Part I. The microstructural evolution in Ti-Al-NbO plus Bcc orthorhombic alloys
Part I. The microstructural evolution in Ti-Al-NbO plus Bcc orthorhombic alloys
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DOI：
10.1007/s11661-999-0240-4
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发表时间：
1999-09-01
影响因子：
2.8
通讯作者：
Miracle, DB
中科院分区：
文献类型：
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作者：
Boehlert, CJ;Majumdar, BS;Miracle, DB
研究了近Ti 2AlNb和Ti-12 Al-38 NbO + bcc斜方晶合金的相变及其组织演变。对于近Ti 2AlNb合金，加工温度低于体心立方转变，而对于Ti-12 Al-38 Nb，加工温度高于体心立方转变。相演化研究表明，这些合金含有几个组成相，即bcc，O和α（2）;当存在时，后者与其他相相比数量较少。采用透射电子显微镜（TEM）、扫描电子显微镜（SEM）和X射线衍射（XRD）对固溶和水淬后的样品进行了分析，得到了Ti = 50 at.修改了PCT。详细研究了该合金的时效转变行为。对于875 ° C和bcc转变之间的固溶温度，通过等轴B2、O和α（2）晶粒的相对尺寸变化来调节近Ti 2AlNb合金的相组成和体积分数。时效行为遵循三种不同的转变模式，取决于固溶和时效温度。当一个新的阶段从一个母相演变时，观察到魏氏组织的形成。因此，对于超转变完全B2组织，以及对于亚转变α（2）+ B2组织，魏氏组织O相在B2相中沉淀。类似地，魏氏合金B2相可以从完全O微观结构形成，这是以前未观察到的转变。在等轴O + B2固溶和水淬显微组织的情况下，魏氏组织O相的形成仅在低于875 ℃时发生。对于亚转变固溶和水淬的显微组织，第二种时效转变模式，胞状沉淀，在低于750 ℃时占主导地位。这涉及到从晶界生长到先前的B2晶粒中的粗的和透镜状的O相的形成。第三种转变模式涉及成分不变转变，其中完全B2超反式固溶和水淬的显微组织在650 ℃下转变为完全O显微组织。这种显微组织随着持续的时效时间从O相中再析出B2相。Ti-12 Al-38 Nb合金中，魏氏组织O沉淀仍是唯一的相变方式。结果表明，subtranssus处理提供了灵活性，通过后处理热处理控制微观结构。
Phase transformations and the resulting microstructural evolution of near-Ti2AlNb and Ti-12Al-38Nb O + bcc orthorhombic alloys were investigated. For the near-Ti2AlNb alloys, the processing temperatures were below the bcc transus, while, for Ti-12Al-38Nb, the processing temperature was supertransus. Phase evolution studies showed that these alloys contain several constituent phases, namely, bcc, O, and alpha(2); when present, the latter was in small quantities compared to the other phases. The transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Xray investigations of samples that were solutionized and water quenched were used to estimate the phase fields, and a pseudobinary diagram based on Ti = 50 at. pct was modified. The aging transformation behavior was studied in detail. For solutionizing temperatures between 875 degrees C and the bcc transus, the phase composition and volume fraction of the near-Ti2AlNb alloys adjusted through relative size changes of the equiaxed B2, O, and alpha(2) grains. The aging behavior followed three distinct transformation modes, dependent on the solutionizing and aging temperatures. Widmanstatten formation was observed when a new phase evolved from a parent phase. Thus, Widmanstatten O phase precipitated within the B2 phase for supertransus fully B2 microstructures, as well as for subtransus alpha(2) + B2 microstructures. Similarly, Widmanstatten B2 phase can form from a fully O microstructure, a transformation that has not been observed before. In the case of equiaxed O + B2 solutionized and water-quenched microstructures, Widmanstatten O-phase formation occurred only below 875 degrees C. For the subtransus-solutionized and water-quenched microstructures, a second aging transformation mode, cellular precipitation, was dominant below 750 degrees C. This involved formation of coarse and lenticular O phase that grew into the prior B2 grains from the grain boundaries. A third transformation mode involved composition-invariant transformation, where the fully B2 supertransus-solutionized and water-quenched microstructure transformed to a fully O microstructure at 650 degrees C. This microstructure reprecipitated B2 phase out of the O phase with continued aging time. For Ti-12Al-38Nb, Widmanstatten O precipitation remained the only transformation mode. It is shown that subtransus processing offers flexibility in controlling microstructures through postprocessing heat treatments.