1/2。經(jīng)BASCA熱處理后，細(xì)長針片狀α相全部轉(zhuǎn)變?yōu)榇执蟮钠瑢应料嗪统?xì)針狀α相，且合金的抗拉伸強(qiáng)度提高至1309 MPa，而斷裂韌性降低至45.5 MPa·m1/2。BASCA熱處理能夠提高合金強(qiáng)度，但會(huì)降低合金韌性。這是由于網(wǎng)籃組織中細(xì)長的針片狀α相能夠大大增加裂紋擴(kuò)展阻力，增大裂紋擴(kuò)展路徑曲折程度，從而提高合金的韌性。而BASCA熱處理組織中大片層α相具有一定的方向性，裂紋只有在穿過不同β晶粒的大片層α相時(shí)才會(huì)發(fā)生偏轉(zhuǎn)；且裂紋擴(kuò)展主要發(fā)生在超細(xì)針狀α相中，而超細(xì)針狀α相尺寸過于細(xì)小，不能阻礙裂紋的發(fā)展或使裂紋偏轉(zhuǎn)，因此經(jīng)BASCA熱處理后合金的韌性變差。;In order to satisfy the requirements of aerospace field for rapid preparation of high strength and toughness complex titanium alloy parts, new Ti-5321 (Ti-5Al-3Mo-3V-2Zr-2Cr-1Nb-1Fe) alloy with high strength and high toughness was prepared by laser cladding forming, which possesses the superiority of rapid prototyping, high efficiency, and good formability. Through single annealing and multiple heat treatment (β-annealing with slow cooling and aging, BASCA) on Ti-5321 alloy, the microstructure evolution was revealed, and the influence of different microstructures on the fracture toughness was explored. Results show that after single annealing, the alloy morphology presents the basket-weave structure consisting of elongated lamellar α phases. Its ultimate tensile strength is 1102 MPa, and fracture toughness is 68.1 MPa·m1/2. After BASCA heat treatment, the elongated lamellar α phase changes to coarse lamellar α phase and ultrafine needle-like α phase. Thus, the ultimate tensile strength increases to 1309 MPa, whereas the fracture toughness reduces to 45.5 MPa·m1/2. BASCA heat treatment can enhance the strength but degrade the toughness of alloys. This is because the elongated lamellar α phase in basket-weave structure can greatly increase the crack growth resistance and aggravate the tortuous degree of crack growth path, thus improving the alloy toughness. Coarse lamellar α phase after BASCA heat treatment has a certain degree of directionality, and the cracks only deflect when passing through the coarse lamellar α phase of different β grains. Crack propagation mainly occurs in the ultrafine needle-like α phase. However, due to the extremely small size of ultrafine needle-like α phase, it cannot hinder the development of crack path or deflect the cracks. Thus, the toughness of coarse lamellar structure becomes more inferior after BASCA heat treatment."/>