The microstructure of laser-fabricated Ti{sub}6Al{sub}4V

摘要

Direct Laser Fabrication (DLF) or Laser Engineered Net Shaping (LENS) is a manufacturing process for fabricating metal parts directly from metal powder and from CAD solid models by using a laser. In this study Direct Laser Fabrication has been used to produce Ti6Al4V samples for microstructural and mechanical property studies. It lass been found that nearly fully dense Ti64 samples can be produced using this technique. The density of Ti64 samples varies, for a range of processing conditions, between 94 to 99%; the density depending upon laser processing parameters, such as powder feed rate, scan speed and z-increment. A much lower density highly porous structure can be obtained when the ratio of the powder feed rate/scan speed is low. The macrostructure and microstructure of a build are influenced by processing conditions and heat extraction rate along x,y,z directions. Long columnar grains are commonly obtained along the length of samples (the z-direction) at low scanning speeds (<800 mm/min). A fine basket-weave microstructure is obtained in most of the samples and alpha and beta laths become even finer with increase of the scan speed. The correlation between the microstructure of DLFed samples and the input energy density has been assessed. The effects of laser processing conditions on microstructure and density are discussed.