Al粉含量对Y_(2)O_(3)基陶瓷型芯性能及组织的影响

Effect of Al powder content on the properties and microstructure of Y_(2)O_(3)-based ceramic core

为获得满足钛合金熔模精密铸造使用的高惰性陶瓷型芯,采用Y_(2)O_(3)作为骨料,引入Al粉作为矿化剂,基于热压注法制备陶瓷型芯。研究了Al粉含量对Y_(2)O_(3)基陶瓷型芯致密化特性、力学性能、微观结构及相组成的影响。结果表明:随Al粉含量增加,Y_(2)O_(3)基陶瓷型芯的烧结收缩率和高温挠度逐渐减小;Al粉氧化膨胀有利于抵御型芯的烧结收缩,基于Al粉的液相烧结协同Al-Y_(2)O_(3)的界面反应烧结和Al_(2)O_(3)-Y_(2)O_(3)扩散烧结机制,促进了型芯的致密化。Al粉与基体生成Al_(2)Y_(4)O_(9)晶体抑制了晶间细小Y_(2)O_(3)颗粒的二次烧结,提升了型芯的高温抗变形能力。引入少量Al粉,型芯中生成Al_(2)Y_(4)O_(9)和Y_(2)Al晶体并附着于基体颗粒表面,基于第二相强化晶间结合强度得到提升;加入2wt%Al粉时型芯获得最佳抗弯强度,约为34.38 MPa,相比纯钇基陶瓷型芯提升了49.15%,表现为穿晶断裂。但过量Al粉氧化产生的膨胀量扩大了骨料颗粒间距,一定程度上削弱了晶间结合强度,型芯出现沿晶脆性断裂的倾向,导致承载能力下降。

In order to obtain ceramic core with high chemical reaction resistance for titanium alloy investment casting,the Al powders were introduced into Y_(2)O_(3)-based ceramic core as the sintering aids,and then the modified ceramic core was prepared by hot injection molding.The effects of Al powder content on the densification characteristic,mechanical properties,microstructure and phase composition of Y_(2)O_(3)-based ceramic cores were studied.The results indicate that the sintering shrinkage and high temperature deflection of Y_(2)O_(3)-based ceramic core decrease with the increasing of Al powder content.The oxidation of Al element led to the expansion of the Al powders,which is beneficial to resist the shrinkage of Y_(2)O_(3)-based ceramic core during the sintering process.The densification of ceramic core is enhanced by liquid-phase sintering of Al powder melting and the interface reaction sintering of Al-Y_(2)O_(3),as well as the diffusion sintering between Al_(2)O_(3) and Y_(2)O_(3) matrix.The formation of Al_(2)Y_(4)O_(9) crystals in matrix inhibits the secondary sintering of intergranular fine Y_(2)O_(3) particles,which improves the high temperature creep resistance of the ceramic core.With a small amount of Al powder introducing,the Al_(2)Y_(4)O_(9) and Y_(2)Al crystals are formed and then coated on the surface of the matrix Y_(2)O_(3) particles,and the interfacial bonding strength is improved by the second phase strengthening.The Y_(2)O_(3)-based ceramic core modified by 2wt%Al powder,exhibits the optimal flexural strength about 34.38 MPa with a typical cleavage fracture,which is 49.15%higher than that of the ceramic core without Al powder.However,the expansion caused by excessive oxidation of Al powder can expands the distance between the ceramic particles.Therefore,the interfacial bonding strength of Y_(2)O_(3)-based ceramic core is weakened obviously,and then the ceramic core tends to fracture along the grain boundaries,resulting in the decrease of the bearing capacity under the load.