合金元素对沉淀强化钴基合金可焊性影响

In the Co-Al-W based alloys, domestic and overseas experts were widely developing the studies of the microstructures, ratio of element distribution, stability of γ′-Co3(Al,W) phase and mechanical behaviors, etc. However, the mechanical properties of precipitation hardening those cobalt-based superalloys do not yet exhibit any advantage until now. Prospective applications of the Co-Al-W based alloys like conventional cobalt-base superalloys are mainly determined by the processing properties,especially weldability. In this project, the weldability of Co-Al-W-X (X=C, B, Cr, Ti, Ta and Nb) quaternary alloys are investigated as the target. The effect of alloy elements and their interaction on the susceptibility of the weld to thermal cracking is systematically investigated. The weld specimens are made of the precipitation strengthening alloys by Bridgman directional solidification technique and argon-arc welding or laser beam welding. By means of OM, SEM, electron probe, X-ray diffraction and DSC, the measuring of cracking numbers and total cracking length, the analysis of the cracking mechanism and the role of elements segregation are systemically carried out. Further, new Co-Al-W based weldable alloys jointly strengthened by solution, carbide and precipitates will be designed and prepared. The mechanical properties of the welding alloys are improved through the optimization of heat treating regime. The relationship among the welding parameters, microstructure and mechanical properties of precipitation strengthening cobalt base alloy are revealed during the welding process, then composition-microstructure-weldabiltiy model will be developed, which provide the fundamentals for designing for the commercial Co-Al-W based superalloy.

国内外学者在Co-Al-W基合金组织结构、元素分配比、γ′-Co3(Al,W)相稳定性和力学行为等方面开展了大量研究，但沉淀强化钴基合金的力学性能还没有发现优势，因而像传统钴基合金一样，沉淀强化钴基合金商业化推广应用的关键在于工艺性能，特别是可焊性。本项目以Co-Al-W-X (X=C, B, Cr, Ti, Ta和Nb) 四元合金可焊性为切入点，系统研究合金元素及其交互作用对沉淀强化钴基合金焊接裂纹敏感性影响。采用定向凝固、氩弧焊和激光焊等制备焊接试样，然后采用光学显微镜、扫描电镜、电子探针、XRD衍射和DSC等观察测量分析裂纹数量、裂纹总长度、元素偏析作用和热裂纹形成机理等。在此基础上，设计沉淀强化、晶界强化和固溶强化等多种强化机制作用下的可焊钴基合金，优化焊接热处理制度，提高焊接力学性能。揭示焊接过程中焊接参数-组织结构-力学性能内在关系，建立成分-组织特征-可焊性理论模型。

新型γ′沉淀强化Co-Al-W基高温有望发展成为先进高温结构材料，然而合金元素对材料可焊性的影响机制尚未明确，限制了该材料的实际应用。本项目首先以Co-Al-W-X(X=C, B, Cr, Nb, Ta)系铸造高温合金为研究对象，制备了合金多道次对接焊接头样品，通过光学显微镜、扫描电镜观察统计了对接焊接头中的焊接热裂纹，采用电子探针、XRD衍射和DSC等测试手段分析接头样品的包括合金可焊性、冷却凝固过程、相体积分数、形态、尺寸和成分等显微组织特征，系统研究了合金元素对可焊性的影响，获得了可焊性优异的Co-Al-W-X系合金成分。通过模拟软件优化了合金焊接工艺，进一步降低了裂纹敏感性。在此基础上，设计制备兼备的新型Co-Al-W-X系铸造多晶合金，测试了不同温度下接头的抗拉强度，揭示接头在不同温度下的失效机制，并通过焊后热处理提高合金高温力学性能，为新型钴基合金的实际应用奠定了理论基础。