半固態(tài)燒結(jié)法制備高強韌新型雙尺度結(jié)構(gòu)鈦合金

半固態(tài)燒結(jié)法制備高強韌新型雙尺度結(jié)構(gòu)鈦合金Fabrication of Novel Bimodal Titanium Alloy with High-Strength and Large-Ductility by Semi-Solid Sintering

提出了一種基于共晶轉(zhuǎn)變形成液相的半固態(tài)燒結(jié)新技術(shù),通過調(diào)控共晶轉(zhuǎn)變的相組成(或共晶液相的含量),利用半固態(tài)燒結(jié)共晶復(fù)相系非晶粉末成功制備出高強韌新型雙尺度結(jié)構(gòu)Ti52.1Fe21.7Co8.2Nb12.2Al5.8合金。其雙尺度結(jié)構(gòu)為超細(xì)晶bcc β-Ti和超細(xì)晶bcc Ti(Fe, Co)構(gòu)成的層片共晶基體包圍細(xì)晶等軸狀fcc Ti2(Co, Fe)第二相,與目前文獻(xiàn)報道的雙尺度結(jié)構(gòu)明顯不同。該雙尺度結(jié)構(gòu)合金具有超高的屈服強度(2050 MPa)和較大的塑性應(yīng)變(19.7%),綜合性能優(yōu)于目前文獻(xiàn)報道的雙尺度結(jié)構(gòu)鈦合金。

According to Hall-Petch relationship, high strength of nano-grain and ultrafine-grain meta-llic materials are always accompanied by the cost of ductility because of the lack of work hardening induced by rare or absent dislocation or slip band. And various strategies including semi-solid processing accompanied by rapid solidification, recrystallization induced by plastic deformation and heat treatment, consolidation of blended powders with different grain sizes, and so on, have been developed to fabricate so-called bimodal/multimodal microstructures in the pursuit of high strength and no sacrificing ductility. As one of the most significant types of phase transformation in metallography, eutectic reaction was frequently utilized to tailor phase constitution and its microstructure due to high strength resulted from resultant lamellar eutectic structure. Generally, eutectic structure is more common in solidification and even traditional semi-solid processing for low melting point alloys (such as aluminum and magnesium alloys). In this work, a fundamentally novel approach of semi-solid sintering stemmed from the formation of liquid phase induced by eutectic transformation is introduced. Through regulation of the phase composition of eutectic transformation (or eutectic liquid content), novel bimodal Ti52.1Fe21.7Co8.2Nb12.2Al5.8 alloy with high-strength and large-ductility was successfully fabricated by semi-solid sintering of amorphous alloy powder with multi-phase eutectic system. The fabricated bimodal microstructure consists of fine nearly equiaxed fcc Ti2(Co, Fe) embedded into ultrafine lamellar eutectic matrix containing bcc β-Ti and bcc Ti(Fe, Co) lamellae, which is different from bimodal microstructures reported so far. The fabricated bimodal alloy exhibits ultra-high yield strength of 2050 MPa and large plastic strain of 19.7%, superior to those of bimodal titanium alloys reported so far. The method is conducive to process high-performance new structural metallic alloys in high melting point alloy systems.

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