【作者】 刘明；

【导师】 郭斌；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2009， 硕士

【摘要】 本文研究了喷丸工艺及其后续热处理对定向凝固γ-TiAl (Ti-46Al-0.5W-0.5Si)板坯显微组织的影响。热处理后得到了表层为细小片层状组织,内部为原始粗大片层状组织的复合组织。利用ABAQUS有限元软件对喷丸工艺进行了动力学分析、对喷丸后的靶材表层进行了应力应变分析。指出了喷丸工艺在塑性加工Z形图中的位置、靶材表层的受力状态及应变类型。模拟结果显示:喷丸是一种表层变形工艺,喷丸后,只有靶材表层产生塑性变形和残余应力;喷丸的动力学过程不大1μs;随着弹丸速度的增大,坯料表层塑性变形越强烈;随着弹丸打击次数的增加,坯料表层的应变量趋于稳定;最大塑性变形并不发生在表层,而是出现在次表面;喷丸后,靶材表层产生压应力,压应力层以下存在拉应力层;根据应力应变顺序对应法则、罗德系数、主应力偏张量第三不变量、应变特征角等理论研究了靶材表层的应变类型,得出了一致的结论,即喷丸后,靶材表层应变类型为拉伸类,拉伸类应变层以下存在一层压缩类应变层;靶材表层的塑性应变深度主要取决于弹丸速度,受打击次数影响不大。对喷丸后的γ-TiAl进行显微组织观察,结果表明:经过受控喷丸后,坯料表层的片层状组织发生明显的弯曲并出现大量位错,而心部组织保持原始状态,位错较少。对喷丸后Q235钢进行显微组织观察,结果表明:表层原始的等轴晶被明显拉长,心部组织保持不变。对喷丸后的γ-TiAl进行热处理和显微组织观察,结果表明:经过相变热处理(α2+γ→α),表层原始粗大的片层状组织变成细小片层状组织,而心部组织保持为冷变形前粗大片层状形态。对喷丸后的Q235钢进行热处理和显微组织观察,结果表明:经过在结晶热处理,表层晶粒发生再结晶,而心部组织保持为冷变形前细小的等轴晶形态。更多还原

【Abstract】 This paper studied effect of shot peening process and its subsequent heat treatment on microstructure of directional solidificationγ-TiAl (Ti-46Al-0.5W-0.5Si) slab. Composite microstructure consisting of fine layered microstructure in the surface and internally original coarse layered microstructure was obtained after heat treatment.Dynamic analysis, stress-strain analysis of surface layer of peened target were carried out using ABAQUS finite element software. The location of shot peening process in plastic processing Z-shaped chart was pointed. And stress type and strain type of the surface layer of the target after peened were illustrataed. Simulation results shows that: shot peening is a surface deformation process, only the surface layer of the peened target has plastic deformation and residual stress; the dynamic process of shot peening is less than 1μs; with increasing projectile velocity, plastic deformation of the surface layer will increase; with the increase in the number of impact, strain variable approaches to a stable state; the largest plastic deformation does not occur in the surface, but appears in the sub-surface; compressive stress is in the surface layer, and tensile stress layer exists under the compressive stress layer; according to stress-strain order corresponding law, Lode parameter, deviatoric stress tensor third invariant, strain characteristic angle and so on, it is concluded that the strain type of target’s surface is tensile strain, a layer with compressive strain exists under the tensile strain layer. The depth of the target’s surface which has plastic strain depends mainly on shot velocity and is not affected by the number of attack.Microstructure observation of peenedγ-TiAl shows that: after shot peening, there was bending-rupture for the lamellae micrstructre in the surface, and a large number of dislocations occured in the surface, while the center maintained its original state with less dislocations. Microstructure observation of Q235 steel shows that: after shot peening, the original equiaxed grains in the surface layer of the target have been significantly elongated, however, the central original grains of the target remain unchaged. Microstructure observation ofγ-TiAl after subsequent heat treatment shows that: after phase transformation treatment(α2+γ→α), the original coarse lamella microstructure in the surface layer transformed to fine lamella microstructure, and the coarse lamella microstructure in the center remained the same as the original one. Microstructure observation ofγ-TiAl after subsequent heat treatment shows that: after the crystallization heat treatment, recrystallization occurs in the surface layer, and the center microstructure maintains the prior equiaxed grains as that before cold deformation.更多还原