In this paper, the microstructure and properties of MX246A alloy laser double-sided welding were studied. Different alloy welding structures were obtained under different laser powers, and the fine-grain zone, columnar-grain zone, and equiaxed-grain zone in the welding structure were analyzed. According to the results of SEM, it was found that the width of the surface fine-grain zone was generally thin, which had little effect on the quality and properties of the welded joint. The quality and properties of the welded joint mainly depended on the proportion of columnar-grain zone and equiaxed- grain zone, as well as the grain size. Moreover, with the increase of laser power density, the number of columnar grains decreased, while the number of equiaxed grains increased. The grain size of equiaxed grains became smaller, and the structure became denser, resulting in better mechanical properties. The double-sided welding was subjected to high-temperature and room-temperature tensile tests. The Laser welding double-sided tensile properties test showed that the tensile strength was 555 MPa at room temperature and 400 MPa at 1000 °C under the laser power intensity of 1704 W/mm2 . The study revealed that MX246A alloy exhibited superior tensile properties and microhardness than the substrate, while the microstructure demonstrated excellent high-temperature durability.
In this paper, the IC10 alloy joints are prepared by laser welding. The effect of process parameters on thermal crack is discussed, and the formation mechanism of welding thermal crack in different types during laser welding of IC10 alloy are analyzed by micro means. The microstructure, element distribution and phase composition of the thermal cracks are studied. When the laser scanning direction is perpendicular to the grain growth direction of the substrate, the crack sensitivity is greater. With the increase of laser power and the decrease of shielding gas flowing, the crack sensitivity is also greater. A faster welding speed could cause thermal stress and increase crack sensitivity. The choice in an appropriate laser scanning speed range could effectively control the tendency of crack formation. According to the analysis of the formation mechanism of different cracks, the results of SEM and EDS showed that IC10 alloy was susceptible to crystallization cracking due to the high content of low melting point eutectic between grains and grain boundaries, and the tendency to produce liquefaction crack becomes greater when coarse carbides precipitate, both types of cracks belong to the thermal cracks caused by liquid films. In IC10 alloy, ductility dip cracking (DDC) is thermal crack caused by the sharp drop of intergranular plasticity, which is closely related to the state of grain boundaries and interstitial phase precipitated from grain boundary. The crack susceptibility of DDC cracks is easier to control than the above mentioned two type thermal cracks.
KEYWORDS: Interfaces, Aluminum, Titanium, Spatial light modulators, Temperature metrology, Chemical elements, Scanning electron microscopy, Chemical analysis, Thermal effects, Silicon
In this paper, Ti6Al4V/AlSi10Mg multi-material specimens were fabricated by selective laser melting (SLM). The influence of process parameters on the interfacial crack was discussed and the formation mechanism of interfacial crack under different process parameters was expounded through the simulation of temperature field. The microstructure, element distribution, phase composition and microhardness of the Ti/Al interface were investigated. The cooling rate and temperature gradient increased with the increase of laser power and scanning speed, which easily led to the interfacial crack. Using chess scanning strategy and increasing the preheating temperature of the substrate could effectively reduce the cooling rate, so as to reduce the stress and avoid the interfacial crack. There was a good metallurgical bonding between titanium alloy and aluminum alloy, the typical molten pool morphology could be seen at the interface. In the heat affected zone near the interface, the grain size of aluminum alloy became coarsen, because the lower thermal conductivity of titanium alloy and heat accumulation in the process of forming aluminum alloy. There were needle-like intermetallic compounds (IMCs) at the interface. According to the results of SEM and EDS, the thickness of IMCs was about 2-4 μm, and the composition of IMCs was mainly TiAl and TiAl3. The results of XRD showed that there were not only Ti3Al, TiAl, TiAl3 IMCs but also TiSi2 ceramic phase at the interface, which made the microhardness of the interface reached as high as 679 HV.
In the paper, the effects of porosities and average particle sizes of powder layer on light absorption during SLM process were investigated, in which closed-packing models based on Horsfieled’s filling method were established and light absorption was simulated using ray tracing based on laser-material interaction mechanism. The results show the absorption of powder layer of Ti6Al4V alloy is higher than 70%. The decrease of porosity of powder layer benefits to improve the absorption, while the absorption tends to decrease if porosity decreases to a certain value due to the reflection. The decrease of average particle size of powder particles benefits also to improve the absorption. If the light irradiates at positions with different particle arrangements, the absorption behavior changes with irradiation condition whether there occurs the multi-reflection. The above research provides theoretical basis for preparation of new powder materials, their parameter developing for SLM technology and even the properties regulation of SLM fabricated component.
A 3D transient finite element model of Inconel 718 nickel-based superalloy processed by selective laser melting was developed to study the heat flux in the molten pool under the condition of different process parameters and its effect on the temperature field and the shape of molten pool, in which a solid heat transfer module and a laminar flow module in the finite element simulation software COMSOL Multiphysics was applied. In the simulation several special phenomenon characterized with SLM process was considered, such as the interaction between the laser and material with stochastic porosity distribution on powder bed, and the nonlinear change of thermophysical properties due to the state change of material and the influence of the Marangoni effect in the molten pool. The results show that the Marangoni effect caused by the surface tension of molten pool makes the convective heat flux play a leading role in the heat transfer process in the molten pool, and its depth/width ratio is changed by changing the magnitude and direction of the heat flow, what determines the shape of molten pool. The increase in laser power or reduced scanning speed can increase the heat input per unit time, and then lead to a Marangoni convection enhancement within the molten pool, thus enlarge the size of the molten pool. The experimental results are in good agreement with the simulation results.
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