P元素含量对GH4738合金高温持久性能的影响

Effect of P Content on Creep Rupture Property of GH4738 Alloy

摘要:

针对不同P元素含量的GH4738合金，结合光学金相、扫描电镜形貌、TEM、EBSD分析，研究了P含量对GH4738合金持久性能的影响机理，探究了对合金性能有利的P元素含量范围。结果表明：合金的持久性能随着P含量的升高，呈先增大后减小的趋势，P元素的最佳添加量在0.0040wt%至0.0091wt%之间，此时断裂形式为混合断裂。继续增加P元素，持久寿命降低30%~50%，持久塑性降低20%~70%，断裂形式变为脆性沿晶断裂。原因在于：P元素为晶界偏析元素，含量较低时，可通过在晶界占据空位缺陷降低晶界自由能，从而提高晶界碳化物形核率，而晶界上均匀弥散分布的M₂₃C₆型碳化物可抑制裂纹扩展，提高晶界强度，从而提高合金持久性能；P元素含量较高时，更倾向固溶于MC型碳化物，因此随着P含量进一步的提高，晶界上MC型碳化物数量增多而M₂₃C₆型碳化物相对减少，块状的MC型碳化物在晶界不均匀分布，从而导致试验合金持久性能不断降低。

Abstract:

The influencing mechanisms of P content on the creep rupture properties of GH4738 alloy and the optimum additive range of P element in this alloy were investigated by OM, SEM, TEM, and EBSD microscopic analyses. The results show that the creep rupture strength of the alloys shows a tendency of firstly increasing and then decreasing with the increase in P content. The optimal addition amount of P ranges from 0.0040wt% to 0.0091wt%, and the fracture morphology shows a mixed fracture type. With continuously increasing the P element, the endurance life is decreased by 30%–50%, the persistent plasticity is decreased by 20%–70%, and the fracture mode changes to brittle intergranular fracture. The main reasons are as follows. P, as a type of grain boundary segregation element, when its content is smaller, the segregated P element occupies the vacancy at the grain boundary to decease the free energy of grain boundary, thereby increasing the nucleation rate of carbides. Meanwhile, the uniformly dispersed M₂₃C₆-type carbides along grain boundaries can inhibit crack propagation and improve grain boundary strength, ultimately enhancing the creep resistance of the alloys. When P content is greater than the critical value, it has a tendency to solute into MC-type carbides. Consequently, with further increase in P content, the amount of MC-type carbides at grain boundaries is increased while M₂₃C₆-type carbides are decreased relatively. The blocky MC-type carbides become unevenly distributed along grain boundaries, leading to a continuous degradation in the creep resistance of the experimental alloys.