Development of ultrafine lamellar structures in two-phase γ-TiAl alloys
Development of ultrafine lamellar structures in two-phase γ-TiAl alloys
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DOI：
10.1007/s11661-998-0163-5
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发表时间：
1998
期刊：
影响因子：
--
通讯作者：
P. Maziasz;C. Liu
中科院分区：
文献类型：
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作者：
P. Maziasz;C. Liu
两相γ-TiAl合金（Ti-47 Al-2Cr-2Nb，或其微小变型）在高于α转变温度（Tα）的温度下加工，在粉末冶金和铸锭冶金（分别为PM和IM）合金中产生独特的细化团/超细片层结构。这些超细片层结构由γ和α 2相的细板条组成，平均片层间距（λL）为100 ~ 200 nm，α2-α 2间距（λα）为200 ~ 500 nm，并以γ/α 2界面为主。这种特征性显微组织通过在1400 °C下挤压PM Ti-47 Al-2Cr-2Nb合金形成，并且还通过热挤压类似的IM合金形成具有更细的菌落尺寸但稍微更粗的全层状结构。添加B和W合金可细化IM Ti-47 Al（铸造并在1400 °C下热处理）和IM Ti-47 Al-2Cr-2Nb合金（在1400 °C下挤压）中的λ和λα。粉末冶金合金中的超细片层结构在900 °C热处理2小时期间保持稳定，但在982 °C热处理4小时后变得不稳定;超细片层结构在800 °C时效>5000小时后保持相对稳定。添加B+W显著提高了IM Ti-47 Al合金在1000 °C时效168 h后的抗λ和λα粗化能力。在PM和IM Ti-47 Al-2Cr-2 Nb合金中，这些细化的团簇/超细片层结构与室温下的高强度和良好的延展性以及高温下非常好的强度相关。当细化殖民地尺寸改善室温延展性时，具有更细λ L的合金在室温和高温下都更强。添加B + W可使IM TiAl合金的加工态λ和λα细化，并在热处理或时效过程中稳定这种组织。
Processing of two-phaseγ-TiAl alloys (Ti-47Al-2Cr-2Nb, or minor modifications thereof) above theα-transus temperature (Tα) produced unique refined-colony/ultrafine lamellar structures in both powder-and ingot-metallurgy (PM and IM, respectively) alloys. These ultrafine lamellar structures consist of fine laths of theγandα2phases, with average interlamellar spacings (λL) of 100 to 200 nm andα2-α2spacings (λα) of 200 to 500 nm, and are dominated byγ/α2interfaces. This characteristic microstructure forms by extruding PM Ti-47Al-2Cr-2Nb alloys at 1400 °C and also forms with finer colony size but slightly coarser, fully lamellar structures by hot-extruding similar IM alloys. Alloying additions of B and W refineλLandλαin both IM Ti-47Al (cast and heat treated at 1400 °C) and IM Ti-47Al-2Cr-2Nb alloys (extruded at 1400 °C). The ultrafine lamellar structure in the PM alloy remains stable during heat treatment at 900 °C for 2 hours but becomes unstable after 4 hours at 982 °C; the ultrafine lamellar structure remains relatively stable after aging for >5000 hours at 800 °C. Additions of B+W dramatically improve the coarsening resistance ofλLandλαin the IM Ti-47Al alloys aged for 168 hours at 1000 °C. In both the PM and IM Ti-47Al-2Cr-2Nb alloys, these refined-colony/ultrafine lamellar structures correlate with high strength and good ductility at room temperature, and very good strength at high temperatures. While refining the colony size improves the room-temperature ductility, alloys with finerλLare stronger at both room and high temperatures. Additions of B + W produce finer as-processedλLandλαin IM TiAl alloys and stabilize such structures during heat treatment or aging.