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A large instantaneous axial forging load is required to be applied for the final stage of rotary friction welding (RFW), which is usually conducive to obtaining clean, compact, and high-quality joints. However, for slender fuel claddings made of molybdenum (Mo) with low stiffness, the instantaneous axial forging load cannot be applied at the final stage of welding. This study carried out RFW tests without upset forging on Mo in the atmospheric environment and investigated the effects of welding time on joint morphology, axial shortening, microstructures, microhardness, tensile strength, and tensile fracture morphology. It found that the excessive and abrupt burning and a lot of smoke were generated around the weld zone during welding and spiral flashes were observed after welding. Under welding pressure of 80 MPa and spindle speed of 2000 r/min, the minimum average grain size and maximum tensile strength can be obtained in 4 s when the welding time is between 2&ndash, 5 s. Scanning electron microscope (SEM) results show that there were morphologies of a large number of intergranular fractures and a small number of transgranular fractures in the fracture. The above results demonstrated that it is feasible to use RFW without upset forging to seal the last weld spot on upper end plugs of fuel claddings made of Mo in high-pressure inert gas, which would not only obtain reliable welding quality but also seal high-pressure inert gas in cladding tubes. The research results have a practical guiding significance of manufacturing accident-tolerant Mo nuclear fuel cladding.

Mechanical bonded SUS304/Q235B bimetallic pipes have been widely used as subsea oil and gas transmission pipeline. Due to the complexity of the subsea environment, the thin inner layer of SUS304 might crinkle and swell locally and then separated from the base layer of Q235B. In this work, lap welding inside the SUS304/Q235B bimetallic pipes was investigated with special emphasis on the corrosion resistance of the near surface region of the lap joint. Nothing the significant difference of weld width between its upper part and lower part of typical laser welded “wine-glass” type bead, laser welding was employed here to reduce the dilution of alloy elements in the fusion zone of inner stainless steel layer. The results showed that content of major alloy elements such as chromium (Cr) and nickel (Ni) in the near surface region of fusion zone could be kept as about 14 and 6 wt.%, respectively, by optimizing the laser lap welding process parameters. The laser welded SUS304/Q235B overlap joints had excellent shear strength, and the shear fracture was consisted of numerous dimples. Finally, laser filler wire cladding of SUS316 stainless steel on the top surface of previously achieved overlap joint was carried out to ensure that upper part of the weld zone had enough corrosion resistance.

Butt welding of explosion welded Ti/steel bimetallic sheet is still a challenging task due to brittle Ti-Fe intermetallic compounds (IMCs) generated in the transition zone between Ti and steel. Laser butt welding of Ti/steel bimetallic sheet was performed in this work. Preliminary results showed that cracks usually observed in the transition zone of arc welded joint could be effectively avoided by using laser welding and a copper interlayer. The key point was the elaborate control of the remolten volume of copper interlayer. The laser butt welded joint achieved was evaluated by using SEM, EDS and micro-hardness test. Tensile tests, bending tests and V-notched Charpy impact tests were conducted to reveal the mechanical properties. The tensile strength and impact absorbing energy of the butt joint were about 73% and 77% that of the CP-Ti/Q235B bimetallic sheet, respectively. The initiation position and propagation path of the crack were observed by high-speed imaging in both face and root bending tests. Finally, improvements brought by the laser butt welding process were concluded and strategies for improving the processing scheme in the future were suggested.

Compared to Ti/steel bimetallic sheets, Zr/Ti/steel trimetallic sheets have improved service performance in severely corrosive environments because the corrosion resistance of zirconium and titanium are complementary. The inhomogeneities of the microstructure and mechanical properties as well as the underlying mechanism of the interactions in the Zr/Ti/steel trimetallic composite sheets fabricated by explosive welding were investigated. The shear strength of the Ti/steel interface and Zr/Ti interface was found to be anisotropic and isotropic respectively, which could be explained by the wide and unambiguous wavy morphology of the former and relatively narrow and obscure wavy morphology of the latter. A transient strain field on the bending specimen was achieved through the digital image correlation (DIC) method during a bending test and it was found that the change of von Mises strain across the Ti/steel interface was much more significant than that across the Zr/Ti interface. This could be related to the through-thickness heterogeneous mechanical properties verified by Vickers hardness tests and tensile tests of the stratified samples of the Zr/Ti/steel plate. Large blocks of Fe Ti intermetallic compounds were formed in the local melted zone (LMZ) at the Ti/steel interface, while uncoordinated plastic deformation across the interface resulted in the failure appearing at the Ti/steel interface during the bending test. Importantly, the values of shear strength and impact energy of the studied Zr/Ti/steel sheet met the requirements of ASME S264.

Owing to excellent corrosion resistance, antifriction property, and economic efficiency, H62/Q235B explosive clad plates have been widely used in various fields. Therefore, detailed and systematic study into the microstructure and mechanical properties of this clad material is necessary. In this paper, the composition, microstructure, and mechanical properties of H62/Q235B explosive clad plates were analyzed by optical metallographic observation, mechanical tests, scanning electron microscope (SEM) observation, and energy dispersive spectrometer (EDS) analysis. The results showed that the bonding interface of this clad plate was periodical wavy, and the interface was bonded in two ways, one through wide transition layer with a width up to 280 μm while the other by narrow transition layer with a width less than 20 μm. The major structural components in the transition layer were supersaturated solid solutions. The microhardness of the transition layer was higher than that of base metals, and the microhardness of the base plates in the region near the bonding interface was affected by both force and heat. The shear strength of the H62/Q235B clad plate showed an obvious characteristic of anisotropy. Furthermore, the clad plate tended to crack along the transition layer when it was stretched because of the discontinuity of plastic deformation across H62/Q235B interface.

Porosity defects are still a challenging issue in the fusion welding of molybdenum and its alloys due to the pre-existing interior defects associated with the powder metallurgy process. Fiber laser welding of end plug and cladding tube made of nanostructured high-strength molybdenum (NS-Mo) alloy was performed in this work with an emphasis on the role of welding heat input. The distribution and morphology of porosity defects in the welded joints were examined by computed tomography (CT) and scanning electron microscopy (SEM). Preliminary results showed that laser welding of NS-Mo under low heat input significantly reduced the porosity defects in the fusion zone. The results of computed tomography (CT) showed that when the welding heat input decreased from 3600 J/cm (i.e., 1200 W, 0.2 m/min) to 250 J/cm (i.e., 2500 W, 6 m/min), the porosity ratio of the NS-Mo joints declined from 10.7% to 2.1%. Notable porosity defects under high heat input were related to the instability of the keyhole, expansion and the merging of bubbles in the molten pool, among which the instability of the keyhole played the dominant role. The porous defects at low heat input were generated as bubbles released from the powder metallurgy base metal (BM) did not have enough time to overflow and escape.

As one of the relatively new titanium (Ti) alloys in the engineering field, &beta, Ti alloy&ndash, Ti55531 has attracted a great deal of attention due to its excellent mechanical properties, while a few research papers on weldability and the post-weld heat treatment (PWHT) process of Ti55531 have been reported. Based on an orthogonal experiment design, the parameters of laser beam welding (LBW) of Ti55531 alloy with a thickness of 2 mm were optimized. Moreover, the influences of welding parameters and PWHT on the microstructures and performance of the laser-welded joint of Ti55531 were analyzed. The results showed that, for microstructures in different zones of as-welded joints of Ti55531: three forms of &alpha, phases (i.e., equiaxial &alpha, p phase, lamellar &alpha, S phase, and &alpha, GB phase at grain boundaries) were observed in base metal (BM), in the heat affected zone (HAZ), part of lamellar &alpha, S phase had dissolved while equiaxial &alpha, p phase had grown, the fusion zone (FZ) mainly consisted of &beta, phase, which presented as coarse columnar crystals. After the PWHT process, the microstructures of the welded joint were changed: in the BM zone, &alpha, phase at grain boundary disappeared and lamellar &alpha, phase decreased, in the HAZ, the edge of &alpha, p phase obviously dissolved, in the FZ, plenty of compact needle-like &alpha, phases were observed. The tensile strength of the as-welded joint was about 940 MPa and then increased to 1161 MPa after PWHT, which were 78.4% and 96.8% of that of the original BM respectively. The fracture position transformed from the interface between the FZ and HAZ to the BM during tensile tests after PWHT.

TA1/X65 bimetallic plate has a bright future of application by combining the excellent corrosion resistance of TA1 and the high strength of inexpensive X65 steel, while manufacturing large size TA1/X65 bimetallic plate is still a challenging task. Multi-pass hot-rolling is the most common way to achieve a large size bimetallic plate. In this work, interface characteristic of explosive-welded and multi-pass hot-rolled TA1/X65 bimetallic plate is experimentally studied. The microstructure, composition and microhardness distribution across the TA1/X65 interface are investigated by optical metallographic observation, scanning electron microscope (SEM) observation, energy dispersive spectrometer (EDS) analysis, and Vickers hardness test. Shear tests and stratified tensile tests are conducted with emphasis on impacts of the angle between loading direction and detonation wave propagation direction on interface strength. A straight TA1/X65 interface with periodic morphology of residual peninsula could be observed on the cross section parallel to detonation wave propagation direction, while in most cases there is no residual peninsula morphology on the straight TA1/X65 interface when the cross section is perpendicular to detonation wave propagation direction. TA1/X65 interface of explosive-welded and multi-pass hot-rolled bimetallic plate presents higher bearing capacity for the load perpendicular to detonation wave propagation direction than that for the load parallel to detonation wave propagation direction. The results of this paper have a certain guiding significance for the fabrication of pipes and containers made of explosive-welded and hot-rolled TA1/X65 bimetallic plate.

Fiber welding of socket-joints made of nanostructured high-performance molybdenum alloy (NS Mo) was carried out to get a better understanding of the role of welding heat input. It was found that low heat input (i.e., high welding speed) resulted in significantly refined grains in the fusion zone (FZ) of fiber laser welded NS Mo joints. When welding heat input decreased from 3600 J/cm (i.e., 1.2 kW, 20 cm/min) to 250 J/cm (i.e., 2.5 kW, 600 cm/min), the tensile strength of welded joints increased from about 250 MPa to about 570 MPa. It was confirmed by energy spectrum analysis that the higher the welding heat input, the higher the oxygen contents at the grain boundary (GB) within the FZ. In addition, the most important reason for poor strength of welded joints of Mo alloys was reported as being that MoO2 was segregated on the grain boundary. Therefore, it was concluded that welding under low heat input (i.e., high welding speed) was able to reduce the segregation degree of MoO2 at the grain boundary by refining grains and increasing the total area of GBs, thus improving the strength of welded joints and reducing the proportion of the intergranular fracture zone in tensile fractures.

With the aim to reduce the total structural weight, this paper presents a novel radial multi-layered elastic metamaterial (EM) shaft in which the scattering layer is circumferentially discretized into several arc-shaped sections with rotational symmetry. The dispersion relations and frequency-response-functions (FRF) of a finite structure are determined numerically first with different discretized geometries. To illustrate the mechanisms of band gaps, the eigenmodes were extracted and analyzed together with dispersion relations and FRF. The results show that in contrast to conventional multi-layered EM shafts, the proposed EM shaft with the weight being reduced by 34% can still yield broadband gaps at low-frequencies and by properly selecting the discretized geometry the band gap ranging from 139 to 197Hz exists for all three elastic wave modes. The results presented in this paper demonstrate a potential design strategy in stabilized shaft engineering.

This paper briefly reports on preparations and applications of two kind multipurpose medical piezoelectrical ultrasonic transducer materials, high-performance medical ultrasonic diagnosis transducers and medical ultrasonic therapy transducers in present work, then, some problems of the piezoelectric materials and devices used for the ultrasonic medicine which need further researches are pointed out.