| HAN Bin-long,TIAN Xiao-dong,LU Peng-jun,QI Xian.Effects of Y2O3 on Pack Boronizing of TC4 Titanium Alloy[J],52(8):451-457 |
| Effects of Y2O3 on Pack Boronizing of TC4 Titanium Alloy |
| Received:August 04, 2022 Revised:February 08, 2023 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2023.08.041 |
| KeyWord:boronizing pack cementation Y2O3 catalytic diffusion |
| Author | Institution |
| HAN Bin-long |
Engineering Research Center of Transportation Materials of Ministry of Education, School of Materials Science and Engineering, Chang'an University, Xi'an , China |
| TIAN Xiao-dong |
Engineering Research Center of Transportation Materials of Ministry of Education, School of Materials Science and Engineering, Chang'an University, Xi'an , China |
| LU Peng-jun |
Engineering Research Center of Transportation Materials of Ministry of Education, School of Materials Science and Engineering, Chang'an University, Xi'an , China |
| QI Xian |
Engineering Research Center of Transportation Materials of Ministry of Education, School of Materials Science and Engineering, Chang'an University, Xi'an , China |
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| Abstract: |
| In order to accelerate the growth of the boronizing layer on TC4 titanium alloy prepared through pack cementation process, the effects of adding Y2O3 into the pack mixture were investigated. The TC4 matrix was boronized at 1 050 ℃ for 8 h with the pack mixtures composed of NaF, B and Al2O3 powders with Y2O3 free and Y2O3 addition of 1, 3, 5 and 7 wt.%. The SEM, EDS, WDS and XRD instruments were applied to analyze the morphology, composition and constituent phases of the boronizing layer. And the surface hardness and the friction coefficient of the boronizing sample were evaluated through a microhardness tester and a ball and disc type friction and wear tester, respectively. When adding 1wt.%~7wt.% Y2O3 into the pack mixture, the boronizing layer obtained on the TC4 substrate was composed of the dense and continuous TiB2 layer and the TiB whisker diffusion layer, which had the same structure as the boronizing layer prepared in the Y2O3 free pack mixture. The catalytic diffusion effect of Y2O3 on the boronizing layer growth was related to the amount of Y2O3 addition into the pack mixture. Adding 1wt.%~3wt.% Y2O3 into the pack mixture increased the thickness of the boronizing layer by up to 40.24% compared with that of the boronizing layer prepared in the Y2O3 free pack mixture. The best catalytic diffusion effect of Y2O3 on the boronizing layer growth occurred in the pack mixture with 3wt.% Y2O3 addition. Nevertheless, adding 5wt.%~7wt.% Y2O3 into the pack mixture restrained the growth of the boronizing layer. The EDS analysis showed that Y atoms could diffuse into the boronizing layer, and the content of Y element in the boronizing layer was about 0.01at.% to 0.34at.%. which increased with the rising of Y2O3 content in the pack mixture. Thermodynamics analysis revealed that Y2O3 could take part in the reactions of the pack mixture to form reactive Y atoms. When Y atoms were slightly incorporated into the boronizing layer, it prompted the matrix lattice distortion and resulted in a certain number of vacancies, dislocations and other defects, which provided a fast diffusion channel for the reactive B atoms and played the positive effect of catalytic diffusion. When too much Y2O3 existed in the pack mixture, however, a large number of Y atoms would be adsorbed on the surface of the TC4 substrate and form a thick aggregated layer to impede the diffusion of B atoms. By using the pack mixture with 3 wt.% Y2O3 addition, the surface hardness of the boronizing layer reached to 990.8 HV0.1, which increased by 35.54% compared with that of the boronizing layer prepared in the Y2O3 free pack mixture, and the friction coefficient of the boronizing layer declined to 0.15, which reduced by 28.57% compared with that of the boronizing layer prepared in the Y2O3 free pack mixture. In conclusion, adding an appropriate amount of Y2O3 into the packing mixture is an effective way to obtain the boronizing layer with high growth rate, high hardness and low friction coefficient on the TC4 alloy surface. |
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