消除粉末高温合金中原始颗粒边界机制

Discussion on mechanism of eliminating prior particle boundary in powder metallurgy superalloy

采用SEM、TEM研究了高温合金粉末颗粒内部与合金中碳化物的类型和组成,采用热力学软件计算了不同Hf含量FGH4096的碳化物组成,结果表明,粉末高温合金中原始颗粒边界上的析出物为以TiC为主的MC型碳化物,MC型碳化物(TiC、ZrC、HfC、NbC、TaC)在镍基高温合金中按溶解度从大到小为TiC>NbC>TaC>ZrC>HfC。TiC在FGH4096中的溶解度较HfC的大,雾化粉末快速凝固过程中,加入Hf的FGH4096合金碳化物析出量大于不加Hf的FGH4096合金碳化物析出量,HfC均匀形核于整个粉末颗粒中。在热等静压过程中,Hf与C的结合力强而形成HfC,最终在FGH4096合金中形成(Hf,Ti,Nb)C,致使C元素无法扩散至粉末颗粒表面形成TiC,避免了原始粉末颗粒边界的形成。加入Zr消除FGH4096中原始颗粒边界的机制与添加Hf的FGH4096相同。

SEM and TEM were used to study types and composition of carbides inside superalloy powder particles and alloys. The thermodynamic software was used to calculate the composition of carbides in FGH4096 with different Hf contents. Results showed that precipitates on the prior particle boundary(PPB) in the studied PM superalloy were mainly MC-type carbides of Ti C, and the solubility of MC-type carbides(TiC,ZrC,HfC,NbC,TaC) in nickelbased superalloys was in the order of TiC>NbC>TaC>ZrC>HfC. The solubility of TiC in FGH4096 is higher than that of HfC. During the rapid solidification process of atomized powders, the precipitation of carbides in FGH4096 alloy with Hf is greater than that without Hf, and the HfC uniformly nucleate in the whole powder. In the process of hot isostatic pressing, the binding force of Hf and C is strong, thus forming the HfC. Finally, the(Hf,Ti,Nb)C is formed in FGH4096 so that the C element can not diffuse to the surface of powder particles to form the TiC, avoiding the formation of PPB. The mechanism of Zr to eliminate the PPB in FGH4096 is the same as Hf.