Study On Investment Casting Property And Microstructure Of Ti-48Al-2Cr-2Nb

As the most promising direction of aeronautics and astronautics, Ti-Al based alloyhave excellent performance, such as high strength, low density, high strength, corrosionresistance,etc.Compared with other processing methods, investment casting has itsunique advantages, but it has a poor fluidity, and the shrinkage is bigger. So it is easy toproduce defects in the process of casting porosity, such as shrinkage cavity, shrinkageporosity and deformation. So the experiment by the grid method explore the effect fromshell material to filling ability of Ti-48Al-2Cr-2Nb alloy, measures linear shrinkagerate and residual stress of it under different process castings conditions with differentshapes and sizes, and observes the effects of various factors on the castingmicrostructure defects, analysis the formation of the cracking.After adding a certain volume percent of plant powder in the shell material,thecoefficient of thermal conductivity of shell reduces,and the porosity increases, so do thealloy’s fluidity in the shell. Analysis of different effect from shell material for the fillingability, it is founded that the texture of alloy in the shell added plant powder becomesdense, numbers of porosity reduce, volumes change, and segregation phenomenon alsoweakened.The shape, size and structure of casting will affect the line shrinkage rate of thesolidification in the process of castings, among them, the thickness hav a importanteffect on free shrinkage of castings. As for hindered contraction, its size and shape had agreater influence on the shrinkage rate. The residual stress of casting whose space like"I" affected by many factors. Among them, affect of thickness, size, type of castingand shell preheat temperature is smaller,and centrifugal rotational speed, the alloypouring temperature and shell material have a large influence.Analysis the microstructure of various process conditions,it is founded thatdifferent process have different influence. The influence of the centrifugal rotationalspeed is mainly manifested in the primary phase volume fraction，alloy pouringtemperature is embodied in the influence of grain size, primary phase volume fractionand porosity，shell material mainly reflected on the grain size and porosity. Afteranalysis casting cracking phenomenons, it is found that "I" type casting whose shellpreheat to200℃and the pouring temperature is1750℃and all of the "L" type casting have hot crack, other cracking because of stress concentration affected by theporosity or other defects, it belongs to brittle fracture at low temperature.