激光熔覆微合金化Co-Al-W合金界面相容性及强化相形成机理研究

The Co-Al-W superalloy with γ′-Co3(Al,W) phase by precipitation strengthening have high temperature strength and excellent high temperature comprehensive performance, which could meet "extreme" environment requirements,such as the coal gasification device and ultra-super critical steam turbine unit.However, the γ′-Co3(Al,W) strengthening phase formation mechanism of cladding layer Co-Al-W superalloy, and the interface compatibility of cladding layer Co-Al-W superalloy and substrate at laser cladding nonequilibrium solidification process are few researches.The project aims to study the effect with microalloyed elements to interface compatibility of cladding layer Co-Al-W superalloy and substrate,such as wettability,thermal expansion coefficient, cracking, and microstructure refinement, reveal the functional mechanism of microalloyed elements to the γ′-Co3(Al,W) strengthening phase formation, the number, size and form of existence,and microstructure refinement of the cladding layer Co-Al-W superalloy.Moreover,the constitutive relation of microalloyed elements to interface compatibility of cladding layer and substrate at laser cladding conditions is studied. The research projects play an important roles for improving the cladding layer and substrate interface compatibility, improved quality and high temperature performance, reduce costs and broaden the scope of application of cladding layer Co-A-W superalloy.

由γ′-Co3(Al,W)相沉淀强化的Co-Al-W合金具有优异的高温强度和良好的高温综合性能，有望满足煤气化或超超临界火力发电等装置中“极端”环境的使用要求。但对激光熔覆非平衡凝固过程中新型Co-Al-W合金中γ′强化相的形成机理，以及熔覆层合金与基体界面相容性的研究较少。本项目主要研究激光熔覆条件下，微合金元素对激光熔覆层Co-Al-W合金与基体润湿性、热膨胀系数、开裂性等界面的相容性和组织细化的影响，揭示微合金元素对熔覆层合金中γ′强化相析出、数量、尺寸、形成和组织细化的作用机理，以及微合金元素与改善熔覆层合金与基体界面相容性之间的本构关系。本项目的研究成果对改善熔覆层合金与基体相容性、提高熔覆层Co-A-W合金质量和高温性能，降低合金使用成本，拓宽合金应用范围具有重要的意义。

本项目围绕合金化元素对激光Co-Al-W合金熔覆层性能和真空电弧熔炼制备微合金化合金组织、性能的影响进行了实验研究，同时，为了验证实验结果的准确性和科学性，对微合金化合金中强化相的组成进行了热力学模拟计算，通过两种方法取得的阶段性研究成果基本吻合。研究结果发现，激光熔覆Co-Al-W合金熔覆层开裂的主要原因是合金与基体的物理性能不相匹配所致，通过微合金化和激光熔覆工艺优化，可以明显抑制裂纹的形成和扩展，在不锈钢基体上制备出了综合性能优异的Co-Al-W合金熔覆层。微合金化可以明显改善Co-Al-W合金中强化相的数量和分布形式、抑制有害相的形成，进而提高合金的抗高温氧化、耐热腐蚀等高温性能，同时，可以显著提高合金的硬度和强度。