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首页> 外文会议>TMS(The Minerals, Metals amp; Materials Society) Annual Meeting and Symposium on Solidification of Aluminum Alloys; 20040314-20040318; Charlotte,NC; US >HOW DOES COALESCENCE OF DENDRITE ARMS OR GRAINS INFLUENCE HOT TEARING?
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HOW DOES COALESCENCE OF DENDRITE ARMS OR GRAINS INFLUENCE HOT TEARING?

机译：树突状臂或晶粒的沉重如何影响热撕裂？

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摘要

Hot tearing, a severe defect occurring during solidification, is the conjunction of tensile stresses which are transmitted to the mushy zone by the coherent solid underneath and of an insufficient liquid feeding to compensate for the volumetric change. In most recent hot tearing criteria, one of the critical issues is the definition of a coherency point which, in low-concentration alloys, corresponds to the bridging or coalescence of the primary phase. A coalescence model has been developed recently using the concept of the disruptive pressure in thin liquid films. It has been shown that large-misorientation grain boundaries, which are characterized by an interfacial energy, γ_(gb), larger than twice the solid-liquid interfacial energy, γ_(sl), solidify at an undercooling ΔT_b = (γ_(gb) - 2γ_(sl))/(Δs_fδ), where Δs_f is the entropy of fusion and δ the thickness of the diffuse interface. When γ_(gb) < 2γ_(sl) (e.g., low-angle grain boundaries), dendrite arms coalesce as soon as they impinge on each other. Using such concepts and a back-diffusion model, the percolation of equiaxed, randomly oriented grains has been studied in 2D : it is shown that the grain structure gradually evolves from isolated grains separated by a continuous interdendritic liquid film, to a fully coherent solid with a few remaining wet boundaries. The implication of such findings for the hot cracking tendency of aluminum alloys are discussed.
机译：热撕裂是固化过程中发生的严重缺陷，是由下面的粘连固体传递到糊状区域的拉应力和液体进料不足以补偿体积变化的结合。在最新的热撕裂标准中，关键问题之一是相干点的定义，该相干点在低浓度合金中对应于初相的桥接或聚结。最近已经使用液体薄膜中的破坏压力的概念开发了聚结模型。结果表明，取向差较大的晶界在过冷ΔT_b=（γ_（gb）时凝固，其界面能γ_（gb）大于固液界面能γ_（sl）的两倍。 -2γ_（sl））/（Δs_fδ），其中Δs_f是融合熵，δ是扩散界面的厚度。当γ_（gb）<2γ_（sl）（例如低角度晶界）时，枝晶臂彼此碰撞时就会聚结。使用这样的概念和反向扩散模型，已经对二维等轴，随机取向的晶粒的渗滤进行了二维研究：结果表明，晶粒结构从被连续的枝晶间液膜分离的孤立晶粒逐渐演化为具有剩下的一些湿边界。讨论了这些发现对铝合金热裂纹倾向的影响。

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