Ti-Al Surface Alloy Formed By Pulsed Electron Beam Melting Of Film-substrate System

TiAl/Ti3Al-based Ti-Al alloys are lightweight high-temperature structural materials and have been extensively used in advanced aerospace engine, weapon and civilian industry owing to their specific properties, such as low density, high strength, good corrosion resistance, good mechanical properties at high temperature, high oxidation resistance, and the service temperature is up to700-1000. The surface property of material is a key factor for the reliability and service life of the workpiece. If fabricate the Ti-Al surface alloys on the surface of the material, which can improve the surface property of the material. TiAl/Ti3Al-based Ti-Al surface alloys fabricated on the Ti substrate can make the surface have the excellent performance and which is suitable for use as structural protective coatings.In this paper, The Ti-Al surface alloys in the wide range of composition were fabricated using procedures of Al film deposition onto a-Ti substrate followed by pulsed melting using microsecond and sub-millisecond low-energy high-current electron beam (LEHCEB).In each synthesis cycle of microsecond mode,100nm thickness of Al film was deposited onto a-Ti substrate firstly, then the coated sample was irradiated by LEHCEB with pulse width3μs and energy5J/cm2, the cycle number varied from5to50.In each synthesis cycle of sub-millisecond mode,1μm thickness of Al film was deposited onto α-Ti substrate firstly, then the coated sample was irradiated by LEHCEB with pulse width100μs and energy10J/cm2, the cycle number varied from3to7.Scanning Electron Microscope, Electron probe micro-analysis, grazing incidence X-Ray diffraction analysis, transmission electron microscopy and nanoindentation were used to investigate the characterization of Ti-Al surface alloy.The main analysis results are following:The TiAl-based surface alloys were produced using microsecond mode. Microcrack was found in all surface alloys, but the post-synthesized electron beam treatment can reduce the cracking in some degree. The thickness of alloy layer is-3μm, Al content in the-1μm thick surface layer is-60at.%. The tetragonal TiAl and TiAl2intermetallics, synthesized at the top surface, have nanocrystalline structure. The main phase formed in the-2.5μm thick surface is TiAl, besides, there are a little of TiAl2and Ti3Al. Dislocation was enhanced in the alloyed layer. The nanohardness of Ti-Al surface alloy increased significantly compared with α-Ti substrate because of the nanostructure and enhanced dislocation. Due to the e-beam remelted repeatedly, the Ti-Al surface alloy mixed sufficiently with α-Ti substrate. There is no obvious boundary between the alloyed layer and substrate.The Ti3Al-based surface alloys were produced using sub-millisecond mode. The microcrack was found in the surface alloys too. Due to the long pulse width and large energy electron beam irradiation, the diffusion distance of Al element increased greatly, the thickness of Ti-Al alloy layer reached～10μm. Ti-Al surface alloy mixed sufficiently with α-Ti substrate and there is no obvious boundary between the alloyed layer and substrate too. But the Al content is below25%in the alloy layer. The～200nm thickness of Ti3Al nanocrystalline was synthesized at the top surface. There is a lot of willow phyllode α-Ti grain in the internal of alloy layer. The Ti3Al content increased in the alloy layer along with the increase of the cycle number. Dislocation was enhanced in the alloyed layer too. The nanohardness increased significantly in the-20μm thickness from top surface to the substrate.In a word, TiAl/Ti3Al-based surface alloy layer is formed on the α-Ti substrate via multiple pulsed liquid-phase mixing of pre-deposited Al film with α-Ti substrate using intense microsecond and sub-millisecond electron beams.