材料期刊网

提出了一种基于共晶转变形成液相的半固态烧结新技术,通过调控共晶转变的相组成(或共晶液相的含量),利用半固态烧结共晶复相系非晶粉末成功制备出高强韧新型双尺度结构Ti_52.1Fe_21.7Co_8.2Nb_12.2Al_5.8合金。其双尺度结构为超细晶bcc β-Ti和超细晶bcc Ti(Fe, Co)构成的层片共晶基体包围细晶等轴状fcc Ti₂(Co, Fe)第二相,与目前文献报道的双尺度结构明显不同。该双尺度结构合金具有超高的屈服强度(2050 MPa)和较大的塑性应变(19.7%),综合性能优于目前文献报道的双尺度结构钛合金。

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 Ti_52.1Fe_21.7Co_8.2Nb_12.2Al_5.8 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.