热处理对Ti90钛合金显微组织及性能的影响

Effect of Heat Treatment on Microstructures and Properties of Ti90 Alloy

摘要:

对比研究了退火温度、冷却速度及多重退火工艺对一种新型近α钛合金Ti90显微组织、室温拉伸性能和腐蚀性能的影响。结果表明：在两相区退火时,随退火温度升高,变形组织逐渐球化,初生α相(α_p)体积分数降低,次生α相(α_s)增多并发生粗化,合金强度逐渐降低,塑性提高；β单相区退火后空冷,组织中原始β晶粒粗大,且有晶界α相析出(α_GB),合金塑性急剧下降；β单相区退火后水冷,β晶粒内部析出细针状α"马氏体相,显著提高了合金强度,同时保持了较好的塑性；多重退火后α_p和β_t尺寸增加,α_s粗化,导致合金强度和塑性同时降低；极化曲线测试结果显示,具有四种不同α_p含量显微组织的Ti90合金在3.5% NaCl溶液中均表现出钝化行为,且钝化电流密度小,耐蚀性较好,耐蚀能力由强到弱依次为双态组织>等轴组织>片层组织。

关键词:近α钛合金;显微组织;力学性能;热处理;极化曲线

Abstract:

The effects of annealing temperature, cooling rate and multiple annealing process on microstructures, tensile properties and corrosion behavior of a new near-α titanium alloy-Ti90 were comparatively investigated.The results show that when specimens were annealed in the two-phase region,as the annealing temperature increased, the deformed structure gradually spheroidized with a decreased fraction of primary α phase (α_p) and an increased fraction of β-transformation structure (β_t), in which the secondary α phase (α_s) precipitated and coarsened gradually. Those changes finally rose up to the reduced strength and improved plasticity. When annealing in single β phase zone, a fine lamellar microstructure was obtained with fairly coarse original β grains, which resulted in a sharp decrease in the plasticity of the alloy. After water cooling, the acicular α′ martensite phase was precipitated inside β grains, which significantly improved the strength while maintaining good plasticity. With multiple annealing, the size of α_p and β_t increased, and α_s coarsened, leading to a simultaneous decrease in the strength and plasticity of the alloy. The polarization curve test results show that Ti90 alloys with four different microstructures all exhibite passivation behavior in 3.5% NaCl solution with low passivation current density, which implicates a good corrosion resistance. The corrosion resistance of different microstructures is in the order of bimodal microstructure > equiaxed microstructure > Lamellar microstructure.

Key words:Near-α titanium alloy; Microstructure; Mechanical properties; Heat treatment; Polarization curve