Preparation Of Ti-Al-Al₂O₃ Nano-material By Mechanical Activation Sintering In Situ

Intermetallics get great attention of materials researcher, because of interesting and particular synthesis capability such as low density, high intension, high melting point and excellent anti-wriggle, anti-oxidation, anti-combustion, and so on. Among of it, Ti-Al intermetallics is high-temperature structural materials, having more progress foreground, which is abroad applied on navigate, spaceflight, automobile,et al. While, Ti-Al intermetallics at present mostly have shortcomings such as crass crystal grain, low room-temperature tractility and bad processability. The crystal grain of Ti-Al intermetallics is mostly decided by preparation method and process technics. If choosing a good method and proper process, we could get fine crystal grain and excellent capability Ti-Al intermetallics.This research item is root in Hubei province 10^th five-year keystone tackle item—Electricity Pulse Processing Block Nano-Materials and Parts (item No. 2001AA101B02). It mainly uses Mechanical Activation-Pulse Current Sintering (MA-PCS) and Mechanical Activation-Spark Plasma Sintering (MA-SPS) technics,with synthesis technique in situ, to process Ti-Al base intermetallics.The two process methods all get nano-powder by mechanical milling. In planet type ball milling machine, mixing milling micro-meter grade Ti powder, Al powder and nano-meter grade Al₂O₃ powder, quickly gaining nano-meter grade Ti-Al-Al₂O₃ mixed fine powder. Through researching reaction course and basic mechanism of ball milling, we can get nano-meter grade activating powder by ball milling, making crystal gain fine at the same time of mechanical activation (MA). The effects of Al₂O₃ during ball miling Ti and Al powder, mainly are advancing nano-course and mechanical activation course of powder, holding element powder state of raw material and enhancing out-powder rate of ball milling and so on.Using the mixing ball milling type of Ti-Al-Al₂O₃ can gain nano-powder, providing good powder material for after sintering course. Through X-ray diffraction (XRD), scanning electron microscope (SEM) coupled with energy-dispersive spectroscopy (EDS) and transmission electron microscope (TEM) analysis, under this research condition, Al₂O₃ mainly have so effects during ball milling Ti and Al powder: (1) Al₂O₃ promotes the nano-course of powder and accelerates powder fine. Under this research condition, the average crystal gain size of Ti and Al powder can be 25-35 nm after 20 hours ball milling. The efficiency of making nano-material is very high. (2) Al₂O₃ promotes mechanical activation course and holding element state of raw material, while depositing a great deal of activation energy. Under this experiment condition, appending 5wt% Al₂O₃ can make powder fine to nano-meter at th same time of no creating newintermetallics. It can restrain the reaction among element powders. At while, nano-powder has more ratio-surface area, so depositing a great lot of surface activation energy. The surface activation energy have not consume out for changing to reaction drive of ball milling alloying. This energy becomes to drive power together with sintering outside forces, such as temperature, current and press, et al.From this, AI2O3 has the effect of course control reagent. So, the mechanical activation effect of A12O3 is great. It also is one characteristic of this research. (3) A12O3 can elevate ball milling powder rate, and enhance milling efficiency very much, advancing milling output. Under this condition, joining 5wt% AI2O3 can advance milling powder rate to more than 98%.The milling powder rate is very high ever no ethanol, at the same time Ti and Al keep element state to nano-powder. The joining AI2O3 has the effects of making fine crystal grain to nano-powder, restraining alloying and making for mechanical activation, and so on. The XRD and TEM show that, under this experiment ball milling parameter (ball-powder ratio is 10:1, rotate speed is 120 rpm, milling time is 20 hours), AI2O3 powder material (grain size is 200-500 nm) is made fine to 30nm average crystal gain size, Ti (gain size is 74//m) and Al (gain size is 37/um) powder material both are made fine to nanometer gain. The nano-powder appears as linking pieces, and every gain is made up of many fine crystal gains. The DTA analysis shows that, T1AI3 is created from solid state reaction before the melting temperature of Al, and the reaction of most midway phase (TiAl3^ TiA^ TiAK Ti3Al) happen during 730-950°C. The pressing characteristic of ball milling powder shows that, the consistency is 47.58% as 40MPa pressing, while 77% consistency as 640MPa pressing. To get higher consistency, it needs GPa grade high pressure.Getting fine element nano-powder by mechanical activation, settles base for the sintering in situ of element powder, which is easy to improve after alloy component design. In this research, mechanical activation is different with mechanical alloying during general mechanical ball milling. Although the shortened forms both are MA, meanings are completely different.After getting element nano-powder by mechanical activation (MA), we research the Ti-Al-Al2O3 block nano-material preparation technics by Pulse Current Sintering (PCS) and Spark Plasma Sintering (SPS). PCS method uses self-produce equipment, while SPS method uses SPS sintering machine of Japan Sumitomo Coal Mining Co. Ltd. The main analysis means are phase analysis, XRD, SEM (EDS), mechanics capability analysis and break-face SEM analysis, and so on.Quick preparation of TiAl3 and TiAl intermetallics by MA-PCS is researched. Tosynthesize Ti-Al-AbC^ block nano-material in low cost, T1AI3 and TiAl intermetallics are main research objects. Research advances the reaction model of Ti-Al base intermetallics preparation by MA-PCS sintering. The reaction between Ti-Al is related with chemistry measure ratio, so the reaction courses of T1AI3 and TiAl during MA-PCS sintering are different. Ti-75at%AI and Ti-75at%Al-5wt%AbO3, chemistry measure ratios both are TiAl3, Ti and Al directly reacts to T1AI3, then the finally intermetallics is TiAl3 single phase. As while, Ti-50at%Al and Ti-50at%Al-5wt%Al2O3, chemistry measure ratios both are TiAl, have some moments during sintering. The midway phases are TiAl3, T1AI2 and Ti3Al, and then the ideal finally result is mixing intermetallics making up of TiAl and Ti3Al duplex phase. During sintering, AI2O3 has the effect of restraining crystal gain quickly grow up.The MA-PCS research shows that, the reaction course of TiAl base intermetallics is complex, having many midway phase reaction, so take it as research emphases of MA-SPS. Thinking over TiAl mainly exists at rich Ti area, the SPS sintering of Ti-50at%Al and Ti-47at%Al joining same AI2O3 is researched.Preparation of Ti-Al-A^C^ block nano-material by MA-SPS is researched. There are two TiAl base intermetallics such as Ti-50at%Al-10wt%Al2O3 (TAA series) and Ti-47at%Al-10wt%Al2O3 (TAB series) . Getting fine Ti-Al- A12O3 nano-powder by mechanical activation, then quickly sintering to block intermetallics materials using SPS sintering machine.Searching optimize sintering parameter by matrix method through milled TAA series powder, and analyzing the effect of parameters to consistency. The result shows that, sintering temperature is main effect factor to consistency, as while micro-rigidity HV has consistent relation with consistency.When TAA powder is SPS sintered at 650°C, Ti-Al phases are TiAl3 and a few Ti. As while at 800 °C, the Ti-Al phases are TiAl, TiAl3, a few TiAl3 and TiAl2. When TAB powder is sintered at 850°C, Ti-Al phases are TiAl and TiAl3, becoming duplex phase TiAl base alloy. The midway phase TiAl3 disappear at 700-750°C, and TiAN disappear at 800-850°C. The basic reaction course is Ti+Al-^Ti+TiAl3—TiAl+Ti3Al+TiAl3+TiAl2 ^TiAl+Ti3Al+TiAl2-*TiAl+Ti3Al. Linking with SPS sintering curve, XRD, phase analysis, SEM results, advancing TiAl base alloy preparation reaction model by SPS. Under this condition, the midway phases are TiAl3 and TiAk The finally island shape a phase directly changes to a2-Ti3Al phase, not a 2/7 layer piece.The room-temperature bend intension and draught intension of TAB9 SPS sintering sample are not high. The causes have experiment factor, consistency factor and AliO3 factor. Microcosmic break-face SEM analysis shows that, main rupture along crystaldisplaying main brittleness, as while a little through crystal rupture showing should have a little tractility.The oxidation behavior of SPS sintering Ti-47at%Al-10wt%Al2O3 is investigated in the temperature range of 800°C-1000°C for 20 hours exposure in air. The oxidation kinetics of Ti-47at%Al-10wt%Al2O3 in the emperature range of 800°C-1000°C follows the parabolic law, and the parabolic constants at 800°C, 900°C and 1000°C are 2.36 X 10"11 kgW1, 6.16 X 10"11 kg2mV and 1.79 X 10"10 kg2mV respectively. The research shows that, joining AI2O3 is not only in favor of mechanical activation, but also advances the oxidation resistant very good.All in one word, this thesis mainly research preparation of Ti-Al base intermetallics by Mechanical Activation-Pulse Current Sintering (MA-PCS) and Mechanical Activation-Spark Plasma Sintering (MA-SPS) technics coupled with synthesis technique in situ. The research results have great help to more understand the reaction mechanism of Ti-Al-A^C^ and the structure character of materials, providing new research route to preparation Ti-Al base high-temperature structure materials.