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Microstructure and mechanical properties of welding–brazing of Ti/Al butt joints with laser melting deposition layer additive
摘要： Laser welding–brazing of Ti/Al butt joints was performed with coaxial Al–10Si–Mg powders feeding. The experimental results indicated that a sound Ti/Al butt joint could be obtained by an additive layer approach. The influence of the laser melting deposition layers on the weld appearance, interfacial microstructure and tensile properties were investigated. High-quality joints were produced when five and seven layers were deposited. The morphology and thickness distributions of the interfacial intermetallic compounds (IMC) at the brazing interface along the thickness direction of the joint varied with the number of deposition layers. Continuous serrated IMC was obtained in joints produced by seven deposition layers, and the IMC layer was distributed homogenously along the thickness direction. The maximum thickness difference of the IMC was only approximately 0.12 μm. The microstructure of the IMC layer was composed of a nanosized granular Ti7Al5Si12 phase and serrated Ti(Al, Si)3 phase. The maximum tensile joint strength reached 240 MPa, 80% of that of the aluminum base metal, and the lower tensile strength of the other joints was caused by insufficient IMC layer or a porosity defect.
关键词： Tensile strength,Laser melting deposition,Interfacial IMC,Laser welding–brazing,Ti/Al butt joint
更新于2025-09-19 17:15:36
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[IEEE 2019 IEEE 4th Optoelectronics Global Conference (OGC) - Shenzhen, China (2019.9.3-2019.9.6)] 2019 IEEE 4th Optoelectronics Global Conference (OGC) - Effect of Deposition Strategy on Fatigue Behavior of Laser Melting Deposition 12CrNi2 Alloy Steel
摘要： In this paper, the 12CrNi2 alloy steel parts were fabricated by laser melting deposition (LMD) using two kinds of deposition strategies, single direction scanning(SDS) and cross direction scanning(CDS). The microstructure and fatigue behavior of LMD 12CrNi2 alloy steel samples were investigated. Thy typical microstructure of both deposition strategy were ferrite and can be divided into two zones: remelted zone and non-remelted zone. The non-remelted zone showed typical columnar crystal morphology while the structure of remelted zone was homogenized. Compared with SDS deposition strategy, the microstructure of CDS deposition strategy had shorter columnar grains and finer grains. The relative densities of SDS and CDS deposition strategies were 98.1 and 97.3, respectively, indicating that SDS had lower porosity. The fatigue strength of SDS deposition strategy was higher than that of CDS deposition strategy, which were 320 MPa and 200 MPa. There were more defects in CDS deposition strategy, which accelerated the initiation and propagation of cracks. CDS deposition strategy had longer interlayer interval time, which will reduce the penetration depth of laser, affect the degree of previous layer remelting, and eventually lead to unmelted powder, porosity and other defects in the lap zone.
关键词： laser melting deposition,deposition strategy,fatigue,12CrNi2
更新于2025-09-16 10:30:52
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Atomic structure revolution and excellent performance improvement of composites induced by laser ultrafine-nano technology
摘要： Carbon nanotubes (CNTs) reinforced high-entropy alloy composites (HEACs) were fabricated on a TA2 titanium alloy by mean of a laser melting deposition (LMD) of the FeCoCrAlCu-(nano-SiB6)-(Ni/Ag-coated CNTs) mixed powders, noting that large quantities of the ultrafine nanocrystals (UNs) were formed, portion of them were able to obtain the enormous energy from laser beam, which were able to permeate into the original ordered atom arrangement due to the high diffusion rates and their ultrafine microstructure. In substance, partial UNs can destroy the balanced state of atoms, increasing significantly the free energy of the crystal boundaries. Such CNTs/UNs modified LMD composites showed the better corrosion/high-temperature oxidation resistance properties than those of the TA2 alloy. Identification of the synthetic UNs in such LMD HEACs, more importantly the UNs transition effect, contributes theoretical/experimental basis to upgrade the quality of the industrial light alloy.
关键词： Metal-matrix composites (MMCs),Surface treatments,Laser melting deposition,Nanocomposites,Powder processing
更新于2025-09-16 10:30:52
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Eliminating continuous grain boundary α phase in laser melting deposited near β titanium alloys by heat treatment
摘要： Continuous grain boundary α phase (αGB) is widely present in laser melting deposited near β and β titanium alloys, and it can lead to intergranular fracture and low ductility. Because of the preferential nucleation and growth of α phase at β grain boundaries, the continuous αGB cannot be effectively eliminated by traditional heat treatment. Thus, in this study, we develop a new heat treatment including beta solution + ultra-slow furnace heating up + traditional heat treatment, to eliminate continuous αGB in laser melting deposited Ti-5Al-5Mo-5V-1Cr-1Fe near β titanium alloy, and the microstructures and tensile properties are investigated. The results indicated that, after beta solution + normal heating up + traditional heat treatment, the continuous αGB still exists, and the elongation is still low about 7.5%. However, after beta solution + ultra-slow heating up + traditional heat treatment, there are almost no continuous αGB, and the elongation increases to 15.2%. The mechanism about the αGB formation during ultra-slow heating up process is simply revealed. Furthermore, this new heat treatment is also suitable to eliminate continuous αGB for laser melting deposited Ti17 alloy.
关键词： ductility,continuous grain boundary α phase,laser melting deposition,heat treatment,near β titanium alloys
更新于2025-09-12 10:27:22
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In-situ measurement of near-tip fatigue crack displacement variation in laser melting deposited Ti-6.5Al-3.5Mo-1.5Zr-0.3Si titanium alloy
摘要： Laser melting deposition (LMD) is an attractive additive manufacturing technique for fabricating titanium alloy components. A variety of distinct layer bands, heat affected bands (HABs), were found in the LMDed sample, which lead to a periodic fluctuation in the fatigue crack growth rate. In this paper, an in-situ fatigue testing was performed to investigate the crack tip opening displacement (CTOD) variation within a full loading cycle. Digital image correlation (DIC) technique was implemented for obtaining the displacement fields at the vicinity of the crack tip. The crack closure phenomenon is observed from the CTOD variation and the crack opening stress level is different between HAB and non-HAB zone. Another key difference between HAB and non-HAB zone is the value of CTOD when the crack is opening. Besides, the variation of the CTOD loop and its influence on fatigue crack growth rate were also discussed in detail.
关键词： Digital image correlation,In-situ,Crack tip opening displacement,Laser melting deposition
更新于2025-09-12 10:27:22
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Microstructure and mechanical properties of TiB2-reinforced 7075 aluminum matrix composites fabricated by laser melting deposition
摘要： In this study, we adopt laser-melting deposition (LMD) technology to fabricate TiB2/7075 aluminum matrix composites (AMCs), and we investigate in detail the effect of the TiB2 content on the microstructure, nano-hardness, compressive properties, and wear performance. We prepare experimental samples by using a laser power of 800 W and a velocity of 0.01 m/s, and the results are evaluated. It was observed that the reinforcement particles dispersed irregularly throughout the Al matrix as the TiB2 contents increased. The grain size of the fine-grain zone decreased appreciably by 31.9% from 8.41 μm (LMD sample without TiB2 reinforcement) to 5.73 μm. Furthermore, the AMCs with 4 wt.% reinforcement exhibited impressive mechanical properties, i.e., nanohardness of 1.939 Gpa, compressive strength of 734.8 MPa, and a wear rate of 1.889×10-4mm3/Nm. The wear resistance improved and the wear mechanism changed from adhesive wear to debris wear with the addition of TiB2 reinforcement.
关键词： Laser melting deposition,Aluminum matrix composites,Microstructure,Mechanical properties
更新于2025-09-09 09:28:46