Study On SRR99Ni-based Single-crystal Superalloy By Selective Laser Melting

At present, directional or single crystal blades are applied in almost all of the advanced commercial and military engines. However, the inlet temperature of the turbine goes far beyond its temperature capability as the thrust-weight ratio develops to higher levels. Single-crystal turbine blades with complex cooling channels have become the optimum choice to solve the above problem. Unfortunately, it is a tough challenge for the traditional casting technology to manufacturing this kinds of blades.Based on the principle of additive manufacturing, selective laser melting (SLM) has virtues to develop a new route of preparing single crystal and fabricating complex turbine blades simultaneously. However, no report of preparing single crystal by selective laser melting technology has been presented till now.In the present work, SRR99superalloy powders were used as the starting material and the thin walls and bulks of samples were fabricated by SLM. The effects of key parameters, such as laser power, scanning speed, layer thickness, scanning line space, scanning strategy and deposition height have been investigated. The primary dendrite space, composition segregation and crystal orientation of SLMed and casted SRR99samples were compared. Finally, the formation mechanism of SLMed single crystal has been discussed in detail.The results show that SLMed SRR99samples are much easier to crack at higher laser powers and lower scanning speeds. The change of laser power causes the sensitivity of cracking more serious than that of scanning speed. The parameters of layer thickness, scanning line space, scanning strategy have no obvious effect on the character of epitaxial growth and crystal orientation. Industrial single crystal of2mm high can be prepared at laser powers of160～200W and scanning speeds of10～30m/min. With the increase of deposition height, the dispersion of crystal orientation increases. Compared with the single-crystal substrate, the SLMed SRR99single-crystal samples have an average primary dendrite space of1～2μm and a uniform element distribution.