Addition of ceramic particles to TIG melted titanium surfaces

Abstract

A surface layer metal matrix composite has been developed by using a tungsten inert gas (TIG) arc with an operating current of 60 A. The 0·5 mm thick coating of a powder mixture containing 80 vol.-% titanium and 20 vol.-% 40 μm SiCp particles was pre-placed on commercially pure titanium surfaces using a suitable binder. The powder coating was then melted by traversing specimens beneath a Miller TIG arc using 110, 90, 55, and 45 MJ m-2 energy densities. Glazing at energy densities from 55 to 110 MJ m-2 completely dissolved the powder mixture and produced 1 mm deep hard (500 to 600 HV) layers which were free from pores, cracks, and cavities. The tracks had smooth and reflective surfaces. The microstructure developed in the tracks is dominated by the reaction of SiCp particles with the molten titanium layer to form titanium carbide (dendrites), Ti5 Si3, and titanium. Processing with 45 MJ m-2 energy density arc produced pores and cavities in the melt pool; the microstructure consisted of agglomerated and partially dissolved SiCp, fine dendrites, and globular particles with hardness ranging from 800 to 1600 HV over a 500 μm thickness.