Abstract
This study investigated the metallurgical, mechanical properties and quality of coatings fabricated by direct laser metal deposition (DLMD) on Ti-6Al-4V, which were affected by the DLMD optimized process parameters. A 3-kW continuous wave ytterbium laser system (YLS) attached to a KUKA robot was used for the process. An analysis was conducted to determine the quality of the coatings in terms of hardness and wear resistance. Variables such as the time of interlayer deposition, thickness of the substrate, the initial temperature of the substrate, and the number of deposited layers were also investigated. The independent/collective effect that each process parameter had on the metallurgical and mechanical properties of the deposited Ti-6Al-4V were made clear when the processing parameters were varied. Minute pores/defects that significantly affect the metallurgical and mechanical properties of clads were also identified. The results obtained from the designed experiments showed that the depth of Heat Affected Zone (HAZ) was inversely proportional to the thickness of the substrate; as the thickness of the substrate was increased, the HAZ depth decreased. Moreover, the intensity of the laser power also affects the HAZ depth. In addition, it was discovered that the initial conditions of the substrate at room temperature also affected the coatings in relation to pre-heated conditions. The analysis conducted in identifying and quantifying the porosity showed indication that the factors such as scanning speed, laser power and powder feed rate had a predominant influence on the porosity. The grain form and structure as well as the mechanical properties of the cladded layer were significantly affected by the optimized process parameters of DLMD process. The parameters investigated had a significant impact on the hardness and wear resistance performance. Furthermore, the results revealed that the highest hardness of one of the coatings was 1.97-times the substrate which had a hardness value of 302 HV. The outstanding wear resistance performance of Al-Si-Sn-Cu/Ti-6Al-4V composite coating is attributed to major hard intermetallic phases.
Highlights
This study investigated the metallurgical, mechanical properties and quality of coatings fabricated by direct laser metal deposition (DLMD) on Ti-6Al-4V, which were affected by the DLMD optimized process parameters
The grain form and structure as well as the mechanical properties of the cladded layer were significantly affected by the optimized process parameters of DLMD process
The results revealed that the highest hardness of one of the coatings was 1.97-times the substrate which had a hardness value of 302 HV
Summary
The base material used in the present investigation was Ti-6Al-4V alloy with the chemical composition shown in Table 1. 80 Â 80 Â 50 mm was the dimension of the base metal. Cleaning of the base metal was necessary before the starting of the DLMD process in order to reduce radiation reflection and improve the rate of absorption of beam radiation unto the substrate ref. A protecting gas to avoid oxidation during the DLMD process ref. Optical microscopy and scanning electron microscopy were engaged to discern the microstructure of the clad in advance and afterwards the laser deposition process in agreement with ASTM F728-81 standard. X-ray Diffraction was engaged to discern the phases in the clad in agreement with ASTM E1426-14 standard. The microhardness of the base metal was measured at 302.29 HV0.1 in agreement with ASTM standard. The laser power levels employed were 900e1000 W, powder flow rate of. 2.0 g/min, gas flow rate of 2.0 L/min, a beam diameter of 2 mm, while scan velocities were 1.0e1.2 m/min
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