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

对比研究了退火温度、冷却速度及多重退火对一种新型近α钛合金Ti90显微组织、室温拉伸性能和腐蚀行为的影响。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(αGB),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αp和βt (β转变组织)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4种不同αp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。

The effects of annealing temperature, cooling rate and multiple annealing processes on microstructures, tensile properties and corrosion behavior of a new near-α titanium alloy-Ti90 were comparatively investigated. The results show that when specimens are annealed in the α+β phase region, as the annealing temperature increases, the deformed structure gradually spheroidizes with a decreasing fraction of primary α phase(α_(p)) and an increasing fraction of β-transformation structure(βt), and the secondary α phase(α_(s)) precipitates and coarsens gradually. These changes result in the reduced strength and improved plasticity. When specimens are annealed, followed by air cooling, in the single β phase zone, a fine lamellar microstructure with fairly coarse original β grains is obtained, which results in a sharp decrease in the plasticity of the alloy. After water-cooling, the acicular α′ martensite phase precipitates inside β grains, which significantly improves the strength while maintaining good plasticity. With multiple annealing, the size of αp and βt increases, and αs coarsens, leading to a simultaneous decrease in the both strength and plasticity. The polarization curve test results show that samples with four different microstructures all exhibit passivation behavior in 3.5% NaCl(mass fraction) solution with low passivation current densities, implicating a good corrosion resistance of Ti90 alloy. The corrosion resistance of different microstructures is in the order of bimodal microstructure>equiaxed microstructure>lamellar microstructure.