精炼及浇注温度对K417G镍基高温合金组织及持久性能的影响

Influence of Refining and Pouring Temperature on Microstructures and Stress Rupture Properties of K417G Nickel-Based Superalloy

采用不同精炼及浇注温度制备K417G镍基高温合金,通过对合金的组织形貌进行观察分析,以及测试合金在760℃/645 MPa下的持久性能,研究了精炼温度、浇注温度等铸造工艺参数对K417G镍基高温合金组织及持久性能的影响。结果表明,提高精炼温度可降低铸态合金组织中的碳化物尺寸,并使碳化物分布更加均匀;降低浇注温度可降低合金的晶粒尺寸、枝晶间距以及碳化物尺寸,并使合金的共晶组织由γ'共晶转变为(γ+γ')共晶。合金在760℃/645 MPa拉伸持久期间的主要断裂机制为裂纹在枝晶间区域内的MC碳化物处萌生,并沿正应力方向扩展,导致合金发生持久断裂。其中,采用1500℃精炼,1450℃浇注的合金中碳化物尺寸较小且弥散分布是其具有较高持久寿命的主要原因。

In this work,different refining and pouring temperatures have been used to prepare K417G nickel-based superalloy.By observing and analyzing the casting microstructure and testing the stress rupture property of the alloy at 760℃/645 MPa,the influence of refining and pouring temperatures on the microstructure and stress rupture property of the alloy have been investigated.Results show that raising the refining temperature could reduce the sizes of the carbides and homogenize the carbide distribution in the as-cast alloy.Reducing the pouring temperature could decrease the size of the crystalline grains,dendrite spacing and carbides in the alloy.It could also transform the eutectic structure from γ'eutectic into(γ+γ')eutectic.The main fracture mechanism of the alloy during stress rupture at 760 ℃/645 MPa is that cracks initiate in the MC carbides in the inter-dendrite regions,and propagate along the normal stress direction,which cause the alloy to occur fracture.Wherein,the smaller size and more uniform distribution of the carbides in the alloy is thought to be the main reason that the alloy prepared by refining at 1500℃ and pouring at 1450℃displays a better stress rupture property.