- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Influence of multiple laser peening on vibration fatigue properties of TC6 titanium alloy
摘要： In this study, typical TC6 titanium alloy was taken to investigate the effects of multiple laser peening (LP) on the vibration fatigue properties and microstructural evolution. The vibration fatigue experiments were conducted, while the vibration fatigue life of the specimens before and after LP was compared and the fracture morphologies were observed by scanning electron microscopy (SEM). In addition, the measurements of residual stress and microhardness were carried out. The microstructures produced by different treatments were also characterized by transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD). The experimental results indicated that multiple LP could indeed enhance the vibration fatigue properties of TC6 titanium alloy. Comparing with the investigated specimen without LP, the vibration fatigue life of the specimen subjected to 5 times LP increased by 105.2%. Meanwhile, after 5 times LP, the surface residual stress transformed from tensile stress (+26 MPa) to compressive stress (?485 MPa), and the surface microhardness was 428 HV, which increased by 32.9% compared with the untreated sample. Additionally, high-density of dislocation and deformation twin were also generated after multiple LP. The improvement of vibration fatigue properties was attributed to the rewarding compressive residual stress and the beneficial microstructural evolution induced by multiple LP.
关键词： TC6 titanium alloy,Laser peening,Vibration fatigue properties,Microstructure evolution,Residual stress
更新于2025-11-14 17:04:02
-
Phase field modeling of grain boundary migration and preferential grain growth driven by electric current stressing
摘要： A phase field model incorporating the electrostatic free energy and the grain orientation effect is developed and employed to study the grain boundary migration and preferential grain growth in widely used beta-tin (β-Sn) under electric current stressing. The directional migration of grain boundaries and the preferential growth of the grain with its orientation having low electrical resistivity along the electric current direction are theoretically clarified. In a bicrystal system containing a circular grain, the shrinkage velocity and morphology changes of grains are dominated by the competition effect between the grain boundary energy and the electrostatic free energy; in particular, the high-density electric current can induce the instability of grain morphology evolution. Moreover, grain morphology evolution leads to the change of the voltage across the β-Sn system; it is found that the voltage decreases over time in a tricrystal system, while the variation of the voltage across the bicrystal system is related to the above-mentioned competition effect. The proposed model and results provide insights into the orientation-related microstructure evolution under electric current stressing.
关键词： preferential grain growth,electric current stressing,microstructure evolution,grain boundary migration,beta-tin,phase field model
更新于2025-09-23 15:21:21
-
Effect of laser parameters on microstructure and phase evolution of Ti-Si-C composites prepared by selective laser melting
摘要： In this paper, blended Ti/SiC powder was processed by selective laser melting (SLM) method to prepare a novel kind of Ti-Si-C composite. Microstructure, elements distribution and phase evolution of Ti-Si-C composites fabricated by SLM were studied. SEM, EDS, TEM and XRD were performed to evaluate the microstructure and phase evolution during the SLM process. The results showed that processing parameters significantly affected the microstructure and element distribution of the samples. It was found that higher laser energy density could promote the densification process and hence suppress balling phenomenon of Ti-rich phases. At the micro-level, the microstructure could be classified into the dense area and the porous area, which was closely related to the redistribution of elements. The phases obtained by the SLM process were composed by TiCx, TiSi2, Ti5Si3, and Ti5Si4, which appeared in different microstructures. The results indicated that composites with different phases and microstructure could be obtained by merely modifying laser processing parameters, which could give experimental guidance for the fabricating of gradient Ti-Si-C composites by selective laser melting without additional apparatus on powder feeding.
关键词： Microstructure evolution,Phase evolution,Ti-Si-C composite,Selective laser melting
更新于2025-09-23 15:21:01
-
Laser polishing of additively manufactured Ti-6Al-4V: Microstructure evolution and material properties
摘要： Laser polishing of metals consists of irradiating the part’s surface with a laser beam, thus generating a molten layer that is redistributed and resolidified to create a surface with reduced roughness. However, the process is also characterized by an instantaneous formation of heat-affected zones with consequent microstructural changes that influence the mechanical properties. In order to understand the microstructural evolution during laser polishing of Ti-6Al-4V laser-based powder bed fusion samples, a thermal model is applied in the current study to predict the dimensions of the melted zones and the heat-affected areas. Furthermore, the results obtained through simulations are discussed and compared to the experimental data, thereby establishing the validity of the process models. Finally, the experimental studies also include the evaluation of material hardness and residual stresses after laser polishing.
关键词： laser polishing,thermal model,material properties,additive manufacturing,microstructure evolution
更新于2025-09-23 15:21:01
-
Densification behavior, microstructure evolution, and tensile properties of selective laser melting additive manufactured TiB <sub/>2</sub> /AlSi10Mg composite
摘要： The fabrication of TiB2/AlSi10Mg composites by selective laser melting (SLM) additive manufacturing has been conducted. The influence of laser processing parameters on the densification behavior, microstructure evolution, and tensile properties of the SLM-processed composites is addressed. With the increase in laser volume energy density, the densification rate increased and reached 99% at a laser speed of 1000 mm/s. Meanwhile, the TiB2 particles underwent a partial melting behavior with the formation of an irregular pattern in the solidified part and complete melting with the smooth surface of the reinforcing particles as the laser volume energy increased. The cellular-dendritic microstructure and the width of the eutectic phase of the as-fabricated composites were significantly refined due to the high cooling rate and complete melting of the reinforcing particles as the nucleation sites using the laser energy density of 117 J/mm3. Therefore, the micro-hardness, ultimate tensile strength, yielding strength, and elongation of the as-fabricated TiB2/AlSi10Mg composites obtained in this process condition were 131.3 HV0.2, 375 MPa, 260 MPa, and 3.1%, respectively, which were significantly higher than those of the unreinforced AlSi10Mg alloy.
关键词： tensile properties,aluminum-based composite,selective laser melting,microstructure evolution
更新于2025-09-23 15:21:01
-
Analytical mechanics modeling of residual stress in laser powder bed considering flow hardening and softening
摘要： Residual stress builds up during the fabrication of components via laser powder bed fusion (L-PBF) process which causes parts to fail due to the crack initiation and growth, low fatigue life, and fall outside of the specified dimensions. During the thermal loading, the grain size affected by strain hardening and flow softening is altered at the subsurface through dynamic recrystallization (DRx) and subsequent recovery. The yield strength of the alloys is largely determined by the size of nucleated grains, and it has a substantial influence on flow stress and residual stress build-up. In this work, a physics-based analytical model is proposed to predict the residual stress affected by the strain hardening, flow softening, and microstructural evolution during L-PBF process with IN718 as a material system for exploration. The temperature field is predicted using a transient moving point heat source approach. Due to the non-uniform heating, materials experience high thermal stress which may exceed the yield strength of the material. The thermal stress is obtained from Green’s functions of stresses due to the point body load. A material constitutive flow stress model known as Johnson-Cook is used to determine the yield surface. This flow stress model is modified to incorporate the effects of flow softening and grain size. The dynamic recrystallization and grain refinement models are used to calculate the grain size using recrystallized volume fraction from nucleation and growth rates. As a result of the cyclic heating and cooling and the fact that the material is yielded, the residual stress build-up is precited using incremental plasticity and kinematic hardening behavior of the metal according to the property of volume invariance in plastic deformation in coupling with the equilibrium and compatibility conditions. Results from the analytical residual stress model showed good agreement with X-ray diffraction measurements used to determine the residual stresses in the IN718 specimens built via L-PBF.
关键词： Residual stress,Microstructure evolution,Strain hardening,Flow softening,Laser powder bed fusion
更新于2025-09-23 15:19:57
-
Formation Mechanism of Dilute Region and Microstructure Evolution in Laser Solid Forming TA15/Ti2AlNb Dual Alloy
摘要： TA15/Ti2AlNb multiple-layer samples and a dual-alloy sample were fabricated by laser solid forming (LSF) in this study. The formation mechanism of the dilute region and microstructure evolution of the dual alloy were analyzed. The results con?rmed a “step” distribution of the composition among several initial layers in the multiple-layer samples, which can be explained by calculating the ratio of the remelted zone to the deposited Ti2AlNb zone in each deposited layer. However, the “step” compositional distribution disappears, and the compositional variation tends to be more continuous and smooth in the TA15/Ti2AlNb dual-alloy sample, which is attributed to alloy elements’ di?usion at the subsequent multiple re-melting and the longer thermal cycle. The macrostructure of the TA15/Ti2AlNb dual-alloy sample consists of epitaxially grown columnar prior β grains at the TA15 side and equiaxed grains at the Ti2AlNb side, while the microstructure shows a transition of α+β→α+α2 +B2+O with increasing amounts of Ti2AlNb, leading to the microhardness also changing signi?cantly.
关键词： dilute region,microstructure evolution,laser solid forming,TA15/Ti2AlNb dual alloy
更新于2025-09-19 17:13:59
-
Modeling of thermal behavior and microstructure evolution during laser cladding of AlSi10Mg alloys
摘要： An improved three-dimensional finite element model has been proposed for studying the thermal behavior and microstructure evolution during laser cladding of AlSi10Mg alloys. Different material properties between AlSi10Mg powders and AlSi10Mg alloys are distinguished from the experiment and theoretical calculation to provide more reliable material parameters for simulation. In order to investigate the melting and solidification process during the formation of cladding layers, a temperature selection judgment mechanism is established to simulate the evolution of AlSi10Mg powders from the powder state to melting state and alloy state. In addition, to simulate the complex thermal behavior associated with powder particles and the voids between particles, a simplified exponential attenuation model is used for correcting the heat source. A complex asymmetric heat source considering about the different material properties and laser absorptivity on both sides of the remelting zone is used for multi-track cladding process. By simulating the temperature distribution of molten pool, the improved FEM could be used to predict the geometric shape of cladding layers (ignoring the effect of melting flow) and the temperature history. The simulation results show that the heat tends to diffuse to the unmelted powder owing to the asymmetric heat source during multi-track cladding, which leads to the asymmetry of cladding layers along the width direction. Based on the results of the temperature field simulations and the solidification characteristics of AlSi10Mg powders, the temperature gradient (G), solidification growth rate (R), cooling rate (G*R) and G/R are investigated to predict the morphology and size of the solidification microstructure under different laser scanning parameters. The scanning speed mainly determines the cooling rate during the laser cladding process, which results in different microstructures. Higher scanning speed leads to higher cooling rate, corresponding to a finer microstructure. Coarse dendrites are generated at the bottom of the molten pool, while finer dendrites are formed at the top.
关键词： Simulation,Microstructure evolution,AlSi10Mg alloy,Laser cladding,Thermal behavior
更新于2025-09-16 10:30:52
-
Operando X-ray diffraction during laser 3D printing
摘要： Laser based additive manufacturing allows to build a designed shape layer-by-layer, offering versatility and flexibility to many metallurgical sectors. The fast cooling rates and repeated heat cycles depending on the laser and scanning parameters are not easily measurable with conventional methods. Thus, advanced predictive computational simulations, required to reduce trial and error lead time, are difficult to validate. A newly developed in operando X-ray diffraction device implemented at a synchrotron beamline, taking advantage of the high brilliance and the fast detectors available, brings the missing link with numerical methods. By performing operando experiments on Ti-6Al-4V with different printing parameters, the temporal evolution of the low and high temperature phases are followed, the heating and cooling rates are measured for the powder and the solid material; and the formation of residual stresses in the b phase is demonstrated. Moreover it is shown that the parameter that has the largest influence on the evolving microstructure is the scanning strategy, introducing a size effect related to the scanning length.
关键词： microstructure evolution,operando X-ray diffraction,scanning strategy,Laser based additive manufacturing,Ti-6Al-4V
更新于2025-09-12 10:27:22
-
Analysis of the fracture mechanism at cryogenic temperatures of thick 316LN laser welded joints
摘要： Laser welding of modified 316LN steel with a thickness of 20 mm was conducted using a YLS-20000 fiber laser. The microstructure of the weld joint was characterized and tensile and fracture toughness tests were carried out. The microstructure evolution of the fracture specimens was studied systematically to elucidate the fracture mechanism. The weld was composed of the single austenite phase and was characterized by cellular and columnar grains, and the grain size became coarser with a weak orientation. The Rm values of the laser welded joints were almost equal to that of the base metal both at RT and 4.2 K, and the fracture surfaces were featured by ductile fracture with quantities of dimples and microvoids. The fracture toughness of the weldments decreased to ?84% of that of the parent metal at 4.2 K. Enhancement of the fracture toughness was attributed predominantly to the presence of twins and to the fine grain size, and the reduction was caused by the partially stress-induced phase transformation of the austenite to martensite. The synergistic effects of these factors result in a favorable improvement in the fracture toughness of the weldment.
关键词： Fracture mechanism,Mechanical properties,Thick plates,Laser welding,Cryogenic temperature,Microstructure evolution
更新于2025-09-12 10:27:22