High Speed Laser Cladding: Optimization of Process Parameters for Medium Thick Coatings

Abstract

The objective of the thesis was to fabricate medium thick (0.4-0.5mm) clad layers by Extreme high speed laser cladding process. Two different base materials such as 42CrMo4 and S355 steel were used with different sets of powders to fabricate a coating with optimum parameters and to achieve a defect-free coating. Two different coatings were made with Inconel 625 (lot 1 and lot 2) using laser power of 3kW and deposition speed of 16m/min to achieve a coating with a dilution of 4.2%, a coverage rate of 0.3m 2/h, powder consumption of 4.6kg/m 2, and a powder catchment efficiency of 78%. Two variations of In625 (lot 1 and lot 2) differed in boron content (where lot 1 contained 0.007% and lot 2 contained 0.003%) and powder size. The sample In625 (lot 1 and lot 2) achieved a thickness of 0.4mm with minimal number of cracks and porosities. The lower boron content resulted in hot crack-free coatings. High entropy alloys such as NiV and TiV were also cladded on top of substrate materials. SEM and EDS analysis also revealed distinct features of the coating and hardness was also measured. However, NiV and TiV HEA’s displayed porosities, brittle cracks and intermetallic that were present in the coating. These intermetallic were the reason for coating to be too brittle. These brittle phases also increased hardness of both the materials. XRD analyses were also performed on both HEA’s. NiV showed presence of dark and bright phases which turned out to be brittle intermetallic leading to cracks. TiV also displayed presence of certain intermetallic which in turn led to brittle cracks too. The findings demonstrate the influence of processing parameters and alloy composition on formation of cracks in laser cladding, highlighting the fact that In625 potentially, is more suitable material for EHLA coatings compared to HEA’s.