V titanium alloy to AZ31B magnesium alloy was developed, and the correlations of process parameters, joint properties, and bonding mechanism were studied. The results show that the offset from the laser beam center on AZ31B side to the edge of the weld seam plays a big role in the joint properties by changing the power density irradiated at the Ti–Mg initial interface. The optimal range of the offset is 0.3 to 0.4mm in the present study. Some lamellar and granular Ti-rich mixtures are observed in the fusion zone, which is formed by intermixing melted Ti-6Al-4V with liquid AZ31B. The maximum ultimate tensile strength of the joints reaches 266 MPa. Furthermore, the fracture surface consists of scraggly remaining weld metal and smooth Ti surface. The higher the failure strength, the smaller the proportion of smooth Ti surface to whole interface is. Finally, the bonding mechanism of the interfacial layer is summarized by the morphologies and test results of fracture surfaces.     

搅拌摩擦焊用钨铼合金的研究进展

搅拌摩擦焊接技术是一种环保、低成本的固相连接技术,已经在航空航天、轨道交通和新能源汽车等领域得到广泛应用。对于高熔点合金材料如钛合金和不锈钢的搅拌摩擦焊接而言,搅拌头材料成了主要制约因素。钨铼（W-Re）合金凭借其高熔点、高硬度和强抗腐蚀性等优点,已成为研究和应用最热的搅拌摩擦焊接高熔点合金的搅拌头材料。本文综述了近年来在搅拌摩擦焊工艺中以W-Re合金作为搅拌头材料的制备方法、复合强化技术和应用场景的研究进展。此外,还展望了拓宽W-Re合金在搅拌摩擦焊领域应用的前景,包括降低W-Re合金的生产成本和提高其服役寿命等方面,旨在推动W-Re合金搅拌头材料在搅拌摩擦焊领域的进一步应用和发展。     

铝锂合金搅拌摩擦焊接热循环

搅拌摩擦焊接过程中，焊件上任一位置于搅拌头行走到该位置所在垂直于焊缝直线的瞬间，热循环温度达到最大值，并随着搅拌头远离而迅速降低。焊缝起点受搅拌头扎入行为的影响，而焊缝终点受搅拌头提起行为的影响，二者经受的热循环温度低于焊缝其它部位。然而焊缝起点和终点间的材料经受稳定的热循环作用。焊缝中心经受的焊接热循环温度最高，为415℃。焊缝两侧材料经受不同的热循环作用，前进侧略高于后退侧7～12℃。     

惯性摩擦焊过程温度场及变形场的数值模拟

惯性摩擦焊接是一种广泛应用的高效、可靠、节能及环保的固态焊接方法.该方法在航天航空领域已广泛应用.本文分析了惯性摩擦焊接过程高度非线性的特点,在此基础上建立了一个基于二维轴对称的惯性摩擦焊接过程有限元热力耦合计算模型.计算区域划分成四节点等参单元,热物性参数和力学性能参数随温度变化,同时考虑了焊接热流随时间的变化、表面对流和辐射换热以及飞边的影响.利用有限元分析软件MSC Marc对同质材料GH4169-GH4169惯性摩擦焊接接头区的瞬态温度场及应力-应变场的分布进行了计算分析.使用热电偶点对焊接接头部分若干点的温度进行了实时测量.结果表明温度场的计算结果与实测值符合较好.另外,还讨论了工艺参数对摩擦焊接接头区应力分布以及飞边形状的影响.