Exeprienmental Study On Direct Laser Fabrication Of Titanium Matrix Composites Based On Single-path Laser Cladding

To develop the wear resistance of the surface of titanium alloys, according to the tendency of the development of composite materials, TC4 powder together with B4C or C/B powder mixture was used as the laser cladding materials on the surface of TC4 titanium alloy substrates. Wear resistant composite coatings were prepared in-situ. The experimental study of direct laser fabrication of titanium matrix composites was also carried out.In this experiment, mix powder with the ratio of 90%TC4+10%B4C (wt.%) was first prepasted on TC4 substrates, on which single and multi-path layers were prepared with laser cladding technology. Based on the results from the laser cladding of prepasted layers, a powder feed head of the synchronized coaxial powder feed laser cladding system was designed by ourselves though which single-path layers and a direct laser fabricated thin wall specimens were prepared. Microstructure and components of the cladding layers were characterized using OM, SEM,TEM, EPMA and XRD. The microhardness of all the specimens and the wear resistant properties of multi-path coatings produced by laser cladding prepasted layers were measured.Optimized processing parameters were obtained though a series of experiments. The optimized laser processing parameters for pre-pasted single-path laser cladding layers were as follow:defocusing distantce of 15mm, laser pulsed current of 150A, laser scanning speed of 3.0mm/s. The optimized parameters of synchronized powder feed laser cladding were as follow:defocusing distance of 20mm, laser pulsed current of 250A, laser scanning speed of 0.3mm/s; the relevant.powder feed parameters:Ar gas powder feed flow rate of 8L/min, powder feed rate of 9.97g/min.Experimental results show that two and more kinds of ceramic reinforcements were in-situ formatted in the matrix of TC4 (Ti-6A1-4V). TiB and TiC ceramic were formed evenly with the morphology of needle, tiny dendrites and disperse particles in the single-path specimens and a small amount of TiB2 in the muitl-path prepasted laser cladding specimens.The average microhardness of the multi-path layer was 650 HV which is twice of that of the substrate (320HV). The wear weight loss is 0.0021g which is far lower than that of the substrate (0.0077g) as well. The wear resistant properties increased over 3 times. Strong connects between coatings and the substrates were also formed according to the thermal shock experiemnt results.The single-path layers of the raw materials with same component ratio were formed by synchronized coaxial powder feed laser cladding system as well. The main ceramic reinforcements were TiB2 (hexagonal prism and rodlike) TiB (needlelike) a small amount of TiC (disperse particles) and some un-reacted B4C.A Ti-6A1-4V/ (TiBx+TiC) thin wall specimen was successfully prepared using the optimized processing parameters of the synchronized coaxial powder feed laser cladding. Primary study on its microstructure was also carried out.