摘要
本文对Al-Ti-CaC_2反应体系进行了热力学计算，实验验证了原位反应方法合成TiC颗粒的可行性；采用Al-Ti-C-CaC_2增强体系及原位合成反应方法制备了TiC_p/Al中间合金，利用中间合金重熔稀释结合搅拌铸造工艺制备了不同TiC含量的TiC_p/AZ91镁基复合材料。为了提高TiC_p/AZ91镁基复合材料的强度、延伸率等性能，对TiC_p/AZ91镁基复合材料进行了轧制。利用金相显微镜、SEM、XRD、EDS等方法对铸造与轧制TiC_p/AZ91镁基复合材料进行了组织、力学性能及摩擦磨损特性测试。
热力学计算可知，Al-Ti-CaC_2反应体系中TiC的生成具有较低的反应自由能ΔG与较高绝热温度Tad，表明满足原位反应方法制备TiC的热力学条件，XRD、EDS测试可见TiC的存在；将Al-Ti-CaC_2体系与Al-Ti-C体系结合，采用Al-Ti-C-CaC_2增强体系成功制备了含Ca的TiC_p/Al中间合金。
采用半固态搅拌法制备了TiC含量为4wt.％，8wt.％，12wt.％的TiC_p/AZ91镁基复合材料。测试分析表明，随着TiC含量增加，铸态TiC_p/AZ91镁基复合材料的晶粒明显细化；β-Mg17Al12可依附于TiC颗粒析出，TiC可作为非均匀形核质点，细化组织。但TiC含量较高时，镁基复合材料中出现明显的微孔、缩孔等缺陷，TiC团聚越来越明显。随着TiC含量增加，镁基复合材料的硬度明显提高，抗拉强度、伸长率则随着TiC含量增加先提高后下降，8wt.％TiC_p/AZ91镁基复合材料最高；随着TiC含量增加，TiC_p/AZ91镁基复合材料的耐磨性明显提高。
在加热温度为653K，热压及轧制总变形量为70%的条件下对TiC_p/AZ91镁基复合材料进行了热压及轧制。随着TiC含量的增加，镁基复合材料的可轧制性下降，8wt.％TiC_p/AZ91镁基复合材料表面出现微裂纹，12wt.％TiC_p/AZ91镁基复合材料明显开裂。轧制后TiC_p/AZ91镁基复合材料晶粒明显细化，抗拉强度、伸长率较铸态明显提高。TiC由4wt.％增加8wt.％，抗拉强度整体相差不多，延伸率则随着TiC含量增加单调下降。
Thermodynamic calculations were carried on in the Al-Ti-CaC_2system to analyze thefeasibility of in situ reaction synthesis TiC particles and the result was verified by experiment.The TiC_p/Al master alloy was prepared by the Al-Ti-C-CaC_2enhanced system and in situsynthesis reaction. TiC_p/AZ91magnesium matrix composites with different TiC content wereprepared by remelting dilution solution and by stir casting process. In order to improve thestrength, elongation and other significant properties, the TiC_p/AZ91magnesium composites wasalso rolled. The microstructure, mechanical properties, friction and wear characteristics ofTiC_p/AZ91magnesium matrix composites which was cast and rolled were test by using opticalmicroscope, SEM, XRD, EDS and other equipments.
Thermodynamic calculation shows that the formation of TiC in the Al-Ti-CaC_2system hada lower ΔG and higher Tad, which came to the thermodynamics condition for preparation of TiC.The presence of the TiC was verified by the means of XRD and EDS test. Ca contained TiC_p/Almaster alloy was successfully prepared by the combining Al-Ti-CaC_2system with Al-Ti-Csystem.
Different TiC content of4%,8%,12wt.%TiC_p/AZ91magnesium matrix composites wasprepared by semi-solid mixing. With increasing the amounts of TiC, the cast TiC_p/AZ91composite material grain could be refined. β-Mg17Al12can be attached to the precipitation of TiCparticles, and TiC was conducted as the heterogeneous nucleation. However, the more TiCcontents the more agglomeration and defects appeared in the microstructure such as obviouspores, shrinkage and so on. With the increase of TiC content, the hardness of the magnesiummatrix composites significantly improved, however, tensile strength and elongation declinedafter first going up with increasing the TiC content,8wt.%TiC of TiC_p/AZ91magnesium matrixcomposites had the best properties among these. The increasing TiC contents improved the wearresistance of TiC_p/AZ91magnesium matrix composites significantly
Hot pressing and rolling of TiC_p/AZ91magnesium matrix composite was carried on under aheating temperature of653K and total deformation of70%. With the increasing of TiC content,the available rolling properties of the magnesium matrix composites decreased. Micro-cracksappeared on the surface of8wt.%TiC_p/AZ91magnesium matrix composites while the obviouscracking on the surface of TiC_p/AZ91magnesium matrix composites who contained12wt.%TiC.The grain of TiC_p/AZ91magnesium matrix composites was refined, whose tensile strength andelongation was significantly improved than the cast one. When the contents of TiC increasedfrom4wt.%to8wt.%, the tensile strength of the magnesium matrix composites did not variedvery much, meanwhile the elongation of the magnesium matrix composites decreased monotonically.
引文
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