Laser metal deposition (LMD) is one of the manufacturing processes in the industries, which is used to enhance the properties of components besides producing and repairing important engineering components. In this study, Stellite 6 was deposited on precipitation-hardened martensitic stainless steel (17-4 PH) by using the LMD process, which employed a pulsed Nd:YAG laser. To realize a favor deposited sample, the effects of three LMD parameters (focal length, scanning speed, and frequency) were investigated, as well as microstructure studies and the results of a microhardness test. Some cracks were observed in the deposited layers with a low scanning speed, which were eliminated by an augment of the scanning speed. Furthermore, some defects were found in the deposited layers with a high scanning speed and a low frequency, which can be related to the insufficient laser energy density and a low overlapping factor. Moreover, various morphologies were observed within the microstructure of the samples, which can be attributed to the differences in the stability criterion and cooling rate across the layer. In the long run, a defect-free sample (S-120-5.5-25) possessing suitable geometrical attributes (wetting angle of 57° and dilution of 25.1%) and a better microhardness property at the surface (≈335 Hv) has been introduced as a desirable LMDed sample.

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Heat-affected zones (HAZs) of Inconel 939 (IN-939) superalloy are susceptible to cracking during welding process. Preventing cracking during the repair welding of turbine components is important. In this study, the effects of heat input and pre-welding heat treatment on the microstructure, mechanical properties and crack formation in tungsten inert gas welding of IN-939 were investigated. The whole specimens were welded using Inconel 625 filler in an Ar atmosphere and characterised by metallographic examinations and hardness measurements. Results showed that the microstructures of IN-939 HAZs were highly susceptible to cracking during welding due to increasing of γ′ volume fraction. All of these cracks appeared in the HAZs and grew perpendicular to the melting zone along the grain boundaries. In this survey, the pre-welding heat treatment and heat input strongly affected the HAZ microstructure and hardness. However, the pre-welding heat treatment with 67% impact was more effective than heat input with 30% impact. Finally, hot tensile tests were carried out on the specimens of the base metal and the optimal specimens under similar operating conditions within 600 °C–800 °C. Welding process did not affect the yield strength of the superalloy but slightly decreased its ultimate strength and elongation by as much as 92% and 50%, respectively, of those of the base metal.

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