铸造试棒形状对K417G镍基高温合金组织及持久性能的影响

Influence of Casting-Bar Shape on Microstructure and Rupture Properties of K417G Nickel-Based Superalloy

通过对不同形状的K417G合金铸造试棒(锥形、R5、R30)进行OM、SEM组织形貌观察,760℃/645 MPa试样持久性能测试以及断裂组织分析,研究了铸棒形状对K417G合金组织及持久性能的影响。结果表明,锥形铸棒芯部为等轴晶,边缘为柱状晶,而R5和R30铸造试棒内部均由等轴晶构成。锥形铸棒枝晶间区域内的碳化物及共晶组织尺寸较大,合金内部疏松数量较多。裂纹在枝晶间及晶界处的碳化物内及共晶边缘处萌生,并沿枝晶间或晶界横向扩展,形成宏观裂纹是合金的主要断裂机制之一。另一方面,合金内部的疏松相互连接也可形成裂纹,加速合金持久断裂,是合金的另一主要断裂机制。其中,锥形铸棒中碳化物、共晶组织及疏松数量较多,被认为是其持久寿命较低的主要原因。

According to the observing on the microstructure of the K417 G alloy casting-bars with various shapes(taper,R5 and R30)by OM and SEM,rupture property tests under 760℃/645 MPa and the analysis of the fracture structure,the influence of the casting-bar shape on the microstructures and the rupture properties of the alloy have been investigated.Results showed that the core region of the taper casting-bar mainly consisted of equiaxed crystals,while the edge region consisted of columnar crystals.However,the R5 and R30 castingbars mainly consisted of equiaxed crystals.In the taper casting-bar,the sizes of the carbides and the eutectics in the inter-dendrite region were obviously bigger than those in the R5 and R30 casting-bars.And the number of the porosities in the taper casting-bar was also great.The cracks initiated from the carbides in the interdendritic and grain boundary regions or the edge of the eutectic,then propagated along the inter-dendrite or the grain boundary to form the macrocrack.It is considered to be one of the main fracture mechanisms of the alloy.On the other hand,porosities connections in the alloy can also form the cracks and accelerate the fracture of the alloy,which is thought to be another fracture mechanism of the alloy.Wherein,the shorter rupture life of the taper casting-bar is thought to be attributed to the more carbides,eutectic and the porosities in the micro structure.