Krishna Ram, Hainsworth Sarah V, Gill Simon P A, Atkinson Helen V
Department of Engineering, University of Leicester, University Road, Leicester, LE1 7RH, UK; Now at Dalton Cumbrian Facility, The University of Manchester, Westlakes Science and Technology Park, Moor Row, Whitehaven, Cumbria, CA24 3HA, UK.
Microsc Res Tech. 2015 May;78(5):336-42. doi: 10.1002/jemt.22359. Epub 2015 Apr 1.
Titanium Carbonitride (Ti(C,N)) decomposition in Inconel 617 alloy creep-exposed at 650°C for 574 hours is reported using analytical electron microscopy techniques. Cr-enriched M23C6-type carbides enveloped in fine gamma prime particles thought to be precipitated from the decomposition reaction are observed in the alloy. The morphology of the M23C6 carbides is irregular and blocky and the particle size up to 5 μm, whereas the morphology of gamma prime particles is mostly spherical and up to 30 nm in size. Intergranular carbides are mostly secondary precipitates of the M23Cc type (M predominantly Cr) and these respond to solution heat treatment and precipitate on the grain boundaries as a result of ageing. The ability of intragranular MX to decompose is sensitive to the N content, high N resists decomposition. Decomposed intragranular MX provides an excess source of C which can react locally with Cr to form heat treatable intragranular fine Cr23C6 precipitates. M6C can segregate in interdendritic locations during melting which may be the reason for high content of Mo in M23C6. These precipitates are generally very small and contribute to an additional hardening effect and are the reason for the onset of voiding and cracking along the grain boundaries that ultimately lead to a reduced creep rupture life.
利用分析电子显微镜技术，报道了在650°C下蠕变暴露574小时的因科镍合金617中碳氮化钛（Ti(C,N)）的分解情况。在该合金中观察到，富铬的M23C6型碳化物被认为是由分解反应析出的细小γ'粒子包裹着。M23C6碳化物的形态不规则且呈块状，粒径可达5μm，而γ'粒子的形态大多为球形，尺寸可达30nm。沿晶碳化物大多是M23Cc型（M主要为Cr）的二次析出物，这些析出物会对固溶热处理作出反应，并在时效过程中在晶界上析出。晶内MX分解的能力对N含量敏感，高N含量会抑制分解。分解后的晶内MX会提供过量的C源，这些C能在局部与Cr反应形成可热处理的晶内细小Cr23C6析出物。M6C在熔化过程中会在枝晶间位置偏聚，这可能是M23C6中Mo含量高的原因。这些析出物通常非常小，会产生额外的硬化效果，并且是沿晶界出现空洞和裂纹的原因，最终导致蠕变断裂寿命降低。
