高合金化难变形高温合金GH4975热裂敏感性研究

Hot Cracking Sensitivity of Difficult-to-Deform Superalloy GH4975 with High Alloying

摘要:

为研究高合金化难变形高温合金GH4975热裂敏感性，对GH4975合金铸锭裂纹形貌和组织特征进行观察，结合其凝固行为和热力学计算等方式分析热裂原因。结果表明，裂纹沿晶界和枝晶间扩展，等轴晶区比柱状晶区具有更大的热裂倾向。铸锭中心区域易出现缩孔，连续缩孔的形成导致枝晶间搭接不充分，易在应力作用下被拉开从而形成裂纹源。同时枝晶间Al、Ti、Nb元素偏析严重，复杂的析出相尤其是大量的(γ+γ′)共晶相促进了裂纹的形核与扩展。JMatPro计算可知GH4975合金固液两相区收缩率大，不可补缩温度范围大，易形成缩孔从而成为裂纹源，同时不可补缩温度区间内合金线性膨胀系数变化大，裂纹易扩展。

Abstract:

To study the hot cracking sensitivity of high alloying difficult-to-deform superalloy GH4975, the crack morphology and microstructure characteristics of the GH4975 ingot were observed, and the causes of hot cracking were analyzed through solidification behavior and thermodynamic calculation. The results show that cracks propagate along grain boundaries and dendrites, and the equiaxed region has a greater cracking tendency than the columnar region. Shrinkage holes are easy to appear in the center of the ingot. The formation of continuous shrinkage holes leads to insufficient overlap between dendrites, which can be easily pulled apart under stress to form a crack source. At the same time, the segregation of Al, Ti and Nb elements between dendrites is severe. Complex precipitates, especially numerous (γ+γ′) eutectic phases, promote the nucleation and propagation of cracks. JMatPro calculation shows that GH4975 alloy has a high shrinkage rate and a wide temperature range for poor feeding during solidification. It facilitates the formation of shrinkage hole that can act as a crack source. Meanwhile, the linear expansion coefficient of the alloy changes significantly in the temperature range for poor feeding, thereby promoting crack propagation.