固溶时效处理对BT25y钛合金显微组织及硬度的影响

Effects of solution treatment and aging on microstructure and hardness of BT25y titanium alloy

研究了固溶处理和固溶时效处理对BT25y钛合金组织形态、物相组成和显微硬度的影响。结果表明,锻态组织呈现典型的双态组织特征。试样在相变点T_(β)之下固溶处理,随着固溶温度的升高,初生α相含量逐渐减少,β转变组织逐渐增多,β转变组织中片层状次生α相的厚度逐渐增大,β相含量逐渐增大。试样在相变点之上固溶处理,初生α相完全消失,显微组织转变为全片层组织。对固溶试样时效处理后,初生α相形态和尺寸变化不明显,β转变组织发生了明显分解。相变点之下固溶试样时效处理后β相含量有所减少,而在相变点之上固溶试样时效处理后β相含量有所增加。试样中片层状β转变组织含量增加与组织细化效应会有效强化两相钛合金,而β相含量提高会软化两相钛合金,与固溶处理试样相比,相变点之下固溶处理的试样时效后的硬度由于β相含量减少和组织细化综合作用而增幅显著,而相变点之上固溶处理的试样时效后硬度由于β相含量增加和组织细化的综合作用呈现少量增加。

Effects of solution and aging treatments on microstructure,phase composition and microhardness of BT25 y titanium alloy were investigated.The results show that the structure of the forged specimen presents a typical duplex microstructure.Below the β transformation temperature(T_(β)),with the increase of solution treatment temperature,the content of primary α phase gradually decreases while that of the β transformed structure gradually increases,the thickness of the lamellar secondary α phase and the content of β phase gradually increase.After solution treatment above T_(β),the primaryαphase disappears completely,and the duplex microstructure completely transforms into the fully lamellar structure.After aging treatment,the shape and size of the primaryαphase are not significantly changed,but the β transformed structure is obviously decomposed,and the content of β phase slightly decreases in the solution treated specimens below T_(β) but increases in the solution treated specimens above T_(β).As known,both the increasing content of lamellar β transformed structure and the refinement of microstructure can significantly strengthen the two-phase titanium alloys,but the increase of content of the β phase softens the two-phase titanium alloys.Compared to the solution treated specimen,the microhardness of the aged specimen significantly increases when solution treated below T_(β),which is attributed to both the reduction of β phase content and the refinement of microstructure,while the microhardness of the aged specimen slightly increases when solution treated above T_(β),which is attributed to both the increase of β phase content and the refinement of microstructure.