空心叶片激光直接制造中超细柱状晶与结构特征的相互作用机制

Advanced hollow blades with complex cooling channel, thinner wall-thickness and more structural characteristics has brought great challenges to blades manufacturing technology. Laser Direct Forming (LDF) is an advanced forming technology with great potential to fabricate hollow blades. However, the structural characteristics of hollow blades will affect the growth of superfine columnar crystal in LDF, so the columnar crystal at the overlapping area of different layers and different tracks may transformed into non-columnar crystal and this transformation will affect the mechanical properties of hollow blades seriously. The study focuses on the interaction mechanism between structural characteristics of hollow blades and the growth of superfine columnar crystal using numerical simulation and solidification principle, and the formation conditions of non-columnar crystal at the overlapping area of different layers and different tracks are investigated in detail. It proposes to illustrate the interaction mechanism between structural characteristics of hollow blades and the growth of superfine columnar crystal and also want to clarify the formation mechanism of non-columnar crystal at the overlapping area of different layers and different tracks. This investigation will lay a foundation for the hollow lades forming with superfine columnar crystal in LDF. The research achievement will provide a new idea to fabricate turbine blades and aeroengine with superfine columnar crystal and it can also be used to repair the directionally solidified turbine blades. In the end, it can meet the demands of hollow blades of national great equipments manufacture and defense industry.

具有复杂冷却流道的先进空心叶片，结构越来越复杂，壁厚越来越薄，给叶片制造带来了巨大的挑战。用激光直接成形（LDF）空心叶片是一种很有发展潜力的先进成形技术。但LDF超细柱状晶定向生长与空心叶片结构特征会相互作用，在搭接处和上下层之间沿基材定向生长方向柱状晶会转变为非柱状晶，从而严重影响超细柱状晶空心叶片的力学性能。采用数值模拟和定向凝固原理相结合的方法，研究空心叶片结构特征与超细柱状晶定向生长的相互作用规律，探讨LDF空心叶片柱状晶在搭接处和上下层之间非柱状晶的形成条件。阐明空心叶片结构特征与柱状晶定向生长的相互作用机制，并揭示LDF空心叶片柱状晶在搭接处和上下层之间非柱状晶的形成机理，为LDF健全的超细柱状晶复杂空心叶片奠定基础。研究成果即可为燃气轮机和航空发动机提供一种制造超细柱状晶空心叶片的新思路，又可用于现役定向凝固叶片的修复，满足国家重大装备制造和国防工业对空心叶片制造的急需。

具有复杂冷却流道的先进空心叶片，结构越来越复杂，壁厚越来越薄，给叶片制造和修复带来了巨大的挑战。用激光直接成形（LDF）和修复空心叶片是一种很有发展潜力的先进成形技术。但LDF超细柱状晶定向生长在搭接处和上下层之间，沿基材定向生长方向柱状晶会转变为非柱状晶，从而会严重影响超细柱状晶空心叶片的高温力学性能。课题主要研究空心叶片结构特征与超细柱状晶定向生长的相互作用规律，探讨LDF空心叶片柱状晶在搭接处和上下层之间非柱状晶的生长特点。重点研究了以DZ125L柱状晶高温合金为基材，粉末为FGH96、DZ125L、DD4（单晶高温合金）三种高温合金粉末的激光直接成形和修复工艺。主要研究内容：（1）研究了LDF三种高温合金定向组织生长的合适成形工艺参数；（2）研究了激光熔覆修复三种高温合金定向组织与高温力学性能；（3）研制了角度可调式四管送粉喷嘴；（4）研究了不同扫描方式对薄壁件随轮廓曲率半径和沉积高度残余内应力分布规律；（5）研究了热处理工艺对三种高温合金柱状晶组织与高温力学性能的影响；（6）探讨了感应加热辅助LDF DD4高温合金定向晶生长；（7）工艺参数对LDF DD4定向晶柱状晶组织的影响；（8）研究了感应加热辅助LDF DD4定向生长沉积层的热处理工艺。并重点研究了感应加热辅助LDF DD4定向生长修复DZ125L柱状晶空心叶片。结果表明：在感应加热1200℃条件下，获得定向晶沿[001]方向连续外延生长的DD4修复样件，定向柱状晶晶粒平均直径从2.5μm增大到15.2μm，晶界减少，部分横向晶界消失，这非常有利于提高DD4修复件的高温性能。沉积层高温合金的室温力学性能优于铸造水平，高温力学性能接近铸造水平。研究成果即可为燃气轮机和航空发动机提供一种制造超细柱状晶空心叶片的新方法，又可用于现役定向晶叶片的修复，满足国家重大装备制造和国防工业对空心叶片制造和修复需要。