In the present work, the TiB2-reinforced AA6061 composites were successfully in situ synthesized by laser surface alloying using a mixture of Ti and AlB2 powders. The microstructure evolution and ...properties of the composites were systematically studied. The results showed that TiB2 particles displayed a homogeneous distribution in the aluminum matrix with controllable contents and morphologies. By adjusting the molar ratio of alloying powders, phase constitution of the composites was varied. Thermodynamic calculation was used to analyze the phase selection during the solidification. It was found that the morphology of TiB2 particles was converted from hexagonal plate into rod-like structure with an increase of Ti contents. Transmission electron microscopy results illustrated that the in situ synthesized TiB2 particles exhibited a well-bonded interface with the Al matrix. Properties characterization revealed a significant enhancement in microhardness and abrasion resistance compared with the aluminum substrate attributed to the presence of the TiB2 reinforcements. The strengthening and wear mechanism were also discussed.
By matching with the welding speed, the distance between the laser focus and butt seam was adjusted to obtain various fusion ratios of the two base metals. The main phases in weld metal were ...martensite and retained austenite whose proportions and morphology were measured by XRD and EBSD, respectively. The proportion of retained austenite, both at grain boundary and among martensite laths in core region of grain, increased with the fusion ratio of SUS304. The maximum content of retained austenite at grain boundary and in core region of grain could reach about 22% and 5.8%, respectively. The low-temperature impact toughness of the joint was improved with the increment of retained austenite content. The low-temperature impact energy at −196°C had displayed a significant raise from 15J to 44.3J. The corresponding impact fracture section also transformed from cleavage fracture to entirely ductile fracture.
Objective. The aim of the present research is to analyze the impact of the bridge combined internal fixation system (BCFS) on efficacy, complications, and inflammatory reactions of periarticular ...fractures of the shoulder. Methods. A retrospective analysis was performed on 100 patients with periarticular fractures of the shoulder admitted between January 2016 and January 2020. Patients were assigned to the observation group (OG) and control group (CG) according to different treatment schemes, with 50 cases in each group. Patients in OG were intervened by BCFS, while those in CG were routinely given plate fixation. The treatment outcome, complications, and inflammatory reaction of the two groups were compared. Results. The results showed better treatment outcome, shoulder joint function recovery, and inflammatory reaction alleviation of OG compared with CG. Besides, statistically shorter fracture healing and hospitalization time as well as fewer complications were determined in OG. Conclusion. These results demonstrate that compared with the plate fixation system, BCFS can significantly improve the surgical efficacy and healing efficiency and alleviate the inflammatory response of patients, with a low complication rate, all of which contribute to faster recovery of periarticular fractures of the shoulder. Hence, BCFS is an ideal choice for periarticular fractures of the shoulder that deserves clinical promotion.
A high-speed camera and X-ray transmission observation system were used to observe the keyhole and molten pool dynamic behavior in laser lap welding T-joints. The oscillation frequency of the molten ...pool and the keyhole increases with increasing gap. The lower keyhole becomes slant with the large gap and large quantities of bubbles are formed at the bottom tip of the keyhole. The molten pool is divided into three different zones by the large gap and a small eddy is formed at the lower molten pool. The bubbles are difficult to escape from the lower molten pool and the gap when the gap is large, resulting in the formation of porosity at the gap and root of weld seam. The distribution characteristics of porosity in different gap have an excellent agreement with the keyhole and the molten pool dynamic behavior. Porosity can be suppressed by maintaining a small gap or adopting high welding speed. The paper provides fundamental insights into the mechanism of porosity formation during laser lap welding T-joints and guidance to aid in its elimination.
Abstract
In the present work, the TiB
2
-reinforced AA6061 composites were successfully in situ synthesized by laser surface alloying using a mixture of Ti and AlB
2
powders. The microstructure ...evolution and properties of the composites were systematically studied. The results showed that TiB
2
particles displayed a homogeneous distribution in the aluminum matrix with controllable contents and morphologies. By adjusting the molar ratio of alloying powders, phase constitution of the composites was varied. Thermodynamic calculation was used to analyze the phase selection during the solidification. It was found that the morphology of TiB
2
particles was converted from hexagonal plate into rod-like structure with an increase of Ti contents. Transmission electron microscopy results illustrated that the in situ synthesized TiB
2
particles exhibited a well-bonded interface with the Al matrix. Properties characterization revealed a significant enhancement in microhardness and abrasion resistance compared with the aluminum substrate attributed to the presence of the TiB
2
reinforcements. The strengthening and wear mechanism were also discussed.
The study investigated laser welding with filler wire to determine the effects of wire feeding modes and the height of intersection of the wire and the beam (
H
) on weld geometry and droplet ...transfer. Droplet transfer behavior was investigated using high-speed imaging. The results showed that the wire melting changed with wire feeding. The leading wire melted completely and the welding depth and width were greater due to higher levels of energy available to heat the plate in the weld pool. The transfer mode changed to liquid bridge transfer and globular transfer with increased
H
value. With increasing
H
, the frequency of droplet transfer and the droplet size varied. At 2 mm
H
, the droplet transfer was very stable resulting in optimum welding.
Nanocrystalline Ni thin film exhibits poor thermo-mechanical properties due to its unstable microstructure at elevated temperature. Here, the paper endows a new approach to solve above issue via ...addition of nano-multilayers and incorporation of W for nanocrystalline Ni-based films, to provide novel Ni/Ni3Al-W nano-composite multilayered structure with high hardness and good thermal stability. The thermal evolution of microstructure and mechanical properties was investigated to reveal nanocrystalline stability and strengthening mechanisms for co-sputtered Ni/Ni3Al-W multilayers with varied W concentrations and annealing temperature. The lamellar structure and nonequilibrium phases are well maintained in 600 °C annealed multilayers, while nano-grains are further refined with increasing W addition. Annealing at 800 °C results in the appearance of elemental redistribution and phase separation in multilayers, leading to the layered structure dissolved and globular W-related particles precipitated. Annealing hardening is founded in most of annealed Ni/Ni3Al-W multilayers. Based upon microstructure observation, grain boundary relaxation and W-related phase precipitation are mainly responsible for the hardness enhancement of multilayers at 600 °C and 800 °C, respectively. Notably, the best hardness is achieved at the value of 15.6 GPa for 800 °C annealed 12.5 at% W doped Ni/Ni3Al-W multilayer, which shows the residual layer interfaces with larger precipitations in microstructure. This hardness increment for annealed Ni-based multilayers can be attributed that the high degree of strengthening is provided by a combination of hardening precipitation and survived lamellar structure via the Orowan mechanisms, offering a feasible insight to develop nano-metallic coatings for further increasing thermo-mechanical properties.
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•Precipitates in coarse-grained heat-affected zones (CGHAZ) of various joints are analyzed.•Effects of welding heat input and different base metal conditions (wrought, as-cast and homogenized) are ...examined in detail.•Diffusion of Nb and the dissolution of carbides and the Laves phase are analyzed.•A detailed picture of the microstructure evolution in CGHAZ of three base metal conditions is proposed.
Wrought, as-cast, and homogenized sheets were welded using the tungsten inert gas (TIG) process. The precipitates in both the base metal and the coarse-grained heat-affected zone (CGHAZ) for each joint were analyzed by optical microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). Statistical data regarding the precipitates were also obtained from metallographs. With the alloy element contents determined by EDS and the phase diagram obtained using ThermoCalc, the diffusion of Nb and the dissolution of carbides and the Laves phase were analyzed. The wrought base metal contained massive M23C6 particles and MC blocks. As the heat input increased, the amount of carbides in the CGHAZ decreased. No Laves phase was discovered in the base metal or CGHAZ. In the as-cast or homogenized base metal, MC blocks and the Laves phase were distributed in the interdendritic segregated region. As the heat input increased, the MC and Laves content did not change significantly. The prewelding heat treatment in the homogenization process reduced the amount of precipitates in the base metal. The CGHAZ of the joint of the homogenized metal lost more dendritic structure than did the CGHAZ of the joint of the as-cast metal.
To solve the problems that the current seam tracking process cannot find the weld line and the control method based on the kinematic model of welding mobile robot leads to low accuracy, a method for ...searching the welding seam is designed firstly. By this method, the initiation point of the weld line can be found and the attitude of the robot parallel to the weld line can be adjusted automatically. Secondly, for improving the tracking precision and anti-interference performance, a new controller based on the kinematic and dynamic model of the mobile welding robot is designed. To deal with the partial uncertainty and the disturbances of welding process, this controller combines the sliding mode variable structure control and low-pass filter, so that it is able to complete the controlling of cross-slider and wheels coordinately. The stability and convergence of the designed controller are proved through the use of Lyapunov theory. The effectiveness of the proposed method is verified by simulation and experiments. In the seam tracking process, the welding torch is able to track the welding seam well and the robot moves steadily without any obvious chattering.
The dissimilar joints between SA553 and SUS304 were produced by CO2 laser welding with the ERNiMo-8 and ER308L filler wire. After welding parameters were optimized, qualified weld formations were ...made. Investigation on the microstructure showed that there were dual phases (martensite and austenite) in the ER308L weld, but only austenite in the ERNiMo-8 weld. For both joints, not only the microstructure gradient, but also the element gradient was observed near interfaces between weld metals and base metals. The Charpy impact and tensile test at room (25°C) and low temperature (−196°C) was implemented. The cryogenic impact energy of the ER308L weldment was 51J, lower than the value (84J) of the ERNiMo-8 weldment. The corresponding cryogenic tensile strength of the two weldments was 1070MPa and 960MPa, respectively. The cryogenic tensile properties of both weldments were rather higher than requirements in the relevant standards. The ERNiMo-8 weldment showed relatively better comprehensive performance when the cryogenic toughness was considered.
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•The dissimilar joints were achieved by laser welding with different fillers.•The microstructure and properties of dissimilar joints were systemically compared.•The joints with both fillers were qualified for using in cryogenic environments.•The ERNiMo-8 weldment showed better comprehensive cryogenic properties.
