激光热力逐层交互增材制造方法及组织/应力调控机制

To solve the challenge of internal stress and metallurgical defects generated by laser melting/solidification process during additive manufacturing, on the basis of the fact that plastic deformation can effectively eliminate internal stress and close metallurgical defects generated by the thermal effect, the laser integrated additive manufacturing technology by layer-by-layer & alternately thermal/ mechanical effects is developed for the first time, and the integrated technology and the corresponding controlling mechanism are investigated. .Three following issues will be focused in this proposal. The first is to analyze the internal stress distribution and metallurgical defects of metallic component manufactured by selected laser melting (SLM), investigate the effects of the process parameters on surface morphology, microstructure and residual stress, and reveal the thermal-mechanical effect induced by laser shock peening without coating (LSPwC). The second is to explore the evolution process of internal stress, the formation process and closure behavior of metallurgical defects for forming metallic component, investigate the effects of technological parameters on the forming precision, and achieve the technic criteria of the integrated additive manufacturing on the basis of the matching relationship between SLM and LSPwC process parameters. The third is to develop the strong correlations between the technological parameters, microstructure and mechanical performance in system, and reveal the couple mechanism controlling residual stress and microstructure of forming metallic component under the layer-by-layer & alternately thermal/mechanical effects..The above research involves many new scientific issues, and these research achievements can not only enrich and develop the laser additive manufacturing theory, but also provide the scientific basis for the manufacturing technology of the key important components.

针对增材制造中内应力造成金属成形件易于变形开裂的“控形”和冶金缺陷导致疲劳性能较差的“控性”难题，结合塑性变形“逐层”消除内应力和冶金缺陷的思想，本项目提出选区激光熔化-激光冲击强化热力效应逐层交互增材制造新方法，开展组合工艺和组织/应力调控机制研究，主要包括：⑴分析熔化成形件内应力分布和冶金缺陷特征，研究无吸收层冲击强化工艺参数对熔化区表面形貌、微观结构和应力的影响，阐明无吸收层冲击强化的热力作用机理；⑵探索热力交互作用下成形件内应力演化过程、冶金缺陷形成和闭合行为，研究工艺参数对成形精度的影响，获得选区激光熔化和冲击强化工艺参数之间的匹配关系，建立组合增材制造工艺准则；⑶建立成形件工艺参数-微观结构-力学性能的关系模型，揭示典型合金激光热力逐层交互的形性调控机制。相关内容涉及众多全新科学问题，研究成果可以丰富和发展激光增材制造理论，为提升关键重要构件制造水平提供科学依据和技术基础。

针对增材制造中内应力造成金属成形件易于变形开裂的“控形”和冶金缺陷导致疲劳性能较差的“控性”难题，结合塑性变形“逐层”消除内应力和冶金缺陷的思想，本项目提出激光热力效应逐层交互增材制造新方法，开展组合工艺和组织/应力调控机制研究。主要取得了以下进展：① 激光冲击强化有效促进了SLM成形Ti6Al4V合金中的马氏体组织细化，同时，显著提升了其拉伸和热腐蚀性能，揭示了其强韧化机理和热腐蚀性能强化机制；② 激光冲击波使两个方向SLM成形Ti6Al4V合金的残余拉应力均转变为较深的残余压应力，两个成形件均具有良好的强度和塑性匹配，揭示了激光冲击强化和成形方向对拉伸性能的影响机制；③ 经LSPwC后，相邻熔化层界面处(i) 冲击波在熔化层表层预先诱导产生高密度位错和纳米孪晶，(ii)快速热处理作用促进了再结晶，细化为超细纳米晶；④ 层间LSP有效阻碍了柱状晶的外延生长，等轴晶和短的柱状晶沿沉积方向交替分布。极限抗拉强度和延伸率分别提高了20.8%和60.4%，实现强度和塑性的同步提升；⑤ LSP使Ni25/Fe104熔覆层残余拉应力转变为残余压应力，同时，表面显微硬度提高了约32%，表层产生了高密度的位错和大量的纳米孪晶结构，从而显著提升了Ni25/Fe104熔覆层的耐磨损性能。.在项目执行期内，圆满完成计划任务书中各项任务。成果获2020年中国国际工业博览会“CIIF创新引领奖”和2019年江苏省科学技术奖一等奖，主要研究成果发表论文18篇，其中SCI收录17篇，EI收录1篇。获美国授权发明专利5件、中国授权发明专利4件，获得软件著作权2件。参加国际/国内会议交流25人次，作邀请报告7次。研究执行期内，项目组获得国家级人才项目1人次、省级人才项目2人次、1人当选为激光加工技术委员会委员。项目培养博士生2名、硕士研究生6名，获校优博1篇。