Alloying of surface layer of the Ti-6Al-4V titanium alloy through the laser treatment

Purpose: The purpose of this paper is modification of the Ti-6Al-4V titanium alloy surface layer properties through laser alloying technology. Design/methodology/approach: Laser treatment was performed on the samples coated by graphite and BN powders in stream of nitrogen. Thopography of the surface of laser melted layer was investigated. Microstructure,fracture surface and chemical composition analysis were made by using Epiphot 300 optical microscope and Novascan 30 scanning electron microscope equipped with EDS X-ray detector. Phase composition was determined using X-ray diffractometry (Philips) with CuKα radiation. The Vickers hardness under load of 1.96 N and thermo-electric power was measured on the surface of cross-sections. Findings: Laser treatment has produced a surface layer which consists of hard ceramic TiC, TiN and TiB particles spaced in ductile martensitic matrix. Under the layer, the heat affected zone containing martensitic Tiα’ phase is present. The hardness obtained on cross-sectioned layer increases clearly in comparison with the base material. The high hardness level (HV 920 - 570) can be attributed to the formation of TiN, TiC and TiB phases. The thermoelectric power decreases noticeably with hardness increase and enables alloying process evaluation. Research limitations/implications: Research range was limited to investigation of microstructure, phase composition and hardness effects of laser alloying process. In order to estimate the influence of the laser alloying technology on durability of the layer, supplementary wear resistance tests will be performed in future research. Practical implications: The surface alloying by laser irradiation is investigated as a process capable to produce coatings composed of metallic matrix reinforced by ceramic particles and this can increase durability of elements made of titanium alloys. Originality/value: The wide range of investigations contained microstructure, phase and chemical composition analysis as well as fractographic and thermo-electric power estimation enables in-depth analysis of alloying process efficiency.