Plate-shaped transformation products in zirconium-base alloys
Plate-shaped transformation products in zirconium-base alloys
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DOI：
10.1007/s11661-997-0178-3
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发表时间：
1997-11
期刊：
影响因子：
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通讯作者：
S. Banerjee;G. K. Dey;D. Srivastava;S. Ranganathan
中科院分区：
文献类型：
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作者：
S. Banerjee;G. K. Dey;D. Srivastava;S. Ranganathan
在本研究中，板状产品产生的马氏体，扩散，和混合模式的转变在锆基合金进行了比较。这些合金特别适合于比较，因为对于不同类型的转变，母体β（bcc）和产物α（hcp）或γ-氢化物（fct）相之间的晶格对应性非常相似。晶体学特征，如取向关系，惯习面，和界面结构与这些转换进行了比较，以检查是否有特征的印记，这些实验观察到的转换机制。在Zr-2.5Nb合金中发现了位错板条、内孪晶板和自适应三板团等马氏体组织。已发现对应于所有这些形态的习惯平面与基于不变平面应变（IPS）准则的预测一致。已经发现不同的形态反映了相邻马氏体变体组装的方式。所有这些情况下的晶格不变剪切（利斯）被确定为{101}α <123>α滑移或{101}α平面上的孪晶。在分步淬火处理中形成的Widmanstättenα沉淀物具有板条形貌，α/β界面被间隔为8至10 nm的<c+a>位错周期性阵列装饰。这些位错的线矢量几乎平行于不变线。在时效过程中残留的β相中形成的α沉淀物具有Z字形惯习面的内部孪晶结构。已发现形态的平均惯习面位于{103}β- {113}β极附近，其接近于{112}β平面的特定变体，其转变为{100}α型棱柱平面。从α和β相形成γ-氢化物相（fct）的晶体学被认为与IPS预测相匹配。虽然β-γ转变可以近似地被视为涉及堆叠序列变化的基面上的简单剪切，但α-γ转变可以在概念上被分解为遵循Burgers对应和简单β-γ剪切过程的α→β转变。Zr-Cu系中β→α + β′的共析分解是通过Burgers对应从β相中协同生长α相和通过有序化过程协同生长部分有序β′（结构上类似于平衡Zr 2Cu相）来描述的。讨论了这些转变的晶体学特征的异同，指出了不变线矢量在决定相应惯习面几何结构中的重要性。
Plate-shaped products resulting from martensitic, diffusional, and mixed mode transformations in zirconium-base alloys are compared in the present study. These alloys are particularly suitable for the comparison in view of the fact that the lattice correspondence between the parentβ(bcc) and the productα(hcp) orγ-hydride (fct) phases are remarkably similar for different types of transformations. Crystallographic features such as orientation relations, habit planes, and interface structures associated with these transformations have been compared, with a view toward examining whether the transformation mechanisms have characteristic imprints on these experimental observables. Martensites exhibiting dislocated lath, internally twinned plate, and self-accommodating three-plate cluster morphologies have been encountered in Zr-2.5Nb alloy. Habit planes corresponding to all these morphologies have been found to be consistent with the predictions based on the invariant plane strain (IPS) criterion. Different morphologies have been found to reflect the manner in which the neighboring martensite variants are assembled. Lattice-invariant shears (LISs) for all these cases have been identified to be either {101}α<123>αslip or twinning on {101}αplanes. Widmanstättenαprecipitates, forming in a step-quenching treatment, have been shown to have a lath morphology, theα/βinterface being decorated with a periodic array of <c+a> dislocations at a spacing of 8 to 10 nm. The line vectors of these dislocations are nearly parallel to the invariant lines. Theαprecipitates, forming in the retainedβphase on aging, exhibit an internally twinned structure with a zigzag habit plane. Average habit planes for the morphologies have been found to lie near the {103}β— {113}βpoles, which are close to the specific variant of the {112}βplane, which transforms into a prismatic plane of the type {100}α. The crystallography of the formation of theγ-hydride phase (fct) from both theαandβphases is seen to match the IPS predictions. While theβ-γtransformation can be treated approximately as a simple shear on the basal plane involving a change in the stacking sequence, theα-γtransformation can be conceptually broken into aα→βtransformation following the Burgers correspondence and the simpleβ-γshear process. The active eutectoid decomposition in the Zr-Cu system,β→α + β′, has been described in terms of cooperative growth of theαphase from theβphase through the Burgers correspondence and of the partially orderedβ′ (structurally similar to the equilibrium Zr2Cu phase) through an ordering process. Similarities and differences in crystallographic features of these transformations have been discussed, and the importance of the invariant line vector in deciding the geometry of the corresponding habit planes has been pointed out.