Evaluation of in-situ synthesised titania-zirconia-boron carbide composite cladding on Ti6Al4V substrate using continuous wave fibre laser

Abstract

In this work, titanium metal matrix composite (TiC, TiB2, TiO2, ZrB2) cladding was synthesised by irradiating a fibre laser beam on a mixture of Ti6Al4V alloy, ZrO2, B4C powders pre-placed on Ti6Al4V alloy plate. The effect of varying wt.% of B4C on the microstructure, hardness, erosion, and wear properties of the composite cladding were investigated using XRD, XPS, EBSD, FESEM with EDAX, nano-indentation, and wear tests. Under the exposure of fibre laser on a mixture of preplaced powders, the in-situ formation of TiC, TiB2, TiO2, and ZrB2 ceramic particles have taken place and get uniformly dispersed in the molten titanium alloy matrix. The volume fraction of these phases increases with the increasing percentage of B4C. A black willow-shaped structure (TiB2) is observed in sample BM3 (30 wt% of B4C), along with grey cellular dendrites (TiC) dispersed uniformly in the matrix. The average microhardness of the claddings increases with the increase of B4C contents. The average weight loss of the cladding samples in dry sliding wear tests decreases with increasing the B4C content. The maximum microhardness of 1582.4HV300 is recorded in BM3 cladding, which is almost four times higher than the substrate material. The decrease in the average value of maximum nano-indentation depth with an increase in the content of B4C is in good agreement with the results of microhardness tests. The hardening of the cladding is also accompanied by increased values of parameters H/E (hardness(H)/Young's modulus (E)) and H3/E2(0.133), indicating better resistance to crack formation during indentation even at higher loads showing the cladding is hard as well as tough. The grain size variation and volume fraction of TiC–TiB2 obtained from electron backscatter diffraction test results agrees with cladding having these properties. The coefficient of friction (0.15–0.25) is found to be lower than the substrate material (∼0.3). The claddings also show good erosion resistance at ambient, 250 °C, 350 °C and 750 °C.