激光快速成形过程中熔覆层的两种开裂行为及其机理研究

The Research on Two Kinds of Cracking Behavior and Mechanism of Cladding in Rapid Laser Forming Process

激光快速成形技术是在激光熔覆技术及快速原型技术的基础上发展起来的一项新的先进的制造技术,能够实现高性能致密金属零件的快速无模近终形制造。但是,如果成形条件控制不当,易于在成形件中产生裂纹、气孔、夹杂、层间结合不良等缺陷,而裂纹是成形过程中最常见、破坏性最大的一种缺陷。本文采用微观测试分析方法,深入研究了激光快速成形某些合金粉末过程中熔覆层的开裂行为及裂纹形成机理。研究结果表明,对于镍基自熔合金,熔覆层的开裂属于冷裂纹范畴,是熔覆合金的低延性及成形过程中热应力双重作用的结果。对于奥氏体不锈钢等材料,熔覆层的开裂属于热裂纹范畴,裂纹产生的主要原因是由于凝固温度区间内晶界处的残余液相受熔覆层中的热应力作用所导致的液膜分离的结果。

Rapid Laser Forming (RLF) was a new and advanced manufacture technology which has been developed on the base of combining high-power laser cladding technology with rapid prototyping to realize net shape forming of high performance dense metal components without dies. However, such defect as crack, pore, oxidation and ill bonding between cladding layers might appear in RLF parts if the process parameters controlled improperly. And crack was a kind of defect, which was the most familiar and companied with the largest brisance. The forming mechanism of the crack producing in the process of laser forming some alloy powders has been studied deeply in the paper through micro measurement and analysis methods. The results showed that the cracking behavior was different with different cladding materials. For the materials such as nickel-base self-fused alloys the cracking of laser cladding belonged to the cold crack domain. It was the result of synergistic effect of low ductility of such alloys and thermal stress inducing during laser cladding. On the other hand, for the materials as austenite stainless steel etc. the cracking of laser cladding belonged to the hot crack domain. It was mainly caused by the separation of the liquid films in the grain boundary under the effect of thermal stress existed in the cladding which was producing in RLF.