High Temperature Evolutions And Laser Ablation Behaviours Of W/ZrC Cermets Fabricated By Reactive Melt Infiltration At Relative Low Temperature

With a combination of refractory metal Tungsten(W) and ultra- high temperature ceramic Zirconium Carbide(Zr C), W/Zr C cermets have a great application prospect in high temperature fields, such as the rocket nozzle and high temperature tensile clamp and so on. As one kind of methods fabricating W/Zr C cermets, the Reactive Melt Infiltration method(RMI) has attracted much more attentions for its advantages of simple processes, low requests for requirements, near net shape for complex components. However, owing to low temperature of fabrication, the compositions, microstructures and properties of RMI-derived W/Zr C cermets may have great changes in high or even ultra-high temperature environment, and sequentially have an influence on the service properties of W/Zr C cermets. At present, there are few studies about these, so in this paper, high temperature evolutions of compositions, microstructures and mechanical properties of RMI-derived W/Zr C cermets were researched. Meanwhile, a laser was used to examine ablation resistance of W/Zr C cermets in dynamic high temperature environment.Ultra-high temperature W/Zr C cermets were fabricated by Reactive Melt Infiltration at relative low temperature. XRD was used to analyze the compositions of RMI-derived W/Zr C cermets, and results shown that W/Zr C cermets not only contained W and Zr C, but also some impurities, such as WC, W2 C, W2 Zr and Zr-Cu alloys. BSE, EDS and Image J software were used to examine the microstructures of RMI-derived W/Zr C cermets, and results shown that W/Zr C cermets were mainly composed of dispersive W phase(44.7vol%, volume percentage), continuous Zr C phase(44.4vol%), residual Zr-Cu alloys(10.6vol%) and pores(0.3vol%), but W2 C and W2 Zr and so on could not be distinguished.High temperature evolutions of compositions and microstructures of RMI-derived W/Zr C cermets were studied. It is found that open porosity and weight loss of W/Zr C cermets increase with the increasing temperature, attaining a maximum of 9.29vol% and 5.51wt% at 2600°C, respectively. While their density decreased from original 10.62 g/cm3 to 9.89 g/cm3 at 2600°C. All these were caused by the melting loss of low melting point of Zr-Cu alloys. Meanwhile, the annealed W/Zr C cermets were composed of dispersive W phase, continuous Zr C phase and pores, and many atoms in different phases diffused into each other during the heat treatment. The carbon atoms in W phases diffuse into Zr C phases, making the replacement reaction of RMI method go on, and the WC phases and W2 Zr phases disappear after heat treatment at 1800°C, also the W2 C phases at 2200°C. Tungsten atoms also diffused into Zr C phases, producing a(W, Zr)C solid solution phase, and arousing a lattice constant decrease of Zr C and a change of W phase from orbicular to be ruleless long strip.High temperature evolutions of mechanical properties of RMI-derived W/Zr C cermets were investigated. With the heat treatment temperature increasing, the flexural strength of DCP-derived W/Zr C cermets first increased and then decreased, attaining a maximum of 428.24±37.19 MPa at 1800°C. While the compressive strength and fracture toughness reduced with temperature increasing, being only 1/3 and 1/2 to original properties at 2400°C, respectively. Moreover, Vikers hardness of RMI-derived W/Zr C cermets enhanced with temperature increasing, and reached to 24.58±2.53 GPa at 2600°C, nearly 2 times of the original value. The extremum of flexural strength was related to the sintering of Zr C crystals and little melting loss of Zr-Cu alloys. The continuous reduce of compressive strength and fracture toughness were aroused by melting loss of Zr-Cu alloy, increase of pores and low interfacial bonding strength. The enhancement of hardness was the result of diffusion of W atoms into Zr C phases.Laser ablation behaviours of RMI-derived W/Zr C cermets were researched. Firstly, a low power density of laser was used to examine the high temperature ablation resistance of W/Zr C cermets for 60 s. During the ablation process, temperature of the ablated surface arrived at 2631°C. However, the ablation rate of W/Zr C cermets was close to zero. Secondly, a high power density of laser was used to study laser ablation behaviours of W/Zr C cermets. There was only a small ablated pit on the surface of W/Zr C cermets under the laser ablation. Though depth of ablated pits increased with laser power increasing and ablation time prolonging, the whole RMI-derived W/Zr C cermets keep in a good condition, exhibiting an excellent high temperature ablation resistance. The main ablation mechanisms include oxidation ablation, melting ablation and thermal decomposition. The compact Zr O2 layer which is produced during the ablation process can protect W/Zr C cermets from being ablated.