Study On Process And Microstructure Evolution Of Tial Alloy Fabricated By Laser Deposition Manufacturing

TiAl inter-metallic alloy,with high specific strength,specific elastic modulus and excellent mechanical properties at high temperature condition,is a new developed structural material and has shown huge potential application in aerospace industry.However,poor ductility and low elongation rate(less than 3%)at room temperature,serious brittleness and bad machining properties obstacle TiAl components production.In order to overcome the shortcomings of the TiAl alloy in forming process and explore an innovative fabricating method,Laser Deposition Manufacturing(LDM)process and microstructure evolution of TiAl were investigated based on the most widely used Ti4822 alloy(Ti-48Al-2Cr-2Nb,at%)in present paper,parameters for LDM processing and post heat-treatment are analyzed for the deposited material.It turns out that the as-deposited ?-TiAl appeared unique microstructure,i.e.,fine lamella of ?,?2 and B2 were embodied in the equiaxed primary grains;when the scanning speed keeps constant,with the laser power increasing,the diameter of primary equiaxed grain increases gradually,the percentage of fine lamella ?2 and B2 phase increases gradually,on the contrary,the ? phase content decreases,and the micro-hardness of the samples increases gradually;when the laser power keeps constant,with the increase of scanning speed,the diameter of primary equiaxed grain reduces gradually,the percentage of fine lamella ?2 and B2 phase reduces gradually,while,the ? phase content increases,and the micro-hardness of the samples increases gradually.According to comprehensive analysis,the optimized processing parameter with laser power at 1200 W and scanning speed at 7mm/s is proposed.? and ?2 are the majority phase constitution after heat treating,and a tiny amount of B2 could barely found.Duplex microstructure compositing block ? and mixture of lath-like?+?2 is obtained by solution treated at 1260?,and in the XRD pattern,diffraction peaks of ?are stronger in intensity and much in amount than those of ?2 slightly,which means these two phases share almost equal percentage in the alloy;near lamellar structure are obtained bysolution treated at 1330?,volume percentage of ? is bigger than ?2 by comparing the peaks' intensity and number in the XRD pattern;full lamellar microstructure are obtained after solution treated at 1350 ?,and the ?2 volume percentage increase slightly compared with treated at 1330 ?.The micro-hardness of the solution treated samples decreases with the increasing of heat-treatment temperature.Major phase,? and ?2,and minor phase,B2,could all be found in samples which experienced hot iso-static pressing(HIP)followed by solution treated at 1260?,1330? and1350 ?,respectively.Intensity and ratio of diffraction peaks of ? phase in XRD pattern increases with the solution treated temperature increasing,on the contrary,those of ?2 in the XRD pattern decrease,which means the volume percentage of ? increases with the increasing of solution temperature,and the volume percentage of ?2 decreases with the increasing of solution temperature,B2 is still in trace amount.Comparing the HIP+solution and solution results,the microstructure shows no obvious variation,except for the increasing of lamellar size in embodied in the primary grain.The micro-hardness increases with increasing of solution temperature after HIP treating,and is bigger than that of sample which experienced only solution treating at same temperature.