Characterization of Laser Additive Manufactured Al-Si Coating on Titanium Alloy

Abstract

Abstract The study is aimed at using laser surface cladding process, by using coating composite of Al-Si cladded onto a Titanium alloy (α/β) substrate. The ratio of the composite metal layer coating used to metallurgically bond with the substrate consisted of 80, and 85% Al and 15 and 20% Si. This was performed by using a YLS laser system that produced a perpetual wave of 3 kW, which consisted of a concentric system of a jet-nozzle and powder feeder. The different layers resulting from the process, consisted of three microstructural zones: the coating, coalesced surface and the substrate. From the observations conducted, it was revealed that the AlSi alloy matrix consisted of a uniform distribution of hard TiSi particles embedded in the cladded area. The intent was to improve the hardness property of the titanium alloy substrate by achieving a uniform distribution of crack and defect free hard particles. The cladding process parameters was optimised to obtain desirable mechanical properties and the desired porous and crack free, Si particles distribution. The final samples fabricated were microstructurally examined, and hardness tested. The X-ray Diffraction (XRD) system was used to identify all the phases formed. The interface had the composite coating powder partially melted around it, due to the high temperature input that was produced, but most of the particles were retained. At the lowest heat input of 90 J•mm-2, the clad layer had a microhardness of 610. 8 HV0.1, and the highest temperature input of 113.8 J•mm-2, produced maximum microhardness of 693.6HV0.1. The substrate consisted of beta and alpha Titanium phases, but the metallic matric clad consisted of AlSi3Ti2, Ti2AlC, Ti3Al, Ti and TiV phases. A relationship between the laser coating and the incident temperature input was found to be in direct proportion. The relationship between the hardness of the coated composite layers on the substrate and the increased dilution ratio was also found to be in direct proportion. The microhardness of the coated layers was found to be improved by 56.2%, when compared to the microhardness of the uncoated Ti-6Al-4V substrate. The hardness of Al-20Si at laser power of 950°C and scanning speed of 1.0 m/min was found to be 694 HV0.1.