【作者】 任涛林；

【导师】 单德彬；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2011， 博士

【摘要】 金属的微观组织决定其力学性能。细小晶粒拥有优良的塑性、韧性和抗疲劳性能,粗大晶粒则拥有较好的抗高温蠕变和抗断裂性能。因此对矩形坯料实施精确的定向表层塑性变形并辅以后续的热处理,使其获得表层是等轴细晶而中心部位是粗大晶粒组成的复合组织,将能同时满足对高温蠕变、断裂韧性和疲劳强度的要求。本文就是在这样的思想下提出来的。依据以上想法,提出了复合辊轧、滚珠滚压、表面挤压和受控喷丸四种表层塑性变形工艺,并依据局部加载理论设计了相应的塑性变形装置。通过物理模拟实验和有限元分析的方法,对四种表层变形工艺的金属流动规律进行了研究,得出表层塑性变形后沿板坯厚度方向的应力应变特点,并揭示了经过四种表层变形工艺和后续热处理后的Q235钢和定向凝固钛铝合金板坯的微观组织演变规律。利用商业有限元软件ABAQUS-6.7对四种定向凝固钛铝合金板坯表层塑性变形过程进行了有限元分析,结果表明经过四种表层变形工艺后,塑性变形基本上被局限在表层的1mm内,最大等效应变值分别能达到0.2、0.22、0.032和0.25。利用弹塑性力学的相关理论,结合定量计算和定性分析,得出了四种工艺的应变类型分布特点,即:经过复合轧制后的坯料表层处于平面应变状态,经过滚珠滚压和表面挤压后的坯料沿特定的厚度方向路径的应变类型由伸长类应变转化为压缩类应变,而经过受控喷丸后的坯料沿特定的厚度方向路径的应变类型由压缩类应变转化为伸长类应变。对经过表层塑性变形的Q235钢坯料进行显微组织观察,结果表明在室温下,经过复合辊轧、滚珠滚压、表面挤压和受控喷丸后,表层晶粒发生强烈塑性变形,呈纤维状,心部组织保持原始形态。对经过复合辊轧、滚珠滚压和表面挤压变形后的Q235钢辅以再结晶退火,得到了表层细晶和心部粗晶的复合组织,而对经过受控喷丸后的坯料进行再结晶退火发现,坯料表层的晶粒由于处于临界变形区而发生异常长大。定向凝固钛铝合金坯料经过复合辊轧后,表层晶粒出现再结晶细化,而中心部分保持粗大的全层片组织。对经过滚珠滚压、表面挤压和受控喷丸后的定向凝固钛铝合金表层组织进行组织观察发现,层片发生强烈的弯曲,在层片的界面处出现了相转变和动态再结晶。对滚珠滚压、表面挤压和受控喷丸后的试样在α相转变线上10~20oC进行短时间的真空热处理发现,显微组织尺寸从坯料的表层向中心方向有明显的梯度渐变特征,即形成了表层组织为细小全片层晶粒,心部组织为粗大全层片的原始晶粒的复合组织;而对受控喷丸后的试样进行相同的热处理发现,表层晶粒由于处在临界变形区而发生了异常的长大。更多还原

【Abstract】 The mechanical property is determined by its microstructure. Fine grains possess good plasticity, toughness and fatigue property. However, large grains possess premium high temperature creep and anti-fracture property. Therefore, the rectangular billet after surface plastic deformation and subsequent heat treatment, which results in fine grains on the surface and coarse column grains in the center, will meet the demands on high temperature creep, fracture toughness and fatigue strength. This thesis is presented on the idea.Based on this idea, four different surface plastic deformation techniques including: compound rolling, ball burnishing, surface milling and controlled shot peening, which will localize the plastic deformation on the surface of the billet and leave little plastic deformation in the center, were presented in this study. Based on the local load theory, equipments for the plastic deformation on the surface of the rectangular billet have been developed. The surface plastic deformation behavior of the Q235 and the directionally solidified (DS) TiAl billet has been studied using these equipments. The metal flow behaviors after four plastic deformation techniques were studied using the commercial finite element method (FEM) and simulated experiments. The stress-strain distribution along the depth of the as-deformed billet was also obtained. What’s more, the microstrucutural evolution of the Q235 and the directionally solidified TiAl billet were investigated after cold deformation and subsequent heat treatment.These four surface plastic deformation processes on the directionally solidified TiAl were simulated with the FEM software ABAQUS-6.7. The results indicate that the plastic deformation was localized within the surface of 1mm and the maximum equivalent strains were 0.2,0.22,0.032 and 0.25, respectively. The strain type distribution of four surface plastic deformation techniques by quantitative and qualitative analysis of elasticity and plasticity was obtained. The strain distribution on the surface of the billet after compound rolling is subject to plane strain; strain distribution along the depth of the billet after ball burnishing and surface milling changes from tension to compression; while, strain distribution along the depth of the billet after controlled shot peening changes from compression to tension.The microstructure after the surface plastic deformation was observed, which indicate that the Q235 grains on the surface of the billet turn into fiber-like line after the compound rolling, ball burnishing, surface milling and controlled shot peening. The compound microstructures that are fine grains on the surface and the coarse grains in the center after the subsequent recrystallization annealing are obtained as for the compound rolling, ball burnishing and surface milling. But for the grains on the surface of the shot peened sample with recrystallization annealing grow coarser because of critical deformation zone.The coarse-column grains of the directionally solidified TiAl on the surface of the billet were recrystallized, while the microstrcuture keeps the original state after the compound rolling. The fully lamellar structures occurs strong kinking after ball burnishing, surface milling and controlled shot peening. The cold deformed billets were subject to vacuum heat treatment aboveαtransus line of 10~20oC for several minutes. The results indicate that the microstructures are characterized by microstructual gradient,namely fine recrystallized grains on the surface and the original directionally solidified microstructures in the center were obtained after ball burnishing and surface milling. The grains on the surface of the shot peened sample with subsequent heat treatment grow coarser because of critical deformation zone.更多还原