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.
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