| TiAl based alloy is expected to develop into a new generation of light heat resistant metal structure material,because of its advantages of low density,high temperature strength,high temperature resistance and good resistance to creep.Among them,the gamma-TiAl alloy has become the forefront candidate for high-temperature structural applications.It has low density,high specific strength,high specific stiffness,good thermal stability and excellent high temperature mechanical properties.A small amount of Nb addition can increase oxidation and creep resistance,and the addition of 5% and 10% can increase the high temperature strength.But the brittleness and high temperature deformation resistance of high Nb-TiAl alloy are very high,and the alloy structure obtained by casting method is coarse and inhomogeneity.In this paper,the preparation of Ti-45Al-8.5Nb(at.%)alloy was prepared by powder metallurgy process.The mechanical ball milling process,the room temperature pressing law,the vacuum hot pressing sintering process and the microstructure and mechanical properties of the obtained alloy were systematically discussed.Ti/Al/Nb composite powder was refined by mechanical ball milling.The powder morphology,particle size,uniformity and alloying of these composite powders obtained by ball milling parameters of different control agents,ball ratio,ball milling speed and ball milling time were analyzed.The results show that the control agent can continuously refine the powder.The effect of powder crushing is obviously strengthened when the ratio of ball to material is 20:1.The ball milling energy reaches the highest when the ball milling speed is up to 400 rpm and the particle size of ball milling powder decreases first and then increases with the extension of time.The minimum particle size can reach 4.78?m.The particle size of ball milling powder decreases with the extension of time,and the minimum particle size can reach 7.64?m when the ball milling speed is up to 300 rpm.The ideal phenomenon of powder milling is to balance the powder crushing and cold welding to break the powder particles to a minimum.The compacting law of the powder after ball milling with a control agent and a ball material ratio of 20:1 is studied.The press curve is fitted linearly by Huang Peiyun's double logarithmic pressing equation.It can be obtained from the cold pressure that the relationship between the density of powder and the pressing pressure is basically the same under different ball milling parameters.When the ball milling speed is 300 rpm,the powder particle gradually decreases with time,the hardening exponent decreases gradually,the minimum is 1.808,the compression modulus increases gradually and the maximum is 22.757 MPa.When ball milling speed is 400 rpm,when the ball milling time is 10 h,the hardening exponent reaches the lowest,1.859,and the modulus of compaction reaches the maximum,20.472 MPa.The pressing pressure and height diameter ratio of the pressing process will also have a significant effect on the cold pressed density of the material.A vacuum hot press sintering experiment was carried out on a Ti/Al/Nb three element composite powder with a ball material ratio of 20:1,a ball milling speed of 400 rpm and a ball milling time of 10 h at a temperature range of 1050?-1450?.The experimental results show that the billets sintered at different temperatures are composed of Ti3 Al,TiAl and a small amount of Ti2 Al C phase.With the increase of sintering temperature,the relative density of billet increases gradually,and the maximum can reach 98.28%.A typical duplex structure is formed when the temperature reaches 1350?.After holding 2h for heat preservation,the highest microhardness can reach 428.156 HV,the maximum compressive strength at room temperature can reach 1725.744 MPa,and the highest elongation can reach 14.089%. |
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