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Study on Formation Mechanism of Lamellar Microstructure and Friction and Wear Properties of TiAl Alloy

Author: GengMing
Tutor: SunDongLi
School: Harbin Institute of Technology
Course: Materials Science
Keywords: Ti-50Al heat treatment lamellar microstructure friction and wear
CLC: TG146.23
Type: Master's thesis
Year: 2008
Downloads: 38
Quote: 0
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Abstract


In the paper, Ti-50Al is successfully fabricated by the infiltration-reaction synthesis method, it is studied that influence of heating speed, temperature, time, cooling speed and other important facts on the microstructure and properties by OM, SEM, TEM and so on. A simple and efficient heat-treatment processing is determined to make Ti-50Al alloy with the fine and homogeneous full-lamellar microstructure. Besides, it is analyzed to the forming mechanism of lamellar microstructure. Furthermore, the properties and the mechanisms of friction and wear of Ti-50Al alloy in the different loads and sliding speeds are studied in the paper.The results show that macrostructure of Ti-50Al alloy appears to be free of porosity and homogeneous hardly with segregation. In terms of the study of heat treatment processing, it is found that the full-lamellar microstructures with grain sizes of about 150μm can be obtained after Ti-50Al alloy make short-time holding above 1400℃and then cooling slowly, and to use rapid-heating double-temperature heat treatment, the grain sizes can be refined to 30μm. During the experiment, the best heat treatment processing is that (rapid heating)1250℃×3h(air cooling)+(rapid heating)1400℃×5min(furnace cooling).The lamellar microstructure of Ti-50Al alloy is made of singleα2 plate and severalγplates.γphase is precipitated out ofαphase. By shearing mechanism, theγγinterface consists of four twin-crystal characteristic: twin, pseudo-twin, anti-phase and order domain doundary. And then these phases grow to the larger lamellars. Hereby it is observed thatγphase is precipitated out of phase boundary, finally forms fine lamellar. So while Ti-50Al alloy is holding at high temperature,γphase is precipitated out ofαphase, while holding at low temperature,γphase is precipitated out ofα2γandγγphase boundaries.The friction and wear tests of Ti-50Al show that wear loss of the full-lamellar microstructure for Ti-50Al alloy increases with load and sliding speed when sliding speed is lower than 1.0m/s, and friction coefficient is relatively invariable at about 0.5, wear mechanism is mainly abrasive wear. When the sliding speed is higher than 1.5m/s, the wear mechanism has changed to mainly oxidization wear and adhesive wear of the counterparts so that wear loss decreases significantly, and friction coefficient increases. Compared to as-cast Ti-50Al alloy, The Ti-50Al alloy with full-lamellar microstructure has better wear resistance, and friction stability at low sliding speed.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metallic materials > Non - ferrous metals and their alloys > Light non-ferrous metals and their alloys > Titanium
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