Effect of Scanning Speed on Microstructure and Mechanical Properties of GH4169 Alloy Formed by Selective Laser Melting

GH4169 superalloy was prepared by selective laser melting （SLM）, and the effect of scanning speed （600, 800, 1 000, 1 200, 1 400 mm·s⁻¹） on the phase composition, microstructure and microhardness and the high temperature tensile properties under the optimal scanning speed of the SLM formed alloy were investigated. The results show that the scanning speed had no significant effect on the phase composition of the SLM formed alloy. As the scanning speed increased, the porosity of the alloy first decreased and then increased, and reached the minimum value of only 0.01% under scanning speed of 1 000 mm·s^-1, indicating the best densification. The molten pools in the longitudinal section of the alloy were alternately distributed to form a fish-scale shape under different scanning speeds. Under scanning speeds of 600, 800 mm·s⁻¹, there were irregular molten pools and circular metallurgical pores in the longitudinal section of the alloy. With the increase of scanning speed, the morphology of the molten pool boundary was significantly improved. Under scanning speed of 1 000 mm·s⁻¹, the alloy with regular molten pool morphology and nearly fully dense structure was obtained. A large number of irregular unfused pores were formed in the alloy under scanning speed of 1 400 mm·s⁻¹. The microhardness of SLM formed alloy under different scanning speeds ranged from 300 HV to 360 HV. With the increase of scanning speed, the hardness of the alloy basically first decreased and then increased. The hardness was the lowest under scanning speed of 1 000 mm·s⁻¹, approximately 307 HV. The optimal scanning speed for SLM forming of GH4169 alloy was 1 000 mm·s⁻¹; as the tensile test temperature increased from 20 ℃ to 600 ℃, the yield strength and tensile strength only decrease by 12% and 13%, respectively; except for 500 ℃, the percentage elongation after fracture exceeded 10%, and the tensile fracture all showed ductile fracture morphology.