Microstructure And Properties Of SiCp/Ti6Al4V Based On 3D Printing

Titanium alloys are widely used in various fields because of their high strength,high modulus,excellent heat resistance and corrosion resistance.However,due to the poor casting performance,poor wear resistance and high coefficient of thermal expansion of conventional titanium alloy,it can not meet the needs of today’s armored vehicles.Adding SiC particles to titanium alloy can not only prepare nano strengthening phases(TiC、Ti5Si4)with high modulus,high hardness and low expansion by in-situ reaction,but also enhance the specific modulus,specific strength,heat resistance and wear resistance of titanium matrix composites,and reduce the coefficient of thermal expansion.Selective laser melting technology has the characteristics of short development cycle,high machining accuracy and complex forming parts.The metal parts prepared by this technology have compact structure,uniform structure,small grain and second primary size,and the interface between strengthening phase and matrix is closely combined.The formed materials have good mechanical properties.Therefore,it is of great significance to prepare SiC Particles Reinforced Titanium Matrix Composites by selective laser melting technology to improve the properties of titanium matrix composites.The selective laser melting process parameters of SiCp/Ti6A14V composites were studied.The laser power(160～280 W),scanning speed(800～2000 mm/s)and scanning spacing(0.06～0.09 mm)were studied by single channel single-layer experiment and with printing size of 10mm×10mm×10mm block 3D printing experiment The influence of three main process parameters on the forming quality of titanium matrix composites was studied.The formation reasons of holes in the forming process were explored.The optimal combination of process parameters and the titanium matrix composites with the best comprehensive properties were obtained.The effects of SiC content on the phase,microstructure,mechanical properties and thermal expansion properties of titanium matrix composites were investigated by X-ray diffraction(XRD),optical microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM),microhardness tester,tensile tester and thermal expansion analyzer.The main conclusions are as follows.(1)With the continuous increase of laser power,the density of the sample increases continuously;with the increasing of scanning speed,the density first increases and then decreases;with the increasing of scanning distance,the density first increases and then decreases.Through the study of SLM forming volume fraction of 0.5vol.%SiCp/Ti6A14V composite,the optimal process parameters are obtained as follows:laser power P is 220W,scanning speed V is 1000mm/s,scanning spacing D is 0.07mm,layer thickness h is 0.03mm.SiCp/Ti6A14V composite samples printed by optimized process have high density and less internal defects.(2)It is found that TC4 alloy is mainly composed of α-Ti phase and β-Ti phase.After the introduction of SiC into TC4,a small amount of SiC reacts with Ti to produce TiC and Ti5Si4 phases,which are distributed in the crystal and play an in-situ strengthening role.With the increase of SiC volume fraction,the number of diffraction peaks,the intensity and the content of SiC phase increase gradually.However,when the content of SiC is 1.0vol.%,the phases of the composites areα-Ti、β-Ti、SiC、TiC and Ti5Si4.(3)It is found that there are mainly acicular α-martensite phase and β-columnar crystal in TC4 alloy.With the increase of SiC volume fraction,the acicular phase in the transverse structure of the sample decreases gradually,the direction and width of the molten pool become clear gradually,the β columnar crystal in the longitudinal structure decreases gradually,the outline of the stacked fish scale molten pool becomes clear gradually,and the interlayer bonding is tight.SEM and EDS data show that the distribution of nano TiC particles and micro SiC particles on different cross sections is different.The results show that tic and SiC are the main reinforcing phases in the transverse structure of the composite,and tic is the main reinforcing phase in the longitudinal structure.(4)The results show that with the increase of SiC content,the microhardness of Ti matrix composites increases at first,then decreases slightly,and then increases greatly,with the highest value of 425HV,which is 26%higher than that of TC4 in the same state.The tensile strength increases rapidly at first and then decreases gradually,and the elongation decreases generally.However,when the SiC content is 0.25%,the tensile strength can reach 1458.77MPa,which is 24%higher than that of TC4 in the same state.Compared with TC4 alloy,the coefficient of linear thermal expansion of Ti matrix composite fluctuates less with the increase of temperature.The SLM formed 0.25vol.%SiCp/Ti6A14V composite has the best comprehensive properties.